schrodinger's backside

Greetings!(Gak! This is a very awkward forum setup. Why no automatic quoting?) The essential property of fine-tuning, in the common usuage of the term, is not the abundance of the fine-tuned feature, but rather its delicacy. In the instance of cosmic fine-tuning, the case being made is that for any life to be possible (let alone abundant), a number of fundamental constants must lie within a tight range (in some special sense of "tight range" - this aspect is actually a bit problematic).This in itself, of course, is not an argument for design. The full argument must be put in terms of (Bayesian/subjective/personal) probabilities. This seems to be the difficult part: I have yet to see a sound fine-tuning argument for design. Usually the proponents of the argument try to appeal to intuition by bringing up semi-irrelevant analogies, such as the firing squad.My intuitive take on it is that there is nothing particularly surprising about our universe being "fine-tuned" for some delicate features, such as life. Life is delicate because it is contingent on a great many prerequisits. Knock out one - and life as we know it becomes impossible. But life is not unique in that respect. There ought to be any number of delicate features in any conceivable universe, including our own - as long as they are complex and long-lived enough (a universe that collapses into a black hole immediately after its birth would not have many features, delicate or not). Which is to say, many, if not all universes will be "fine-tuned" for one thing or another - most likely, a great many things. The mere fact that a complex, long-lived universe has some highly contingent, and therefore delicate, features is not in itself surprising, and therefore does not cry out for an explanation.

But this is not the point that is usually made by fine-tuning proponents. The argument being made concerns the habitability of the universe. The argument, as I said, is rarely developed into a robust probability argument, and instead appeals to intuition. Naturally, the fact that our universe is habitable is a lot more "interesting" than it merely being large or complex or long-lived. A barren, though otherwise feature-rich universe does not excite imagination as much as a life-bearing one. We are naturally biased that way.As for the point that you wish to make, is it a fact that complex, long-lived universes are rare in the parameter space of the fundamental constants? I don't recall this argument being made, because, as I said, most people are more interested in the more specific class of habitable universes. No, we do not need to make assumptions about an actual multiverse. Though I personally think that such a hypothesis would still be more probable than the one involving some kind of cosmic Designer, it is simply unnecesary to invoke it. Thanks!

One apparent problem is that if we allow the range of constants to be infinite (since we don't know of any natural bounds at least for some of them), the probabilility becomes not just small, but exactly 0. But this invalidates the fine-tuning argument (FTA), since it requires the probabilities to be small but non-zero. Besides, the probability in this case doesn't depend on the actual habitable range, as long as it is finite (this is known as "coarse-tuning" problem). But there are some clever arguments that attempt to get around this issue.And as you note, it is quite possible that the constants that are independent in the present models will be made dependent in some future "theory of everything". Whether fine-tuning will be true in such a theory is anyone's guess.It is also possible that there are plenty of as-yet unexplored ranges and combinations of constants where some kind of life would be possible.Another thing is that there is no reason why only the constants (which are themselves somewhat arbitrary) are allowed to vary and not the form of the laws. I am not aware of anyone trying to formulate the FTA for the fundamental equations. Well, under some obvious conditions, such as when the universe collapses into a black hole, it is difficult to imagine any kind of life developing. Yes, there is enough uncertainty that even if the FTA was valid (which it isn't), the payoff for the theist would probably be nugatory.

But it is not just the design crowd. For example, in a recent review paper Multiverse cosmological models physicist P.C.W. Davies discusses the "anthropic fine tuning problem" as a motivation and even justification for multiverse models. Davies traces the history of the anthropic fine-tuning idea from Boltzmann to Hoyle to Brandon Carter (who at a 1974 conference brought it to the attention of cosmologists) to the much-cited Barrow and Tipler, authors of The Anthropic Cosmological Principle. I could contest this on several fronts, such as (a) fine-tuning is ill-defined, (b) fine-tuning is not surprising, i.e. does not cry out for explanation, and possibly (c) a multiverse does not change anything in this respect. However, it would be better to start a new thread for this discussion. I am game, but not right this moment (have too much work right now and would like to go over some literature that I've saved away but haven't had a chance to read).P.S. Thanks for the paper, Nosy. Looks interesting. I have a text copy from Lexus-Nexus, if anyone needs it.Edited by SophistiCat, : P.S.

