Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

October 22

Temperature of Distillate during distillation

My chemistry teacher claims that during a salt water distillation, the temperature of the vapour should be equal to water's boiling point and not salt water's boiling point. He did not even give the name of this phenomenon, let alone an explanation. Can someone point me to a relevant article or external link? Thanks in advance. --99.237.96.81 (talk) 00:01, 22 October 2008 (UTC)

Distillation is interesting...you're "boiling" a mixture, but you're only monitoring the vapor coming out (the distillate, not the pot). During distillation of salt water, what is the vapor (mostly)...salt, water, or both? That tells you what (mostly) is "actually" boiling into the vapor. To think another way, what is the boiling point of salt, or water, and of salt-water? During distillation, you started at room temperature and heated until "distillation occurred", so you got to "the temperature of the lower of those answers" first, at which point you're distilling "whatever that is". Okay, I'm glossing over some details for the sake of what is mostly happening for this particular case. See our article about how distillation works for more technical info. DMacks (talk) 01:42, 22 October 2008 (UTC)

Sorry for not being clear. My class was divided into groups and each group conducted a distillation. The temperature was taken many minutes after the salt water started to boil. My group's thermometer indicated 102 degrees Celsius, which is near salt water's boiling point, but the teacher claimed it was broken and that it should read 100 degrees. I have no idea what the reason is.

Suppose the salt water is maintained at a temperature slightly below its boiling point. Since water is not yet escaping quickly, surely it's possible to wait for thermal equilibrium, make the solution a tad hotter, and have water vapour at least as hot as the water was? Or do all water molecules that reach 100 degrees escape? If the latter, why is it necessary to heat the solution a few degrees above 100 just because some ions are in the way? --99.237.96.81 (talk) 02:45, 22 October 2008 (UTC)

The question is good. Consider the salt solution, which has - ideally, assuming the activity is the same as the mole fraction - less water in it than pure water, so at the boiling point of pure water the vapor pressure will be less. You will have to heat it higher for its vapor pressure to reach atmospheric pressure and boil. The vapor is in your case pure water (because salt boils IIRC at 900 °C), but in the general case the composition depends on the requisite vepor pressures. Then consider your distillation apparatus. If done correctly, there ought to be a drop of condensate hanging from it. The temperature measured at the top of the apparatus is the boiling point of the condensate.

As usual, sadly, the teacher is a dunce. When you teach distillation you must introduce p-x diagrams, 'cause without them it won't make sense. 74.67.113.167 (talk) 05:25, 22 October 2008 (UTC)

Unfortunately, there is way to much variability that we don't know about to answer the question reliably. Any of the following could be what is going on. Measureing the temperature of the vapor is going to be tricky at best. There is LOTS going on. Lets look at some of these.

1. You are right in assuming that the temperature of the vapor immediately upon boiling will be the same as the boiling salt-water solution, however, this temperature quickly drops for several reasons, not the least of which is that this vapor is instantly hitting 25 degree air, and is condensing (which is an endothermic process, and thus removing heat energy from your thermometer as it does this) and all sorts of really complicated dynamic effects are going on. If you measure the vapor immediately above the boiling solution it will be warmer than even a few centimeters away.
2. Classroom analog thermometers are notoriously imprecise. Its not that the thermometer is "broken;" a 2 degree differenc on an alcohol thermometer of the type represents less than a 1% error (2 degrees out of 373 kelvin). This is pretty good, actually.
3. Barometric pressure will have an effect as well. Weather can vary the barometric pressure by +/- 30-40 torr or so and this could easily throw off boiling points by 1-2 degrees celsius. Also, a partially closed system, where the release of the steam is constricted in some way, will likely raise the local barometric pressure over the water, further raising the boiling point.

The upshot is that your teacher is probably expecting a level of precision that is unreasonable. The experiment could be done to precision, just not with the equipment you would likely have access to... --Jayron32.talk.contribs 11:41, 22 October 2008 (UTC)

20 minute chimes

I have acquired an antique spring-powered pendulum clock with a strange malady: instead of chiming N times at N:00 and once at N:30, it chimes N times at some time, then once a half hour later, then once again a half hour after that, and then $(N{\bmod {1}}2)+1$ times after a further half hour. (Obviously this quickly bears no relation to N:00 or any other time.) It gives the warning at N:22 and N:52 as one would expect, but somehow its internal notion of time is only advancing "20 minutes" per half hour. What could possibly be causing this, and how might I fix it?

As it is new to me, I unfortunately do not know what put it into this state, except that it may have been working properly before an attempt to set it that included moving its hands (forward) while it was preparing to chime or chiming. I suppose that it is possible that it is meant to chime at every quarter-hour and is missing one instead of every half-hour and gaining one, but the chiming mechanism starts very reliably every half-turn of the minute hand, so that seems unlikely. --Tardis (talk) 01:14, 22 October 2008 (UTC)

Sounds like the hands are no longer on the shaft in the same orientation as whatever tells the chimes what the time is (i.e. forcing the hands twisted them on the shaft; if so this is likely not the correct way of setting the time). If so then they need to be reset on the shaft. It would probably be fairly inexpensive to have someone who knows what they are doing fix this. If you can find a local clock repair facility you could call and ask for an estimate. RJFJR (talk) 21:10, 22 October 2008 (UTC)

How could any constant phase difference between the hands and the arbors (or any other object) explain that it performs the half-hour chime twice before doing the whole hour again? --Tardis (talk) 21:38, 22 October 2008 (UTC)

The Reference Desk volunteers should refrain from giving horological advice, and refer the questioner to a qualified clockmaker. Edison (talk) 21:48, 22 October 2008 (UTC)

Medical, legal, now horological. Where will it end? ;O) Wanderer57 (talk) 01:11, 23 October 2008 (UTC)

It seems hard to imagine how its striking interval could have gone from 30 minutes to 20 while the rest of the clock keeps good time - but I suppose we could hypothesise some missing teeth in the gearwheel that interfaces the hand-motion part of the mechanism to the chiming mechanism. Those clocks are generally pretty easy to take apart because they were made to last a long time and the mechanisms need occasional professional cleaning. I'd take a look inside and see if it's obvious from watching what happens when it chimes. I had a problem with my 30 day pendulum clock - it has two springs that have to be wound separately and one of them had somehow gotten jammed more than 50 years ago (before I was born aparrently) - it was the work of about 10 minutes to figure out what had jammed it (some fluff in one of the ratchets) - and since the second spring drives the chiming mechanism, we were able to get the clock to chime again for the first time in 50 years! It amazes me that nobody ever so much as peeked inside in all that time! SteveBaker (talk) 05:42, 23 October 2008 (UTC)

It turned out that the clock's count wheel was out of phase with the follower that reads it and determines how many times to strike (really, with the wheel that the follower stopped when it was time to stop striking); this was causing it to not make it out of the pits in the wheel on the second try and thus to strike only once (again). Unfortunately, rotating the count wheel independently of the follower's wheel involves disassembling the movement, but at least it's understood now. Thanks. --Tardis (talk) 02:38, 29 October 2008 (UTC)

Energy output of hydrogen using oxygen, fusion, and antimatter?

Hi all. I was wondering, given a fixed amount of hydrogen (let's say a gram), what it's energy output would be for:

1. chemically bonding it to oxygen.

2. nuclear fusion into helium.

3. energy discharge from antihydrogen.

Much help appreciated ! -=- Xhin -=- (talk) 03:18, 22 October 2008 (UTC)

1. Oxyhydrogen

2. Proton-proton chain reaction

3. e=mc²

All three give the answeres you want.--Stone (talk) 07:33, 22 October 2008 (UTC)

Wow. Answer 3 looks like about $250,000 worth of energy if it were in the form of electricity at 10 cents per kilowatt hour. Edison (talk) 14:22, 22 October 2008 (UTC)

Yeah, as long as you can find a way of making a gram of antihydrogen for less than $250,000. Confusing Manifestation(Say hi!) 22:23, 22 October 2008 (UTC)

According to Antimatter, a gram of antimatter costs $300 trillion. - Akamad (talk) 02:09, 23 October 2008 (UTC)

It's not just that it costs more - it takes more than $250,000 worth of electricity to do it. SteveBaker (talk) 05:33, 23 October 2008 (UTC)

Keep in mind, there are losses in energy in antimatter-matter annihilation due to neutrinos. 98.221.85.188 (talk) 23:04, 22 October 2008 (UTC)

Details, details. Edison (talk) 04:10, 23 October 2008 (UTC)

Bottom line is that IF you have a handy source of antihydrogen and some way to handle it (not so trivial!) then this would by far be the largest amount of energy you could make...but we don't have such sources so as a practical matter - it's not a way to make energy at all. Fusing to helium is the next best - but again, we don't really have the technology to do this on any kind of useful scale. Fusion power is probably out there in our future - but it's gonna take a while. So we're left with by far the least efficient of those three things - good old fashioned combustion in air. Sad - but true. SteveBaker (talk) 05:33, 23 October 2008 (UTC)

UK BODY FARM

I would be interested in donating my body to a Body Farm upon my death - does anybody have any idea who to contact in the United Kingdom - to be able to carry out my wish - all help appreciated - thank you ROEBUCK32 (talk) 06:50, 22 October 2008 (UTC)

I'm not sure that there are body farms in the UK. But you can donate your body to medical science (which is what I intend to do). Go to the Human Tissue Authority website http://www.hta.gov.uk/about_hta/faqs/body_donation_faqs.cfm you can donate to a specific medical school but usually they will only accept bodies of people who died locally. Local authorities impose a fee for transporting dead bodies across county borders, shocking but true. Jooler (talk) 08:04, 22 October 2008 (UTC)

According to Body farm, there is currently no body farms in the UK. Only 3 in the US. The complexity of an international donation may discourage any of the body farms from accepting your donation although they may be willing if you are responsible for the costs and arrangements. For example the University of Tennessee Anthropological Research Facility will only pay for transport if you are within a 200 mile range of them so you'd definitely need to make arrangments to fly the body out to them. This will probably be quite complicated since the body obviously can't be embalmed before being sent and there will be a bunch of regulations that would need to be take care. All in all, I personally don't think it'll be worth the effort but it's obviously up to you. There are a bunch of other things you could donate your body for. The most obvious one is for medical schools where it will be used in teaching (either anatomical or for to practice). I'm sure this has been discussed on the reference desk before and while some people seemed to disagree, those who have encountered the process and common sense suggests your body will be treated with a great deal of respect. Bodies can also be donated for various research. I also came across Body Worlds (although I'm not sure if they have any centres in the UK, they have them in Canada, US and of course Germany, however there is Bodies Revealed in the UK which does similar things). Obviously in most cases your body may only be accepted if it is local, or you pay for transport costs although at least if it's not international it's not going to be so complicated. You should also consider organ donation. While this is often mutually incompatible with body donation (although you may be able to donate organs or tissue) there's no guarantee you will be suitable for organ donation (and of course it is possible your body may not be suitable for donation either). Since there is definitely greater need for live organ donations then body donations, I would presume live organ donations always take precedence. These links should hopefully answer the specifics for the UK [1] & [2]. One key point... Whatever you do it is important that not only do you ensure the consent process is complete but you make your wishes clear to your family/next of kin. The death of a loved one can be a traumatic time and by making sure they know what you want, they hopefully won't have to worry whether they are making the right decision. For organ donation, and I suspect body donation, in most countries your next of kin can overide any prior consent you have given. Nil Einne (talk) 08:50, 22 October 2008 (UTC)

Thank you all for the information ~ most interesting! ~ I have already listed my body to be used for medical research ~ so I shall stay with that option ~ it is listed in my will and my next of kin is fully aware of my requests ~ again thank you all for your attention. ROEBUCK32 (talk) 20:02, 23 October 2008 (UTC)

Clipperton Island lagoon

Two questions concerning the lagoon on (inside?) Clipperton Island:

• The bottom of the lagoon is known to be highly acidic due to sulfuric acid. In one article I found on the web, it was mentioned that this acid is a product of the decay of vegetable matter in the absence of oxygen. What's the chemical mechanism behind that?
• It is also mentioned that the lagoon's water is "undrinkable". Being stagnant, I doubt it's healthy, but is it really totally undrinkable, i.e. will it not save you from death if you were stranded on the island during a dry spell? 24.160.175.196 (talk) 06:55, 22 October 2008 (UTC)

There is a two step process, first anaerobic decay produces hydrogen sulfide and iron sulfides. This is then oxidized by oxygen from the air to make sulfuric acid or iron sulfate. The water probably tastes foul. You may ask why does not normal organic matter decay produce the acid directly? I assume that the alkalies are left in the mud at the bottom, such as potassium or calcium trapped in clay. Graeme Bartlett (talk) 02:05, 23 October 2008 (UTC)

Mutation in mitosis

On average how often does a mutation occur during mitosis? Only a rough estimate is required. But a sourced answer is preferred. Jooler (talk) 08:05, 22 October 2008 (UTC)

Our article on Mutation has some references that may lead to the right answer. Mutation is a rather vague term, there errors that can occur at ANY point in the transcription or translation process, and many different mechanisms by which this occur. --Jayron32.talk.contribs 10:39, 22 October 2008 (UTC)

Try this article, which estimates the somatic (i.e. mitotic) mutation rate for one particular gene at 10.6 x 10(-7) mutations per cell division. Assuming that all stretches of DNA have the same mutation rate (a big assumption) one could then estimate the number of mutations per genome per cell division, which is (I think) what you are really asking. However, there are some BIG caveats to this estimate.

• First, they are basing their estimate on the detection of alterations in post-translational modifications of cell-surface molecules caused by mutations that change the functional properties of a particular enzyme that catalyzes those post-translational modifications. It is definitely a clever and elegant assay, but I'm almost certain that this assay would be "blind" to either mutations that do not cause an amino acid substitution or mutations that cause only a slight decrease in enzyme function (hypomorphic alleles). So perhaps what they are really estimating is the rate of pathologic mutations at a given gene per cell division.
• Second, the assay uses an immortalized cell line derived largely from B-lymphocytes, which are already known to have different characteristics in terms of somatic hypermutation duing immunoglobulin formation. Therefore, the mutation rate estimate may be true only for this cell line and not necessarily generalizable to all other tissues of the body.
• Third, there are other types of DNA mutations (amply described in the Mutation article) that involve larger genome-scale changes such as deletions, duplications, inversions, translocations, loss of heterozygosity, aneuploidy, etc. which are not necessarily considered in the typical "mutation rate" question (i.e. changes at the level of the DNA nucleotide) but are just as important (perhaps more-so, depending on your point of view) in terms of human disease.

I hope this helps. It turns out that by asking a simple question you have discovered that it's actually a VERY complicated question (which, in my experience with biology, is almost always the case). Medical geneticist (talk) 14:36, 22 October 2008 (UTC)

Biting your lip

Why, when you bite your lip, does the small cut in your lip expand so much that you can readily feel it with your tongue? And why does feeling it with your tongue sting so much? Attn: Over zealous editors, I'm not asking for medical advice! Dismas|^(talk) 09:40, 22 October 2008 (UTC)

Aphthous ulcer is what this is called, and the article is pretty detailed. Cheers! --Jayron32.talk.contribs 10:35, 22 October 2008 (UTC)

Didn't know they had a name! Thanks! Dismas|^(talk) 12:20, 22 October 2008 (UTC)

Most commonly, they are called "canker sores". I typed "canker sore" into the search box, and it redirected there... --Jayron32.talk.contribs 12:23, 22 October 2008 (UTC)

I didn't know what a canker sore was but I thought it was something different. I've learned a few things today... Dismas|^(talk) 12:26, 22 October 2008 (UTC)

You're conflating sense-organ size and sensitivity, when they're not related at all: what's important is nerve-density. Relative to the area of the tongue populated by somatic (touch sensitive) nerves, the cortical map of the tongue in the somatosensory cortex (area of the brain that receives touch info) is huge. I've always found that when I bite my lip, it always feels much bigger when I inspect it with my tongue than it actually appears when I look in the mirror. Your tongue is a pretty sensitive insturment to detail, don't let it trick you into thinking those ulcers are exploding. Your tongue can identify even the tiniest scrathes in your mouth, probably better than your fingertips! --Shaggorama (talk) 09:03, 23 October 2008 (UTC)

jet flow

what are researching centers aboat "jet flow". —Preceding unsigned comment added by 78.39.192.29 (talk) 09:43, 22 October 2008 (UTC)

Do you mean the Jet stream? Or do you mean Wind tunnels used to test the aerodynamics of Jet aircraft? --Jayron32.talk.contribs 10:34, 22 October 2008 (UTC)

Osmosis Experiment

Hi all I am doing the age old osmosis experiment where u chuck discs of potato into different molarities of sucrose solution and record the change in mass. However one of the questions I have to answer is: 'When you dry the discs with a paper towel before putting them in the solution should you try and get them as dry as possible by squeezing all the water out?' Well I presume the answer is no, but I can't really think of a good explanation why not. Would squeezing the discs be a bad idea as it would damage the cell membranes of the potato cells and therefore when the discs are put into a very dilute solution/water the cells will not be able to take up water because their membranes have been ruptured and the water will just come out of the cell (I'm picturing a burst water balloon here!) even though water should diffuse in. Hope this makes sense and please share your thoughts! Thanks. —Preceding unsigned comment added by 139.222.241.40 (talk) 11:01, 22 October 2008 (UTC)

Your impressions of the situation look accurate to me. Causing excess cellular damage would likely ruin the experiment as described. --Jayron32.talk.contribs 12:22, 22 October 2008 (UTC)

This is just a random idea I just had, so I can't say I've tried it experimentally (but it's based on the principle behind plastination so it's not like it's never been done), but if you want to get those potatoes really REALLY dry, submerge them in acetone. The water should diffuse into the solution, and the acetone should enter the cells. When you remove the slices, leave them out to dry in a warm place: all the acetone should evaporate. Compare the weight difference with the potatoes you put in the most concentrated solution. For a real difference in weight, put the acetone-dried potatoes in deionized water and see how much they take up. If you decide to try this experiment, do it underneath a fume hood and make absolutely sure you're nowhere near any ignition sources. --Shaggorama (talk) 08:41, 23 October 2008 (UTC)

When you carry out the experiment you will find that some of the disks gain weight, others lose it, depending on the concentration of the sucrose solution. What happens when their neither gain nor lose weight? What is the actual purpose of your experiment? What are you trying to find out? The answer to this question should provide you with an answer to why you don't want the disks dried out. Theresa Knott | The otter sank 15:26, 24 October 2008 (UTC)

Discoveries made on space

From Feynman, What do you care what other people think?: "In the newspaper I used to read about shuttles going up and down all the time, but it bothered me a little bit that I never saw in any scientific journal any results of anything that had ever come out of the experiments on the shuttle that were supposed to be so important".

Is there any notable discovery made on space? Or any notable discovery based on data gathered on in space? Mr.K. (talk) 12:12, 22 October 2008 (UTC)

Yes, innumerably many so. See our article on NASA spinoffs for a start on the practical applications. Also, "in space" rather than "on space" is the correct usage. — Lomn 12:45, 22 October 2008 (UTC)

This article lists many discoveries made for space. Mr.K. (talk) 13:10, 22 October 2008 (UTC)

See also this RefDesk thread from last summer, where I asked a similar question: Wikipedia:Reference_desk/Archives/Science/2008_July_1#Space_program_benefits. jeffjon (talk) 12:47, 22 October 2008 (UTC)

Yes, that answers my question. Mr.K. (talk) 13:10, 22 October 2008 (UTC)

A lot of these are from the Aeronautics part of National Aeronautics and Space Association. The ones that are related to space exploration seem to be stuff that they developed in order to make space travel easier, rather than principals learned from the experiments themselves. Although they are useful, you will find similar things in extreme sports. Nobody talks about car racing as scientific, even if it did improve tires and engines. — DanielLC 15:13, 22 October 2008 (UTC)

Also, it would be fair to acknowledge the contributions made with scientific instruments installed and serviced by the shuttle, most notably the Hubble Space Telescope. --Sean 15:16, 22 October 2008 (UTC)

There's also the notion that patience needs to be practiced here. Initial forays into space are needed to set up future success. An arguement can be made that the progress has stalled somewhat, but one cannot judge the success or failure of the space program merely on short-term financial returns. If, 200 years from now, we are able to mine mineral wealth on asteroids, we may well see the early space program as entirely vital to that development. We don't have enough history to judge the situation on yet. Indeed, its if we judged all of the Age of Exploration only on Columbus's first voyage. If we said "Look, all this guy brought back was some trinkets and a nasty case of syphilis" then it may not have been judged a success. One could make the case, with the exponentially hard task of exploring extraterrestrial space, we are still at the "proof of concept" phase of space exploration, and may be there for many decades to come. The real returns of space travel may not be realized in our life time, but that does not mean that the entire project has been a failue... --Jayron32.talk.contribs 15:45, 22 October 2008 (UTC)

Of course, Columbus was not really doing his work for its own sake. He was looking for a trade route, which would have been worth a lot. It wasn't exploration for exploration's sake. For the record, most scientists hate the idea of funding science for its own sake as the only justification. Why? Because there's no way to tell what an appropriate budget expenditure is for something like that; there's no way to pressure politicians for more funding than they currently have. --98.217.8.46 (talk) 01:49, 23 October 2008 (UTC)

The thing is that NOT ONE of those 25 things in our NASA spinoff article are inventions that were made in space. They were made right here on earth for the purpose of sending people to space. Feynman was exactly right - it's very hard indeed to find any significant science that's been done by humans in orbit. NASA consumes around 20 billion dollars a year. Do you seriously imagine that a research organization funded to the tune of 20 billion dollars per year (in modern dollars) for a period of 50 years would have come up with just 25 (mostly rather mediocre) inventions? That's $40,000,000,000 per invention! Worse still, most of those are not even "inventions" - they are mostly minor improvements of well-known technologies. Did we really spend $40bn to invent the LED? Well, LED's are rather important - perhaps that was worth it? ...but um...actually...NASA didn't invent the LED - go ahead, read "LED" - it was invented by some British guy in 1907, or perhaps by a Russian guy in 1920, maybe perfected by "the Radio Corporation of America" in 1955 and finally became mass-manufacturable in 1961 - thanks to a couple of guys at Texas Instruments. In truth, NASA's $40bn contribution has been to make them a teeny-tiny bit brighter by growing crystals in orbit to avoid certain imperfections. Of course that's a completely infeasible way to make LED's - and it would be cheaper by far just to use two regular earth-grown LED's...NASA's PRACTICAL contribution to LED technology is precisely zero.

What does it REALLY take to make an invention? I worked on the team that invented the CD-ROM. I think that rates about as highly as the entirely trivial NASA "invention" of the cordless vacuum cleaner. There were about 50 engineers working on the project within Philips and SONY over a few years. A few millions of dollars for an invention that's at least as intellectually difficult and generally vastly more useful than portable vacuum cleaners.

The fact of the matter is that the idea that spinoffs are a justification for the existence of NASA is really very silly. As usual, Feynman is right...good science doesn't happen in space - and even if it did, 20 billion dollars a year would produce vastly bigger returns if it were directed at pure research down here on Earth. That's not to say that NASA shouldn't exist - I think they're very important - but please, let's not kid ourselves that they are earning their keep with spinoffs - that's just laughable.

SteveBaker (talk) 05:24, 23 October 2008 (UTC)

I mean, if you really want to find published research, all you have to do is look. --Shaggorama (talk) 08:30, 23 October 2008 (UTC)

Does the wavelength of light change in a time varying magnetic field?

I am part of a research project which requires the use of optical fiber to send a constant frequency clock through a 3 Tesla pulsed magnetic field. There has been a debate centered on the idea that the varying magnetic field will shift the frequency of the light in the optical fiber adding jitter to the encoded clock. I have not been able to find any research on anything similar. My simple understanding of the wave properties of light are that it is composed of "B" field and "H" field components. As these propagate down the fiber, the magnetic field component would receive a local temporary "bias", but since there is not a corresponding shift in the electric field, the wavelength of the light should be unchanged. Monkeyfire (talk) 16:20, 22 October 2008 (UTC)

Due to the glass or impurities in the glass you may get some sort of low level effect. Even if the field causes vibration in the fibre, this can affect the light traveling though, with phase or amplitude modulation. With intense enough fields you will get a distortion of space with a general relativistic effect. To a first approximation though the electromagnetic effects will be linear and add without affecting each other. If you use frequencies close to absorption lines due to impurities you will likely get the biggest effects due to changes in magnetic field. Graeme Bartlett (talk) 21:12, 22 October 2008 (UTC)

More specifically look at Magneto-optic effect. Here a magnetic field causes a delay in circular polarized light. This will affect the wavelength. Graeme Bartlett (talk) 01:25, 23 October 2008 (UTC)

Internal organs

While watching replays of an American football game, I saw a bit about a player having a spleen injury; they didn't say what it was exactly, but I'd guess a ruptured spleen. We hear about ruptured spleens occasionally, and very occasionally about gall bladder injuries, but why do some organs (for example, the pancreas) never get injured this way? Or do they get injured, and I simply don't remember hearing about it? Nyttend (talk) 17:10, 22 October 2008 (UTC)

According to Pancreas#Diseases of the pancreas (a section that needs to be rewritten so as to actually summarise the article it's meant to be a summary of...), a punctured pancreas is a serious injury, however I've never heard of one either which probably means they aren't very common. It may be due to the relative positions in the body, perhaps the spleen is less protected. --Tango (talk) 17:17, 22 October 2008 (UTC)

The spleen sits under the lower left rib cage margin, so in principle is well protected unlike the pancreas in upper abdomen. To injur some organ as implied above, it needs to be compressed between things, and the pancrease is burried under loads of squishy guts that would absorb most blows. By contrast one American Footballer landing on another's chest may crack a rib, the sharp end of which may cut the spleen. Also will depend upon how friable the various organs are - maybe the spleen will tend split easily for a blow landing below & under the rib cage. Anyway that's my best guesses David Ruben ^Talk 19:41, 22 October 2008 (UTC)

According to the Grey's anatomy links from our articles on spleen and pancreas, the spleen weighs 2 or 3 times as much as the pancreas. Perhaps the larger size makes the spleen more susceptible to damage? Wanderer57 (talk) 01:31, 23 October 2008 (UTC)

speed of ripple vs speed of sound

The article speed of sound discusses the speed of sound, a longitudinal wave. A ripple on the surface of water is a transverse wave. Does it have a constant velocity? Do we have an article discussing the velocity of transverse waves? RJFJR (talk) 20:11, 22 October 2008 (UTC)

Actually, a ripple on the surface of the water is a surface wave. The characteristics of a surface makes it behave distinctly different from a transverse wave. The velocity of transverse waves is calculated exactly like all other waves. Velocity = Wavelength * Frequency, or v = λ*ν --Jayron32.talk.contribs 20:24, 22 October 2008 (UTC)

I think part of the question was whether the product is constant. If you throw a pebble into a lake, you will create a wave which travels at a certain speed. Same thing if you throw a big rock into the lake. Will the velocities of the two waves be equal? (No lake nearby, can't do the experiment right now). --NorwegianBlue ^talk 20:36, 22 October 2008 (UTC)

It's an excellent question and I'm watching this space... --Tango (talk) 21:52, 22 October 2008 (UTC)

I can't remember well, but I *think* that in the general solution the velocity of propagation is constant, but dependent on wavelength. Of course, they probably derive that from an equation that assumes those two things anyway, so I'm not sure how useful it is. Confusing Manifestation(Say hi!) 22:17, 22 October 2008 (UTC)

For a surface wave the velocity is not constant, and longer wavelengths travel much faster, eg tsunamis are much faster than normal ocean waves or ripples. Read Ocean surface wave#Science_of_wavesGraeme Bartlett (talk) 01:56, 23 October 2008 (UTC)

There it is! Thank you. (It includes the note on the effect of depth of water that I was also curious about). RJFJR (talk) 13:32, 23 October 2008 (UTC)

Spurs

What's going wrong? —Preceding unsigned comment added by Tony May (talk • contribs) 22:14, 22 October 2008 (UTC)

