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Fine-tuned universe

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The Universe seems to be 'fine-tuned' (for life), because any small changes in the 20 or so physical constants would make it very different, and presumably not hospitable to life. For example, stars would not be able to fuse hydrogen and helium if the electric charge of the electron had been only slightly different, or if the strength of the strong nuclear force had been only 2% greater diprotons would be stable and hydrogen would fuse too easily.

Another related point is that the early universe had a very low entropy, a very unlikely situation: statistical mechanics says that the most probable state of matter has a very high entropy, a state where life is not possible. The universe is now going towards that state, according to the second law of thermodynamics, resulting eventually in heat death. This paradox can be treated in the same way as fine-tuning.

Does "fine-tuning" need an explanation?

Some, like Stephen Jay Gould, believe that fine-tuning does not need any more explanation than a particular roll of dice that would result in a double six. Our universe had to have physical constants, and they just happen to be the ones that permit our existence. Moreover, any other combinations of physical constants may have resulted in a very different universe, one in which a human-like civilization may not emerge, but who is to say that it would not be hospitable to other, very different, forms of intelligent life?

What are the possible explanations?

There are actually three broad types of explanations: the universe is not finely tuned, the multiverse, and the intelligent designer. While the latter two are not incompatible with each other, accepting one of them makes the other one less necessary.

  • The universe is not finely tuned explanation questions whether the universe is in fact finely tuned. The fact that a universe with different physical constants might be inhospitable to life as we know it does not necessarily mean that it is inhospitable to any form of life, and there is no known way of actually experimentally verifying whether a universe allows for life or not. Further, the overwhelming majority of this universe, especially the interstellar vacuum, appears to be devoid of life; other physical constants may exist that allow a much greater density of life than in this universe. The apparent rarity of life in our universe is, however, evidence that life does indeed require 'finely tuned' conditions for existence.
  • The multiverse explanation assumes the existence of a mechanism that has created many universes with different physical constants, some of which are hospitable to intelligent life. And because we are intelligent beings, we would happen to be in an hospitable one. This approach has led to a lot of research into the anthropic principle. This explanation has been of particular interest to particle physicists because theories of everything do apparently generate large numbers of universes in which the physical constants are random. As of yet, there is no evidence for the existence of a multiverse, but some researchers studying M-theory and gravity leaks hope to see some evidence soon.
  • The intelligent design explanation assumes the existence of a being, principle or mechanism with the purpose to create a universe with intelligent life. It would thus somehow set or manipulate the physical constants as we know them. This agent could be a God-like being.

Ikeda/Jeffreys Argument Critique

A Bayesian probabilistic discussion by mathematician Michael Ikeda and astronomer Bill Jefferys argues that the traditional reasoning about intelligent design from the presence of fine-tuning does not properly condition on the existence of life, and is also based on an incorrect reversal of conditional probabilities (in an example of the prosecutor's fallacy), which in this form erroneously claims that if fine-tuning is rare in naturalistic universes, then a fine-tuned universe is unlikely to be naturalistic. (In this context, "naturalistic" is taken to be synonymous with "not intelligently designed".)

They offer a proof that they say indicates one should in fact draw the opposite conclusion: the presence of fine-tuning actually argues against intelligent design. Their main theorem — under the assumptions that

  1. our universe exists and contains life (L),
  2. our universe is "life friendly" (F), and
  3. life can exist in a "naturalistic" (N) universe only if that universe is "life-friendly" (N&L ⇒ F), while life might exist in a "designed" universe even if it is not "life friendly"

The proof goes on to say that, given our universe contains life (L), the probability that our universe is naturalistic, P(N|L), is less than the probability that our universe is naturalistic given that it is also fine-tuned, P(N|L&F) = P((N|L) | F). (That is, adding the assumption of fine tuning increases the probability that our universe is naturalistic, given that we know our universe contains life.) Thus, they argue ironically, supporters of intelligent design should try to prove that our universe is not fine-tuned. The philosopher of science Elliott Sober makes a similar argument.

The counterintuitive conclusion that this attempted proof generates (that a designed universe should be haphazardly organized) results from a flaw in the proof. Their argument supposes that life can exist in a non-life friendly universe. This assumption is impossible to prove (there is no "non-life friendly" universe for us to look at). Another way of looking at this is that the third assumption in the proof is that life will arise in a purposeless universe only if random chance creates life-friendly conditions) P(N|L) while life could occur in a purpose-driven universe even if it was not geared for life ("God could break the rules and make life not supported by the universe"). Simply put, the essential flaw in the proof is that it assumes that God would create a Universe where he would not follow the rules he set down (i.e. the proof allows for universes where life could exists in contradiction to established laws of physics within that universe).