On the contrary - I was giving you examples of physicists contemplating anthropic fine-tuning, contra what you claimed earlier. You lost me here. IIRC, Weinberg does not count anthropic fine tuning as evidence for a multiverse, but I'll look into it.You know, you don't have to get snippy with me. If you aren't interested in this discussion, then I'll just be on my way...

And I never said or implied that it was. I was merely replying to your remark:

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You are missing the point. It is the complex, long-lived universe that is "surprising" and which requires an explanation. You actually provide the very one I have expounded...

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which I took to mean that you do not consider habitability (the presence of observers) to be relevant to cosmological fine-tuning. Yet in all the treatments of this topic by physicists and philosophers (not necessarily design advocates) that I have seen anthropic fine-tuning seems to be at issue. But if a multiverse with widely varying parameters is already a given, then fine tuning is not an issue at all (if it was an issue to begin with). As you say, the WAP takes care of that. My point is that it is not the case, as some creationists think, that we are forced to contemplate a multiverse in order to deal with some "problem" with fine-tuning. Mutiverse models are proposed because they appear to provide better, i.e. more parsimonious, explanations of our observations - not because they allow us to weasel out of the fine-tuning "problem". No offence, but I don't think that you can accurately judge my understanding by our exchange so far. It appears as if we have been talking past each other.I am by no means an expert on the issue, but I have done some reading (mostly from the philosophical perspective).

Depending on what fine-tuning argument you have in mind, it could be anything, actually. The argument that I have in mind is the one that points to the fact that habitability (in a narrow sense of life-as-we-know-it, or in a broader sense of any observers capable of contemplating these questions) is sensitive to the variation in some fundamental constants and initial conditions. It is then argued that this fact is surprising and requires a special explanation. However, you could substitute any phenomenon observed in this universe (stability of some heavy element not essential for life, for instance) and, provided that it too is delicate, make the same argument. In other words, the universe could be fine-tuned in the above sense for any number of things, not just habitability. Yet it is habitability that attracts all the attention. Right, observer selection effect in this case applies only to anthropic fine-tuning problems. But I think observer selection effect is not endemic to the general problem that I outlined above. Not all coincidences are anthropic.

Well, that's more or less the whole argument, such as it is - or at least the part of the argument that I have have focused on here: if a feature is "fine-tuned" (i.e. delicate), it cries out for an explanation - presumably, more so than one that is not "fine-tuned".Note, I am not the one making the argument. For a relatively sophisticated creationist version of the fine-tuning argument, see for instance Robin Collins's (a physicist ) Fine-Tuning Website, in particular How to Rigorously Define Fine-Tuning. Collins claims that a constant is fine-tuned for life

if the width, W_r, of the range of values of the constant that permit, or are optimal for, the existence of intelligent life is small compared to the width, W_R, of some properly chosen comparison range R: that is, if Wr/WR << 1 *

There follows an actual probabilistic argument for design, which is invalid on its own merits. But here I am just noting that the problem setup applies equally to any delicate features of the universe - not necessarily the life-permitting ones.Let's say, for instance, that bismuth is stable only within a tiny range of the cosmological constant (I am just making stuff up here). Is this fact surprising? Does it cry out for an explanation? Is the cosmological constant fine-tuned for the stability of bismuth? I suppose that Collins would have to admit that it is, for the same reasons that he claims that the cosmological constant is fine-tuned for life. Even without going into details of the rest of his argument, at this point it already looks somewhat ridiculous, don't you think?* This is consistent with the way fine-tuning (for life) is defined elsewhere. For instance, Paul Davies writes (ibid.): "Anthropic coincidences" is another name that is often used for anthropic fine-tuning. This was a toungue-in-cheek usage on my part.Edited by SophistiCat, : No reason given.Edited by SophistiCat, : No reason given.