You're going to have to be a *lot* more specific than that. What spurs? Where? What makes you think something's going wrong? What *appears* to be going wrong? Confusing Manifestation(Say hi!) 22:20, 22 October 2008 (UTC)

Why do I get the feeling this question is about the terrible start to the football season for the British club Tottenham Hotspur (a.k.a. the Spurs) However, I don't think it has anything to do with science. —Cyclonenim (talk · contribs · email) 22:27, 22 October 2008 (UTC)

It might, if the Daleks have slipped them a tailored pathogen so as to clean up in wagers. —Tamfang (talk) 02:27, 23 October 2008 (UTC)

I accidentally an entire spur! Mac Davis (talk) 03:33, 23 October 2008 (UTC)

Maybe bone spur? RJFJR (talk) 13:35, 23 October 2008 (UTC)

"Natural" and "artificial" selection in humans

In humans, is it possible to cleanly distinguish natural from artificial selection? NeonMerlin 23:08, 22 October 2008 (UTC)

Since humans are, by any definition, "natural", what are you asking? Saintrain (talk) 00:42, 23 October 2008 (UTC)

What he's getting at is that the "artificial/natural" distinction is usually one of human agency or not. I would say, "it really depends on your definitions of artificial and natural selection here." The differences between the two are not really scientific in nature—humans exist as part of the "natural" world, and human agency does not have any particularly non-natural component than, say, termite or chimpanzee agency. Keep in mind that even trying to determine the most extreme form of human agency into human selection, eugenics, is fraught with definitional difficulties. --98.217.8.46 (talk) 00:49, 23 October 2008 (UTC)

Only if you're against it. Mac Davis (talk) 03:32, 23 October 2008 (UTC)

Even if you are "for" eugenics you can have trouble defining it. Only sloppy propagandists are happy with defining a term as everything under the sun. --98.217.8.46 (talk) 12:32, 23 October 2008 (UTC)

I don't think you can distinguish the words "natural" and "artificial" cleanly under any circumstances. What does it mean when you buy a food item that claims "No artificial coloring or preservatives"? Would cyanide be considered "natural"? Actually, there are bacteria and algae that produce the stuff - so yes...it's perfectly natural. Because humans are "natural" animals - why should the processes we engage in be any less "natural" than the ones produced by animals. Silk worms make silk - and it's "natural" - humans produce something that's pretty similar - and it's "artificial"...why? If you answer that anything that humans do is "by definition" artificial - and anything we had nothing to do with is "natural" - then by that definition, all human selection is "artificial" because simply because humans are responsible SteveBaker (talk) 04:51, 23 October 2008 (UTC)

The OP may be interested in reading the works of Jared Diamond, particularly The Third Chimpanzee. As others have noted above, the distinction between artificial and natural selection is at best a tough one to make, but Diamond argues (somewhat convincingly) that some of the things we assume to be responses to natural selection have significant cultural components. The example he uses is skin colour, which while it obviously varies grossly in proportion to the amount of UV light a population would be exposed to, also displays quite a lot of variation that cannot be explained by that. Matt Deres (talk) 16:17, 23 October 2008 (UTC)

October 23

Longevity of satellites

With our current quality of satellites, is it possible to build a satellite capable of surviving at least 1,000 years without contact with Earth, and then broadcasting a signal to a specified location? (Also, if possible could you provide a source for me to cite?) --Ye Olde Luke (talk) 01:59, 23 October 2008 (UTC)

no, things like batteries wear out, solar cells degrade, attitude fuel runs out, metal recrystallizes or migrates in the circuits, electrolytic capacitors dry out, cosmic rays damage the small stuff and insulation. It may be possible to build one though! Graeme Bartlett (talk) 02:12, 23 October 2008 (UTC)

But Vanguard 1 is still floating, and they think it'll continue to float for another thousand years. Would there be a way to keep the satellite in sleep mode or something until it comes time to transmit the broadcast? --Ye Olde Luke (talk) 02:25, 23 October 2008 (UTC)

Longevity in a dormant state does not seem to be a factor that has been studied to any great degree. Engineers design things to be economical and to meet the specifications. I have maintained equipment which has functioned in power systems for as long as 80 years, when longevity was not a major objective. I have seen light bulbs which still work after 100 years (not 100 years of being continuously illuminated). I own telegraph relays which work after 110 years, telephones which work after 100 years, and vacuum tubes which work after 75 years. Certainly lubricants can gum up, and copper conductors exposed to oxygen corrode and fail, batteries fail, and insulation can crack and shorts out. If long dormancy and revival after 1000 years (in space) were the goal, I would look to develop suitable technology. I have seen Egyptian glass and ceramics, and implements made of gold and copper. Ceramics can insulate and survive thousands of years. So clearly copper or gold conductors with ceramic insulation on jeweled bearings could function as electromagnets, motors, or relays after a thousand years in space. Vacuum tubes could likely function after a thousand years in space. Ways could likely be found to extend the service life of semiconductors such as solar cells and transistors. This has not generally been an important design goal. Attitude control fuel? Let it twist slowly in the solar wind without control, until it reaches the target solar system, or until sufficient time has passed in our own solar system.. Stored energy? A superconductor can store energy in the form of current without appreciable loss for a thousand years, out where it is cold and no nitrogen flow is needed to maintain the low temperature. Ordinary lead acid storage batteries have an extremely long shelf life when the electrolyte is stored separately, to be thawed and added when the time is right. Solar cells? Drift of dopant might be a problem, leading to degradation. Perhaps solar energy could be used via a heat engine poweredby the sun or some distant star the probe has reached. Chips and microminiaturization of electronic components would seem to lead to early failure, but redundant circuits could be used with the failed ones detected and turned off by devices such as a "deadman switch" circuit. Nuclear fuel would not be a solution with types of fuel assemblies I have read about. Edison (talk) 03:59, 23 October 2008 (UTC)

Space is an environment that's a lot different from what we're used to here on earth. Without oxygen, things can't rust or corrode in the normal way - but substances are subjected to much more intense radiation and more violent temperature changes - which cause stress fractures. I'd want to think in terms of something very crude and unsophisticated. Power held in a big spring - a generator to produce the electrical burst that would be as simple as possible with little reliance on fancy bearings. The 'trigger' mechanism would be an interesting problem. If the timing doesn't have to be too precise, maybe you could design a material to deliberately fail due to some kind of well-understood but slow process...as it fails, the spring does its job - generates a short burst of electricity into the simplest, most chunky radio you could imagine. If the signal doesn't have to be a radio - then perhaps simpler still would be to allow two liquids to mix and generate a chemical laser or something. It's an interesting problem. SteveBaker (talk) 04:44, 23 October 2008 (UTC)

Like a beacon: Break the glass, release chemical which mix and initiate action. Crude and clunky may work better for longevity. I just threw away a 1997 high tech phone which failed, and a 1950's dial phone still works fine. The amount of radiation might depend on where the satellite was. Solar radiation could indeed hit it hard on occasion if it were in Earth orbit for 1000 years. Edison (talk) 04:57, 23 October 2008 (UTC)

I think it probably would be possible and not with too much difficulty, weight is the main problem that makes things flimsy. But not anywhere near the earth with the way it is getting surrounded with space debris. Dmcq (talk) 12:40, 23 October 2008 (UTC)

Haul a small asteroid into earth orbit (we have the technology, but it would be insanely expensive), bore to the core and place your satellite at the core of the asteroid. This will protect it from debris, temperature fluctuations and certain types of radiation. Once the timer activated, have it bore its way out (or leave the original bore unfilled) and transmit. Yes, it would be prohibitively expensive, but it would be possible with today's technology. 152.16.59.190 (talk) 10:32, 24 October 2008 (UTC)

You would still have to be careful that your electronics (and power source) didn't degrade over time. Even just whiskers forming on the contacts would be an issue.

Not to mention time-keeping. How does the satellite know when 1000 years have passed? APL (talk) 12:56, 24 October 2008 (UTC)

That's why "big and chunky" is good. Whiskers grow short distances and are thin and flimsy. Sure, they are enough to take out a teeny tiny chip - but if you had 1" brass bars carrying large voltages and currents - whisker formation would be an irrelevance. If the satellite has to know that 1000 years have passed PRECISELY - then I think this is a tough problem - but you could (for example) use a small nuclear-power source with a half-life of around 1000 years to generate a voltage to hold open a good-old-fashioned solenoid against a big-assed spring. Once the voltage drops below some critical level, the solenoid can't be held open against it's spring and it shoots forward and mechanically smashes the glass vial containing the liquids that combine to make a chemical laser. Perhaps the solenoid also starts a slotted disk spinning in front of the laser that modulates the signal into morse-code...or to send out the first 20 prime numbers in binary or something. You could arrange that it would trip somewhere between maybe 900 years and 1100 years - if that's good enough. The solenoid could be HUGE and chunkily built so it won't fail. Think "steam-punk" here! SteveBaker (talk) 20:05, 24 October 2008 (UTC)

Time to replenish an oil well

Sorry to ask two questions, but how long does it take to replenish an oil well? (I know it takes longer than a lifetime, but does it take less than 1,000 years? If so, how long? And again, if possible, could I get a source?) --Ye Olde Luke (talk) 03:35, 23 October 2008 (UTC)

The article Petroleum says it took geological time to create the material an oil well extracts from ancient organic material. Thousands of thousands of years, in other words. With modern synthetic fuel technology, the creation of hydrocarbon fuels from organic matter might be a fairly quick process. Edison (talk) 04:04, 23 October 2008 (UTC)

We're talking millions of years - certainly not thousands. Petroleum#Formation says "Geologic timescales". The problem is that the formation process requires heat and pressure and an absence of air. So lots and LOTS of dead algae and other ocean-bottom goo has to be layered under hundreds of feet of rock. That's not something that can possibly happen quickly. Then the pressure of all of those rocks compresses and heats the goo - eventually forming oil. The actual oil formation might happen relatively quickly once the conditions are right - but those conditions will take an enormous amount of time to get started - simply because the requirement to have enough pressure means that the goo at the ocean bottom has to accumulate enough layers of sediment to compact into hundreds of feet of heavy rock. But even that's not enough because the oil would tend to form in a very thin layer - which would make it almost impossible to extract. The ground has to fold and crinkle to form natural underground domes into which the oil is squeezed. Only then can we drill down and extract it. Those processes are geological in nature - so "Geologic timescales" is indeed an appropriate term. Mountains don't form in thousands of years. SteveBaker (talk) 04:20, 23 October 2008 (UTC)

Note that "Thousands of thousands" = "millions." Edison (talk) 03:10, 24 October 2008 (UTC)

Plus "an oil well" would never be replenished in the sense of being able to pump oil again. The entire landscape would be utterly transformed, the oil well long long gone. Pfly (talk) 06:08, 23 October 2008 (UTC)

Yeah...oil ain't water. When an oil well runs dry, that's it for that well. Asking when an oil well will be replenished is like asking how long it will take for the sites of archaeological digs to turn up new fossils: once they're gone, they're gone. The well will be long gone before any oil will turn up where the well once was. Try this article out to better to understand where petroleum comes from. --Shaggorama (talk) 08:20, 23 October 2008 (UTC)

Yep - it's wrong to think of those big empty spaces where the oil was gradually filling up again. No - what has to happen is that existing shallow oceans have to have new rivers start depositing sandy silt onto the top of the layers of dead algae. As the silt builds up - it presses down on the stuff beneath - forming sandstones and other rocks. This process alone could take a million years. That stuff sinks downwards and with luck, more layers get built up on top. Maybe a volcano deposits a few feet of lava onto the top of this - adding granite layers on top of the sandstone. Once enough millennia have gone by - the original goo is buried under hundreds of feet of rock - that's probably come from thousands of feet of accumulated river sediment and who-knows-howmany volcanic events.

Then when the temperature and pressures are just perfect, the goo undergoes a couple of stages of chemical change and turns into a THIN layer of oil - this might happen quickly once the conditions are right. Perhaps (and I'm guessing here) a 10 foot layer of dead algal ooze might form a layer of oil-soaked sandy rock maybe just a few inches thick. That's impossible to extract economically with current drilling or mining technology - so it's useless to us like that. But we see "oil shales" and stuff like that all around the world - so we know it exists.

If a continental plate happens to bump into the edge of the continent where our oily layer formed then the rocks will crumple under the lateral pressure. Maybe a major earthquake makes the rock layers tilt at an angle. Some parts of our thin oily layer get pushed deeper underground where the pressures are higher - some get pushed upwards into mountains. The oil in the layers that went deeper is now under even more pressure - but the areas that were pushed up are under less pressure - the oil is slowly squeezed out from the deep areas to the shallower areas. Sometimes, the oil is squished all the way to the surface where it gradually gets washed away - but in a few lucky areas, the underground rock formation forms a dome - like an up-side-down bowl - and the oil collects there.

If we're even more lucky, the rock on the upper-side of the 'dome' is impermiable to oil so the oil collects there. With luck, there are no underground streams to wash it all away again. If we're yet luckier still - that bowl doesn't get eroded from above to form a 'tar pit' which dries out and becomes useless as "oil" because all of the interesting volatile chemicals have evaporated. If we're lucky, the entire bowl doesn't get 'subducted' down under another continental plate and be pushed towards the core of the earth where we can't reach it anymore. Hopefully it doesn't end up under ocean that's too deep or too stormy to drill there. If absolutely everything works out just right (which is surprisingly rarely) then eventually - there is a reservoir - perhaps hundreds of feet deep and a few miles wide that's completely full with millions of barrels of crude oil. Now if we can find that dome - we can drill down into it and pump out the oil - but once it's empty - that's that. There is no more algae there to form sediments and to be squished - so the dome will eventually either collapse or fill up with water or something. Either way - that's it...no more oil will ever come out of it. "New" oil is indeed gradually forming somewhere where the bottoms of shallow oceans were long ago covered over by newer layers - but it'll be millions of years before we can get at it - new mountains are formed more rapidly than new oil! We're extracting oil tens of thousands (perhaps millions) of times faster than it's being formed - so once we've used it all - we'll have to wait for millions of years before we can do that again.

SteveBaker (talk) 14:12, 23 October 2008 (UTC)

Guinea worm extinction

If the attempts to eradicate dracunculiasis succeed, is there any way to keep the worm itself from going extinct? I understand that ending the disease will improvbe people's lives, and I support it -- but could the species be saved, too? Unlike smallpox, it's not just a germ, but a complex animal - and we saved samples of smallpox anyway. It seems like there's a non-negligible amount of genetic information and, well, biological uniqueness in this creature, more than in germs which evolve new species in mere years. Could they be somehow kept alive in some sort of human-substitute chemical bath for that phase of their life cycle? It seems like that might be the only possibility, as finding human volunteers to host it would be nearly impossible and counterproductive anyway.

Even if not, has someone sequenced the DNA so that information, at least, survives? 128.194.161.154 (talk) 03:54, 23 October 2008 (UTC)

Dozens of minor species go extinct every day. Extinction says that experts expect half of the species on earth today to be gone by 2100. Species says that we estimate that there are between 2 and 100 million species on earth right now. So over 100 years - between 10,000 and 500,000 species disappear each year. that's between 30 and 1500 species lost every single day. More importantly - it's believed that the "natural" rate of extinction (ie without us humans messing things up) is 100 to 1000 times less than this rate. So between one species every couple of years to 15 species per day is the NATURAL rate of extinction. So this one species disappearing isn't really a big deal. There are better ways to spend our conservation efforts. If it goes extinct...big deal...it's a drop in a bucket. SteveBaker (talk) 04:34, 23 October 2008 (UTC)

Although we like to generally treat the concept of species with the attitude of "the more the merrier," the fact is that there are a few around that we'd just as well be happier to do without. You raised the example of smallpox: we held onto that one just in case it pops up again (or something close comes along). If we're going to fight to keep a species around, the question needs to be asked: why? Conservation is an investment and we can't build reserves for every inconsequential species on the verge of disappearing. The reason ecologists and biologists generally fight extinction is to retain genetic diversity in the wild; most endangered species we hear about are fought for by the general population because they're cute, quite frankly, and are used to spearhead efforts to garner support for the conservationist movement in general (the panda is a great example).

Given our impact on the planet we like to act as curators of nature to try and minimize the negative effects our lifestyle has on the planet, but protecting nature will always be done in a manner that is beneficial to humanity as well. No sympathy well ever be felt for parasites and diseases, and if any samples are retained after their extinction in the wild it will only be for the sake of their potential for designing future cures, as was (presumably) the case with smallpox. --Shaggorama (talk) 08:08, 23 October 2008 (UTC)

We (as responsible beings and 'custodians' of the planet) have a duty not to go around destroying species at a rate of a thousand species per day...but the loss of at least a few species per year is completely natural - and indeed a necessary part of evolution. As a few individuals of a species get mutated into new forms (new species) - they will naturally start to out-perform the members of their former species - and when that happens, the old species will become extinct. This is how creatures adapt to changing conditions. A part of that change is the rise of humanity...the unfortunate part is that we're wiping out species who can't compete with us for land because they have yet to invent defences against the bulldozer - or who can't tolerate the toxins we put out or the climate changes we're causing. Given enough time - they certainly would evolve to handle that - but evolution can only creep along fairly slowly and the rate at which we're changing things is causing the system to fail. This kind of 'mass extinction' has happened in the past - when the dinosaurs were wiped out, for example. One day there are dinosaurs - and a few years later...no dinosaurs - suddenly, all of the species who relied upon dinosaurs for their livelyhood went extinct - but other species suddenly found there were large tracts of land with no large carnivores - and they thrived. The earth did recover - and it will this time too. The problem is whether humanity will be one of the species who can't adapt fast enough to the changes that we, ourselves are causing. If our crops fail due to global warming and we over-fish the oceans - then there won't be enough food and we'll be quite likely to die out. Other species will survive - evolve and repopulate the planet...but it will be a very different planet afterwards - just as it was after the dinosaurs vanished.

In a sense, the Guinea worm and the smallpox virus simply failed to mutate fast enough. They needed to evolve into a form that either survives all the efforts of humanity to eradicate them (the HIV virus is managing to do that - but smallpox couldn't) - or they had to evolve to attack other creatures so as not to cause humans to want to kill them (there are plenty of viruses that don't hurt humans at all - and we're not really not trying to eradicate them). There is an old science fiction story (I think maybe by Isaac Asimov) in which all of the creatures of earth have evolved to not harm humans - because in some future world, that's the only way to avoid extinction. So humans can walk safely through the middle of a pride of wild lions because the lions have evolved a mechanism to avoid killing people - and thus avoid people killing them. It makes perfect sense that this should happen - indeed it's been argued that animals such as dogs have "evolved" to be good with human children because the vicious baby-killers don't survive to reproduce. We think of this as humans breeding gentle dogs - but we're just another evolutionary pressure on the canine genome. The guinea worm failed to do that - and it's about to pay the price.

If we're going to expend effort to save species - it makes more sense for us to try to preserve the ones that are harmless - or even beneficial to humans. That will place evolutionary pressure on the ecosystem to be more friendly to us. Evolution is relentless - and if we can avoid wiping ourselves off the planet - the planet will eventually bounce back.

SteveBaker (talk) 13:44, 23 October 2008 (UTC)

This rings of Social Darwinism. Besides the OP asked HOW could dracunculiasis be preserved, not whether it should. Does anybody know an answer to the question? --S.dedalus (talk) 04:13, 24 October 2008 (UTC)

It has nothing whatsoever to do with Social Darwinism, as Guinea worms have no society. As for the original question: the guinea worm is a parasite, but humans are not its only host. So it would be possible, for example, for a dedicated staff of personnel to preserve the worm after the disease's eradication by inflicting it upon successive generations of captive dogs, horses, cows, wolves, leopards, monkeys or baboons. But it would probably be more humane to simply sequence its genome and let it go extinct. - Nunh-huh 04:26, 24 October 2008 (UTC) P.S. Actually, now I wonder if a "behavioral" eradication program would really result in the eradication of the organism, as there would seem to be pockets (dogs, horses, cows, etc.) that wouldn't be affected by such manipulations. The program might be aimed at minimizing human disease, and may not actually wipe out the organism in animals. - Nunh-huh 05:48, 24 October 2008 (UTC)

I disagree. This is reminiscing of social Darwinism in that the latter ethical theory is based on a “might makes right” philosophy. The idea that because this creature is harmful to us, and because many species go extinct without our help, it is morally acceptable for us to exterminate the Guinea worm is suspect in my mind. --S.dedalus (talk) 05:42, 25 October 2008 (UTC)

You misunderstand Social Darwinism, which is about the evolution of human society, not shorthand for "might makes right" (which is in itself a gross mischaracterization of Darwinism). - Nunh-huh 06:15, 25 October 2008 (UTC)

No, I don’t think I’ve misunderstood. “Might makes right” is the characterization used by my professor of ethics. I agree that it is a bit of an oversimplification when it comes to the theories of contemporary philosophers, but it’s actually quite accurate when describing the ways in which the theory was applied (by Andrew Carnegie for instance). Remember that social Darwinism is NOT the same as evolutionary ethics. --S.dedalus (talk) 21:08, 25 October 2008 (UTC)

Well, you can keep misusing the term Social Darwinism if you like, but it's not "might makes right", and you can't count on everyone sharing the same misunderstanding of the term that you share with your ethics professor. - Nunh-huh 02:10, 26 October 2008 (UTC)

We have to agree to disagree then. --S.dedalus (talk) 07:30, 26 October 2008 (UTC)

Humans are the only hosts for the adult stage of the worm, at least according to our article and [this] cite. It's kind of the entire point of the eradication campaign and the OP's question. Where did you get your list of "captive dogs, horses, cows, wolves, leopards, monkeys or baboons" from? Matt Deres (talk) 10:47, 24 October 2008 (UTC)

It would seem our article and the cartercenter.org site are definitely wrong, as the medical literature definitely contains case studies of dog dracunculiasis as well as other species which can be affected. [3][4][5][6]. I don't recall the exact source of the list I used, but if you google "Dracunculiasis" with the various species you'll find similar lists, as at [7], [8] The Carter Center could perhaps make its statement true by sticking in a "significant": "Humans are a Guinea worm's only significant host": They seem to have simplified for didactic or polemic reasons. - Nunh-huh 19:04, 24 October 2008 (UTC)

Can we get rid of ticks and mosquitos too? I mean, I know we're supposed to value all species equally.. but I definitely don't! --98.217.8.46 (talk) 15:40, 24 October 2008 (UTC)

I would say that would be nearly impossible, beyond perhaps some sort of super virus or perhaps nanobot, which IMHO would be too risky to try. (Eradicting a parasite which needs a host is a far easier goal) Nil Einne (talk) 15:13, 25 October 2008 (UTC)

Animal search.

Its a very small microbe kind of organism which lives in waters, mainly rain forests. and lighten when any disturbance created in the water they are in. I don't know its name, but it starts with "Noctal---". I would be glad if i could get any article based on this organism. Thanking you.

Dishant Kamble —Preceding unsigned comment added by Dishant kamble (talk • contribs) 04:10, 23 October 2008 (UTC)

Hmm...sounds to me like you're looking for dinoflagellates. They like to collect in calm, warm water, I think bays especially, and glow when disturbed. You may also want to read Bioluminescence. PS: in the future, sign your posts by ending with "~~~~" to generate a signature with a timestamp like this one: --Shaggorama (talk) 07:53, 23 October 2008 (UTC)

the Noctilucales or the species Noctiluca scintillans? They're dinoflagelates. However, they're Noctil- and not Noctal-. --Lenticel ^(talk) 07:58, 23 October 2008 (UTC)

"Universe" clusters; matter/energy beyond our own universe

Since I was a child, I was taught that time started with the Big Bang, and that all existence is contained within this universe. And yet I rarely if ever hear anything about the possibility of matter/energy clusters well outside the range of the localized Big Bang. I am preciously interested in reading about this, yet little to no information appears to be present on Wikipedia or elsewhere on the net.

In case my wording is not clear, let me give another explanation. What exists beyond the current universe? In all likelihood, it is empty space (it clearly was before, or the universe would not have been able to expand). What if there is matter or even other "universes" there, even if really far away? Is there any way whatsoever to detect matter coming from outside, and/or is anyone else theorizing about this? The more I think about the theory, the more likely it seems (i.e., providing explanations of our own universe; perhaps matter did not come from the Big Bang, but the Big Bang sucked in energy until it exploded under its own weight). Magog the Ogre (talk) 08:17, 23 October 2008 (UTC)

See Multiverse. There are lots of theories about other universes in various senses. I don't think any of them allow information to travel from one universe to another, though, since that rather goes against the definition of "universe". The universe is, by definition, everything in some sense. What we often mean when we say "the universe" is "the observable universe" which is everywhere from which light has had time to reach us. Anything outside that can't possibly have had any effect on us (given our understanding of the laws of physics, at least). That means that discussion of other universes isn't really scientific (it's not "falsifiable", it's more in the realms of philosophy. --Tango (talk) 09:35, 23 October 2008 (UTC)

Whether there is anything "beyond the current universe" depends on how you define "beyond", "current" and "universe". Here are a few possible answers:

• There are, almost certainly, regions of space-time that originated in the Big Bang but lie beyond our current observable universe - we might be able to interact with these regions of space-time at some distant point in our future.
• It is fairly likely that there are regions of space-time that originated in the Big Bang but will always lie beyond our observable universe - we will never be ale to interact with these regions of space-time unless we develop some form of faster than light communication.
• It is fairly likely that there is some stuff that originated in the Big Bang, is present all around us, but has no interaction with the rest of the universe apart from a gravitational effect.
• It is possible that there are other dimensions beyond space-time that originated in the Big Bang. Although regions of these other dimensions may be technically within the observable universe, it will probably be very difficult for us to interact in any direct sense with them (otherwise we would have done so before now).
• It is possible (although very speculative) that there are separate quantum timelines that originated in the Big Bang but which we will never be able to interact with because they split off from our current timeline at some point in our joint past.
• It is possible (although very, very speculative) that there are regions of space-time or some different dimensional structure that did not originate in the Big Bang - that may indeed have existed "before" or "outside of" the Big Bang, if such terms can have any possible meaning in an entirely different set of dimensions. It is very, very unlikely that we will ever be able to interact with these separate universes. Gandalf61 (talk) 10:39, 23 October 2008 (UTC)

I just want to note that you've made a critical error in your description of the Big Bang. It did not expand into empty space. The Big Bang was the creation of empty space, along with everything else. It did not expand "into" anything. --98.217.8.46 (talk) 12:28, 23 October 2008 (UTC)

Yeah - it's a very common misconception to think of the big bang as if there was this infinite empty vacuum of space - and a gigantic explosion goes off, spewing matter into that space...we think of it in our mind's eye as if we're a few miles away from the explosion and something goes "bang" like a stick of dynamite going off with bits of matter flying outwards from that point. But that's a totally wrong idea. That's not at all like how it actually happened.

The big bang created the space itself - as well as all of the stuff inside that space. There also isn't a "before" the big bang because it created time as well as space. At the literal beginning of time the universe was a dot - something with zero size - and because time is also crunched up, the idea of time passing is meaningless too. At the instant of creation - that infinitely dense point expands rapidly - time starts running forwards and space gets bigger. It's hard to imagine a nothingness in which there isn't even any vacuum and the concept of distance and time don't exist - but that's what we have to envisage. When the big bang happens, space and time are formed - and rapidly expand - and they are already full of matter. It's not that the matter gets hurled outwards into empty space - it's that space itself expands outwards - remaining full of matter all the time it does that. And it's still happening. When we talk about the universe expanding and all of the galaxies receding from us - we're emphatically NOT saying that the galaxies are moving though space away from us - we're saying that space itself is stretching outwards and carrying the galaxies along with it. It's possible for very distant objects to recede from us at faster than the speed of light - but nothing can travel faster than light...what's going on is that the object is staying pretty much stationary and space itself is stretching away from us at that phenomenal speed. So asking whether there was something else 'outside' of the big bang is meaningless because there was no 'elsewhere' or 'outside' for anything else to exist in.