Of course, this logic is deeply flawed and results in a flawed conclusion. Using the same proof on Windows XP (Life) and a Computer (Universe):

  1. Windows XP runs on a computer (L),
  2. The nature of the computer is coducive to having Windows XP run on it; it is "Windows XP friendly" (F), and
  3. Windows XP can appear without forethought in a "Naturalist" (N) Computer (lets say a monkey jumped on the keyboard a couple times to compile the machine code) only if that Computer is "Windows XP-friendly" (N&L ⇒ F), while Windows XP might exist with forethought both in a "Windows XP friendly" Computer and in another Computer even if its design is not conducive to making Windows XP work.

Besides making clear the flaw in the third assumption (how could Windows XP run on a computer that couldn't support Windows XP?), as we continue with the proof we get:

Given our computer runs Windows XP (L), the probability that our Computer was programmed by a monkey jumping on the keyboard, P(N|L), is less than the probability that our computer was programmed by a monkey jumping on the keyboard given that it is also Windows XP friendly, P(N|L&F) = P((N|L) | F). (That is, adding the assumption of a Windows XP supporting computer increases the probability that our Computer randomly was programmed by a monkey to be conducive to the running of Windows XP, given that we know our computer runs Windows XP.) Thus, the proof argues ironically, that people who believe Windows XP is the product of forethought should try to prove this by trying to prove that the computer running it is NOT conducive to running Windows XP (i.e. this proof expects that a computer that runs Windows XP should have its machine code be programmed more poorly by an intelligent designer than by a monkey jumping on a keyboard). Similarly circular and nonsensical results can be achieved with a number of substitutions to this formula.

In addition to this point, supporters of intelligent design (at the cosmic, rather than the organismic, level) might counter-argue that a finely tuned, life friendly, "naturalistic" universe could have been designed and brought into being by a "supernatural" entity or entities who would not need to intervene, thereafter, in the "naturalistic" functioning of his/her/its/their creation. Thus, the Ikeda-Jefferys Theorem does not drive a stake into the heart of "supernaturalism" in so far as the latter pertains to the creation, as opposed to the functioning, of the universe.

Supporters of organismic intelligent design might further counter-argue that the challenge posed by the Ikeda-Jefferys Theorem requires revision because the challenge is based on the false assumption that fine-tuned life-friendliness cannot consistently be claimed for a universe not governed solely by "naturalistic" law.* The universe is more complex than the computer of our earlier example: a computer is either Windows XP-compatible or it isn't; the "naturalistic" universe (for all its fine-tuned life-friendliness) may well be necessary but not sufficient for life as we know it. To meet a revised Ikeda-Jefferys challenge, the proponents of organismic intelligent design must demonstrate that our universe is not sufficiently fine-tuned/life-friendly to produce the highly complex organic structure and functioning which we observe. [*NOTE. Revised Ikeda-Jefferys assumptions might be as follows: (1) Our universe exists and contains life (L); (2) Our universe is sufficiently fine-tuned/life-friendly (F) to create and sustain life; and, (3) Life can exist in a solely "naturalistic" (N) universe only if that universe is sufficiently fine-tuned/life-friendly. The Ikeda-Jefferys Theorem remains unchanged: P(N|F&L)>=P(N|L) OR P(~N|F&L)<=P(~N|L) where ~N signifies "supernaturalism." The assumption that our universe is sufficiently fine-tuned/life-friendly (F) to create and sustain life strengthens the thesis that our universe is solely "naturalistic." Just as clearly, negation of the sufficiency assumption (~F) strengthens the intelligent design thesis that the universe is not solely naturalistic but requires "supernatural" agency to create and sustain life. {Some would argue: "this still assumes that P(~F&L) (that life can exist in a non-fine tuned universe) is in the probability space, which is impossible to prove." But, in the context of the counter-argument, P(~F&L) means "probability that life can exist in a universe not sufficiently fine-tuned/life-friendly [~F] to create and sustain life." If the universe is N (solely "naturalistic"), the probability is 0. If the universe is ~N (not solely "naturalistic," wherein "intelligent design" could create and sustain life by supplementing the universe's insufficient fine-tuned life-friendliness), the probability is > 0. What remains an unresolved question is whether F or ~F is true. Some would also argue: "if one replaces the N with I (Intelligently Designed) in the third assumption, one obtains an equally rational pro-design conclusion." But, in the context of the counter-argument, I ("Intelligently Designed") = ~N ("not solely "naturalistic"). The proof of the Ikeda-Jefferys Theorem relies on the Weak Anthropic Principle: P(F|N&L)=1. The proposed substitution of ~N [=I] for N renders P(F|~N&L)<1, breaking the logic of the Ikeda-Jefferys proof.}]

References

  • John Barrow (2003) The Constants of Nature, Pantheon Books, ISBN 0375422218
  • Nick Bostrom (2002) Anthropic Bias: Observation Selection Effects in Science and Philosophy, Routledge, New York, ISBN 0415938589

See also

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