I want to expand on what I posted earlier, while getting closer to the original topic.What is the essence of design arguments, such as the fine-tuning argument (FTA)? In its popular form, the FTA is expressed along these lines:If science is to be believed, then abiogenesis (the sequence of biochemical events leading to the first organism), or life-permitting conditions on Earth (its orbit, atmosphere, etc.), or life-permitting parameters of the universe (values of the fundamental constants, etc.) are very improbable. Therefore, science is inadequate (and hence goddidit).This argument can be expressed as a Bayesian inference. LetN = "naturalistic" hypothesis, i.e. the sum of the relevant scientific theories and hypothesesL = evidence of lifeThen by Bayes' theoremP(N|L) = P(L|N)P(N)/P(L)where P(N|L) is the posterior probability of "naturalism", given the evidence of life, P(L|N) is the probability of life that follows from current science, and P(N) and P(L) are prior probabilities of "naturalism" and life.Let us accept, for the sake of an argument, the explicit thesis of the FTA, i.e.P(L|N) << 1The proposed conclusion of the FTA can be expressed asP(N|L)/P(N) << 1i.e. evidence of life strongly disconfirms "naturalism". But in order to reach this conclusion, one essential assumption must be made:P(L) ~ 1i.e. life is assumed to be a priori highly likely or even inevitable. This, I think, is the root of the confused intuition behind the FTA.The following toy example will help us understand this intuition. Suppose someone offers to demonstrate a card trick to you. The would-be magician offers you to arrange the cards of a standard 52-card deck in some order known to you, then carefully shuffles the deck and hands it back. To your amazement, you find that the cards are ordered precisely the way you ordered them in the beginning. The probability of this observation under the random shuffling hypothesis is 1/52! ~ 10^-68. You conclude that you've been fooled somehow, i.e shuffling was not really random. But why? After all, any given sequence is equally improbable if the cards were shuffled randomly.The difference, of course, is that one particular sequence - the one that you had chosen - was pre-specified. It is more suprising to see that particular sequence than any other. By analogy with the FTA,R = random shuffling hypothesisO = observation of the pre-specified order of cardsP(R|O)/P(R) = P(O|R)/P(O)Here again we haveP(O|R) = 1/52! << 1and the intuitive conclusion that evidence strongly disconfirms the random shuffling hypothesis:P(R|O)/P(R) << 1depends on the assumption that the prior expectation of the pre-specified order is high (much higher than the average 1/52!, anyway):P(O|R)/P(O) << 1Since you know what the object of the trick was, the above assumption is pretty well justified*.And here we can see the crucial difference with the FTA: life is not pre-specified! Life is just one of many contingent features of this universe that might not have happened under different conditions. A priori, there is no more reason to expect life to exist in this universe than any other feature, such as the stability of some obscure heavy isotop. It is, of course, natural to think of ourselves, and hence life in general, as having some special cosmic importance. Which is why we are more surprised by this particular outcome. Yet our sense of self-importance is not independent of the fact of our existence, which constitutes part of the evidence of life. Therefore, when making an inference from the evidence of life, we must "forget" about our own existence and not consider it to be given a priori. It is not true then that P(L) ~ 1, and the FTA doesn't stand.* A more standard hypothesis testing procedure involves comparison with an alternative hypothesis - in this case, the hypothesis that the trickster didn't shuffle the cards randomly, but instead illicitly fixed the desired result. The advantage of this approach is that the problematic P(O) term cancels out. However, this would only justify the conclusion that the "trickster" hypothesis is better supported by the evidence than the "random" hypothesis, but not the intuitive conclusion that the "random" hypothesis is strongly disconfirmed by the evidence.Let me know what you think. Are there any Bayesians in the house?