This is really almost impossible to get your head around - but that's what we're talking about here. I like to think of space as a sheet of graph-paper - printed on an amazingly stretchy rubber sheet. Matter is 'glued' to the graph paper. At the moment of the big bang, all of the matter is there - but the graph paper is squished into a teeny-tiny point. The 'explosion' corresponds to the rubber sheet rapidly stretching outwards - all of the grid lines on the sheet stretch out too and get further and further apart - moving the matter that's glued to it outwards too. The 'speed' of the matter across the grid lines is zero because it's all pretty much glued down - but they still get further apart because the grid itself is stretching. Now - the tricky part is that the universe might actually be infinite...so the sheet of graph paper has an infinite number of lines on it and it's infinitely "large" even at the instant of the big bang when the lines are squashed together until the are all touching each other. So something that is infinite is also zero in size...but since time doesn't exist when that happens - we don't have to think about it. In the first picosecond of time - the zero-yet-infinite sized thing becomes truly infinitely big - but the grid-lines are still insanely close together - the grid lines shoot away from each other as the early universe grows explosively.

The grid lines are still moving apart even now - and science has not yet decided whether they'll continue to move apart - or whether they'll gradually slow down and stop - or eventually reverse and shrink back to a big-crunch - like the big-bang played backwards...the smart money is saying that not only is the 'grid' still expanding - but it's actually expanding faster and faster! SteveBaker (talk) 13:17, 23 October 2008 (UTC)

I wouldn't say the universe "pre-big bang" was infinite and zero sized, it was infinite and infinitely dense. Therefore, any finite amount of matter (for example, the matter which makes up our observable universe today) would be in a zero sized region of it. (This is all very imprecise and involves lots of hand-waving, if you want to do things properly you need to wait until around a Planck time after the big bang, then the laws of physics start making a bit of sense.) --Tango (talk) 17:52, 23 October 2008 (UTC)

I think talking about expanding grid lines can be helpful, but it emphatically IS the same as saying that the galaxies are moving away from us in the usual sense. General relativity doesn't distinguish the two situations. See this old thread. -- BenRG (talk) 17:58, 23 October 2008 (UTC)

There really is no information to be had on this subject, just a lot of speculation. Until we can test the possibilities against each other—which may never happen—the speculation is more science fiction than science. It's entirely possible that the uniform expanding cosmos we see doesn't extend forever, and that beyond it are other regions with very different characteristics. Unfortunately in these models the different regions are causally disconnected, i.e. nothing (moving at the speed of light or less) can get from one to another because they're expanding too fast. In other words, these models all but predict their own untestability. Being untestable is not at all the same as being wrong, but testability is profoundly important. There's a quote on this subject that I like a lot:

"About 500 years ago man's curiosity took a special turn toward detailed experimentation with matter. It was the beginning of science as we know it today. Instead of reaching directly at the whole truth, at an explanation for the entire universe, its creation and present form, science tried to acquire partial truths in small measure, about some definable and reasonably separable groups of phenomena. Science developed only when men began to restrain themselves not to ask general questions, such as: What is matter made of? How was the Universe created? What is the essence of life? They asked limited questions, such as: How does an object fall? How does water flow in a tube? etc. Instead of asking general questions and receiving limited answers, they asked limited questions and found general answers."

— Victor Weisskopf (as quoted in "Nature's Greatest Puzzles" by Chris Quigg, hep-ph/0502070)

That's why, like Peter Woit, I'm more interested in electroweak symmetry breaking than eternal inflation and brane worlds: because there's a real chance that we'll learn something new about electroweak symmetry breaking within my lifetime (in fact, within the next decade, from the LHC). We've gotta stick with questions we know how to answer. -- BenRG (talk) 17:58, 23 October 2008 (UTC)

I find staggering the degree of confidence that comes through in some of this discussion of the big bang, and especially of the conditions prior to it.

For example, "The big bang created the space itself - as well as all of the stuff inside that space. There also isn't a "before" the big bang because it created time as well as space. At the literal beginning of time the universe was a dot - something with zero size - and because time is also crunched up, the idea of time passing is meaningless too. At the instant of creation - that infinitely dense point expands rapidly - time starts running forwards and space gets bigger."

Wanderer57 (talk) 18:50, 23 October 2008 (UTC)

Well, the "According to our current understanding of physics" bit is implied in any such answer. Is that what you mean? --Tango (talk) 19:53, 23 October 2008 (UTC)

It seems to me the certitude with which the statements are made is, shall we say, very bold. I accept the implied qualification "according to our current understanding of physics". However, with our current understanding of physics, we can't accurately predict the weather a month from now. This is not meant to be critical; just to express an element of disbelief. Wanderer57 (talk) 02:11, 24 October 2008 (UTC)

Thank you, Wanderer (no offense, Tango!) - the answer simply failed to understand that I was looking beyond those assumptions. I am operating under the quite possible assumption that space is of indefinite or indiscernibly large size. However, all of the matter in the local universe was in a very small area pre-big bang within this space (as a note, I find explanations that the area was "infinitely small" also to be presumptive, given our lack knowledge of quantum physics).

BenRG: the question is infinitely relevant to me, because it involves the nature of the universe. It may be that observable universe will eventually expand to the point of no return for life (this would be unavoidable under current theories). Would it all be over forever, or might another mass of energy form elsewhere from the remnants of other big bangs, gathering mass until it also explodes.

However, most importantly, I believe that matter/energy from other localized big bangs (or whatever other systems) may indeed be detectable, especially were it approaching us. I doubt any such research has been done; it would be enormously diffucult to establish a way to detect.

But: does anyone know of any literature on this? Magog the Ogre (talk) 04:49, 24 October 2008 (UTC)

I think what you're describing are called "bubble universes" and there has certainly been theoretical research done on them. I don't think there has been any real attempt to detect them since the theory says that's impossible. Remember, matter doesn't move outwards after a big bang, space just expands and the matter goes along for the ride (from the inside, it looks the same, of course), so another universe wouldn't be expanding towards us, it would be expanding within itself and would always be outside our observable universe. --Tango (talk) 09:41, 24 October 2008 (UTC)

No, I am decidedly not talking about those. I am talking about very distant big bang clusters in the same space-time continuum with the same physical constants as our own. If hope if you read my posts carefully, you will see that. Just like another galaxy is relatively far away to our own galaxy, perhaps there are other big bang thingies really far away from our own. Before, the idea that there were other galaxies was completely out of the paradigm of science; now, the idea of multiple big bangs at far distances is outside its paradigm.

And, again, you have given a confident assertion that empty space is tied to the big bang, a completely unproven and frankly presumptuous theory (if you have proof otherwise, I will listen). Magog the Ogre (talk) 03:44, 25 October 2008 (UTC)

In what way would they be a different universe if they are part of the same space-time continuum and have the same physical laws and constants? They're just distant parts of the same universe. That the big bang involves expansion of space and not just matter within space is a critical part of the theory, it doesn't make sense without it (for example, the speed of light limit doesn't apply to the expansion because the matter isn't actually moving, in your version it would apply and the universe wouldn't be able to expand as fast as it has done). --Tango (talk) 13:26, 27 October 2008 (UTC)

diabesity

what is the current status of diabesity in India? —Preceding unsigned comment added by 123.252.166.228 (talk) 11:51, 23 October 2008 (UTC)

Are you asking about "metabolic syndrome"? See this article. Axl ¤ [Talk] 12:38, 23 October 2008 (UTC)

I think the OP may have been referring to diabetes mellitus type 2, along with the related obesity. —Cyclonenim (talk · contribs · email) 17:29, 23 October 2008 (UTC)

Sugar bowl

In a nutshell ... and in lay terms that are not too scientific ... why exactly does sugar "clump" together when in a sugar bowl? And why do you get several little clumps mixed in among some non-clumped sugar? In other words, why does only some of the sugar clump together (while some does not), so that you don't get just one big massive clump? Thanks. (Joseph A. Spadaro (talk) 13:39, 23 October 2008 (UTC))

And, by the way ... is "crystallize" a correct term to describe the above situation? Or is that word inappropriate for some (scientific) reason? Thanks. (Joseph A. Spadaro (talk) 13:49, 23 October 2008 (UTC))

pockets of dampness? 194.221.133.226 (talk) 14:07, 23 October 2008 (UTC)

Yeah, dampness. And no, clumping is not the same as crystallization, though sugar is generally a crystal. — Lomn 16:47, 23 October 2008 (UTC)

I assumed something to do with dampness. What about dampness, though? If you have a sugar bowl in a cupboard, is one section of the cupboard significantly more/less damp than a section of the cupboard that is less than an inch away? A sugar bowl is perhaps 5 inches or so in diameter. In the kitchen cupboard, how much difference can the levels of dampness possibly be within that tiny amount of space contained by the sugar bowl? Thanks. (Joseph A. Spadaro (talk) 17:03, 23 October 2008 (UTC))

I don't know that it has to be significantly more damp; I would expect that simple variation is likely enough to start the process. Once begun, some mechanic (I'd guess something akin to surface tension) causes a preference for more water to accumulate on the clumps. So long as there's a positive feedback mechanic, you don't need much starting moisture, either absolutely or relatively, to get the end result. — Lomn 17:59, 23 October 2008 (UTC)

If you don't disturb the hardening sugar, you will end up with a crust or hardened grains. Putting in the spoon will break up that surface crust into lumps. Graeme Bartlett (talk) 20:38, 23 October 2008 (UTC)

Sugar is incredibly hygroscopic; that is, it attracts water very strongly. This is part of the reason why jams, etc. can preserve without becoming mouldy - no water is left available for the mold to use. In lay terms, the clumping occurs as a result of that hygroscopy as well as the purity of the sugar in your bowl. Unlike most things in your kitchen, sugar is a very pure substance; something like 99.9% sucrose is the estimate I've heard. We don't seem to have an article on it, but some cooking application actually require you to add a different sugar (such as corn syrup), to prevent that clumping. So you've got a material that draws moisture from the air, that bonds easily with water, and that is very pure so that nothing can get in the way of the creation of clumps. Matt Deres (talk) 15:34, 24 October 2008 (UTC)

Wow! That's interesting. I had not realised that lack of available free water was the reason why jam doesn't go bad. However, our OP's question is not so much "Why does it absorb water and stick together?" - it's "Why are there clumps?" - after all, a bowl of uniform, granular, dry sugar seems like it would absorb water evenly throughout the mass and end up with either a crust on the top or as one solid mass. What explains the clumps? It seems like there must be some kind of mechanism that causes sugar that's already glued together a couple of grains to preferentially cause water to be absorbed on the boundaries of the growing clump rather than elsewhere in the still-unclumped bowl. That seems kinda counter-intuitive to me - which is what makes this a difficult question. SteveBaker (talk) 15:45, 24 October 2008 (UTC)

I'm just speculating, but my guess is that it has to do with the way water is attractive to itself. A random molecule of H₂O might be more attracted to an already "damp" bit of sucrose than the surrounding dry sugar. That could create a situation where a bit of sugar that starts to become "damp" would have a tendency to attract more water rather than allowing the water to distribute itself evenly, which would create a crust.

The bit about sugar drying out jam and preserves is true, but not the entire story (which is why I said "partly" :-). A better example would have been for me to say that was true of honey, since it cannot go rancid (millennia-old honey is still "good") and the effect is, so far as I know entirely due to the hygroscopy of the sugar therein. Jams are "preserved" because they're cooked into jars in such a way that there should be no living mold or bacteria inside it; the sugar comes into play after the jar has been opened. When you think about it, jam should be a mold and bacterial heaven - a jellied material filled to the brim with nutrients and sugars. An opened jar of jam kept in the fridge should turn green long before the bread and fruit would, but it doesn't and that (so far as is my understanding) is due to the dryness. Matt Deres (talk) 17:22, 24 October 2008 (UTC)

Thanks for all of the above replies and input ... it was very helpful and informative. Thank you. (Joseph A. Spadaro (talk) 12:52, 25 October 2008 (UTC))

nature

why oxygen is combustible? —Preceding unsigned comment added by 121.247.248.185 (talk) 14:00, 23 October 2008 (UTC)

It isn't. Algebraist 14:07, 23 October 2008 (UTC)

To expand on Algebraist's answer, oxygen itself isn't combustible, only fuels are. However, fuels require oxygen to burn. —Cyclonenim (talk · contribs · email) 16:34, 23 October 2008 (UTC)

And to expand on that, the key oxygen-related processes are redox reactions. Our combustion article may also be of interest. — Lomn 16:43, 23 October 2008 (UTC)

What's going on is that the chemical bonds that hold two oxygen atoms together to make an O₂ molecule and the chemical bonds that hold whatever the fuel molecules start off as - contain more energy than when oxygen is combined in the same molecule as the fuel. So (to pick an easy one) the energy bound up in two H₂ hydrogen molecules plus the energy bound up in an O₂ oxygen molecule is much greater than the energy found in two H₂O molecules. So when you mix hydrogen and oxygen - the molecules try very hard to get into that lower energy state. If you can just supply a tiny spark to get the first few hydrogen and oxygen molucules to rearrange themselves - then the left-over energy when all you have left is water is enough to start more molecules reacting. This kind of chain reaction pumps out massive amounts of 'left over' energy. Oxygen is good at doing this because there is a fair amount of energy bound up in the oxygen molecule - and the nature of the bonds that oxygen can form with other elements means that the reactions generally go rather easily and produce lots of left-over energy. SteveBaker (talk) 00:58, 24 October 2008 (UTC)

what happens if we give AC excitation to alternator

what happens if we give AC excitation to alternator instead of DC excitation ? —Preceding unsigned comment added by Sai krshn (talk • contribs) 15:40, 23 October 2008 (UTC)

The answer might depend on the polarity and phasing of the AC field comparede to the rotor position. Do you mean AC excitation which is not rectified to DC? "AC excitation" in books sometimes refers to rectified AC [9]. Variable frequency AC excitation might be useful for wind or hydro generators [10]. Edison (talk) 03:07, 24 October 2008 (UTC)

Oil Creation

(relating to the earlier question on oil well replenishment)

Not to suggest for an instant that I think this is practical, but suppose hypothetically that we had a system for collecting "dead algae" from the present oceans, as well as a quick process for converting it to oil.

How much oil could be produced per annum, just based on the amount of raw material that is created per year? Wanderer57 (talk) 17:17, 23 October 2008 (UTC)

If we removed all the dead algae we would probably destroy the ecosystem. We could only take the dead algae that reached the bottom of the ocean and wasn't going to be eaten by anything, and that's going to be a very small amount over short time spans. --Tango (talk) 17:32, 23 October 2008 (UTC)

If one assumes that you only remove organics that would otherwise be stored in rock, and avoid more aggressive action at the risk of damaging the ecosystem, then you would be limited annually to about 1/500th the amount of carbon humans release through fossil fuel burning. Dragons flight (talk) 19:06, 23 October 2008 (UTC)

It's not exactly a silly idea. There are companies out there looking to farm algae on industrial scales (see Algae fuel). There are certainly ways for us to turn almost any plant material (algae are plants) into biodiesel or ethanol that could be used in place of oil in many applications. What they are doing is effectively using the plants as little machines to capture sunlight and turn it into carbohydrates - and from carbohydrates to hydrocarbons is not such a huge step. So farming algae as a means to trap sunlight and turn it into fuel is not so silly. However, digging up algal deposits from the ocean bottoms isn't going to be particularly effective. Remember - the process I described in mind-numbing detail earlier today is all about concentrating the oil from large areas of ocean bottom - over millions of years - into convenient puddles. The actual oil formation step is not conceptually very difficult. You might have to dredge thousands of square miles of ocean bottom (with the obvious horrific environmental consequences) just to make a relatively small amount of oil - and once you've done that - it's going to take a long time to replenish.

What makes oil so potent and useful as a fuel is that it's the result of a LOT of sunlight being absorbed by a HELL OF A LOT of algae - and then squished down to a tiny fraction of it's original volume by all that pressure. Oil is (in effect) highly concentrated sunlight (it's the same with coal and natural gas). But to concentrate it to that degree - you have to start off with an insane amount of the stuff. The oil we have burned in just a couple of hundred years is all of the oil formed by all of the ocean bottoms over millions of years. There just isn't that much naturally occurring algae out there.

SteveBaker (talk) 00:51, 24 October 2008 (UTC)

Confusion with organoselenium compound toxicity

It was my understanding that it is the electrons in an atom which account for its chemical properties. In this case, selenium should interact very similarly to oxygen, which is does by forming C-Se organoselenium bonds in compounds such as selenols (alcohols with SeH functional groups rather than OH). Why would the equivelent of usually non-toxic alcohols, but where the OH is replaced with SeH, be toxic if chemically these compounds should act the same? I hope this makes sense. Thanks.

—Cyclonenim (talk · contribs · email) 17:34, 23 October 2008 (UTC)

Life is very finely balanced, even the slightest change can make a big difference. Alcohols are toxic, we just have enzymes that can deal with them (in small quantities). Those same enzymes, which are highly optimised, aren't going to work as well (if at all) for selenols, so they have a greater effect. There's probably nothing stopping there being enzymes to deal with selenols, but the fact that we very rarely ingest them means there has been no evolutionary pressure to create them. --Tango (talk) 17:48, 23 October 2008 (UTC)

(ec) Careful: "similar" is not the same as "same". It's only similar, and electrons only account for some properties. "The s and p valence electrons" might look similar for Se vs O, but they are further from the nucleus and there are lots of other electronic differences. There's a whole paragraph in the organoselenium chemistry introduction talking about patterns of differences within that column on the periodic table. Bond strengths are different, so anything that relies on the C-(Se/O) bond breaking or (not-breaking) during a reaction is susceptible to that difference. The atoms are different sizes and have different covalent radii (related to bond-length to C), so anything that relies on the part of a molecule having a certain physical shape or atomic position may be affected. The two elements have different electronegativities (stability regarding charge), so anything that relies on the ionic form having a certain reactivity may be affected. The atoms have different masses, so anything that relies on the atoms moving may be affected (although it's only a slight difference here). DMacks (talk) 17:54, 23 October 2008 (UTC)

Thanks, that pretty much solves my query :) —Cyclonenim (talk · contribs · email) 19:11, 23 October 2008 (UTC)

Question involving special relativity

Hi! If I sent a friend at a little more than half the speed of light and I ,myself, went in the opposite direction at the same speed, and looked back, what would I see? How much heavier will the friend seem?? —Preceding unsigned comment added by 116.68.77.65 (talk) 17:56, 23 October 2008 (UTC)

You would see your friend redshifted by a factor of ${\tfrac {1+(v/c)}{1-(v/c)}}$, where $v/c$ is your speed as a fraction of $c$ (i.e. a little over 1/2). There's no natural answer to the "how much heavier" question, since your friend is far away and getting farther all the time; you can't put him/her on a scale. You'd have to carefully define what you mean by "weight" before this question could be answered. I think you're thinking that the two speeds of a little over $c/2$ would "add up" to a speed of a little over $c$, but it doesn't work that way. You're both traveling at a little over $c/2$ with respect to the reference frame you chose when you specified the speeds. With respect to a reference frame moving with one of you, the other is moving at a little over $4c/5$. -- BenRG (talk) 18:03, 23 October 2008 (UTC)

There is an important thing here. Your friend is moving at half the speed of light away from the starting point - and you are moving the other way at half the speed of light...BUT...that nice Mr Einstein pointed out that you cannot move away from your friend (not he from you) at the speed of light. That's not allowed because (a) all motion is relative so the starting point isn't in any way special and (b) you can't move faster (or even as fast) as light. So the odd things you're suspecting you might see because the light from him to you can't catch you up won't possibly happen and (aside from some time/space/mass distortions due to your high speeds) - nothing particularly odd happens. There would be some significant red-shift in the light coming from your buddy. SteveBaker (talk) 00:37, 24 October 2008 (UTC)

Physics Exhibition

Please suggest me a working model for Physics Exhibition in my schhol of class XIth standard. —Preceding unsigned comment added by 117.199.176.59 (talk) 19:02, 23 October 2008 (UTC)

What areas of physics interest you? It's a very broad subject. --Tango (talk) 19:54, 23 October 2008 (UTC)

Perhaps you could do something with polarized light. a piece of stressed transparent plastic between crossed polarizing filters looks great. Or perhaps you could make something to measure the speed of light, or speed of transmission down a cable. For this have an oscillator that sends a pulse down a "long" cable and then regenerates it and sends it again. Then you can have a counter to measure the frequency. Graeme Bartlett (talk) 23:14, 23 October 2008 (UTC)

My son made a Lego machine that counts the number of licks it takes to get to the center of a tootsie-pop (the company advertising always used to say that "nobody will ever know" because people have to crunch through the coating to get to the center before they've licked it enough. So he built a totally dispassionate robot that would lick the pops and be totally incapable of crunching them! Silly though this sounds - it was very successful. He came first out of a couple of hundred projects in his school - got a special award from the science staff (who said it was the best science fair project they'd ever seen!) and it got him a plaque from the company that makes tootsie-pops after someone wrote to them to tell them what the answer was. Photos of the "lick-o-matic" can be found here. The answer (my son claims) is (on average) 332 licks - with a surprisingly narrow standard deviation. But I think we'd be hard-pressed to justify that claim in terms of human licking! He did a fairly detailed analysis of the statistics of his results - comparing different flavors of pop and different brands. Interestingly, there was a very solid statistical difference between tootsie pops of different flavors - cherry and orange tootsie pops stood up to a lot more licking than grape or chocolate.

Another project that my kid got awards for was a study of which brands of paper kitchen wipes were strongest when wet and when dry. He used a long vertical plastic tube with holes cut into the side every 5cm and dropped a ball bearing through each hole in turn (starting at the lowest) until it could tear through a single sheet of the test material (which was held across the bottom of the tube with an elastic band). He tested a dozen brands - ten tests each both wet and dry - and also tested some other kinds of paper product for comparison purposes. Interestingly - his conclusion was that in almost every case "you get what you pay for" and the cost of the paper (per sheet) was almost exactly proportional to it's strength in terms of the kinetic energy of a ball bearing that could just tear through the sheet. At the actual science fair, he used the same apparatus to measure toilet tissue in a 'live' demonstration of his technique. He got awards for that one too.

The message is that you can do well with an amazingly silly or highly trivial topic - if you do the science properly. That means using proper controls (where appropriate), double-blind testing if humans are involved - analysing the results from a reasonable number of trials, showing your data, relating your results to other researchers, stating a clear conclusion...all of those good things are what you score points on...not on the 'gravitas' or 'appropriateness' of your subject.

SteveBaker (talk) 00:23, 24 October 2008 (UTC)

That that lego lollipop licker is impressive. From your description I had assumed he used Mindstorms. He took no such new-fangled short-cuts. I am impressed. APL (talk) 01:01, 24 October 2008 (UTC)

Yeah - we have a couple of LEGO Mindstorms sets and it would have been a lot easier to count the revolutions of the 'licker' using the RCX computer and a rotation sensor. But because the machine was going to be on show, and needed to be visually attractive - Oliver decided to build the gearing stages to make a device like a car odometer to do the lick counting. Lego gears come in 40, 20, 16 and 8 tooth varieties so it wasn't too tough to get the 10:1 gearing you need to build an odometer-style counter.

Another hard part was finding the right amount of water to get into the sponge 'tongue' so that it would slide over the surface without sticking to it if everything dried out - and yet wouldn't splatter water everywhere as it whirred around. The level of the water in the plastic container is very critical to operations - and because it gets kinda sugary after licking through half a dozen tootsie pops - the water had to be replaced and carefully filled to the right level after every few runs. The machine does about two licks per second - so it takes about two minutes to get to the oh-so-delicious center of the tootsie-pop - which is just about right as a crowd-pleaser. In the end we used that dense black electrically-conductive foam because it seemed to best match the rate of 'erosion' that we were getting by licking the tootsie-pops the old-fashioned way...but that's definitely the weak spot in the experiment.

I was helping him with one part of the design because he originally wanted to automatically detect when we got to the center of the tootsie-pop - perhaps by drilling a hole through to the center from the opposite side of the 'pop and pushing the drill-bit through the soft center until it hit the underside of the hard candy shell. The idea was that we should be able to measure the electrical conductivity between the tongue and the metal rod and see a voltage spike at the same point in every revolution when we got to the soft center - but with water everywhere and the foam tongue not being as conductive as we thought - we never did get that part to work reliably - and on the night before the presentation, we yanked that part of the gizmo and ran without it. So in the end, we just stopped the machine manually when we could see the soft-center showing through. Fortunately, nobody seemed to mind!

SteveBaker (talk) 05:27, 24 October 2008 (UTC)

While not for a science fair and not physics, you may be interested in [11] & [12] Nil Einne (talk) 15:38, 27 October 2008 (UTC)

• Wow, that is some impressive science. :) I have no doubt your son will become a great scientist if he wants to (and probably a good wikipedian too). - 131.211.211.25 (talk) 07:18, 24 October 2008 (UTC)

Pulsejet afterburner?

Could you put an afterburner on a pulsejet if the injectors were timed perfectly? Would it work or does it only work on other types of jet? Thanks. 92.5.107.9 (talk) 20:44, 23 October 2008 (UTC)

Perhaps. The afterburner's job is to burn up any unburned fuel or carbon monoxide in the outflow from the main engine. Doubtless pulsejets leave just as much unburned fuel and CO as conventional jets - so presumably more energy could yet be extracted. However, the mechanisms that make these wierd machines operate make unusual demands on the shape of various chambers in the engine and it may well be that obstructing the outgoing jet would somehow stop them from working. SteveBaker (talk) 00:11, 24 October 2008 (UTC)

Thanks, but the afterburner doesn't just burn up unburnt fuel but it injects fuel in the exhaust flow which then gets ignited, so you could put the injectors in the exhaust section. Would that work? 92.0.49.113 (talk) 00:25, 24 October 2008 (UTC)

Indeed according to the article the efficiency is reduced because your adding more fuel but there is already not much oxygen Nil Einne (talk) 15:43, 27 October 2008 (UTC)

Unknown firstborn vaccination

While on my trip to Brazil I noticed that most native Brazilians have a small circular scar on one of their upper arms. I havent seen anyone with this type of scar in the US, where I live. I presume this scar is from a vaccination taken as an infant, and seeing as Brazil is a third world country with many endemic diseases the US has long eradicated, I wonder if this is a vaccination for some kind of tropical disease or a disease that hasnt been eradicated yet. —Preceding unsigned comment added by 189.58.26.29 (talk) 21:01, 23 October 2008 (UTC)

Lots of people in the UK have a very similar scar from the BCG vaccination against Tuberculosis. --Tango (talk) 21:09, 23 October 2008 (UTC)

Probably a Smallpox vaccine scar. You see them in the USA too. Mostly in people over 40. APL (talk) 21:10, 23 October 2008 (UTC)

I live in the UK and my dad has that scar, I think from the BCG. I have had all the vaccines I need to have (that includes the BCG), but I don't have that scar and nor does any other young person I know. I hated the BCG though, 9 injections in one go - torture.

