schrodinger's backside

This New Scientist article:
My other universe is a Porsche 2006 Oct 05says that there are ways of varying more than one 'constant' and arriving at habital universes.

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It all comes down to numbers. Harnik argues that there will be countless more universes with myriad properties different from our own. By varying just one property, cosmologists have been too conservative. Harnik, Kribs and Perez decided to highlight this flaw in anthropic reasoning by taking a radical measure: they switched off the weak nuclear force, one of the four fundamental forces in nature. In practice, this means changing a multitude of parameters and constants simultaneously.

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The weak force is responsible for the radioactive beta decay of atomic nuclei and is considered essential for a complex universe like ours. Take it away, and you might expect the "weakless" universe to be wildly different from our own.

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Only Harnik, Kribs and Perez have discovered it isn't. They considered what would happen to crucial processes in the history of the universe - the forging of elements in the big bang, the powering of stars and supernovae explosions. By examining the equations that describe these processes, they made an astonishing discovery: the weakless universe is still capable of supporting observers.

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and

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Aguirre knew a good parameter to vary. Before the triumph of the hot big bang model, researchers had explored so-called cold big bang models to see the effect on phenomena such as galaxy formation. The crucial parameter that determines whether the big bang is hot or cold is the number of photons per baryon. In our universe it is about a billion. Aguirre wondered what would happen if it was in the range 0.1 to 100 - much, much cooler.

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Aguirre's universe started off quite unlike our own (Physical Review D, vol 64, p 083508). After our hot big bang, the universe took tens of millions of years to cool to the point where matter could clump into stars. "But in the cold big bang universe, stars can begin to form within 100 years of the big bang," says Aguirre.

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He even modelled an extreme cold big bang universe where the cosmological constant was 1017 times what it is in our universe. By rights, this strong repulsive force ought to fling matter apart, preventing the formation of galaxies. However, in the cold big bang universe, stars form so quickly that they are in place before this cosmological repulsion takes hold. "The stars then rush away from each other," says Aguirre. "It's a pretty dull universe with each star isolated in a vast ocean of space. Nevertheless, there is nothing to prevent such stars having planets and observers."

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Now that we have found two islands in the multiverse - three, including our own - the question is: are there more? "Undoubtedly," says Harnik. "However, imagining what forms life may take and the finite time available to us to do this will always be an obstacle."

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That is because they don't know what they are talking about. Just becasue a concept of theoretical cosmology is incorrectly usurped by the design crowd does not invalidate the original concept. I see a great deal of misunderstanding here concerning what fine-tuning is actually about. Us physicists do not let the design crowd define our terms for us. Just becasue they talk about fine-tuning in terms of making our universe habitable does not mean that fine-tuning is now synonymous with design and designer... I don't know. It is my conjecture for which I have some evidence, but it needs exploring. When you want to learn about theoretical cosmology, you don't go to "most people". We need the assumption that the universe repeats in some fashion in order to be able to appeal to the WAP to explain why we see the values that we see. Otherwise as I said we are left looking for other explanations. Again, "other explanations" does not imply a cosmic designer. Despite what you may have heard, we don't go running to God every time we find a gap in our knowledge...

I'm sure this is true. Check out here for the original paper. Interestingly to me, these guys are currently working with an old colleague of mine who went on to great things.Read the intro for some background on what I am talking about. Their work is fascinating and wonderfully counterintuitive. BUT it doesn't invalidate the prior work, and merely shows that some parameters are more flexible than others. Hmmm, and these planets and observers are going to just coalesce from the hydrogen? There's a reason we observe a universe of Pop I, II, and III stars! Edited by cavediver, : No reason given.

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.

Well, Paul certainly ranks as one of "us physicists"... are you suggesting that we shouldn't be discussing our own field? you could try, but if you check out what I said it essentially boils down to: A... if not, then not A. I like my arguments to be tight But let's take some of your ideas: You've got some major sources in Paul's paper, and you better check out Weinberg's work very sigificant work on the cosmological constant (references in the Harnik, et al paper). Show me you know better...

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...

I think you are confused. I was castigating design. I myself have been talking about WAP (Weak Anthropic Principle) fine tuning in most of this sub-topic. The Anthropic Principle... IS NOT DESIGN!!!! Arrgghh anthropic fine tuning REQUIRES* a "multiverse" by definition - a multiverse in this context refers to a population of possible universes over which various parameters can vary - this population could be provided by a sequential oscillating type universe, or through multiple parallel universes via say Linde's chaotic inflation scenario, or simply through a huge 10/11d megaspace where branes span and intersect, forming an infinitude of sub-universes with varying dimensions. This enables even our 3+1 dimensions to be anthropically picked, as Tegmark discusses.There are not many theoretical cosmologists that don't believe in a multiverse of one form or another - nothing to do with the WAP - but simply just about every theory we have predicts it. Even boring old inflation gives us millions of observable-universe sized volumes to play with. Consequently, it would be simply amazing if some aspects of the universe are not anthropically fine-tuned. My apologies... but you need to back up a little and understand this topic before being so ready to critique it.ABE: *I guess a caveat to this is possibly the most obvious example of anthropic fine (actually very coarse) tuning, which is the age of the universe. The universe cannot possiby be much younger than we obseve it, as sentient life almost certainly requires the heavier elements... a generation of stars and their dying supernovae are required before we get chance to play.Edited by cavediver, : No reason given.Edited by cavediver, : No reason given.

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).

All fine tuning is anthropic - it is an anthropocentric viewpoint so how could it be otherwise? We are only ever going to see an observer-friendly universe.The issue of habitability is the argument often used by the design crowd - that our universe can support *our type of life* - that there is a suitable star, planet, right place in the Galaxy, etc. This is all rather us-specific. As many will point out (as you did yourself), life could exist in any number of unimaginable niches.On the contrary, give me a suitably large, long-lived complex universe and observers start to become possible.That is why it is the reasons for the universe to be large, long-lived and complex that interest me - becasue that is what I need to exist. Bingo! Science looks for problems to solve/understand... while we're still looking, there are always those that say "heh, heh, you stupid scientists - God did it!" Once we have solved that particular problem and moved on to our next, those same hecklers follow us along and repeat their mantra. Just look in the QM and Thermodynamics thread for recent examples of this. Buz in this case seems to be under the impression that we just make stuff up to conceal our ignorance. Same with some type of multiverse - just becasue it sounds sci-fi and ludicrous does not mean that we're making stuff up to weasle out of difficult problems. This is all pretty basic and mundane when you're in the field. We're just in rather an esoteric field.

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.

Try! Make the argument. Why do we see this particular heavy element have this particular stability? Fine-tuned by what? Try making the above argument work. Again, please make the argument. Let me see it work. Huh? If something is anthropically selected it's not a coincidence. And of course coincidences exist, and these are not anthropically selected, else they wouldn't be coincidences! So what? There are many values and parameters in the Universe that are probably not anthropically selected...

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?

Well, my sister tried to send me a e-mail message from Miami and MICROSOFT tagged it as "spam" citing the use of "Bayesian filter" even though it contained crucial (for me) information about a plane flight from Syracuse I needed to visit my Episcopal Priest Brother-In-Law and family.You had

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are very improbable. Therefore, science is inadequate (and hence goddidit).

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This argument can be expressed as a Bayesian inference. Let

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Well if the filter used would also "catch" your parenthetical then NO there is no way for !!any!! Bayesian inference to match the message.Saying science is inadequate and HENCE saying something about to God, are two cats of a differnt tail. God could care nothing about "science" but thoughts of God may make what seemed adequate later add equated etc.

Spam hiddenEdited by AdminModulous, : No reason given.