Also, I didn't have it as an infant, I had it in school at twelve or thirteen and so did all the other people in school. Or maybe I did have it as an infant and the one I had in school was a top-up vaccination...I dunno. 92.5.107.9 (talk) 21:50, 23 October 2008 (UTC)

In the US, vaccinations for smallpox and tuberculosis have not been routinely given for thirty years or so. In the case of smallpox this led to a number of concerns, a couple years back, that the US would be particularly susceptible to bioterrorist attacks from smallpox. --98.217.8.46 (talk) 22:12, 23 October 2008 (UTC)

Here's a nice PowerPoint file showing how to tell a BCG scar from a smallpox vaccine scar: [[13]] --Scray (talk) 01:31, 24 October 2008 (UTC)

Data point: I was born in Brazil in the 1970s, and have a BCG scar as shown in those slides, but on my right arm, while they say it's usually on the left. --Sean 15:11, 24 October 2008 (UTC)

I once noticed a model from the UK on a non-nude porn site I used to go to had a scar on her arm and I wondered why she had a smallpox vaccination but she was so young. —Preceding unsigned comment added by 63.245.144.77 (talk) 07:17, 24 October 2008 (UTC)

The BCG is a single injection. The "nine injections in one go" are probably the Heaf test: six needles at once. The Heaf test is now obsolete in the UK. Axl ¤ [Talk] 16:58, 24 October 2008 (UTC)

I had the Heaf test (probably one of the last that did) and it's not very unpleasant at all. It's about the same as the finger prick tests they do for blood sugar or iron levels, just 6 of them. However, I was Grade II, so didn't have the BCG. According to friends that did have it, that wasn't pleasant at all. While it's one needle, it's one pretty big needle. --Tango (talk) 17:07, 24 October 2008 (UTC)

I can't remember the needle but the swelling post injection is rather painful and it takes quite a while to go down (depending on the person). Incidentally, in some countries (including Malaysia) the BCG is given more then once (usually at birthas a baby and ~12 years old) so is more then one injection (albeit not at the same time). And AFAIK, the BCG in Malaysia is usually given to the left arm Nil Einne (talk) 15:06, 25 October 2008 (UTC)

Burj Dubai

How deep do the foundations need to be for the Burj Dubai? Thanks 92.5.107.9 (talk) 21:45, 23 October 2008 (UTC)

Burj Dubai#Construction says there are piles buried more than 50m. --Tango (talk) 22:29, 23 October 2008 (UTC)

Thanks, I must have missed that. 92.5.107.9 (talk) 22:39, 23 October 2008 (UTC)

Lactose Intolerance

Why does consuming lactose if lactose intolerant result in diarrhoea ? —Preceding unsigned comment added by 80.5.198.130 (talk) 21:56, 23 October 2008 (UTC)

See lactose intolerance. Basically, since a lactose intolerant can't process lactose, any lactose consumed will reach the large intestine intact. When it does, the bacteria that reside there go on a feeding frenzy and their waste products prove very unpleasant for the host. Someguy1221 (talk) 22:04, 23 October 2008 (UTC)

The fascinating thing about lactose intolerance is that it's not some kind of unfortunate mutation or disease. Almost all mammals are lactose intolerant. Animals who drink their mother's milk when they are babies have to be weaned off onto regular food at some point. Most mammals (and also humans) have evolved to lose the ability to digest milk once they get past the age when they should be on solid food. This makes the process of weaning off of the mother's milk happen automatically when the young animal gradually finds that milk makes them feel sick. This is a good thing for most mammals because it means that the next set of babies don't have to fight with older siblings for their share of the mother's milk supply - and the mother doesn't have to eat as much to keep the supply going. For non-human mammals, there is no down-side to this because once they are weaned, they have no way to get milk products anyway. Humans are the sole exception - and it seems that even we have been 'naturally' lactose intolerant and we are literally in the process of evolving the ability to continue to digest milk into adulthood. But humanity hasn't finished that evolutionary step yet - so some of us have a specific gene mutation on chromosome 2 that prevents the "normal" shutting down of the lactose-digestion pathways when we are a couple of years old - and that allows those freakishly lactose-tolerant mutants to pull off this highly unusual trick! Meanwhile the 'normal', un-mutated humans can't cope with milk products once they are more than a few years old.

Since this evolutionary change can only possibly have started when we first started farming and domesticating other mammals - perhaps as little as 10,000 years ago - this is an interesting take on how fast evolution can operate. The ability to consume the milk of other animals into adulthood has probably been only a fairly small benefit - and in more civilised countries where there are plenty of alternatives to milk products, the evolutionary advantage must be close to zero - so humans will probably end up only patchily lactose tolerant off into the indefinite future. Those societies that have been domesticating cattle for the longest time (basically, Europeans) are the most lactose tolerant - those that never did get around to doing that are still mostly lacking this handy little mutation.

According to our article on lactose intolerance the problems for intolerant adults arise because the bacteria that naturally live in our gut take advantage of all of this undigested food passing into the intestines - and they go into overdrive. That causes much gas production. Gas in the intestine prevents it from working efficiently - so water is not absorbed well and the excess liquid winds up in the fecal material along with the gas. This easily explains the symptoms of bloating, flatulence and runny poop.

Fortunately - I'm one of the freakish mutants - which really makes me fancy a piece of ripe brie right now. Thank god for that little 'oopsie' on chromosome 2! SteveBaker (talk) 23:57, 23 October 2008 (UTC)

Would the genetic mutation be the only reason why some people can eat dairy or is there also an environmental effect. If you ate dairy products regularly, would there be no sign of lactose intolerance even though the child does not carry the mutation? As a "weaned" (as in old enough to eat normal food) Chinese person, I can still drink milk with no ill effects (although I can't say that about my parents). 96.242.34.226 (talk) 01:19, 24 October 2008 (UTC)

Steve, I'm pretty sure that lactose-intolerant people can eat brie, too. It's a low-lactose cheese. --Scray (talk) 01:27, 24 October 2008 (UTC)

The Lactose intolerant page has an error I think, the table has messed up data, correct me if I'm wrong. What happened there? 96.242.34.226 (talk) 01:44, 24 October 2008 (UTC)

To ansawer 96.242.34.226, whilst there are genetic differences (hence more of problem in Far East and less in Europe), can also be acquired due to bowel inflammation affecting lactase production: temporarily after childhood episodes of gastroenteristis is common (may last upto 12 weeks), and sometimes perminantly so (especially after a bout of giardiasis). David Ruben ^Talk 01:59, 24 October 2008 (UTC)

Sure - there are diseases that make even tiny babies (who should NOT be lactose intolerant through genetics) incapable of digesting milk...which (since that's all they eat) is a pretty serious matter. But the vast majority of people who are lactose intolerant are 100% "normal" - and those of use who have lactose tolerance even into adulthood are mutants. (It's less exciting than on X-men...trust me!) SteveBaker (talk) 05:01, 24 October 2008 (UTC)

According to this source (and many others), for example, over 90% of Asian-Americans are lactose-intolerant. ~AH1^(TCU) 13:17, 24 October 2008 (UTC)

But can you be lactose tolerant without the mutation? Which was what I was saying before. 96.242.34.226 (talk) 00:28, 25 October 2008 (UTC)

I don't see how. If you have lactose-intolerant genetics, you simply don't have the mechanism to make the lactose-digesting enzymes. It's hard to imagine any kind of disease that would somehow restore that ability. SteveBaker (talk) 22:14, 25 October 2008 (UTC)

Apologies if this is too repetitive of SteveBaker's points, but I don't see it put quite this way on a cursory glance above. In most cases of what people call "lactose intolerance", the genetics is as follows: "Normal" humans are born with the ability to digest lactose: that is, they produce lactase in amounts adequate for digestion throughout their childhood. But they also normally lose that ability when they mature. It's people who have persistence of lactose tolerance into adulthood who have a mutation, located on chromosome 21, that causes lactase persistence. "Lactase persistence is a heritable autosomal dominant condition that results in a sustained ability to digest the milk sugar lactose throughout adulthood." - Nunh-huh 00:35, 26 October 2008 (UTC)

I thought I'd already posted this but must have previewed or something. Anyway I believe people who regularly consume milk (well lactose), particularly those who consume it from childhood and don't stop tend to have a higher tolerance for lactose (in other words they can drink a great amount without symptoms) even if they lack the lactase persistence mutation. I suspect they'd still usually be called lactose intolerant however. This isn't that surprising since as mentioned by Nunh-huh, humans do have the ability to digest lactose, they just lose it over childhood. Most of our regulatory and development systems are quite complex so it's not unlikely there will be some feedback mechanism that comes in from the continual consumption of lactose. This is partially supported in our article which says "Some cultures, such as that of Japan, where dairy consumption has been on the increase, demonstrate a lower prevalence of lactose intolerance in spite of a genetic predisposition" (well okay this supports the idea that people who are genetically lactose intolerant can in fact be lactose tolerant but it suggests to me there is resonable chance what I'm suggesting is true). It also describes how lactose intolerance arises. It's not a simple process and in some people it develops over many years. And the levels of lactose intolerance in a population increases with age. Nil Einne (talk) 13:40, 27 October 2008 (UTC)

Trees in Mongolia

Why do trees only grow on the north side of mountains in Mongolia?70.88.40.1 (talk) 23:40, 23 October 2008 (UTC)

What makes you think that's true? I just surfed over to Google maps - and typed in Ulaanbaatar - and it looks to me like there are trees on the southern slopes too. But if it is true (and to the extent that it's true) - I would imagine it's because the northern slopes are retaining rainwater better because they get a little less sunlight and any wind blowing onto them would have to come from the North - where it's presumably cooler. It's also possible that winds blowing from the North carry lots of water which is dumped onto the hillsides as the air is forced upward into the cooler altitudes...where the wind from the south comes over the desert steppes and therefore contains no water to dump onto the southern slopes. Most of Mongolia is pretty arid (think "The Gobi Desert"!) - and on a steep mountainside - what little rain does fall would run downhill pretty fast...so avoiding evaporation would be a good thing. This is just an educated guess though - I don't know for sure. SteveBaker (talk) 00:07, 24 October 2008 (UTC)

October 24

Contrail, crepuscular ray, zodiacal light, or other?

Hi. At around 6:30 pm EDT today, I saw a glow in the East West. The sky was orange near the horizon, but below the orange was a layer of cloud stretching horizontally across the horizon. The pillar/tail-like glow was more reddish and brighter than the surrounding sky, and I estimate it stretched about 35 degrees tall and 10 degrees wide. By the time I got home, I couldn't take a picture because it had dissapeared. At the time I saw the glow, the sky was too light for me to find either Venus or Jupiter. Could it have been a contrail? I've seen contrails spreading to 10 degrees wide, but today I saw a contrail persist, but I don't think it was humid enough today to allow contrails to spread that far, although an earlier contrail appeared reddish in colour (location: S. Ontario). I think it might have been a crepuscular ray, but do those occur after sunset? Or, could it have been another type of sky glow associated with the sun? I know it wasn't illuminated by anything other than the sun, because it was really close to where the sun had set and higher up it was dimmer. I might have also seen other lower glow patches similar to this one apparently eminating from behind the cloud, perhaps suggestive of a crepuscular ray, but those were less distinct if they existed. What about the zodiacal lights? Very few streetlights had turned on near where I was observing this from by the time I first saw it. However, don't they usually spread up to 60 degrees from the horizon, appear as a triangle, and occur later after sunset? In SkyNews magazine, they mentioned an opportunity to see the zodiacal lights, but that was for late September and in the early morning. So, any ideas? Could it have been something else? Thanks. ~AH1^(TCU) 01:21, 24 October 2008 (UTC)

Do you mean in the West? In the East after sunset wouldn't be close to where the sun had just set... --Tango (talk) 11:45, 24 October 2008 (UTC)

Oops, yes I did mean in the West. ~AH1^(TCU) 13:05, 24 October 2008 (UTC)

Earths atoms

How many atoms are in the Earth? Is it even possible to calculate this, and if so, how many pages of numbers would you need to display the amount? 63.245.144.77 (talk) 02:14, 24 October 2008 (UTC)

Don't know if this is homework or not, but I'll assume good faith. Google show several answers for number of atoms earth: [14], [15], [16]. They roughly agree on the number, ~10^50. And as you can see, thanks to the benefit of scientific notation, the answer is very short. Even if you were to write out every digit, it would still easily fit on one page (1 followed by 50 zeroes). - Akamad (talk) 02:27, 24 October 2008 (UTC)

130 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 atoms, give or take. Dragons flight (talk) 02:33, 24 October 2008 (UTC)

Can I get a recount? :) 67.184.14.87 (talk) 16:01, 25 October 2008 (UTC)

Well - the others have given you the correct answer - but you should really know why it's actually VERY easy to calculate this number - so I'm going to show you which Wikipedia pages I went to and how I did the math.

If you made the assumption that it was very roughly 1/3rd iron, 1/3rd oxygen and the other third was about as dense as silicon - (you can look it up in Abundance_of_elements_on_Earth) then you could look at the mass of the earth 6×10²⁴kg (from our article Earth)- which is 6 followed by 24 zeroes - and say that there was roughly 2x10²⁴kg of each of those three elements. The Avogadro constant says that there are 6×10²³ atoms in every "mole" of a substance. A mole is defined as the atomic weight of the atom times one gram - and we can go to the articles on Iron, Oxygen and Silicon to find out their atomic weights. So there are 6x10²³ atoms in every 16 grams of oxygen, in every 56 grams of iron and in every 28 grams of silicon. There are 1000 grams in every kilogram - we have to divide the mass of each of the elements in the earth (roughly 2x10²⁴kg - or 2x10²⁷grams) by the number of grams we just figured out - and that gets us to get the number of moles of each substance in the entire earth - then we can add those up and multiply by Avogadro's constant to get the number of atoms. So we get out our 12" slide-rules (you can use a calculator) and figure:

( 2x10²⁷ / 16 + 2x10²⁷ / 56 + 2x10²⁷ / 28 ) x 6x10²³ = 1.3 x 10⁵⁰

...which is 13 followed by 49 zeroes - which is (suspiciously) identical to the number that Dragons flight just gave us...suggesting we both made the exact same decisions when it came to approximations (or SOMEONE was looking over my shoulder). Anyway - with the limited information we have about the precise composition of the earth's core - this is a fairly rough estimate - it couldn't be twice that number - or half that number - but we could easily be 25% off if the geologists are wrong about the amount of nickel in the core or something like that.

Oddly - we could tell you the total number of protons and neutrons in the entire earth - that's MUCH easier and we know the answer to surprisingly good precision! It's just Avogadro's constant times the mass of the earth in grams - and that comes out to about 3.60x10⁵¹. That's actually a fairly accurate number because it doesn't depend much on what the earth is made of - only on how heavy it is and what Avogadro's constant is - both of which we know to better than a tenth of a percent.

SteveBaker (talk) 04:56, 24 October 2008 (UTC)

I posted two hours before you. I can only conclude that you are spying on me. AAAHHHH!! Dragons flight (talk) 11:25, 25 October 2008 (UTC)

Thanks, guys! and this was not homework, by the way, I was just curious. While we're on the subject, how many atoms are in the entire solar system? :D

And how did they calculate the earths weight anyway? I would imagine it has something to do with it's motion or something, but there I go pretending to understand anything Newton said. :P 63.245.144.77 (talk) 07:14, 24 October 2008 (UTC)

Wheighing the Earth was traditionally done with the Cavendish experiment. This doesn't actually weigh the earth, but the gravitational constant. If we know this constant, then using the shell theorem for simplification, we only need to measure the acceleration of gravity and the Earth's radius to weigh it accurately. Someguy1221 (talk) 07:21, 24 October 2008 (UTC)

Entire solar system is easy. From our article on the Sun, we find that the Sun represents about 99.8% of the total mass of the solar system. For practical purposes, we can safely ignore all the other planets, asteroids, dust, comets, and what have you. The Sun's mass is about 2x10³⁰ kg, its composition is about 25% helium and 75% hydrogen. (There are traces of other elements totalling about 1% of the Sun's mass; again, we can safely ignore those for an atom count.) The actual math is left as an exercise for the reader. TenOfAllTrades(talk) 13:17, 24 October 2008 (UTC)

Yep - so it's the same calculation as for the Earth - but with different numbers: 5x10³²g of helium (atomic weight 4) and 1.5x10³³g of hydrogen (atomic weight 1) - so 3.5x10³³ moles which is 1.2x10⁵⁷ or 1,200,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 atoms in the sun (or the entire solar system...it's about the same number). Since I just KNOW you're itching to ask...for the entire milky-way galaxy - it's about 6x10¹¹ times the mass of the sun - and has about the same composition (except for dark matter, black holes, neutron stars and other things that maybe don't have atoms per-se) - so we'll go with 7x10⁶⁸ for the entire galaxy. For the entire universe we don't know - it's probably infinite. But for the "observable universe" - which is all we can ever see or interact with - every single atom that "matters" to us - it's about 10⁸⁰ atoms:

100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000

Since that's mostly hydrogen - the number of protons and neutrons is about the same - if you add in the electrons you can roughly double that number. Toss in the photons, and count quarks and maybe you get to add one more zero...but it's still not enough to fill even one line of text on my monitor - let alone an entire page! Heck it's not even close to a Googol.

For really big numbers, the number of possible games of chess is estimated to be 10¹²⁰ - which might just take two lines of zeroes if you use a nice big font size.

For afficianado's of really REALLY big numbers, it's hard to top Graham's number (which genuinely comes up in real mathematics in Ramsey theory). It is truly, unimaginably large - you'd need more zeroes (by far) than there are hydrogen atoms in the visible universe to write it down...even in 10^N notation - there would be more digits in N than there are atoms to write it down with. Mathematicians have invented an entirely new notational system just to express this number in any reasonably compact form!

I hope Graham's number doesn't disappoint as much as atom-counting does! SteveBaker (talk) 13:55, 24 October 2008 (UTC)

Apparently, there are "specific integers known to be far larger than Graham's number", but it's hard/impossible to comprehend what "far larger" means in relation to something that's already incomprehensibly large. -- JackofOz (talk) 23:11, 24 October 2008 (UTC)

Conway chained arrow notation can easily produce numbers which are far larger than Graham's number and express them in a very compact form. I was led to believe that Graham's number's claim to fame is that it is the largest number that has appeared in a published mathematical paper. SpinningSpark 23:33, 24 October 2008 (UTC)

"Build a better mousetrap, and someone will build a better mouse"

Are there any confirmed cases of increased trap resistance in mice (in general, or at a particular site) following a particular advancement in the mousetrap (in general or at the site), comparable to antibiotic resistance in bacteria?

On a related note, might building better mice be a more promising line of endeavour than building better humans, if undertaken for the same ultimate purposes? If so, might building better mousetraps be a more cost-effective way to do it than more direct human intervention? NeonMerlin 06:24, 24 October 2008 (UTC)

It really seems unlikely that they'd become resistant to mechanical traps. That would really require some kind of genetic change that made them avoid traps specifically - but not become so timid and nervous as to be unable to function in the world. So few mice out of a typical population are caught by traps that the probability of such a very specific evolutionary change being statistically beneficial is rather low. On the other hand, it's known that some vermin have become resistant to poisons we put out for them. Rats (and perhaps mice) that have evolved a resistance to warfarin (a common rat poison) certainly do exist. In that sense, someone built a better mouse poison - and nature produced the 'better' mouse. We now have still better poisons - and it's only a matter of time until still better mice appear. So the old saying isn't so far from the truth. SteveBaker (talk) 13:26, 24 October 2008 (UTC)

Indeed, resistance to mouse traps would require a way to tell the difference between food and bait, which is very hard seeing as they are usually the same thing! I could see mice evolving a fear of plastic, or something, so avoiding plastic traps (I'm not sure what most traps are made of these days) but that's about it. --Tango (talk) 17:37, 24 October 2008 (UTC)

I read somewhere that Australian natives had thicker skulls probably because of fights where they hit each other over the head. And I've wondered what adaptations will occur in Americans because of the large number of young people killed by guns and cars. If mechanical traps kill more than about 1 in a thousand then it's pretty certain evolution will change them in a way to compensate somewhat if at all possible. So yes we're probably eventually going to have either smarter or more hardy mice. Dmcq (talk) 14:38, 24 October 2008 (UTC)

The snap-traps (I assume we're talking about those) are a valid envionmental factor, might be noticeable if the population were isolated. In my West Philly apartment years ago, I wound up placing both snap-traps and glue-boards in the same places since after a while of using "just one type", I stopped catching them reliably. Lighter? Faster? Able to smell something about the glue? Ultra-short tails? Sacrifical/regenerative feet? Who knows when kind of Frankenmouse I would have been able to evolve if I hadn't moved. OTOH, given um, "the scale of the experimental population I appeared to have", I was happier not hanging around to see the results. DMacks (talk)

I used to live in a mouse infested house and I too can confirm that after an initial period of catching lots of them, the rate then falls off with no discernable reduction of the mouse population. Pure opinion, but I believe the answer is quite simple: the surviving mice can see the dead or injured one in the trap and they then learn that traps are dangerous. Changing the bait, position or type of trap will often succeed in catching out another batch. SpinningSpark 23:51, 24 October 2008 (UTC)

Did you wash the traps? I'd be willing to bet that mice can smell where another mouse died a nasty death. My experience with mice is to first of all eliminate the food sources that may have brought them around, then put out some tasty, tasty bait and the snap-traps work 100% over the course of 3-4 weeks. Finding and cutting off the food source is the big one, cleaning the death-smell off the trap is next, then move the traps around and change the bait. Mice rely on rapid reproduction as an evolutionary strategy, there's no particular genetic pressure to evolve mechanism-awareness. Franamax (talk) 11:16, 25 October 2008 (UTC)

We're in a pickle if people do that to cope with gun crime and cars. Dmcq (talk) 12:14, 25 October 2008 (UTC)

Do any animals shed tears through grief or pain?

I’ve wondered about this since I saw the documentary movie “The Weeping Camel”, which deals with a nomadic Mongolian family. This family’s camel gives birth to an albino calf, which she rejects. Following an ancient tradition, the family recruit a musician from a nearby town who plays the violin to the camel, whose attitude softens, and with tears flowing freely from her eyes, takes the infant to her teat. These scenes are not recreations, but actual footage of real events.

When I was little, my mother told me that on her family’s farm she saw cows weep when separated from their calves. And I myself have seen an ancient Egyptian engraving of a man milking a cow. The cow’s calf has been tied up nearby so it cannot access its mother’s udder, and the cow is depicted weeping profusely. Is this just anthropomorphism, or are animals capable of weeping through sadness or pain. Of course, I imagine that all animals can shed tears if they get grit or onion vapour or suchlike in their eyes, but that is not the kind of weeping I mean. Has anyone seen or heard anything which can throw light on this? Myles325a (talk) 06:37, 24 October 2008 (UTC)

I don't recall specific examples, but the book When Elephants Weep did provide (admittedly rare) examples of animals crying from grief. 152.16.59.190 (talk) 10:42, 24 October 2008 (UTC)

Observers of a band of gorillas reported that when the mate of a retired leader was killed by a young band of tough guy gorillas, the old guy cried. Edison (talk) 15:14, 24 October 2008 (UTC)

:( --98.217.8.46 (talk) 15:18, 24 October 2008 (UTC)

My dog Harry, a Border Collie, wept once.130.86.14.12 (talk) 04:07, 27 October 2008 (UTC)

oil and butter

why butter gets solidify but oil does not in refigerator. —Preceding unsigned comment added by 117.99.20.15 (talk) 09:18, 24 October 2008 (UTC)

I'm going to guess something to do with fat is the reason. 194.221.133.226 (talk) 09:20, 24 October 2008 (UTC)

butter: long straight saturated fatty acid chains => good fitting into crystal => high melting point

oil: long bend unsaturated fatty acid chains => not so good fitting into crystal => low melting point--Stone (talk) 12:53, 24 October 2008 (UTC)

nicotine

how long does nicotine remain in the blood after a person ceases smoking —Preceding unsigned comment added by 121.222.177.13 (talk) 11:29, 24 October 2008 (UTC)

Nicotine says it has a half-life of 2 hours in the body. So after 2 hours, there is half as much, after 4 hours a quarter as much - and so on. In practical terms, it's essentially gone in less than a day. SteveBaker (talk) 13:20, 24 October 2008 (UTC)

Is that why I need a cig at least every 2 hours?--GreenSpigot (talk) 19:46, 26 October 2008 (UTC)

It's why you think you need one. ;) - Mgm|^(talk) 08:18, 27 October 2008 (UTC)

Common cold and temperature

Or flu. In any case, I've heard a "common sense" wisdom that getting frozen outside in cold wheather, or even eating something cold when you are sweating, increases the chance of getting infected. I could never find a scientific explanation for that; is it just a folktale or is there some science behind it? --_{Piotr Konieczny aka Prokonsul Piotrus| talk} 13:35, 24 October 2008 (UTC)

Add to that, getting your hair wet in a rain. :) Zithan (talk) 14:42, 24 October 2008 (UTC)

Nope - no truth to it at all. SteveBaker (talk) 15:20, 24 October 2008 (UTC)

Other than the fact that when it is colder out, you stay inside with others more than when it is warmer out, thus increasing your chances of standing next to a disease vector. --98.217.8.46 (talk) 15:37, 24 October 2008 (UTC)

But then, when your mom says "you can't go outside because you'll catch a cold" - so you stay inside more - then (if your theory is correct) you'll be far more prone to colds than if you went outside to play. SteveBaker (talk) 18:49, 24 October 2008 (UTC)

When in doubt, do the exact opposite of everything your parents tell you. Seems like a good rule to me! :) --Tango (talk) 19:42, 24 October 2008 (UTC)

Colds or flu are viruses that don't survive well outside of the nice, wet, warm environment of a human being. There are a number of theories of why they exist more often during the winter months, but it could be everything including lower levels of UV radiation during the winter which eradicates airborne viruses, dryer air in winter which causes respiratory passages to be more sensitive to infection, closer proximity to other virus carrying individuals, or poorer nutrition. It's probably a combination of that and much more. OrangeMarlin ^{Talk• Contributions} 17:01, 24 October 2008 (UTC)

The "rule" I was taught was that it's ok to have a window open to let in some fresh air, even in cold weather, if you like a cold breeze. But if you have 2 windows open, then you'll create a draught, and draughts cause colds, flu, pneumonia and even death. This always seemed utterly absurd to me. Is there any truth to it, whatsoever? -- JackofOz (talk) 23:02, 24 October 2008 (UTC)

I'm pretty sure this question has been asked many times before. Although the cold temperature itself will not give you a cold, I've seen a lot of studies implying that when it's cold, your body heat is more restricted, and since body heat helps blood flow, and blood has white blood cells in it, the cold may slow down the immune system, and if viruses are present, then your body is more likely to catch a cold than otherwise. I've found that especially in a close public envorironment, such as a school, the first flu outbreak often seems to coincide with the first rapid cooldown in temperature (I live in Canada). Of course the cold temperature itself cannot give you an actual cold or flu, it may help start one if viruses are present, because "viruses can live on surfaces for days" (source: Lysol commercial). I remember a while back that one time I was outside for about two hours at night with the wind blowing at 40 km/h and the temperature about -10C. The next day, I had a fever of 40C, I barely went outside for a week, and lingering symptoms may have lasted a month (although it was different from a severe common cold where your body would ache all over). Although I probably already had a cold/cough by the time I went outside, the going outside in the cold seemed to make it worse each time. Also, it has been said that being in cold, wet clothes or by walking on cold surfaces barefoot can cause joint pain. I'm not sure if this is true, but one time after being wet I had back muscle pain and a minor cold (but there was already a cold going around). So the point is, and again I'm not an expert on this, that although cold temperatures won't give you a cold, the viruses might. Also, it seems that what always happens is that until something has solid proof, it is considered nonexistant. ~AH1^(TCU) 23:18, 24 October 2008 (UTC)

(Also, we cannot give medical advice) ~AH1^(TCU) 23:20, 24 October 2008 (UTC)

I can't see how the number of windows open is going to be what's important, it will be the actual temperature. Having two windows open causes air to flow in one and out the other and more effectively ventilate the room which will make it colder, however I can't see the difference between that and having one window open on a day when it's just colder outside to start with. There might be a difference to the humidity with a through breeze rather than just one window (it will be lower in a well ventilated room, I would think) which may make a difference, I suppose. --Tango (talk) 00:42, 25 October 2008 (UTC)

Thanks, that's what I've always believed too. But I couldn't tell you how often I was told to be more wary of "draughts" than of simple "breezes". Some old wives tales die harder than others, apparently. (Not saying my mother was an old wife .... well, she is these days, I guess. ) -- JackofOz (talk) 01:38, 25 October 2008 (UTC)

See also Common cold#Exposure to cold weather. PrimeHunter (talk) 01:56, 25 October 2008 (UTC)

http://www.newscientist.com/article/dn12808-cold-weather-really-does-spread-flu.html --Digrpat (talk) 02:15, 26 October 2008 (UTC)

Jury still out? [17]--GreenSpigot (talk) 20:14, 26 October 2008 (UTC)

See Lowen AC, Mubareka S, Steel J, Palese P (October 2007). "Influenza virus transmission is dependent on relative humidity and temperature". PLOS Pathogens. 3 (10): 1470–6. doi:10.1371/journal.ppat.0030151. PMC 2034399. PMID 17953482. --Arcadian (talk) 22:23, 26 October 2008 (UTC)

Dehumidifier crystals

Anyone know what the dehumidifying chemical in car antifreeze is called? I want to get some in crystal form to use as a cheap room dehumidifier. Last week I read on a forum that it will soak up water from the air without any fans or pumps, if I just spread it out in a large tray on the floor. It can be dried out over a barbeque and reused many times. But I lost the link and can't remember what the chemical is called.

If this stuff is actually poisonous then please let me know before I use it...!! Thanks! — FIRE!^{in a crowded theatre...} 14:06, 24 October 2008 (UTC)

Dehumidifiers in antifreeze? That's silly. You mix the stuff with water in your car and it's sold as a 50/50 mixture of the actual chemicals and water! According to our article antifreeze contains ethylene glycol (the actual stuff that messes with the freezing point of the water) - which is horrifyingly toxic but smells and tastes really sweet so that animals and children are attracted to it, some pretty colored dyes (to make it look like gatorade as well as taste like it?!?!)...plus (sometimes) an embittering agent to make it taste terrible (guess why?!) and some stuff to prevent corrosion in your engine. No 'dehumidifiers' there! You are probably thinking of those little pouches of Desiccant crystals that come with some electronic equipment to keep them dry during shipping. Our article offers some possible dessicants you could try. Rice is an interesting choice! SteveBaker (talk) 14:32, 24 October 2008 (UTC)

Here's an interesting fact. If somone drinks ethylene glycol and are unable to get to a hospital, give them ethanol and it acts as the antidote. They'll be drunk AND safer than before, just don't top them with loads of vodka. —Cyclonenim (talk · contribs · email) 17:12, 24 October 2008 (UTC)

• Sounds like silica gel to me. --jpgordon^∇∆∇∆ 15:22, 24 October 2008 (UTC)

• • If you want to try silica gel, your local pet supply store may carry jugs of silica gel, intended for use in a cat litter box. Since my cat is content with clay litter, I did not try the silica gel and I can't say if it is better than using clay. But you may find a pet supply an economical place to buy silica gel. Wanderer57 (talk) 15:41, 24

October 2008 (UTC)

Thanks!! It was calcium chloride. Hope it actually works though. You're right (now I stopped to think) that dessicants in antifreeze would be a really stupid idea... :-) It does seem to be used in window deicers though, or is that another red herring? — FIRE!^{in a crowded theatre...} 18:58, 25 October 2008 (UTC)

Hardware stores sell "dehumidifiers" consisting of calcium chloride crystal in a container. They absorb a modest amount of moisture from the air gradually, not as fast as a typical dehumidifier. Edison (talk) 00:38, 26 October 2008 (UTC)

Freak Of Nature?

Okay i got a hampster like 4 weeks ago its grown ALOT since then Well let me explain what happned i sorta left the lid off his container and he got out i lost him for like 3 days then in the living room i see like a dog sized hapster on the floor alive but the carpet was all ripped up any idea what happned? (this is a serious question i want a serious answer) mostly what happned to the carpet...—Preceding unsigned comment added by Nikkicole08 (talk • contribs) 16:17, 24 October 2008 (UTC)

Well, they do have little claws and like to make burrows. My question is, can we have a picture of your gigantic hamster? o.o --Masamage ♫ 16:39, 24 October 2008 (UTC)

Is the hamster actually gigantic or does it just have its pouches stuffed with carpet? Hamsters like to collect nesting material and will sometimes fill their pouches (in their cheeks) with so much of it that they look ridiculous! --Tango (talk) 16:41, 24 October 2008 (UTC)

Dog sized hamster? What breed of dog? I am afraid the most likely explanation is that a hamster-like dog (Griffon Bruxellois perhaps?) has broken into your house and eaten your hamster. It is likely that your dog-hamster is also responsible for eating the carpet. SpinningSpark 22:58, 24 October 2008 (UTC)

By any chance are we talking about a miniature giant space hamster? Plasticup ^T/C 00:34, 25 October 2008 (UTC)

Writing after laughing hard

I often find I have enormous difficulty writing after I have had a good hard laugh. My hands feel like rubber, and I cant hold the pencil much less touch the tip to the paper. I was wondering what happens in the nervous system while this is going on. —Preceding unsigned comment added by 189.58.26.29 (talk) 16:24, 24 October 2008 (UTC)

It sounds like a mild form of cataplexy. Axl ¤ [Talk] 17:55, 24 October 2008 (UTC)

Of course we NEVER give medical advice or make diagnoses based on vague symptoms. Edison (talk) 20:57, 24 October 2008 (UTC)

Laughing causes your muscles to relax. If you try holding something heavy and laugh at the same time, you'll likely drop what you're holding. This is not a medical condition; It's a natural response.CalamusFortis 02:43, 25 October 2008 (UTC)

Laughing very hard for a long time can often make you short of breath, and almost always increases your heart rate. The weakness in your hands could well be due to the release of chemicals such as epinephrine —Cyclonenim (talk · contribs · email) 09:15, 25 October 2008 (UTC)

Satellite dish cable

I shall be grateful to learn what currect passes through the cable from the decoder to the dish. Can it be cut without insulated cutters ?90.0.133.146 (talk) 16:46, 24 October 2008 (UTC)DT

How difficult would it be to unplug it? It's always best to err on the side of caution when dealing with electricity. I wouldn't trust random people on the internet with my life! --Tango (talk) 16:57, 24 October 2008 (UTC)

If you have to cut it, unplug it first or buy insulated cutters. —Cyclonenim (talk · contribs · email) 17:10, 24 October 2008 (UTC)

Preferably both. --Tango (talk) 17:33, 24 October 2008 (UTC)

There is probably not a good answer to this as it probably depends a lot on the type and brand of dish. APL (talk) 18:18, 24 October 2008 (UTC)

Usually, there is some electronics in the dish itself - that must require power from the decoder. The video stream coming from the dish to the decoder is going down the same cable - so it must be a co-axial cable. Cutting that will almost certainly not harm you because the voltage isn't gonna be huge - but cutting co-ax almost always puts a short across the end of the cable. If it's still plugged into the decoder and the decoder is powered up - that could easily short out it's power output to the dish - and that could damage the decoder. Hence you should certainly unplug the decoder from the wall when you do this - and REALLY it would be best to disconnect the wire at the back of the decoder before cutting anything. SteveBaker (talk) 19:46, 24 October 2008 (UTC)

The voltage could be around 12 volts, and perhaps a quarter to half an amp. The decoder gear I have seen can detect a short, so it would not be damaged, but if you get the oportunity disconnect. The voltage is probably not dangerous to you as a cutter. In some systems the voltage can be changed to signal the LNB to change bands or polarization. Graeme Bartlett (talk) 20:45, 24 October 2008 (UTC)

Thank you.86.219.39.92 (talk) 15:52, 25 October 2008 (UTC)DT

Staining in chilly weather

Some paint cans have warnings on them not to use below 45 or 50 degrees F. What happens if you paint or stain below that temperature? Will it just be slower to dry, or will it fail to dry correctly? I apologize for such a boring question. It's almost as boring as, well... damnit. Fletcher (talk) 19:45, 24 October 2008 (UTC)

I don't know the precise mechanism - but I know that when I painted some wood at around 35 degF, it didn't turn out well. It was almost as if the oil and the pigment wouldn't stay mixed and there was this oily residue on top of the finished surface. It never did really dry properly and it was streaky and patchy. I ended up scraping it all off and re-doing it. The paint manufacturers have nothing to gain from lying to you about this - so you should probably believe it when they tell you. SteveBaker (talk) 19:49, 24 October 2008 (UTC)

Interesting...thanks. I'll be hoping for warmer temperatures. Fletcher (talk) 20:01, 24 October 2008 (UTC)

This explains it pretty well. --jpgordon^∇∆∇∆ 20:19, 24 October 2008 (UTC)

Seems oil has a 10° advantage over latex, which is good for me. Just hope it doesn't rain! Fletcher (talk) 20:44, 24 October 2008 (UTC)

It is more likely to adhere poorly and peel off later if applied when it is colder and/or damper than recommended. Edison (talk) 20:53, 24 October 2008 (UTC)

October 25

Looking at Earth

What does Earth look like in the multiple dimensions (say 7th dimension) of M theory ?

Would the answer to such a question be useful to someone without seven-dimensional eyes? —Tamfang (talk) 07:54, 25 October 2008 (UTC)

Ordinary physics is confined to 3+1 dimensions in these models, so there's nothing to see in the extra dimensions (no light) and nothing to see it with (no way to construct an eye). -- BenRG (talk) 16:21, 25 October 2008 (UTC)

So are everyday objects 0-sized in the extra dimensions or just very very small? --Tango (talk) 16:32, 25 October 2008 (UTC)

Objects will retain their size if you add extra dimensions, it is just if you measure in the extra dimension, there will be no thickness, of course this will depend on your fabricated physics if there is or is not any extent onto the extra dimension(s). Graeme Bartlett (talk) 20:13, 25 October 2008 (UTC)

Of course it depends on the theory, I'm asking whether there is any spacial extent to everyday objects in the extra dimensions of String/M theory. --Tango (talk) 21:21, 25 October 2008 (UTC)

I don't know, sorry. I gather than in brane cosmology the Standard Model particles are supposed to be open strings whose ends are confined to a 3+1 dimensional subspace, but the middles aren't confined, so I think the answer is "sort of". -- BenRG (talk) 22:22, 26 October 2008 (UTC)

a 2D projection of a 4D object

There are some misconceptions here. One is that we can't possibly answer this question...when in fact we can...and it's rather easy in fact. First we have to think carefully about how our visual system works. Our eyes don't see in three dimensions - each eye is like a camera - it sees a two-dimensional projection of the 3D world onto the backs of our eyes. Using two eyes - separated horizontally in space, we can infer some information about that third dimension by a process of triangulation. So - if there were additional dimensions - we'd see projections of those onto our same 2D eyes - and because the separation between our eyes only adds ONE new piece of information (the lateral displacement of the image in our two eyes), we would be unable to deduce anything 'new' about the 4th and subsequent dimensions. When you see pictures of things like tesseracts (four-dimensional hyper-cubes) - they are generally represented as 2D projections.

Some people are going to argue about this (they did the last time we answered this kind of question). I'm a computer graphics guy. I can quite easily program my computer to generate 2D, 3D, 4D, 5D...or any other number of dimensions inside the computer's memory - the computer really doesn't care how many dimensions there are - the software is very similar no matter how many dimensions there are. But the computers' display is only a 2D surface - so I have to write software - even for three dimensional objects that explicitly reduces them to two dimensions so I can display them onto that 2D screen. We do this in various ways - but the one that's simplest to envisage here is called "Ray Tracing". The idea is that you calculate an imaginary 'ray' that comes out of your eye - passes through a pixel on the computer's screen and goes off into the 'virtual world'. We calculate what part of what object that ray first hits. We take the color of that object and place that color onto the pixel that the ray passed through. We do this thing for every single pixel on the screen - and then we have an image. This process is identical to what happens with our real 2D eyes - and that process of tracing rays is just the process of figuring out where a ray of light came from on it's journey onto our eyes. That process is EXACTLY the same in 3D as it is in 4D, 5D, and so on.

So it's really easy to have the computer draw things in more dimensions - in a manner that PRECISELY shows what it would be like if we lived in a 4D, 5D or more-D world. So what does it look like? We might hope that some amazing revelation would appear - but really, it doesn't. It's pretty disappointing actually. Even when we do ray tracing separately for each eye and feed the two views into our eyes using a virtual reality helmet or something - the 4D world doesn't look any different from our normal 3D world. There are plenty of places on the web with animations of 4D objects which are spinning or something. They look much like ordinary 3D objects (which we're seeing in 2D because that's how our eyes work) - except that they seem to change shape in strange ways.

Hence - we know exactly what a 7D world would look like with our normal 2D retinas. What we don't know (and can't easily imagine) is how it would look if we were in a 7D world with 6D retinas...but it's a somewhat meaningless question because if we had bodies (and especially brains) with more dimensions, we wouldn't be anything like we really are - so asking how we would see things if we were not ourselves is a really meaningless question.

SteveBaker (talk) 21:55, 25 October 2008 (UTC)

So if we lived in a 7D world but were surrounded by 3D objects and we only moved in the standard 3 dimensions then everything would look the same - we could not tell that extra dimensions existed. But if we moved along one of the extra dimensions - well, it's not clear that we would "see" anything, since (I think) the inverse-square law tells us that photons only travel in 3 dimensions (on a macroscopic scale). I suppose we might conceivably wander into "parallel" 3D worlds filled with their own 3D objects and 3D photons. Gandalf61 (talk) 10:58, 26 October 2008 (UTC)

I think you're basically describing brane cosmology. --Tango (talk) 14:02, 26 October 2008 (UTC)

When you move around a 3D object in our 3D world - viewing it with our 2D eyes the shape of the projection of the object changes. A cube morphs from a square (when it's exactly lined up in front of us - to something that's almost a rectangle if we move off to one side or a hexagon if we move up or down and off to one side. The only reason we know it's a cube is because we have two eyes - and each gets a slightly different view - and because the effect of light striking the cube and reflecting different amounts at different angles makes the faces appear in different colors. The same thing happens if you move around 4D objects in a 4D world with our 2D eyes. The 3D projection of a tesseract looks like a cube from some angles (like the view in the picture above) and like four cubes that are slanted together at other angles. Which means that when you project it into 2D - to us it's like a square or a rectangle or a hexagon or an octagon - and just like the cube in 3D, it changes shape as you move around it. The effects of light reflection in the 4th dimension will allow us to recognise more of the shapes of things - but it's really not going to look all that strange. But you don't have to take my word for it - there are plenty of web sites that show 4D (and more) objects projected into 2D. Everyone is acting as if there is some deep mystery - but there really isn't.

It's possible that the physics of light transmission in the presence of additional dimensions might be wildly different. But I suspect that can't be true because if it was, we'd have concrete proof that the 26 dimensions of string theory were not a physical truth. Since we have not yet debunked string theory - I don't see how there can be solid proof that light acts differently in universes with more than 3 spatial dimensions. If you want 'weird' - start thinking about cosmologies with multiple temporal dimensions! SteveBaker (talk) 19:04, 26 October 2008 (UTC)

You say "That process is EXACTLY the same in 3D as it is in 4D, 5D, and so on", but it's not the same: if you cast rays from a point (the eye) through a 2D surface (the computer screen), the locus of points that those rays intersect is three dimensional. You would only see a slice of the 4D object if you ray-traced that way. Pictures like that one of the tesseract are made by a two-step process, first projecting the tesseract onto a three-dimensional "screen", then reinterpreting that screen as a new 3D scene and projecting that onto the real screen. The human eye won't do that intermediate step, and I'm having trouble imagining any physical object that could. Even if you can concoct a 4D physics in which all four spatial dimensions are on equal footing (so that shapes like the tesseract make sense) and in which a 3-dimensional eye can somehow exist, there's no way the 3D eye will see pictures like that one of the tesseract, unless maybe with the help of some magical material that's transparent to "3D light" but emits 3D light when it's struck by "4D light". If there's only one kind of light and it travels through all four dimensions then the 3D eye will just see a uniform blur, because the interior of the eye will be flooded with light that gets in via the extra dimension. I can't figure out what you mean by "different" in your last paragraph. On the one hand light in these theories behaves like light in the real world: it's confined to three spatial dimensions. On the other hand that makes the other dimensions different from the three usual dimensions with regard to how they transmit light. You seem to be pulling a definitional switcheroo, saying that since these models haven't been falsified, light transmission must be confined to three dimensions (anything else would be "different" from what we observe) and then saying that the tesseract picture makes sense (because otherwise the extra dimensions would be "different" from the usual three). -- BenRG (talk) 22:22, 26 October 2008 (UTC)

Well, you'd stand a chance of being right if I hadn't actually done this with computer software. There is absolutely no problem in tracing the path of a ray in four dimensions instead of three. 4D geometry works just fine. I can simulate the motion of our 3D eye with its 2D retina inside that 4D geometry - have it translate and rotate about all four axes, place 4D objects into that simulated world - and so long as we can assume that 4D photons would somehow transfer energy into our retinal cells and that 4D photons travel in straight lines in a 4D world, everything works out just fine. If those assumptions are not true - then the idea of 'being in a 4D world' becomes rather meaningless anyway - but taking the premise that "IF we could be in a 4D (7D) world - what would it look like?" - then this is a reasonable supposition. With such software, I can use a joystick with some extra axes to manouver around in the 4D world and watch pictures of the results at close to realtime rates (for a small image area) - and there is no special difficulty. I'm emphatically NOT converting a 4D image into 3D and then into 2D - I'm tracing the path of photons directly in 4D and seeing where they impact the 2D screen (which might as well be a "retina" except that I don't want to model a lens and deal with flipping the image up the right way at the end). SteveBaker (talk) 14:28, 27 October 2008 (UTC)

A small niggle. You show a picture of a projection of a tesseract. But it would have to be transparent like a transparent cube to see all those cubes and lines in it. If one was 4 dimensional and had an analogue of our eyes you'd see only the four nearest cubes of the tesseract at most - like you only see the nearest 3 squares of an opaque cube at most. Dmcq (talk) 15:33, 26 October 2008 (UTC)

Yes - I agree. Images of "solid" tesseracts look pretty much just like normal 3D polyhedra that change shape as they move. SteveBaker (talk) 19:04, 26 October 2008 (UTC)

I've sen those too, I prefer just to remove the extra lines in the projection picture. Just because the 4d figure is opaque doesn't mean the image has to be. Really one would have to see the 3D in depth like a dolphin with sonar to have the equivalent of an eye for 4D. Dmcq (talk) 20:56, 26 October 2008 (UTC)

ISS flyby and binoculars

In a few hours, the ISS is going to make a visible pass almost directly above where I live. heavens-above.com says that it will be magnitude -2.2 which should be about the brightest I've ever seen it. It will fly almost directly overhead. Anyway, I've heard of some people viewing the ISS through binoculars and supposedly you can see solar panels and other doohickeys (couldn't think of a better word) with them. I was just wondering if the glare from the ISS would be too much to see anything in detail if it's so bright or if I should wait for a dimmer flyby to see if I can't see shapes. What would be the ideal brightness to see shapes?

If I can get a good view of it through binoculars in the limited time I have during the flyover, I might try to place my digital camera behind one lens of my binoculars to try to get a good picture of the station, so stay tuned for updates! (if the video is good, I'll post it on youtube) 63.245.144.77 (talk) 06:38, 25 October 2008 (UTC)

Does the pass enter the Earth's shadow while still above the horizon? If so, then even if it's too bright to see close up for most of the pass you should be able to see it for the last couple of seconds. --Tango (talk) 11:58, 25 October 2008 (UTC)

Hi. I've never been able to see the solar panels of the ISS on binoculars on my 8x30, but I think I have been able to see a bit of detail with my telescope operating at 36x. It's really difficult to catch one on camera through the telescope because it moves so quickly (and you'd need a special camera adapter). Nevertheless, there are videos on youtube showing the ISS. Thanks. ~AH1^(TCU) 19:06, 26 October 2008 (UTC)

An Electronic Planet

Is it possible to have an electronic planet. By that I mean, imagine lots and lots of electrons in space with no protons or neutrons. Imagine the mass of electrons is such that gravity takes hold and forms a spherical gravitational body like a planet. How big would the planet be and what colour is it? Can a spaceman with a spaceship land on the electronic planet?

122.107.147.49 (talk) 09:48, 25 October 2008 (UTC)

Since Coulomb repulsion is going to be several orders of magnitude larger than gravity, it will require some other kind of external force to stabilize it. On top of everything, you will have the Fermi pressure destabilizing the sphere even more. In other words, no, it is not possible. MaNiAdIs-Talk-GuestBook 09:56, 25 October 2008 (UTC)

• You can have neutron stars though. I guess if I fired an enormous number of electrons at a black hole I could get an immense electrical field.I'd like to do this in near earth orbit, the funding agency just won't give me the money though. Peasants, they just don't understand the importance of science. :) Dmcq (talk) 14:17, 25 October 2008 (UTC)

  Highly charged black holes have some strange properties - I think one made up entirely of electrons would contain a naked singularity. --Tango (talk) 15:11, 25 October 2008 (UTC)

The current thinking is that it's impossible to have a black hole with a charge/mass ratio larger than 1 (in natural units where G = 1/4πε₀). The electron's charge/mass ratio is about 10²¹. Simply firing electrons at a charged black hole won't work to increase the charge because electric repulsion will prevent their getting anywhere near the event horizon. -- BenRG (talk) 16:47, 25 October 2008 (UTC)

Ben - could you calculate that for a couple if different sizes of black hole? On a previous question there was consideration of the energy to have one mole of electrons in a confined space with out other protons. Graeme Bartlett (talk) 20:19, 25 October 2008 (UTC)

Calculate what? The largest possible charge? That's just a matter of plugging numbers into formulae. If my derivation is correct, the formula you need is $Q=2M{\sqrt {G\pi \epsilon _{0}}}$. Give me a minute and I'll convert that into something more usable. --Tango (talk) 21:10, 25 October 2008 (UTC)

Ok, taking constants to 1 sig fig, that comes out in SI units as $Q={\frac {\sqrt {7}}{3}}\cdot 10^{-10}\cdot M$. --Tango (talk) 21:14, 25 October 2008 (UTC)

So that means a proton or electron with mass 1.6x10^-27 or 8.1x10^{-31 kg}and with charge 1.6x10^-19 Coulombs could not be compressed to a black hole, In fact only if 1 in 10^-18 of particles in an object are charged you still could not make a black hole out of it, is that roughly correct? Graeme Bartlett (talk) 21:38, 25 October 2008 (UTC)

I haven't checked your arithmetic, but basically yes. If a charged sub-atomic particle (or collection of them) were to collapse into a black hole it would result in naked singularity and it is hypothesised that they cannot exist. --Tango (talk) 22:04, 25 October 2008 (UTC)

I suspect that the energy in the electric field when converted to mass would exceed the mass in the black hole if the charge were too high. This means all the earlier speculation about micro black holes we had before is probably irrelevant as the tiny black hole could not swallow a charged particle. Graeme Bartlett (talk) 10:44, 26 October 2008 (UTC)

My guess then is that a highly charged black body would emit an enhanced amount of Hawking radiation which had a preponderance of negatively charged particles in it. Does that sound about right? Dmcq (talk) 20:18, 25 October 2008 (UTC)

A highly charged black hole (by which I mean one with greater charge than mass in the appropriate units) just leaves the laws of physics in shreds. If such things are possible, our theories can't handle them. A black hole with a lower, but non-zero, charge is called a Reissner-Nordstrom black hole - I have no idea what the Hawking radiation is like for a R-N hole, but someone here might. --Tango (talk) 21:10, 25 October 2008 (UTC)

The Hawking temperature is ${\frac {\kappa }{2\pi }}$ where $\kappa$ is the surface gravity. For a charged unrotating black hole that's ${\frac {1}{2\pi }}{\frac {\sqrt {m^{2}-q^{2}}}{2m^{2}-q^{2}+2m{\sqrt {m^{2}-q^{2}}}}}$. So a charged black hole radiates less than an uncharged black hole at a given mass, and an extremal black hole (|q| = m) has zero temperature and doesn't radiate at all. Large black holes radiate mostly photons, so a large charged black hole in a vacuum will tend to lose mass until |q|/m reaches one and then stop radiating. I think a small black hole will tend to lose its charge by radiating electrons or positrons. -- BenRG (talk) 21:19, 26 October 2008 (UTC)

That's interesting, thanks. How are you defining "large" and "small"? --Tango (talk) 11:37, 27 October 2008 (UTC)

Instead of a electron planet, look out for a cold neutrino planet. Perhaps these will form later in the life of the universe. Graeme Bartlett (talk) 10:44, 26 October 2008 (UTC)

Grounding & Bonding - static electricity safe guards

Moved question from VPT Franamax (talk) 09:30, 25 October 2008 (UTC)

According to the NFPA all flammable containers must be grounded and bonded to ensure no static electricity build-up resulting in an explosion. The question: is bonding necessary when the transfer container is plastic?

Ira Hayes —Preceding unsigned comment added by IraHayes46 (talk • contribs) 08:50, 25 October 2008 (UTC)

You said it yourself. "All" containers. --Russoc4 (talk) 13:40, 25 October 2008 (UTC)

This is a question that can't be met by a simple yes-or-no. A proper answer will depend on the type of container, the size of the container, the environment, and the type of flammable liquid being transferred, not to mention local health and safety regulations. You need to consult an expert to get a reliable answer to this type of question; some random guys on the Internet just aren't going to cut it. Your local fire department may be able to offer your advice, or at least be able to point you to appropriate resources. TenOfAllTrades(talk) 16:33, 25 October 2008 (UTC)

Static electricity builds up more efficiently on plastic containers than on metal ones - so yes - they do need to be grounded. SteveBaker (talk) 21:32, 25 October 2008 (UTC)

How do you ground a plastic container? Do you need to cover it in some kind of metal mesh? Just connecting a grounded wire to one part of it wouldn't seem to have much effect. --Tango (talk) 22:07, 25 October 2008 (UTC)

Exactly. For this to make sense, the plastic would need to be at least a little bit conductive, like and antistatic bag. Perhaps plastic gasoline containers are made that way? I can't find my DMM, or I would go check.-Arch dude (talk) 00:58, 26 October 2008 (UTC)

human eye.

when we come from intense light to dim light why human eye take time to see thing clearly? —Preceding unsigned comment added by 119.154.22.96 (talk) 12:06, 25 October 2008 (UTC)

See the article Adaptation (eye), which explains the phenomenon. The article doesn't really answer the question as to why it takes so long (20-30 minutes), however. --NorwegianBlue ^talk 12:36, 25 October 2008 (UTC)

20-30 minutes seems excessive. I'm typically able to see well in a changed lighting environment in 5 minutes maximum. —Cyclonenim (talk · contribs · email) 12:42, 25 October 2008 (UTC)

From this article, full light adaptation takes from tens of seconds to several minutes. There are two phases. Important factors are changes in calcium levels and cGMP. Axl ¤ [Talk] 12:58, 25 October 2008 (UTC)

The longest times are for full adaptation to night vision, and are correct. It takes up to 30 minutes for rhodopsin (a retinal pigment sensitive to very low levels of light) to recover after being bleached by exposure to bright ambient light. Rhodopsin is essentially insensitive to long-wavelength (red) visible light, which is why amateur astronomers are often seen carrying red-filtered or red-LED flashlights at observing sites. TenOfAllTrades(talk) 13:12, 25 October 2008 (UTC)

There are two completely separate things that happen. Firstly the iris in your eye shrinks down to let less light in - this takes less than a second. Secondly - IF you've been sitting in the dark for long enough to get dark-adapted, the chemical rhodopsin has formed to make your retina more sensitive. When the sunlight hits your light-adapted eye, the extra sensitivity you've built up causes that extra jolt of pain - but the rhodopsin is bleached out and ceases to function within just a few seconds. Going back into the dark - the process reverses - your iris grows large to let in more light and the rhodopsin starts to form again to make your retina's more sensitive. The 10 to 30 minutes time that some people here are thinking of is the time it takes the rhodopsin to build back up to its maximum level again. We can get un-dark-adapted very much quicker than we can become adapted again. SteveBaker (talk) 21:30, 25 October 2008 (UTC)

chemicals

how can we prepare low temperature colours which can stick on ceramic tile? —Preceding unsigned comment added by 119.154.22.96 (talk) 12:18, 25 October 2008 (UTC)

Public Health Question:Handwashing & faucets w/sensors-transfeered frWater Conservation

water-saving mechanisms for washing hands--how have public health experts reacted to them, does anyone know about this? I've experienced in restaurants how frustrating they can occasionally be as the mechanism ages and it takes longer to provide less water, so I wonder if boards of health have voiced concern about impatient food workers etc leaving the bathroom without washing their hands. As experts have gotten more worried about possible epidemics, perhaps literature critical of the new faucets has appeared? Thanks, Rich (talk) 03:24, 25 July 2008 (UTC)

not that i know of. However, Elementary School Washroom Faucets in Ontario (not saying anything about Canada as a whole) have become frustrating to use, according to a friend of mine's son (and many others that I have asked around our community). He says: "I wish the water would come out faster! I spend, on average, about 10 minutes in the washroom, 7 of which are spent waiting for the water to come out fast enough to clean my hands!"

-GameLoRDz (talk) 21:18, 22 October 2008 (UTC)

---

Thanks for any and all responsesRich (talk) 13:24, 25 October 2008 (UTC)

I can't answer the specific question but I don't know whether water is the biggest issue when it comes to hand washing. The biggest issue is most people don't wash their hands properly. Proper hand washing with soap, as described in Hand washing and Hand washing with soap generally requires about 20 seconds or so of rubbing wet soapy hands together and this is outside the stream of water. Only then should the hands be (thoroughly) rinsed. They then have to be dried thoroughly (usually for around 20 seconds as well). Many people don't rub their hands for close to long enough. Many people don't even use soap at all. And many people don't dry their hands properly (ironically if you don't dry your hands at all it may actually be worse then not washing your hands). I would say if people would wash their hands properly it would make a far bigger difference then whatever negative effect from water conservation measures. P.S. Yes I'm one of the many poor hand washers. Nil Einne (talk) 14:51, 25 October 2008 (UTC)

tsunami

What is the name given to the time interval when the sea recedes and the tsunami arrives? —Preceding unsigned comment added by Paulpearn (talk • contribs) 14:05, 25 October 2008 (UTC)

The article tsunami indicates that there is not necessarily a draw back prior to the wave itself hitting the shore. The article also gives the effect of wave shoaling as "the wave length diminishing to < 20 km" travelling at below 80 km /h. Thus the time for the tsunami travelling 1/2 of a wavelength can be roughly calculated. In ocean surface waves the time of a full wave is termed the wave period, so the time between the trough and the crest may be called "half a wave period". Of course, different topologies of the sea floor rising to the shore line will make this a variable. If at all, there may be a Japanese name for it, but I could find no reference. --Cookatoo.ergo.ZooM (talk) 16:35, 25 October 2008 (UTC)

How do violin strings make sound?

How do strings on a violin make music? I know that you use the bow and draw it across the strings. What I want to know is how does it make sound?

Clare age 7 —Preceding unsigned comment added by 72.81.184.136 (talk) 16:55, 25 October 2008 (UTC)

Christyn2 (talk) 17:02, 25 October 2008 (UTC)

See String_instrument#Sound_production. Axl ¤ [Talk] 17:38, 25 October 2008 (UTC)

You've got to be kidding, she's 7. Theresa Knott | The otter sank 20:12, 25 October 2008 (UTC)

When the bow is moved across the string it's scratchy surface makes the violin string jiggle to and fro. This is called "vibration" and all sound is made by something vibrating. The vibrating string makes the air jiggle as well and it is this vibration of the air that gets picked up by our ears and we hear it as a sound.

The faster the air vibrates the higher the note we hear. There are a few ways of making the string vibrate faster. One is to make the string shorter, and this is what you do when you put your finger on it to play it. Strange as it may seem bowing the bow faster will not make the string vibrate faster. It will make it vibrate more and this makes the air vibrate more. We hear this as a louder sound.

Our ears can hear many different sounds but note that are too low or too high cannot be heard even though the air is vibrating. Interestingly children can hear high sound better than grown ups can, but I bet even you will not be able to hear sounds as high as a dog can. Try looking up dog whistles! Theresa Knott | The otter sank 20:12, 25 October 2008 (UTC)

(Edit conflict) Clare, your question is a good one. I was about to answer something like this: When the bow first makes contact with the string, the bow will take the string along in its motion. The displacement of the string makes it longer, and creates a force which within a fraction of a second will become greater than the force between the bow and string. At that point, the built-up energy will make the string move back towards its starting position. Because of inertia, it will move a little past the starting position, then back again a couple of times, but the vibrations will be dampened, and when its energy of motion is smaller than the frictional forces between bow and string, the bow will again take the string along in its motion. The result is that the string vibrates, the vibration is transmitted to the body of the violin, through the air and to your eardrum. "Sound" is what you experience when your eardrum vibrates.

Then I thought, "why is the frequency of a violin string played pizzicato style the same as when it is played with a bow?", and really couldn't come up with a convincing answer. --NorwegianBlue ^talk 20:52, 25 October 2008 (UTC)

Because the frequency depends on the natural frequency of the string and that is a property of the string only not how it is caused to vibrate. The bow has multiple strands and I would think that the bow is likely to cause vibrations at multiple frequencies, However only those that are resonant with the string will build up any kind of serious vibration in it. Theresa Knott | The otter sank 21:04, 25 October 2008 (UTC)

The vibrating string would not be very loud, except that the body of the violin is made to be a sounding board, to send the sounds out to the listener. Edison (talk) 00:30, 26 October 2008 (UTC)

Initially, when the bow is moved across the string, static friction causes the string to momentarily move with the bow. As the string moves, its tension increases. A point is reached at which string tension is great enough to overcome the static friction between the string and bow. The string is then released. The coefficient of sliding friction allows the string to return almost to its starting point. When tension becomes low enough, the entire action is repeated. The process continues, alternating between static friction and sliding friction. The vibration of the string produces the sound. Rosin on the bow increases its coefficient of static friction with respect to the string, allowing the bow to momentarily pull on the string (if string tension is not too great) instead of sliding over the string. The form of the violin, its wood thickness, varnish etc., modifies the sound produced. —Preceding unsigned comment added by 98.17.36.129 (talk) 11:11, 27 October 2008 (UTC)

Spectacles deglazing

Is it possible to deglaze plastic scratched lenses in the home? —Preceding unsigned comment added by Stargazermum (talk • contribs) 17:34, 25 October 2008 (UTC)

Deglazing says it means removing a shiny surface. Do you want to change the lens surface to look like Frosted glass , or are you trying to remove scratches and leave the surface smooth and clear? Edison (talk) 00:27, 26 October 2008 (UTC)

You can use acetone to turn clear glasses into frosted glasses (if they're made of polycarbonate). 96.242.34.226 (talk) 01:38, 26 October 2008 (UTC)

From experience, you cannot use heat to remove scratches, the lenses are not made from a thermoplastic. They just crack. Polypipe Wrangler (talk) 20:52, 26 October 2008 (UTC)

something we dug up in our back yard!!

Hi, I hope someone can help with this question/explanation of my circumstances. Today, my husband was going to plant some things in the backyard of our 1923 home and while digging, he hit concrete. He followed it as he dug and it goes down 4 feet and is 6 foot in cir. It is made of concrete and has one 4" hole on one side at the bottom of the thing. There is a round indentation on the bottom but is concreted over. We don't know what it could be. It seems too small for a septic tank, too small for a cistern (besides, it is underground), and too shallow for a well tank. There are no pipes but the one near the bottom on the wall that goes into the earth. If there is anyone out there who could tell me what this is, it would be appreciated. This area was owned for over a hundred years by one family and it was all farmland. It is located on the central west coast of Florida.

Thanks, JSRny1JSRny1 (talk) 18:52, 25 October 2008 (UTC)

Maybe it's the remains of a dried up borehole, with the water pump on the surface removed and sold once the water stopped. Does anyone from the previous owners' family still live nearby who you could ask? — FIRE!^{in a crowded theatre...} 21:10, 25 October 2008 (UTC)

The description is unclear. Is it a solid concrete cylinder 6 ft diameter and 4 ft high? That would make no sense. Is it a hollow cylinder of those dimensions? Does it have a lid or hatch or manhole cover. or metal rings for lifting the top off? Is (or was) there inlet and outlet pipes at opposite ends? It could be part of a well, part of a cistern, or a septic tank. Or perhaps Amelia Earhart, Jimmy Hoffa, Judge Crater , Peking Man and the Ark of the Covenant are inside it. Edison (talk) 00:25, 26 October 2008 (UTC)

I think the OP meant 6' in circumference, not diameter (at least, I can think of anything else "cir." could mean). --Tango (talk) 00:43, 26 October 2008 (UTC)

Whatever it is, it was probably meant to store water, either fresh or waste. I'm sure you know, living in Florida, no one digs more than 5 feet in the state and builds a structure that can stay dry. There are no basements or cellars in houses. --Moni3 (talk) 02:42, 26 October 2008 (UTC)

A photo would be helpful! --S.dedalus (talk) 07:34, 26 October 2008 (UTC)

Actually, it is hollow with no lid or hatch. It might have had one at one time, but there seems to be no hinges or anything. The only previous owners passed away and we got it as an estate sale 15 years ago and am always finding obstacles in our way when we do any work. The old man who built it didn't appear to have any logic in some areas. They have no family left to ask. As for a basement, this old house has a cellar..unheard of in Florida, but we have it. It's only 10' x 10' with a 7' ceiling but hey, it's there. At any rate, nothing was inside it but dirt, which we dug out. It is now empty and even clean. We are contemplating turning it into a concrete pond but just wanted to know what the heck it was to begin with. It just seems too small to be a cistern or a septic tank due to it's dimensions of 4' deep by 6' in circumference. I have a pic, will upload later today. Thanks, JSRny1JSRny1 (talk) 10:21, 26 October 2008 (UTC)

Hole In Yard

I uploaded a photo of this thing in the common upload area. The file is named holeinyard.jpgJSRny1 (talk) 12:22, 26 October 2008 (UTC)

Maybe I haven't got the perspective right, but it doesn't look like it's four feet deep. Axl ¤ [Talk] 15:29, 26 October 2008 (UTC)

Agreed. That looks wider than it is deep. 6ft circumference would be about 2ft diameter, so it should be about half as wide as it is deep... Was the photo just taken at a strange angle or are your measurements off? --Tango (talk) 16:46, 26 October 2008 (UTC)

Perhaps the bottom is a total of four feet below ground level? In any case, it looks like it was once taller and has been partially demolished. APL (talk) 19:36, 26 October 2008 (UTC)

Thanks for the picture! It looks like the sides are sloping, rather than cylindrical, and like it has rather thin sides. I wonder if the builder dug the hole, then lined it with concrete, perhaps with wire mesh reinforcement, to seal it. The sides look fairly thin, and it looks like the surface was crudely formed. Could it be a small "cement pond?" [18]. In Florida it would not be destroyed by the ground freezing as might be a problem up north. The drain could have once had a plug, or it could have been connected to the inlet of a pump. The hole or the bottom indentation might have been part of a filter system/aerator system (fountain) connected to the discharge line from the pump. "Cement pond" reminds me of the Beverly Hillbillies, where they used the term for their swimming pool. Try digging by the visible exit hole to see if there is a pipe and where it goes. Perhaps there was once a pump and a little waterfall above the pond, to make a "water feature." There would have been a buried electric line from the fuse box/breaker box in the house to power the pump. Edison (talk) 22:07, 26 October 2008 (UTC)

My parents have something similar to this at their house in South Carolina--a big hole with one exit pipe near the side of their house. The pipe runs to the ditch in the front yard to help drain water away from the side yard. Laenir (talk) 14:31, 27 October 2008 (UTC)

October 26

Twins from different fathers

Is it possible to have non-identical twins with different fathers, if the mother was involved in an orgy or something? If so, has this ever been documented? --76.173.201.40 (talk) 01:58, 26 October 2008 (UTC)

Yes, it is possible to give birth to half-sibling dizygotic twins. I cannot think of any specific documented cases, but it is possible because sperm survives for about 3 days (5?) in the woman's body. If two eggs are released, and fertilized by sperm from different fathers, there will be two half-sibling twins.CalamusFortis 04:04, 26 October 2008 (UTC)

This case is rather well documented ;) but still doesn't count. --Dr Dima (talk) 05:06, 26 October 2008 (UTC)

Yes, the phenomenon is known as Superfecundation. From the article: "The first recorded case was made by John Archer, an American physician in 1810 and is discussed in Williams Obstetrics (1980). According to Archer, a white woman who had sex with a black man and a white man within a short time subsequently gave birth to twins—one white, one of mixed-race. Other cases have been reported since." Among humans this is rare, but in reptiles where sperm can be stored for long periods of time, it's not as uncommon. bibliomaniac15 05:41, 26 October 2008 (UTC)

If memory serves, the honey bee reproduces like that routinely. The queen flies around for a bit, receives sperm from a variety of drones and then lays eggs. --Tango (talk) 14:09, 26 October 2008 (UTC)

As an aside, this was the basis of one of the patient's storylines in an episode of Grey's Anatomy. Dismas|^(talk) 15:27, 26 October 2008 (UTC)

After reading the article for the episode, I see that I was a bit off in my remembrance of the episode. It seems the woman had two separate uteruses. Dismas|^(talk) 16:32, 26 October 2008 (UTC)

It is not necessary that there be separate fathers for twins to be one black and one white. See the recent Daily Mail story where one man and one woman had fraternal twins, one quite black and one quite white [19]. Its called Genetics. Edison (talk) 21:56, 26 October 2008 (UTC)

In domestic cats it is not unusual for kittens in a single litter to have a different male begetter. This can sometimes be seen in the different coloration of the kittens. —Preceding unsigned comment added by 98.17.36.129 (talk) 10:42, 27 October 2008 (UTC)

first nutritional supplements

What year were nutritional supplements first available to the general public for purchase in USA? And where? What was the first supplement available? —Preceding unsigned comment added by 12.215.237.58 (talk) 02:06, 26 October 2008 (UTC)

They have always been available. See snake oil for a surprisingly balanced history of that balm, which should give you an idea of the time range involved. From there, it might seem that the next choice would be to determine when the first effective supplement was marketed, but see multivitamin to see how ambiguous the results are for even modern supplements. Matt Deres (talk) 15:48, 26 October 2008 (UTC)

handwoven wool rug cleaning

ow would I clean an antique, multi colored, hand woven(with nap) wool rug myself, at home?75.36.147.148 (talk) 03:01, 26 October 2008 (UTC)

Well, If it's a Persian rug, the best and easy option is to hang it over a horizontal bar and beat the dust out (best done outside). If you choose to use a vacuum cleaner, use the bare floor setting (so the beaters do not turn). If there is a stain, it is probably best left to a professional, but if you feel brave, and you are sure it its a high quality rug (low quality Persian rugs often are ruined by washing because the colors run) you can give it a deep cleaning by laying it out on some sunny concrete, and using Orvis Horse Soap (sodium Laural sulfate) under running water (from a hose), and scrubbing with a push broom. However, this is best done in warm weater, as the rug will take several days to dry. —Preceding unsigned comment added by Hacky (talk • contribs) 18:58, 26 October 2008 (UTC)

I've heard of rugs like this being placed face down on the snow and beaten on the back to remove dirt. Face down makes sense since the heavy dirt needs to come back out rather than be forced against the rug's woven base. OR here, but I washed a small carved wool chinese style mat thinking it was quality and all the pastel colours ran out. Another time washed a filthy large oval version face down on the grass and it came out clean and original. Patch testing first might be a good idea. Julia Rossi (talk) 22:15, 26 October 2008 (UTC)

Shock waves

Is it true that during areal bombing windows and doors of the house should be open in order to "balance" out the pressure after the explosion? That used to be the rule in case of tornadoes, but National Weather Center now advises to keep the windows closed. So what about during bombing from the sky - open or close the windows and doors?

thanks!

Lana —Preceding unsigned comment added by 72.224.207.32 (talk) 04:44, 26 October 2008 (UTC)

Well, opening doors and windows certainly reduces - or perhaps even eliminates the possibility of the windows blowing out - but doing so must therefore increase the amount of 'over-pressure' entering the interior of the building - which could mean more damage inside than there would have been if the windows had withstood the initial pressure-wave for a while before breaking. That's probably why the advice over tornadoes has changed. SteveBaker (talk) 05:38, 26 October 2008 (UTC)

The tornado warning was changed because even an F5 tornado doesn't create enough of a pressure differential to cause damage; even a "closed" house will be able to breathe enough to compensate. My understanding is that the idea it helps at all is flawed, not that the net amount of damage was re-assessed. The current wisdom from the NWS is not to close or open the windows but rather, "Never mind them. The tornado will open them if it wants." IOW, get your ass to safety. If I knew/suspected that my neighborhood was going to be bombed and I already had a safe place for myself and family, I would shut and board all windows and doors; the pressure difference will be nothing compared to the blast itself. Matt Deres (talk) 15:37, 26 October 2008 (UTC)

Don't bother opening the window. The bomb or tornado will open it for you. As for boarding it up, a documentary about a controlled demolition of a building in the downtown of a city showed the contractors putting plywood over the stained glass windows of a church to reduce the chance of the pressure wave breaking them. Boardup is also encouraged when hurricanes are expected, both to protect against wing pressure and flying debris. Sturdy shutters could also be helpful. Edison (talk) 21:50, 26 October 2008 (UTC)

Controlled demolition is designed to avoid producing large shock waves...the blasts are small and contained and the only "danger to the public and neighbors" I ever hear about it from flying debris. So I call : were they really trying to protect the stained glass from a pressure wave and if so did they actually have an engineering basis for doing so, or were they just protecting from an errant brick? DMacks (talk) 13:12, 27 October 2008 (UTC)

Unfortunately I do not keep a acrd file of references for every fact presented in every TV documentary I have ever seen. They said it was to increase protection against the pressure wave, since the clearances were marginal. Better safe than sorry. Edison (talk) 19:30, 27 October 2008 (UTC)

Thanks for the info! I was curious as in Yugoslavia during bombing we used to open doors and windows as I was told that that is done to reduce the pressure. —Preceding unsigned comment added by 72.224.207.32 (talk) 05:17, 27 October 2008 (UTC)

It's perfectly possible that people in Yugoslavia thought it was a good idea - when in fact it was not. People do a lot of dumb things with the idea that they are doing some good based on 'common sense' reasoning - even when the science points the other way. Drive along any road in Texas and look at the number of pickup trucks where people have either removed or lowered the tailgate "to reduce air resistance" in an effort to get better gas mileage. It SEEMS like a perfectly rational idea - right up to the point when you put a truck into a wind tunnel and find that the manufacturers actually did their homework - and the truck's aerodynamics are better with the tailgate up. However, even though the owner's manual tells you this in words that a child could understand - that doesn't stop hundreds of thousands of truck owners going by "gut instinct" alone. SteveBaker (talk) 14:12, 27 October 2008 (UTC)

Here: http://www.fourmilab.ch/bombcalc/instructions.html we find that windows will be broken by between 0.2 and 1.0 psi of overpressure - and that walls of a typical house require between 1 and 5 psi to demolish them. That's not really surprising - a 4'x4' pane of glass contains 2300 square inches of glass - so between about 500 and 2300 pounds of force will be applied to it - that's like between 3 and 15 adults standing on it...and it doesn't surprise me that it would break!

So the question is this: If the overpressure outside the building compared to inside is going to exceed the amount needed to break windows - but not be enough to demolish the house - then will opening the doors help? The problem with answering it is this: As the pressure wave travels towards the building, does the pressure rise sharply or more slowly? This matters because if the pressure builds slowly enough, high pressure air will be able to gradually leak into the house through small gaps and equalise the pressure inside and out - thereby preventing the windows from blowing in because of the overpressure...whether the doors are open or not. (Sure, flying debris might take them out anyway - but this is a thought experiment - and I want to imagine there is no debris.) If the pressure builds really quickly then even if the doors are wide open, the high pressure air will not be able to flow through the doorway and around to the insides of the windows before the overpressure reaches 1 psi and they blow out.

Therefore, there must be some middle range of rate-of-pressure-increase at which (with doors closed) the air cannot get in through the small holes fast enough to keep the pressure difference on the two sides of the glass down below 0.2 psi - yet if the doors were opened, the reduced resistance to passage of the air into the house would allow the air to flow into the house fast enough to keep the pressure difference under 0.2 psi - so the windows will be saved. So to answer the question rigorously - we'd need a plot of the rate of change of pressure in the shockwave from whatever kind of bomb we're considering.

However - I'm pretty sure the rate of pressure increase gets less as you get further from the explosion (the actual overpressure also gets less too - but that's not the question here). I'm pretty sure this is true because of the business of low frequency sounds travelling further through the air than high frequencies - so the sharp, high-frequency leading edge of the pressure curve must get softened. So this suggests that there must be some distance from the bomb where leaving the doors open will indeed save your windows. So the idea has some merit.

The problem is though that by leaving your doors open - you are increasing the sharpness of that pressure wave on the things inside the house...such as the interior walls. The thought experiment I did for the windows applies equally to the interior walls. If the 'sharpness' of the overpressure curve is too steep - the interior walls will be destroyed - but if it's gentle enough, they won't. With the outside doors open - the interior walls will feel more sharp overpressure than if the outside doors are shut and therefore slow down the pressurization of the interior. So there is the problem - if you are at the right range from the explosion - opening the doors will save your windows - but MIGHT cause more extensive interior damage. At other ranges, your windows will blow out even with the exterior doors open - but you are making matters much worse for the interior structures of the house. So unless you somehow know in great detail how big the explosion is going to be - and how far away it is - there is no way to know whether it's worth opening your doors or not. Overall, therefore, you're better off leaving them shut.

SteveBaker (talk) 00:13, 28 October 2008 (UTC)

Diseases by Mortality Rate

NOTE: This is out of sheer interest.

Is there a list somewhere of diseases by mortality rate? Vltava 68 (talk contribs) 08:33, 26 October 2008 (UTC)

List of causes of death by rate. Axl ¤ [Talk] 10:00, 26 October 2008 (UTC)

But something by percentages? 203.188.92.70 (talk) 19:32, 26 October 2008 (UTC)

...Of the people who get the disease every year? 203.188.92.70 (talk) 19:33, 26 October 2008 (UTC)

Making a movie in PyMol

I would like to make a movie in PyMol based on "mset 1 x60" followed by "mdo 1: turn x,3; turn y,5;" but whereas this makes a rotating molecule on-screen, exporting to PNG files yields only a single file. ----Seans Potato Business 11:39, 26 October 2008 (UTC)

Can you export to .gif format? These can be animated, otherwise you will have to go to .mov or .mp4 format, and then convert to animated .gif or ogg format for use in Wikipedia. Graeme Bartlett (talk) 23:40, 26 October 2008 (UTC)

PyMol only gives me the option to export movies as a series of PNG images which then have to be put together with another program. The problem is that I am only getting a single frame when there ought to be many. ----Seans Potato Business 23:51, 26 October 2008 (UTC)

"eMovie is a free tool that makes the creation of molecular movies both easy and intuitive via a breakthrough storyboard interface, similar in nature to what is used in the creation of traditional movies. eMovie is a plug-in for PyMOL ...". Seems relevant. --Sean 13:21, 27 October 2008 (UTC)

Free energy idea needs debunking

Ever since I was a kid I've occasionally come up with free energy and wacky propulsion ideas. Ultimately they've all proved to be fatally flawed in some way, based on my misunderstanding of energy conversion. But I can't figure out what's wrong with this new idea. I'll keep it in its simplest terms.

Okay, imagine a glass tank filled with water, like a fish tank. Through electrolysis we can split the water into hydrogen and oxygen. These gases will float up, in air, right? So if we let the gases separately float up two pipes and collect them in upside-down glass jars, we have potential energy at the top. Then if we recombine that into water, suddenly we've got something that wants to run down again, down another pipe gathering momentum until it hits a turbine at the bottom at speed, driving an electric motor, before falling back into the original tank.

Now this wouldn't generate enough energy to do the electrolysis in the first place. But I don't see why we couldn't extend the height of the system to exploit gravity more, say to 10m. The gases will still float up, and the water will still run down, but now the water will gain additional speed because it's falling further, and it will hit the turbine with much more momentum, thus pushing it round much further for the same amount of water.

Why couldn't this idea be extended until the water reaches terminal velocity, to generate a simply huge amount of energy for the same amount of effort put into electrolysis? There must be something I've got wrong. Can anyone share some insight? • Anakin ^(talk) 14:33, 26 October 2008 (UTC)

Some things wrong which I notice are; when recombined, don't hydrogen and oxygen form water vapour?; why should both gasses rise to the top of the jars (hydrogen is lighter so it will rise above oxygen)? --Seans Potato Business 14:43, 26 October 2008 (UTC)

This is rather simple to debunk on your own if you like experimenting. Get an electric motor and try to split some water. Notice how much energy it takes - as a sanity check, think about the lack of hydrogen as a fuel source. If hydrogen was so eager to split away from oxygen in water, wouldn't it be possible to have hydrogen producers running on tiny batteries in our back yards? Another sanity check - if it was so easy to split water into hydrogen and oxygen and recombine into pure water, wouldn't that be used all over the world to desalinate ocean water? You will find that it takes a lot of energy to split a water molecule. Then, put a water wheel out in the rain and see if a constant rainfall can produce enough electricity to do the job. Of course, it won't. But, you can see how big the gap is between the energy needed and the energy produced. -- kainaw™ 15:07, 26 October 2008 (UTC)

Ah, but 'common sense' arguments by analogy have no place in physics. Putting a 'water wheel out in the rain' is – at its heart – essentially how all modern hydroelectric power plants operate. To make it work, we collect a lot of raindrops from a wide area, and concentrate them into lakes and rivers. It's just a question of scale. Similarly, concerns about the energy cost of electrolysis don't immediately sink the proposal — putting a fuel cell on the uphill end of the device allows us to recapture a substantial portion of the energy used for electrolysis when the hydrogen and oxygen recombine into water. Sure, electrolysis takes a lot of energy for a given amount of gas production, but the reverse process also releases a lot of energy. (There's a reason why hydrogen is used as a rocket fuel.)

What we really have in this proposal is (nominally) a method for moving water from a low altitude to a high one. In hydroelectric plants, the energy to drive this process comes from sunlight (ocean water is evaporated, this water vapor eventually condenses and falls at higher altitudes, we capture some of its gravitational potential energy as it flows back to the oceans). In this perpetual motion device, the source of energy is not immediately obvious, but (since in this house, we obey the laws of thermodynamics) we know that there must be unaccounted energy 'leaking' in somewhere. DanielLC, below, has hit on what I think is the explanation — the conditions at the top and bottom are such that the energy costs of inflating bubbles of gas against atmospheric pressure will offset the apparent energy gained by moving the liquid water to a higher altitude. TenOfAllTrades(talk) 16:16, 26 October 2008 (UTC)

The amount of energy released from burning hydrogen is the same amount used to separate it, assuming the conditions are otherwise the same. Energy is conserved, not destroyed. The problem with your idea is that the conditions aren't the same. The further down the water is, the more pressure it's under and the harder it is to separate into hydrogen and oxygen. The higher up it is, the less pressure it's under and the less energy is released burning it. — DanielLC 15:19, 26 October 2008 (UTC)

I came across a case where a person wanted to bring water up a hill by having the pipe go downwards so the water would get up speed and then rush upwards. Nonsense of course, but even something as silly as that could lead to an idea like the hydraulic ram. So keep up with the wacky ideas and then see if something else occurs to you. Dmcq (talk) 15:46, 26 October 2008 (UTC)

DanielLC, that sounded like the right explanation at first, but it seems to me that balancing the pressures is a bit of a flimsy way for the universe to ensure that we can't violate the laws of thermodynamics. I mean is it really that much harder to do electrolysis of water under an extra 10m of air pressure, compared to the increase in acceleration provided by gravity when the water falls again?

One way to rule out the pressure problem is to see if there's any conceivable way it could work in the absence of air.

Imagine, for example, a sealed room in a lab with all the air sucked out. The water tank would be the same, but this time, instead of upside-down glass jars to collect the gases in, we'll use two open tubes. The bottom end of each tube would be under the water, around the electrodes to collect the gases. The top ends would just be left open. As the gases bubble out from the electrodes, they would float out of the water then sit and float on its surface (near the bottom of the tubes). Without air in the room, they wouldn't float up any further. But if this process was given enough of a kick-start the tubes would gradually fill all the way up. A littler pipe could run between the two tubes near the top and the gases could be recombined into water again in the middle, providing a perfect stream of water to run down an open shoot again, onto the turbine to generate electricity (which would now spin faster, in the absence of air resistance!).

So I'm not sure it's debunked yet. Is there another reason this wouldn't work? • Anakin ^(talk) 18:18, 26 October 2008 (UTC)

If there were no air pressure the water would boil. Even if it didn't, the gas released wouldn't just sit there it would spread out to fill the vacuum. --Tango (talk) 18:30, 26 October 2008 (UTC)

It's very definitely debunked - because the laws of thermodynamics say it's debunked and that's enough.

If you really have to break it down, the fatal theoretical flaw is that the cost of splitting water into oxygen and hydrogen is the cost of breaking the bonds between them PLUS the cost of overcoming the pressure in the water to create the bubbles. When you recombine the gasses at the top end of the equipment, you rejoin those chemical bonds - but you only get back the energy you used to break them - not the energy you used to make the bubbles form. The energy you get back from the flowing water is the same as the additional energy used to create the bubbles in the first place. I used to have a reference for the additional electrical energy it took to do this (as a function of the temperature and pressure of the water) - but sadly, I can't find it right now so you'll have to take my word for it.

The much more obvious practical flaw is that neither electrolysis nor recombining hydrogen and oxygen are remotely close to being 100% efficient - there is friction everywhere in the system and the turbines for recovering power from the flowing water can't ever be close to recovering 100% of the kinetic energy because to do that they'd have to stop the water from flowing - which would block the output of the system.

There comes a point in your life when you've seen enough of these crazy perpetual motion machines. We have a set of thermodynamic laws that step back from the details of the mechanism and do an end-run around all of the detailed explanations. When someone suggests such a system - you may safely start from the principle that it definitely won't work. The details of why are then just an intellectual exercise with little or no practical value.

SteveBaker (talk) 18:39, 26 October 2008 (UTC)

Speaking of perpetual motion machines, can't a solar system or galaxy count as a perpetual motion machine? 67.184.14.87 (talk) 02:07, 27 October 2008 (UTC)

What extracts energy from it? —Tamfang (talk) 03:00, 27 October 2008 (UTC)

Neither a solar system or galaxy is a perpetual motion machine. Both start, last a long time, and end. The universe as a whole is debatable. It did begin. Will it end? Most theories say that it will, so it isn't perpetual. However, it is possible that it will keep going forever. -- kainaw™ 04:15, 27 October 2008 (UTC)

A perpetual motion machine is usually defined as something that moves perpetually while giving off energy. If you don't include that last bit, a pendulum in a vacuum is a perpetual motion machine (give or take the difficulties in producing a perfect vacuum). --Tango (talk) 11:40, 27 October 2008 (UTC)

It would have to be a pendulum in a perfect vacuum with a frictionless bearing - which is impossible because anything that bears the weight of the pendulum is going to produce friction of some kind. Worse still: an-anything-in-a-perfect-vacuum is impossible to start with because as soon as you put something into a vacuum - it'll shed a few molecules and you won't have a perfect vacuum anymore. If you ignore the problems of the imperfect vacuum then a simple spinning disk (in a perfect vacuum and someplace where there is no gravity) might

work - except that in our universe, there is ALWAYS some gravity from somewhere.

Solar systems clearly aren't perpetual. The star runs down and explodes or collapses or something...and a galaxy is just a bunch of solar systems - and all of them give off light that they can't get back - so they definitely aren't perpetual. The universe as a whole...well, that's a bit tricky. Entropy is going to cause the universe to change - but arguably, that's an exponential process that never actually goes to zero. (Although a lot depends on things we don't know about like dark energy/matter). However, we can discount the idea of getting 'free energy' this way because if you are considering the universe to be the 'closed system' in thermodynamic terms - then any machine that's supposedly extracting energy from it is a part of the system that the energy is being extracted from - so the laws of thermodynamics are happy about that. SteveBaker (talk) 14:02, 27 October 2008 (UTC)

Actually, in theory it does work: if your electrolysis device and fuel cell are both 100% efficient, the energy used to split the water is exactly the same as the energy gained from recombining it. You can then extract energy from the water as it flows down to the electrolysis device. It needs to be open to the atmosphere, though, because you're using the gravitational potential energy of the atmosphere to lift the gasses generated to fuel cell. --Carnildo (talk) 22:30, 27 October 2008 (UTC)

No - even in theory there has to be energy lost due to friction and heat and turbulance and things like that. You can make a thought experiment in which all of those annoying things are magically handwaved away - but that's true of even the simplest of perpetual motion ideas. Connect a magical 100% efficient motor to a magical 100% efficient generator and use magical zero friction bearings and magical zero-resistance wires - and you have a perpetual motion machine. Heck - you don't even need to go that far - pick up any object and set it spinning and in an idealized world, you have perpetual motion. But you can't justify this kind of nonsense on the basis of UTTERLY unreasonable frictionless, lossless parts. As I explained before - to extract 100% of the kinetic energy from the water as it goes through the turbine, the turbine has to utterly stop the liquid from moving. The trouble with that is that the dead stationary water now blocks the output of the turbine. So no matter how far 'out there' you want to go with your 100% efficient turbine 'thought experiment' - it can never extract 100% of the kinetic energy. So as the water enters the tank at the bottom of the machine - ready to be re-electrolysed, it has to have a tiny bit of residual motion - which ultimately leeches energy from the system and causes it to stop. The laws of thermodynamics tell us that even in the uttermost airy-fairy theory, you can't get back 100% of your energy unless you are operating it at the absolute zero of temperature - and it also says that you can't ever get to the absolute zero of temperature - so no machine can ever be 100% efficient...even in theory.

SteveBaker (talk) 23:31, 27 October 2008 (UTC)

transformer

i have tried a lot but dint got a satisfiable answer,so plz tell me wat exactly happens when we apply a heavy ac signal on primary of a single phase transformer ,but keep secondary open.although power at primary is same as in normal cases because input voltage and current will be same.then where does this huge power goes.116.71.185.65 (talk) 16:43, 26 October 2008 (UTC)

Nowhere if it is all ideal. No power is drawn from the input if the output doesn't draw off any power. Dmcq (talk) 17:38, 26 October 2008 (UTC)

Input voltage is the same but, on no load, input current will be only the magnetising current. As this is 90 deg out of phase with the applied voltage, then the input power (VI cos phi) is also (very nearly) zero. --GreenSpigot (talk) 19:22, 26 October 2008 (UTC)

See Transformer. There will also be a little real power dissipated with an open secondary due to eddy currents and due to I² R losses in the primary winding, due to magnetizing current. Even the humming of an unloaded transformer means that a little power is being consumed to cause vibration of the metal. The real point of misunderstanding in the question is the mistaken assumption that "power at primary is same as in normal case." If "normal case" means a normally loaded transformer, then the comparatively low current into the primary of the unloaded transformer means that the input power is much lower than the normal case. Remember that for an ideal (lossless) transformer, "power in = power out" even though the voltage and current levels vary with the number of turns in the primary and secondary, directly for voltage and inversely for current. Edison (talk) 21:46, 26 October 2008 (UTC)

How are all sciences interrelated?

Hello, I am looking for a kind of scheme in which important topics/fields of exact science are related. Most of the articles on scientific subjects (take semiconductor devices for example) relate it to more fundamental topics (quantum physics--> solid state an semiconductor physics) and to applied topics (transistors--> chips etc), but I would like to see all that information on one (perhaps giant) picture. Any ideas?

Thanks —Preceding unsigned comment added by 87.67.44.42 (talk) 18:47, 26 October 2008 (UTC)

• http://imgs.xkcd.com/comics/purity.png SteveBaker (talk) 19:20, 26 October 2008 (UTC)

Except that in the diagram the mathematician appears to be a woman. ;-) Axl ¤ [Talk] 19:29, 26 October 2008 (UTC)

I have seen that cartoon before: it kind of made me start wondering so it's funny to get as an answer :-). I'm looking for something more in detail, though. —Preceding unsigned comment added by 87.67.44.42 (talk) 20:19, 26 October 2008 (UTC)

I suppose, at the end of the day, it all comes down to (quantum?)physics (and- not to upset the mathematicians- some maths)--GreenSpigot (talk) 19:27, 26 October 2008 (UTC)

"Some" maths? :'-( --Tango (talk) 11:41, 27 October 2008 (UTC)

What you are basically looking for is a classification of knowledge. Some people have tried to do that. It's not easy to do and it requires a lot of hand waving. One of my favorite attempts to do this comes from the Encyclopedie: Figurative system of human knowledge. --98.217.8.46 (talk) 23:43, 26 October 2008 (UTC)

I can kinda imagine the sort of diagram you're looking for - and I'm surprised I couldn't find one anywhere (I did spend a while hunting for one). I kinda imagine a diagram with the words "PHYSICS", "CHEMISTRY", "MATH", "BIOLOGY" and so on in big letters in regions of the diagram - with all of the sub-disciplines (things like "ELECTRONICS") placed in relation to the main topics (eg Electronics straddling physics and chemistry - but nowhere near biology) - perhaps with arrows between sub-disciplines showing how they relate to one-another. I think you could make a coherent diagram like that - but it would be hard to do a perfect job because most things touch mathematics - and (as the XKCD cartoon so elegantly points out), chemistry is technically a sub-field of physics and biology a sub-field of chemistry...so it's not really going to be perfect. However, I was unable to find such a thing (although I'm sure I've seen one someplace in the past). SteveBaker (talk) 13:45, 27 October 2008 (UTC)

The article The central science on chemistry's role as the "connector" between the physics-based sciences and biology-based sciences contains the exact diagram, with attribution, that you are looking for. --Jayron32.talk.contribs 17:14, 27 October 2008 (UTC)

Yeah - that's the kind of thing - but that one only has the sciences that relate directly to chemistry - I was thinking of a much denser diagram with hundreds of fields connected with arrows showing how they interrelate. The annoying thing is that I'm almost sure I've seen something like that. SteveBaker (talk) 23:20, 27 October 2008 (UTC)

That's indeed what I was looking for. Thanks for help me searching, and if you happened to stumble across something similar I would be happy to know. --Gnorkel (talk) 23:35, 27 October 2008 (UTC)

Photons released while burning?

Since photons are the carriers of light and when anything (like paper, wood, candle wicks, etc.) burns light is emitted, does this mean that photons are part of the atomic structure of all matter?Terran2034 (talk) 18:50, 26 October 2008 (UTC)

No. Photons are created whenever energy is released as electromagnetic waves (E=Mc² - the energy released is converted into the mass of the photons that are carry the energy away). They aren't tucked away inside the atoms waiting to be released. Aside from anything else, photons have to move at the local speed of light which means that they can't be stationary inside the atom. SteveBaker (talk) 19:11, 26 October 2008 (UTC)

Photons are created or absorbed when an electron in an atom loses or gains energy. In the course of burning, lots of energy is released from the breaking of chemical bonds. This energy, among many other things, causes electrons to move into higher orbitals, where they are in an "excited state". As the electrons "relax" back to their native, or "ground" state, they release photons. Its not that the photons are "part" of the electron; you need to stop thinking of sub-atomic models as having convenient macroscopic analogs. The electron "releases" the photon, but it does not "contain" the photon itself. The electron is releasing "energy", which at this scale is basically exactly the same as releasing mass. Whether you think of light as a "photon" (i.e. a "mass") or as a "wave" (i.e. "energy") depends upon which model best fits your application. Light is light, and it does what it does. Photons are a convenient model for explaining some behaviors of light, but that doesn't mean that photons behave like little billiard balls... --Jayron32.talk.contribs 17:10, 27 October 2008 (UTC)

Harmonic distortion in Wein bridge oscillator

What do people think is the prime source of (ie largest contributor to) harmonic distortion in a Wien bridge oscillator (Not homework Im researching low distortion oscillators ATM)--GreenSpigot (talk) 20:26, 26 October 2008 (UTC)

My guess would be due to non linear gain due to the amplifier element being not ideal. If you use ceramic capacitors you may also get non linear response. Graeme Bartlett (talk) 21:11, 26 October 2008 (UTC)

Bot of those Im sure will have some effect but what about the gain control mechanism: is that going to give an effect?--GreenSpigot (talk) 14:35, 27 October 2008 (UTC)

If you use a light bulb that should be reasonably linear as long as the oscillator is much higher frequency than the response of the filament in the bulb. At audio frequencies you may have some detectable effect. Graeme Bartlett (talk) 20:31, 27 October 2008 (UTC)

What does the 5 in Saturn 5 and Ares 5 mean?

What does the 5 in Saturn 5 and Ares 5 mean? 67.184.14.87 (talk) 23:50, 26 October 2008 (UTC)

As far as I'm aware, it just means it's the 5th version of that technology. See Saturn V#Development. --Tango (talk) 00:32, 27 October 2008 (UTC)

How about Ares? Ares 1 isn't even finished yet. Also, I don't think that there's a Ares 2, 3 or 4. Maybe NASA decided to borrow the Saturn version numbers for the Ares rocket program? 67.184.14.87 (talk) 00:39, 27 October 2008 (UTC)

I'm actually quite surprised that NASA didn't save the 'Ares' designation for future hypothetical Mars missions... --Kurt Shaped Box (talk) 00:49, 27 October 2008 (UTC)

Actually, they are planning on using Ares V as the launch vehicle for manned Mars missions. 67.184.14.87 (talk) 01:30, 27 October 2008 (UTC)

Ares IV was planned, but the project was later scrapped. I assume that the same is true of Ares II and III, though perhaps these got no further than rejected proposals. Deor (talk) 10:51, 27 October 2008 (UTC)

Indeed, it's quite common for some versions to never get past the drawing board or maybe some testing which results in strange orderings. (eg. Apollos 2-6) --Tango (talk) 11:44, 27 October 2008 (UTC)

Like Preparations A-G? Arakunem^Talk 16:56, 27 October 2008 (UTC)

Or WD-1 through WD-39. SteveBaker (talk) 05:17, 28 October 2008 (UTC)

October 27

Indoor marijuana cultivation retardant

I heard of a chemical that can be put into a house's air ducts that will hamper marijuana growth by I think preventing pollination or something. I've read the mj cultivation and indoor cultivation articles and looked on google - does anyone know? —Preceding unsigned comment added by 206.116.59.222 (talk) 02:16, 27 October 2008 (UTC)

Preventing pollination is often considered a good thing, so that's probably not it. —Tamfang (talk) 02:58, 27 October 2008 (UTC)

Narking on the cultivator would be a more efficient solution to the problem of having someone in the household cultivating marijuana, of course with its own risks. Edison (talk) 03:06, 27 October 2008 (UTC)

No, preventing cultivation in the first place is the more efficient solution. Turning in a grower does nothing to prevent the property damage or protect the property owner from legal and property seizure ramifications of owning a marijuana house. Telling potential renters that dope wouldn't grow because of the retardant DOES.

Putting a chemical into a house's air ducts could be a health and safety hazard, and your tenant might have a claim against you in law. There is only a remote chance that a particular tenant would be intending to grow marijuana. Depending on the jurisdiction it would be better to build into the tenancy agreement a right for the landlord to inspect the property at regular intervals, and a heavy financial penalty if they were found to be engaging in an illegal activity. Itsmejudith (talk) 20:35, 27 October 2008 (UTC)

None of which prevents the landlord from TELLING his tenants that he did this in order to discourage them from undesirable behaviors. Not everyone is smart enough to think these things through to their logical conclusions. SteveBaker (talk) 05:16, 28 October 2008 (UTC)

Dimensions

I haven't read Flatland in years, so maybe this is answered there, but anyway: An object in a 2-dimensional land such as flatland would appear from inside the land as a line segment, possibly changing length is the object turned. Except -- the only way it would be visible is if there was some non-zero third dimension ("height") to this figure; otherwise, there would be nothing to see. (Similarly if in the real world you drew a line segment with zero thickness, you wouldn't see anything.) So this implies that there must be a non-zero infinitesimal third dimension. This would then imply that a 3-dimensional world must have an non-zero fourth dimension to be able to actually perceive anything (aside from time: time would apply in the 2-dimensional land as well), and that the fourth dimension world would have a non-zero fifth dimension, and so on. Therefore, the universe has infinite dimensions.

What's wrong with how I'm thinking? zafiroblue05 | Talk 03:07, 27 October 2008 (UTC)

By "see", you are referring to a light particle bouncing/reflecting/emitting from a surface and hitting a sensory organ in some sort of eye. Light particles may be defined as having width, but it is just as easy to define them as a zero-size wave of energy. So, it is not necessary for the surface to have height since the wave of energy coming from it doesn't have to have height. Also, the point of flatland isn't that there isn't height, it is only that the beings living in flatland cannot comprehend or sense height. So, flatland doesn't say there isn't height. In fact, it uses a demonstration of height - shoving your finger through flatland. The beings there will see a weird object that changes shape as your finger moves through and they see it slice by slice. -- kainaw™ 03:59, 27 October 2008 (UTC)

Why shouldn't a Flatlander's eye have a one-dimensional retina that sees one-dimensional images? Consider the cross-sectional diagrams you've seen of light entering an eye and forming an image; now take that diagram literally. In our world something with no thickness has no substance, but Flatland is not our world. A four-dimensional observer might make the same comment about our vision that you make about Flatland vision. —Tamfang (talk) 05:29, 27 October 2008 (UTC)

(I think?) that's what I'm saying - that we shouldn't be able to see each other unless there is another physical dimension in which we are "thick," just as flatlander wouldn't be able to see each other if they really had no height. And that by induction this would continue to an infinite amount of dimensions. But Kainaw's explanation that we don't have to be "thick" in another dimension because light can be a zero-seze wave (that can be absorbed and therefore processed and seen) seems to work for me. zafiroblue05 | Talk 05:59, 27 October 2008 (UTC)

Well, I see two problems in your reasoning. First off, the flatland example only suggests that you need N+1 dimensions to be able to perceive in N dimensions. Once N dimensions are present, perception in N-1 dimensions becomes possible. Nowhere in this argument is an N+2 dimension necessary unless there are beings that percieve in N+1, and so on.

The other problem I see in your reasoning is that your premises are about the nature of perception, but you draw conclusions about the nature of the universe. Our perceptions are structured from sense data we receive from our body and are structured into experience by the mind. How we understand the universe through our perceptions does not need to match up with reality as long as our perceptions remain consistent. Mathematically, we could actually live in a 2D holographic universe, and we wouldn't even know it because our experience is 3D! It's even possible that we don't have accurate access to the content of our minds (a very wierd but fun idea). In the very least, you must concede that the fact that you can watch TV and see more than flashing lights is testament to the fact that our brains perceive depth in our world in ways that at least aren't always accurate. --Shaggorama (talk) 07:21, 27 October 2008 (UTC)

I think the problem is that you're not seeing things from a truly 2D viewpoint. There is no reason why truly 2D photons coming from a 2D light source should not bounce off a 2D object, be focussed through a 2D lens and land on the viewer's (presumably) 1D retina - thereby forming a 1D image. There is no need for any extra dimensions to make this work. Hence your extrapolation (which in itself is a bit 'iffy') is entirely invalid. Incidentally - the book 'Flatland' was written in 1884 and it's basically crap. You won't learn anything about the nature of a 2D world from it. It's mostly a diatribe about class distinctions and politics - it's sexist as all hell (quite an embarrassment to read, actually) and its ideas about a 2D world are poorly thought out from any kind of scientific perspective. If you want a truly great book on the subject, I strongly recommend "The Planiverse" by A.K.Dewdney. It's by far the best book to cover the idea of a 2D world and it has a really careful treatment of what it would mean to live in two dimensions - the world is fleshed out in great detail with lots of interesting diagrams (you can easily spend 20 minutes looking at the 2D steam engine or the structure of a 2D 'house' or a fishing boat. The appendices to the book cover some serious scientific issues that probably mean that a 2D world with the kind of richness needed to form stars, planets and creatures could probably not exist at all. For example, it's believe that 2D atoms would be unable to form chemical bonds at all. But the book also has a great plot and I recommend it to anyone with an enquiring mind (which means everyone here at the science ref desk!) - read it to your kids too. SteveBaker (talk) 13:34, 27 October 2008 (UTC)

Urgent need to pee

Suppose someone really really really goes to go but they don't want to because it would be embarrassing (eg, marching in a parade) or very messy to clean up (eg, driving a car) or very both (eg, riding in the boss's car.)

Can a person hurt themself by trying to hold it till they get to an "appropriate" place? Or is it safe to hold on as long as they can?

Second part of the question -- are there any strategies to help people "hold on"? (Please, no suggestions to carry clothespins at all times.)

CBHA (talk) 03:23, 27 October 2008 (UTC)

PS: Just on the off-chance that anyone wants it, I irrevocably agree to release this contribution under the terms of the GFDL. CBHA (talk) 03:26, 27 October 2008 (UTC)

Spontaneous rupture of the bladder is very rare, but does occur. To quote a case study, one scenario is: "The pathogenesis involves bladder overdistension and thinning of the dome from diuresis. The patient ignores natural cues to void due to alcoholic stupor. Thereafter even trivial increase in intra abdominal pressure like coughing can rupture the bladder." - Nunh-huh 03:52, 27 October 2008 (UTC)

See Tycho Brahe#Death for a well-known case where someone was claimed to have killed himself in this way, although not with a rupture. --Anon, 05:53 UTC, October 27, 2008.

BTW, there is no need to include a statement licensing your contribution under the GFDL. By posting any text to wikipedia, you've already agreed to release your contribution under the terms of the GFDL, without exception. And it is not as odd as it may seem since there are many wikipedia mirrors who mirror our content completely legally. And we archive all reference desk questions so who knows, maybe some day someone will want to publish a book or CD or whatever 09:45, 27 October 2008 (UTC)

I need to go to the toilet now.I bet that was your suggestion. There's probably a word for that like one yawn making everyone else yawn but it 'scapes me now - gotta go :) Dmcq (talk) 16:34, 27 October 2008 (UTC)

Contagiousness. PrimeHunter (talk) 18:08, 27 October 2008 (UTC)

or suggestion. --Tango (talk) 23:36, 27 October 2008 (UTC)

I've heard your kidneys just stop producing urine after a while. If that's correct, you could probably get kind of sick if you let the toxins in your bloodstream build up long enough. I'd consider that hurting yourself. — DanielLC 23:42, 27 October 2008 (UTC)

As a practical matter, wouldn't bladder control give out long before the kidneys ceased to operate (leaving aside the case of someone with kidney disease)? CBHA (talk) 04:45, 28 October 2008 (UTC)

Eye

Can objects stuffed up the eye go down the optic nerve? February 15, 2009 (talk) 04:18, 27 October 2008 (UTC)

Sorry, but your question isn't clear. If you're asking for medical advice (For example, if you've crammed something into your eye.) then we can't give medical advice but if you're worried then you should probably get to an emergency room.

If you're just curious, you might be thinking of an ice pick lobotomy. I don't think that actually touches the optic nerve, but it's a path from the eye-socket to the brain. APL (talk) 05:01, 27 October 2008 (UTC)

Sorry OP, APL seems to have confused a question about human anatomy with a request for medical advice. Objects don't really travel down nerves, just chemicals. But, the optic nerve passes through the a hole in the orbit called the optic canal, which does go directly to the brain. A quick browse around google gives the canal a diameter of 4-6mm in adults, so some objects (such as icepicks, as APL gruesomely suggested) can pass through the without damaging the bone. But please, do not stuff anything into your or anyone elses eyes. —Preceding unsigned comment added by 96.231.89.120 (talk) 07:02, 27 October 2008 (UTC)

I did not entirely assume it was a request for medical advice as you're suggesting. My first sentence was a statement that I didn't find the question clear. The second was an answer for if it was medical advice, and my third and fourth sentences was an attempt to offer an informative link about my best guess of what they were asking about.

However, I had assumed that the article on ice pick lobotomies would at least briefly discuss the route from the eye-socket to the brain. Looking more closely, I see that isn't the case. APL (talk) 07:23, 27 October 2008 (UTC)

The questioner did not present any intent to either put in or pull out something out of his optic nerve. Sounds unlike medical advice to me. Mac Davis (talk) 19:00, 27 October 2008 (UTC)

Solar-To-Electric Efficiency (STEE)

In Wiki–page vide-http://en.wikipedia.org/wiki/Solar_power numerous method of harnessing solar energy is explained. But only under sub section- "solar pond" I came across this parameter "Solar-To-Electric Efficiency"(the S-pond has STEE 2%).Whilst under section Photo Voltaics therein, I read

"converted less than 1% of incident light into electricity".

Is the same STEE intended therein? What about Concentrating solar power? Under its main article vide http://en.wikipedia.org/wiki/Concentrating_solar_power I read

"Parabolic dish systems display the highest solar-to-electric efficiency among CSP"

without any mentioning of any percentage under the same sub-section. Apart from these, there are numerous methods of harnessing solar power. It would be delighting to compile a short article of STEEs of different methods, history, development, breakthroughs, etc.

Would this be a valid contribution (by anyone)? "Solar-to-electric efficiency of different methods".

By a reader of Wikipedia 121.247.218.58 (talk) 12:32, 27 October 2008 (UTC)

Yes - anything we can add to the encyclopedia in these areas of increasing importance is worth doing. I would only caution you though that we require our contributors to supply 'references' for every significant fact they provide - so you'd need to come up with reliable references to books, scientific journals, trade magazines and things of that kind to back up most of what you say. Also, if you happen to work for a company that makes or sells those things (so that there might be a conflict of interest) - then you should probably NOT write the article yourself - but rather use the article's Talk: page to pass on information and references to the people who are actually doing the writing. But aside from those two concerns - YES! PLEASE! SteveBaker (talk) 13:18, 27 October 2008 (UTC)

It's worth noting that the "less than 1%" figure applied to the very first solar cells, which were little more than a nineteenth-century curiosity. Silicon solar cells, developed in the 1950s, started out at roughly 5% efficient. Widely-deployed photovoltaic panels today run from about 12 to 24% efficiency. Costly special-purpose panels (primarily used aboard spacecraft) are better than 30% efficient, while experimental cells have exceeded 40% efficiency in the lab. TenOfAllTrades(talk) 14:15, 27 October 2008 (UTC)

You also need to be aware that terrestrial and space solar cells efficiencies are computed with a different standards so they cannot be simply compared. The standard for space-faring solar cells includes UV intensities that are not seen on Earth because of atmospheric blocking. Rmhermen (talk) 20:12, 27 October 2008 (UTC)

We would be really glad to see you (and anyone who has contributed to this) on Talk:Solar energy, as there are lots of improvements to the article that we are currently discussing there. Itsmejudith (talk) 20:30, 27 October 2008 (UTC)

Ketchup

I came across Thixotropy which suggests ketchup shows thixotropy. I'm not however certain if this is true (or for that matter, any of the other examples are correct). I believe it is definitely Shear thinning (from a NASA article) but both wikipedia articles note there is a distinction and the terms are often confused (although I presume itcould be both). Searching didn't help because there are far too many references which treat the two as the same thing. I had the same issue previously with with silly putty where there was confusion over whether it showed dilatant or rheopecty (it appears it is a dilatant but the article had inaccurate information for a long while) Nil Einne (talk) 14:12, 27 October 2008 (UTC)

Ketchup seems thixotropic to me. exactly the way toothpaste is. Mac Davis (talk) 18:57, 27 October 2008 (UTC)

There are a lot of Non-Newtonian fluids out there - and the precise classification of which is of which type is a bit tricky. Fortunately, our article on the subject specifically names Ketchup as a non-newtonian fluid and labels it as being Thixotropic. SteveBaker (talk) 23:14, 27 October 2008 (UTC)

How is the phase between electric and magnetic waves in a lightwave determined?

Hi,

Consider this image of a lightwave.
What I want to know is how is the phase relationship between E (electric force) and B (magnetic force) determined?
How is it measured? I mean, how do we know the phase is 0° and not, say, 90°?

Thanks! —Preceding unsigned comment added by InverseSubstance (talk • contribs) 17:55, 27 October 2008 (UTC)

Maxwells equations can explain this, these are from Faraday's law of induction and Ampère's circuital law with Maxwell's correction. To understand the 90° angle between the magnetic field, read Curl (mathematics). When you look at the equations you can see that E and B are related by differentiating twice (in a linear material), so that a sine turns into a -sine with a 180 degree shift. Graeme Bartlett (talk) 20:44, 27 October 2008 (UTC)

That's not what I'm asking. I'm trying to understand why it is that the electric force E and the magnetic force B are synchronized. I'm wondering how we know that when E is at maximum, B is at maximum too. I mean, is it possible for E to be to a maximum, and B to be at zero? So this question is about the phase in time, not in space. —Preceding unsigned comment added by InverseSubstance (talk • contribs) 23:14, 27 October 2008 (UTC)

OK if you look at Sinusoidal plane-wave solutions of the electromagnetic wave equation the equations have a solution. The derivative of the Electric field with respect to z the distance along the travel direction is proportional to the derivative of the magnetic field with respect to time. When you consider the wave is traveling, then z is equivalent to time, and then derivative of E is proportional to derivative of B, ie they are in phase. Do you need a more symbolic expression of this? Graeme Bartlett (talk) 05:46, 28 October 2008 (UTC)

Very good!
It looks like the E and B forces can in fact be out of phase, which makes the light have an elliptical form.
Thanks, --63.249.87.165 (talk) 06:28, 28 October 2008 (UTC)

Why do Budgerigars have such crappy night vision when compared to humans?

Question as topic. From my experience with my own birds, it seems that they are unable to see objects in the dark until they are mere inches away (at which point, the budgie freaks out). If a budgie has a 'nightmare' (or a night fright, or whatever) and falls off its perch, it seems to be completely unable to find it again will flap around wildly and screech until the light is turned on. --Kurt Shaped Box (talk) 18:47, 27 October 2008 (UTC)

Well, they're not nocturnal birds so the obvious feature (specially adapted eyes) aren't present. In the article under vision here[20] their vision is maybe more strictly designed for full spectrum sunlight. Compare this with human adaptation, making our sight more versatile (sunlight, twilight and night). It'd be interesting to look at a budgie's eyes in terms of size ratio and compare that with human eyes ratio to body size as well. Julia Rossi (talk) 21:43, 27 October 2008 (UTC)

(after edit conflict)You'd think that a bird as low down in the food chain as the Budgerigar is would at least be physically capable of keeping something of a look out for nocturnal predators when roosting though, wouldn't you? If they are unable to spot a human at a distance of six feet in a room with the lights turned off, what chance would they have in the wild against an owl? --Kurt Shaped Box (talk) 23:13, 27 October 2008 (UTC)

Humans have about 7 million 'cone' cells that are responsible for daylight, color vision - and between 75 and 150 million 'rod' cells that are there for low light level monochromatic vision. If we didn't need to see in poor lighting conditions, we could either have eyes that were 10 to 20 times smaller (and therefore require less energy and less weight) - or we could have daytime vision that would be 10 to 20 times sharper. So we pay a LARGE price for our night vision. A creature such as a non-nocturnal bird might well do much better without reasonable night vision. SteveBaker (talk) 23:10, 27 October 2008 (UTC)

Harmonic Vibration

Two part question

1 - Is Sympathetic resonance the same concept as Harmonic vibration - i.e. a sound vibrating an object at a frequency that can eventually cause an object to shatter?

2 - Is it possible to weaponise this concept for use against humans? Could we induce SR/HV in the human skeleton, causing someones bones to shatter into powder?

Exxolon (talk) 19:21, 27 October 2008 (UTC)

Vibrations can only be sustained or built up if the Q factor is high. Bones and humans do not have such a response to vibration, so you need to put in very high power. The target will probably be affected less than the shooter. Graeme Bartlett (talk) 20:50, 27 October 2008 (UTC)

Staying underweight by thinking?

I was reading the article of L (Death Note), and noticed that one line read, "he remains underweight because the brain uses the most calories of any organ in the body." First of all, how much of this is true or false? Like for instance, if one were a deep thinker, would they be able to keep their weight down? What other metabolic functions are involved in this as well? Thanks, Valens Impérial Császár 93 20:09, 27 October 2008 (UTC)

While the brain does consume quite a fair share of the body's energy intake, the largest amount of the brain's function is not necessarily consumed by conscious thinking. Large areas of your brain are devoted to lots of unconscious processes, such as regulating all the processes that simply keep you alive. Also, there is no reason to assume that a person who spends more time in "deep thought" (i.e. thinking about really important or difficult problems) exhibits more brain activity than people who spend their time thinking lots about boobies and brands of beer. Also, what is "deep" for one person is not "deep" for another. Bill Belichick likely spends lots of time thinking about different things than does Stephen Hawking, yet each is as likely to spend as much brain activity in his own field. As a last thought, should not spend too much time looking for logical consistency or scientific stringency out of anime. Most of the time, people who write fiction just make stuff up. --Jayron32.talk.contribs 20:28, 27 October 2008 (UTC)

Maybe you could try some of these deep thoughts. --S.dedalus (talk) 22:37, 27 October 2008 (UTC)

<Anecdotal evidence warning> I remember ending up with terrible headaches after study sprees, exams that (mostly due to lack of preparation) needed a lot of improvisation and after endless hours of chess games. Something that definitely didn't happen after equally long hours of day-dreaming during boring trips. --Taraborn (talk) 22:39, 27 October 2008 (UTC)

<Not medical advice however much it may look like it warning ;)> My guess would be that you were focusing close up for long periods of time - it's your eyes that caused the headaches, not your brain. You should take regular breaks from close up work and allow your eyes to focus on something in the distance. If you get such headaches regularly, then see a doctor or optician, of course (I did and it worked for me!). --Tango (talk) 23:32, 27 October 2008 (UTC)

Just because your brain uses more calories than the rest of your body - doesn't mean that you can make it use yet more by doing something differently. SteveBaker (talk) 23:04, 27 October 2008 (UTC)

Actually, despite a lot of the anecdotal pessimism in the answers so far, the brain actually does consume a huge amount of energy and what you are doing with it does affect how many calories it consumes. "Even at rest, the brain consumes 20% of the body's energy."[21] "During periods of peak performance, adults increase that energy consumption by up to 50%."[22] Thinking "deep thoughts" is probably not enough—doing challenging mental work, though, is more on par. Speculating about whether there is a God by itself is probably not deep enough—trying to rigorously prove it one way or another, working your way through all of the logical ends, probably is. Many "deep thoughts" are pretty cognitively empty unless you back them up with rigor.

Could you keep thin through mental activity? Potentially. It would depend on your overall calorie consumption, size of brain, amount of mental activity, etc. There are also basic metabolic issues that differ from person to person. Clearly just engaging in regular mental activity is not enough for some people—think of Herman Kahn, for example, who was an active thinker by any definition, but he was a complete sybarite and probably far out-consumed any calories burned by thinking (and probably did do enough walking in any case—cutting out normal calorie-burning activities like walking is pretty much the equivalent of chowing down on cake). --98.217.8.46 (talk) 01:14, 28 October 2008 (UTC)

Studies at MUSC (shown on Mythbusters) use brain activity (which may possibly relate to calorie usage) to identify if a person is telling the truth or not. As shown in the episode, when a person lies, it takes more effort and shows up as more brain activity. So, you could stretch this all very thin and make an unscientific claim that telling nothing but lies will cause the brain to burn more calories. Of course, everyone here should know at least one person who constantly lies without apparently burning many calories. -- kainaw™ 01:19, 28 October 2008 (UTC)

"Hi Honey...sorry I lied to you - but I'm on a diet." Hmmm - well it's worth a try. SteveBaker (talk) 05:10, 28 October 2008 (UTC)

Offhand can't think of any obese fiction writers. Anyone? Julia Rossi (talk) 06:33, 28 October 2008 (UTC)

Depending on your definition of fat, Victor Hugo, Alexandre Dumas, père & Alexandre Dumas, fils, George Sand, Chaucer? - Nunh-huh 07:48, 28 October 2008 (UTC)

Analyze a liquid

I currently pay a lot of money for a certain commercially sold product (a special type of cleaning solution, no ingredients listed on the label) and wanted to explore the possibility of creating my own at lower cost. How do I go about reverse-engineering a liquid? Do I lookup "labs" in the Yellow Pages and ask them how much it would cost to come up with the recipe? If yes, how much would such a venture typically cost?

I would assume that the solution is patented, and so I don't know if it would be illegal to produce this yourself. I guess it would probably be OK if you are only using it for yourself.

If I were you, I would look for a cheaper alternative. If you have already searched, and one doesn't exist or it doesn't live up to the standards you expect then I would take further action.

You could ask the company for the ingredients, and I am under the belief that they have to give it to you (I may be wrong) - obviously if you were to do this, make up a lie such as "Could you please provide me with a list of the ingredients that go into your Product XXX. I need this because I clean very sensitive substances that can't come into contact with many commercial cleaning products, and I need to check if your product can be used with these substances." That is a pretty poor lie so don't use it, but I'm sure you can come up with something better.

If they don't tell you, you could get a lab to find out the ingredients. The cost of this could be anything, it depends on how long it would take them to work out the ingredients, which depends on the complexity of the recipe.

Even if you do get the list of ingredients, how do you expect to manufacture it? The ingredients might be impossible for you do get hold of - simply because of the danger. Even if you do get hold of ALL of them, you might need a lot of equipment to manufacture it, including safety equipment. As you would be making this on a small scale this would probably be false economy. Even if we ignore all of these things, the ingredients might not just have to be mixed together, but to go through various processes, for example, heat Ingredient 1 for 5 minutes, then add Ingredient 2 and allow to react for 10 minutes when you will then add Ingredient 3. You would probably not be able to work out what these processes are.

I think your safest bet is to try and find a similar product. W.i.k.i.p.e.d.i.a - Reference desk guy (talk) 22:27, 27 October 2008 (UTC)

Making it yourself is almost certain to be more expensive. Just go to the supermarket and buy the cheapest cleaner that says it does what you want and try it out, if it doesn't work, buy a more expensive one and work your way up the market until you find something suitable. --Tango (talk) 22:40, 27 October 2008 (UTC)

Blindly figuring out what is in a liquid could be difficult, especially if the mixture is complex. What is more reasonable would be figuring out the concentrations of the various components based on an ingredients list, which some products do provide. This is what an analytical chemist can do. Alternatively, if the product is patented, you could try searching for the patent information. It might be difficult to read and won't contain everything, but it is a start. What product is it that you are using? --Russoc4 (talk) 22:49, 27 October 2008 (UTC)

On the subject of patents: To obtain a patent, the patent-holder must specify in detail how to create the patented product. For a liquid, this means specifying precisely what they put into the liquid and in what proportions, and how it was treated if applicable. If he hasn't done this, then there is no patent, and it is perfectly legal to recreate. In that case, it is likely a trade secret, so reverse-engineer to your heart's content if you can find a way to do it ;-) Someguy1221 (talk) 23:01, 27 October 2008 (UTC)

In many countries, manufacturers and most retailers are required by law to provide you with an MSDS sheet for chemical products. You can also look them up online (just type the product name in full with MSDS in Google). The MSDS will tell you the active ingredients in the product. If I was a gambler, I would bet decent money that the actual cleanser is no different than a dozen others on the shelf. Matt Deres (talk) 23:06, 27 October 2008 (UTC)

Uranus disc color

Though Uranus looks pale blue most of the time, could it look bluish-purple sometimes? Since methan gas could make the planet look purple sometimes depend on the sunlight.--Freewayguy 22:46, 27 October 2008 (UTC)

I would think that the colour would depend on the angle of the sunlight on Uranus, and maybe even where Uranus is in relation to the Earth.W.i.k.i.p.e.d.i.a - Reference desk guy (talk) 23:03, 27 October 2008 (UTC)

It's always a very tricky matter to talk about absolute color for things like far distant planets. What you'd probably want to know is what color the planet would appear if you were in orbit around it looking down. But sadly, there is VERY little sunlight out that far - and the planet would be exceedingly dim - almost black. So with your dark-adjusted eyes, things would look more blue than they usually do - but pretty much monochromatic. Well, that's not really the answer most people actually DO want - so when NASA shows pictures of these things, they boost the brightness and juice-up the color to show the details...but it's very rare that the pictures were taken with electronics that have similar properties to human eyes - they are often looking in the infra-red or the ultra-violet - or in colors other than the red, green and blue that our eyes can detect. The cameras may not actually have captured any significant reflected light in red, green or blue. So you see a wide variety of 'interpretations' of remote imagery. It's tough to say what's "right" because nothing is really "right". SteveBaker (talk) 01:11, 28 October 2008 (UTC)

• Isn't Saturn very far from the sun too. The photos Voyager taken can be closely right or little off. Well, some iamge from Voyager finds Uranus green or blue-green, Uranus from space may look blue-purple, I was told to be pale blue. For Saturn I was told if blue-silver color, it may be yellow or gold sometimes, this all depends on sunlight and chemical. Neputne looks usually dull blue from Voyager 2, sometimes neptune is VERY blue, maybe a little purple dye sometimes.--Freewayguy 02:44, 28 October 2008 (UTC)

My understanding is that the Voyager crafts use a Vidicon camera - black and white. They put color filters, such as orange and violet, in front of the camera. Then, NASA combines snapshots taken through different filters and apply color "correction" to make the image appear pleasing. It is not a true color of the objects being photographed. -- kainaw™ 02:51, 28 October 2008 (UTC)

• From this view Neptune's color is blue but duller. This all matters on chemicals, and depends on cluds. For instant Venus may be very yellow sometimes sometimes Venus is white. All spacecraft going through distant palents colors goes in differ color. Jupiter is a distant planet too, sometimes it have black, white, gray, yellow stripes too maybe blue and green.--Freewayguy 02:55, 28 October 2008 (UTC)
• What about Jupiter and Saturn. Cassini, pioneer, and Galileo gone through those planets. You said Jupiter and Saturn may not be a true color is it right. Do pineer, Cassini, and Galileo use black-and white cameras like Voyagers, then put into orange-violet filters for NASAS photos. Which spacecraft of Jupiter and Saturn is true colors?--Freewayguy 02:55, 28 October 2008 (UTC)

• is tan or gray for Mercury a true color, or all spacecrafts use black-and white for all panets. Mercury is only visit by one spacecraft so far, is those photos true colors for Mercury?--Freewayguy 02:59, 28 October 2008 (UTC)

Mercury has been visited by two spacecraft. See Exploration of Mercury. Rmhermen (talk) 03:39, 28 October 2008 (UTC)

• My question is is almost all the planet in fake color, when spacecraft visit it. Jupiter and Saturn have been visit by at least 5 spacecrafts. If I go orbiting it truly in space will disc be blue, white? Jupiter looks orange through spacecraft Pioneer, Galileo too, or those is not true color either. Do most spacecraft work same way as Voyagers?--Freewayguy 03:52, 28 October 2008 (UTC)

• Can you answer this quickly. You seem to lose me a little bit. Gas giant interior is white-hot and generate off mor heat than it gets from the sun, menas it's interior is white, very white, then at each cloud layer they scatter numerous of light waves. The atmospheric layer is thick, menas every point of layers have differ colors. uranus and neptune have methane, I doubt the true color will be black, but maybe not blue. Methane usually makes things look purple, amybe around blue-purple colors to both planets (Uranus maybe a little lighter, Neptune maybe a little darker). jupiter and Saturn is mostly hydrogen gases, and it have a very light interior, part of sky may have white, gray, light brown colors, the disc colro might vary green, orange, yellow paly through every single color. Venus may be perfectly white, all CO2-brightest planet. For Titan may be like burnt orange.--Freewayguy 04:34, 28 October 2008 (UTC)

The gas giant's core produces heat but no light. So that's an irrelevence. It doesn't affect the color. The gas giants don't "glow" - they reflect light just like the rocky planets do. Since they don't glow with their own light - the remainder of your statements are unimportant. SteveBaker (talk) 05:04, 28 October 2008 (UTC)

• Just answer quickly, you seem to be confusing me. I doubt gas giant's sky is black. Which planet have absolute true color or none of them do?--Freewayguy 04:41, 28 October 2008 (UTC)

No - the sky isn't black until you get VERY deep into the atmosphere. Just like here on earth, the materials that make up their atmospheres will scatter sunlight via the Raleigh and Mei scattering mechanisms - so their sky's will appear colored from moderately shallow distances into the clouds up to the outer reaches of the atmosphere when the sky doesn't scatter enough light and it appears black...just like here on earth. But that doesn't affect what I've been telling you. The AMOUNT of sunlight out at Uranus is not enough for humans to see colors. So if you were near Uranus - it would be a very dim, dark swirling mass below your feet. The sun would look like a candle flame 50 or 100 feet away - hardly enough to cast any light on the subject. At those low light levels, we humans don't see colors - just shades of blueish grey...irrespective of the "true" color of the object. We can produce fake color pictures using the various sensors on the spacecraft but to answer the question "what color would it look like"...the answer is more or less "Black". SteveBaker (talk) 05:04, 28 October 2008 (UTC)

Mercury, Venus, Mars, Jupiter and Saturn are all VASTLY closer than Uranus. You can see them all with small telescopes or binoculars and they are quite bright. Jupiter is five times further from the Sun than we are - sunlight there is 25 times dimmer than here on earth - pretty much the same as the sunlight we get here on Earth on a very cloudy day - so it's obvious that you'd be able to see Jupiter very clearly if you were in orbit above it. Saturn is about ten times further from the sun than we are - so the light there is 100 times dimmer than on earth - but that's still enough to see quite clearly and in full color. The lighting inside your house at night is probably around 100 times dimmer than the sun. But Uranus is twice as far away as Saturn - that's 400 times less sunlight than here on Earth. The sun is only as bright as a candle flame halfway down my backyard...you wouldn't see Uranus at all well until your eyes got dark-adapted - and that means no color vision. Spacecraft use peculiar colored filters so that they can maximise the scientific value of the images they produce. They don't often carry a set of red/green/blue filters in order to produce 'natural-looking' photographs for the benefit of human vision. SteveBaker (talk) 04:55, 28 October 2008 (UTC)

Mistaking memory for reality - how?

A friend said recently his mother - who had Alzheimer's before she died - "thought it was her wedding day each day in her last months." A sweet way to go, to be sure.

In reading the Alzheimer's article I think I understand why - flashbulb memory connected with the fact emotions do seem to be recalled, even in the latter stages of Alzheimer's. My question is: 1. is minea correct presumption; and, 2. If so, how does this explain the person who thinks something more mundane is taking place. For instance, I have heard of non-Alzheimers patients who have thought they were in their home, when in fact they were in a nursing home thousands of miles away. (And, with no reminder of home, i.e.: an old picture that was always sitting out.) But, it is not as if anything special is "going on" for them at that moment. Or, could this be an entirely different part of the brain being triggered when that happens?Somebody or his brother (talk) 23:14, 27 October 2008 (UTC)

I think the only accurate response to your question is: "we don't know". Its a fair hypothesis though. When the neurons in the brain die during the progression of the disease, those that would normally wire together to form what we can consider to be a "memory unit" may become disrupted. But, as the Hebbian theory goes, "those that fire together, wire together". The neurons that are left are now misfiring, and they are likely to form synapses with other neurons. So neurons that, for example, "store" the memories of your wedding day could get wired up the the neurons that one uses to "store" short term memory. The result is that the person with dementia, almost literally, gets their wires crossed and recalls inappropriate memories in response to mundane cues. It seems intuitive that the "special" flashbulb memories would be the most persistent, and this is why they seem to survive until the end. But its also possible that there is some kind of recording bias. Memories that are meaningful to the caregiver are the most likely to be documented among the jumble of minor memories the person with dementia may recall each day. Its also comforting to think the sufferer is re-living happy times, and so there is a type of positive re-enforcement in the caregiver believing this. Either way, if significant memories really do persist more than other less significant memories, how and why is unknown. Rockpocket 08:06, 28 October 2008 (UTC)

October 28

Alcohol consumption strange side-effects

Hello, all!

I have volunteered and worked with person(s) who have various severities of alcoholism, from merely excessive to outright insane levels of consumption.

I was curious if someone could explain some of the stranger side effects I have witnessed:

1. Brightening of colors -- White colors becoming blinding, yellow becomes white, confusion of black/blue or yellow/green, etc.

2. Having nonexistant conversations -- with people whom are not speaking, or, thinking there is someone in the room speaking to them when there is not. Not a delusion - the person, even when confronted, thinks there is someone talking to them.

3. The ability to drink a large amount of alcohol (1/5 of vodka, etc.), and, in a relatively short amount of time (1 hr.), the person is relatively sober and able to pass a breathalyzer test (.08 BAC). I was under the impression that this is physically/anatomically impossible.

4. Blindness that fades in and out, however, the person remains able to speak clearly without slurred speech and has generally unaffected motor skills.

5. Phantom-limb type symptoms (w/ people who have lost limbs), but only when heavily inebriated.

Thanks, --70.156.13.172 (talk) 03:58, 28 October 2008 (UTC)

3. This is not physically impossible for people who regularly consume large amounts of alcohol. Their bodies will eventually become adapted to higher than normal BAC levels and will metabolize alcohol faster, allowing them to consume larger amounts without actually intoxicating themselves. Unfortunately, in order to achieve intoxication, they must drink larger and larger amounts of alcohol, which really damages their livers.CalamusFortis 04:09, 28 October 2008 (UTC)

Also - (for #3) it takes a while for the alcohol in the stomach to make it into the blood stream - and from there into the lungs so it'll show up on the breath tester. Over a very short period, I guess it's just about possible.

For all of the other symptoms: Cell membranes can't block Ethanol - so it can attack any cell in the body. Hence, a huge range of side-effects are possible. Heavy drinkers that have varieties of liver problems will suffer another huge range of symptoms from whatever toxins are in their bodies that a healthy person could metabolise without side-effects - but their broken livers are unable to get rid of fast enough. So the consequences for heavy drinkers go beyond the primary effects of the alcohol and into secondary effects that could be due to medications or other things in their diet that would ordinarily be no problem for a healthy person.

But anyone who's ever had more than a couple of drinks in their lives knows that alcohol screws with your brain...once someones brain is screwed - you shouldn't be at all surprised at all of the blindness, bizarre vision issues, phantom limb stuff and auditory hallucinations. It's like you're taking this very large, delicate and super-sophisticated computer and smashing random bits of it with a hammer...the result is entirely predictable...the computer starts to break down. Precisely HOW it breaks down is a lot less predictable. Brains are massively parallel machines so they don't have a single point of failure. So instead of 'crashing' like your PC probably does when you smash it with a hammer - the brain merely generates incorrect results. Since the ethanol is attacking the entire brain at once - it's impossible to predict which bits are going to break first - or what the consequences will be. So for some people - the vision system gets hit - for others it's the nervous system - for others it's memory or hallucinations or insomnia or hypersomnia. Once the brain is broken somewhere at random, almost anything is possible. SteveBaker (talk) 04:29, 28 October 2008 (UTC)

Alcohol withdrawal or the rarer Korsakoff's psychosis could explain these symptoms. Axl ¤ [Talk] 07:38, 28 October 2008 (UTC)

If time is Infinite...

..and there is no irreversible equilibrium state in which the properties of all matter and energy are either fixed or in a repeating loop, then logic suggests that any event that could possibly happen will happen an infinite number of times.

Discuss.NByz (talk) 06:55, 28 October 2008 (UTC)

(edit conflict) It seems to me the phrase "any event that could possibly happen" is ambiguous. Do you intend this just to mean it is possible to imagine an event happening, or does it mean something stronger than that?

For example, it is possible to imagine a streetcar plunging into the Grand Canyon. However, unless there are streetcar tracks very close to the rim, I suspect it won't happen.

I think the statement as it stands is incorrect, that a lot more things "could possibly happen" than actually do happen. CBHA (talk) 04:40, 28 October 2008 (UTC) (More philosophy than science, ISTM.)

I highly suggest that we don't address this question here. It should be addressed on the science reference desk. Magog the Ogre (talk) 04:45, 28 October 2008 (UTC)

I'll give it a try out there. I guess the purpose of the question is to make you test just how big your minds concept of "infinity" is. Even though there is no logical reason that a streetcar's tracks would lead into a 'Grand Canyon', the very concept of "dividing infinity", to me, always meant that regardless of how small the chance of something is (like for example, atoms with identical properties reforming an infinite number of exact replicas of earth) will happen an infinite number of times in the universe I described.NByz (talk) 06:52, 28 October 2008 (UTC)

I moved this from the misc. desk. I am interested in articles about this type of thinking. Or people shooting it down with better logic.NByz (talk) 06:56, 28 October 2008 (UTC)

Even in a finite time period in a finite region of space, any event that could possibly happen...could happen. But that says nothing of what will happen. You run into an issue of our own universe. Depending on the ultimate fate of the Universe, and assuming the universe is finite in extent, then not everything may happen. If the universe hits an abrupt end somewhere, then time is finite, and not everything will happen. If the universe is inifinite but suffers heat death or explosive expansion, then the probability of certain events will shrink even closer to zero as time proceeds, and so the infinite time integral of a certain event's probability may still be close to zero. But under certain scenarios, including that the universe is infinite in extent, then yes, it would certainly seem the case that anything that can happen, since it can happen anywhere with some probability, has a probability of 1 of happening somewhere. Your chance of witnessing it may still be close to 0 if it is something dramatically unlikely, like a grand piano appearing out of thin air. For further reading, you may be interested in boltzmann brain and quantum immortality, the latter being on a supposed consquence of the (perhaps) infinitely many, and completely encompassing many-worlds. Someguy1221 (talk) 07:06, 28 October 2008 (UTC)

Those were cool articles. I guess we'd have to alter some of the assumptions about the universe in order to suggest my conclusion. I'm thinking that this hypothetical universe had no tendency towards entropy, and no eventual state of repetition or 'boredom'; there is always the potential for something to change (but not in some repeating loop or in some way that it has before), but not to the point where each 'state' of the universe was stochastic. Doesn't the fact that 1) something will change between this state of the universe and the next, 2) that the change won't be repetitive (everything isn't just clumping up, or spreading out) and 3) time is infinite mean that, no matter how many units of matter and energy exist in the universe, they will eventually be arranged in every conceivable way?NByz (talk) 08:00, 28 October 2008 (UTC)

Every way that is reachable from the initial state under the laws of physics, maybe. It may be possible that there are two states which can't be reached from each other without violating the laws of physics - a mathematician would say that the action of the laws of physics on the state of the universe isn't transitive. Of course, those assumptions don't fit with our universe, so this discussion is entirely academic. --Tango (talk) 11:44, 28 October 2008 (UTC)

Simplest oscillating reaction?

Just looking for the cheapest way to set up an oscillating reaction for part of my halloween costume. The only one I know of is the Briggs-Rauscher, which is pretty, but expensive to make.

Anyone know any others that are easier to slap together? Also, how do I tell exactly how long such a concoction will oscillate for? —Preceding unsigned comment added by 66.158.193.46 (talk) 09:04, 28 October 2008 (UTC)

Though I think it probably not very practical, I would think the Halloween Reaction would be the most seasonal. We have articles on Briggs-Rauscher reaction, Belousov-Zhabotinsky reaction, Bray-Liebhafsky reaction, and the Iodine clock reaction as well. (They probably should have their own WP:Category).- Nunh-huh 11:07, 28 October 2008 (UTC)