Saturday, 23 June 2012

The anthropic principle goes wild

The anthropic principle has been much discussed and it is likely that you have already come across it. It's a strange and counter-intuitive idea because it seems to place human beings in a privileged central place in our account of why our world is the way it is.

I want to raise the subject because the anthropic principle is exactly the kind of logical or philosophical argument that might have a bearing on the fundamental existential questions I mentioned in my last post.

The anthropic principle is a simple but profound idea that at first sounds like a useless tautology. It explains that we shouldn't be too surprised to find ourselves in an environment that is so well suited to us, because if our environment were not as it is then we would not be as we are.

To paraphrase Douglas Adams: to marvel at the many wonderful and hospitable aspects of our world that enable our existence is like a sentient puddle being impressed with how well its pothole fits its shape.

The anthropic principle explains why the earth is positioned in the narrow band of space at just the right distance from the sun to allow liquid water to exist. It explains how life can have come into existence despite the long odds of its arising by chance. It explains how this life can have evolved into intelligent self-reflective creatures such as ourselves.

The apparently designed qualities of earth are many. It has a gravitational field strong enough to support an atmosphere but small enough to allow macroscopic lifeforms to develop. It has a rocky surface which provides support. It is neither so close to the sun that the seas boil, nor so far from the sun that liquid water is unavailable. It has clear skies which allow light to reach the surface. When combined with the abundance of water and carbon dioxide, this enables plants to photosynthesise. Even the moon may have a part to play in enabling our existence, as this satellite may help to reduce the number of catastrophic impacts that hit earth by acting as a kind of blocking bodyguard.

But according to the anthropic principle, it is not in the least bit surprising to note that the earth exhibits so many apparently designed features. Apparent design is not always the hallmark of a designer, rather it can be an artefact of a process of impersonal selection, as we see in evolution.

The key thing to remember in resolving this conundrum is that the number of planets in the universe is staggeringly huge, and may in fact be infinite (as I argue in this post). Of this incredible number, we might expect that the vast majority will prove to be inhospitable to our kind of life. On reflection, it should be obvious why we don't find ourselves on such worlds. If the number of planets is so huge, however, then it should also be no surprise that some planets exist which are perfect for us, and so of course it is on one of these planets that we find ourselves. We simply couldn't have evolved elsewhere.

The same reasoning holds in explaining how first life, and then intelligent life arose despite all the odds. If these staggeringly unlikely events had not occurred, we wouldn't be here wondering about how miraculous it is that they did. If the universe is so large, with an effectively or actually infinite number of planets, then we should expect such improbable events to occur all the time somewhere in the vast reaches of space. To protest that our existence is so unlikely that life must have been sparked by a divine creator is akin to being amazed that out of all the billions of sperm present at your conception, the unique one that would ultimately lead to you is the one which succeeded. A staggeringly unlikely event without which you would not exist, but not ultimately a surprising one in retrospect.

The idea of applying this kind of reasoning to the universe as a whole is a controversial one, but it is a view that appears to me to be gaining ground. The fundamental constants and laws of nature appear to be tweaked so as to make life possible. If the anthropic principle explains why this is so then the implication is that there must be a vast number of universes.

This only scratches the surface. If there are a vast number of such universes, then might there not also be universes with physical laws wholly dissimilar from ours? This would go a long way towards answering those ultimate questions that I discussed in the last post. It could be that matter and energy warp space simply because if they did not do so then stars and planets could not form and life would be impossible. If there are an infinite number of universes, then we should not be surprised to find ourselves in one where gravity exists.

Many physicists dislike this explanation. It seems to be taking an intellectually lazy shortcut. This answer discourages deeper investigation in precisely the same way that "God did it" does. As such, we must not accept this as an ultimate explanation for any particular physical phenomenon we observe. We may, however, adopt this as a likely explanation for why the fundamental grand unified theory of everything, should we ever discover it, is of the form it is.

We exist in a world which is suitable for us because it is impossible for us to exist in an unsuitable world. The anthropic principle is essentially a tautology, which is usually taken to be a bad thing. In rhetoric, a tautology is a series of self-reinforcing statements which each assume the truth of the others. However, in logic, a tautology is merely the opposite of a contradiction. A tautology is a logical conclusion which follows with absolute necessity from its premises.

I think that wherever logical arguments purport to explain deep questions like this, then they will look like tautologies. The problem with tautologies is that they add no information, they just express trivially true statements that are perfectly obvious. I think Darwin's theory of natural selection is similar in many ways, and in fact it is often criticised by creationists on the basis that it is a tautology. "Survival of the fittest" can be rewritten as "survival of those best equipped to survive", and so it seems to be a tautology. While this is sometimes disputed by evolutionists, I'm perfectly happy to call it a tautology.

I agree that it adds no new information. Its logic really is trivial, and the conclusion, in retrospect, seems to be perfectly obvious. But this does not mean that it is not true. Quite the reverse, in fact. Instead, it means that it is so self-evidently correct that to doubt it is to doubt that which is staring you in the face.

In searching for these ultimate answers, I think we should be looking for tautologies like these.

And one important question remains unanswered. Why should there be any universes at all, much less an infinite number of them?


  1. I largely agree with you on this one, but I don't acknowledge a distinction between asking why we exist on this planet, and asking why the universe seems tuned for life at all. I think both questions fallaciously understand life to be something special because of its apparent rarity amidst an abundance of inanimate matter.

    In reality, asking why life is permitted in our universe is no different whatsoever to asking why this star is forming heavy metals at its core while that star is only constituted of hydrogen and helium. Well, that's just the way the universe works and if you trace its history, you'll see why one star is the way it is while another is different. Life is just an expected property of the universe in the same way stars are, and this planet has this kind of life because of the universe's history.

    We treat these questions differently only because we place value on life. To be consistent, we ought to consider life no more a conundrum than the existence of the hydrogen atom.

    Of course, when we instead focus on the apparently inane question, "why is the universe tuned for the existence of hydrogen?" we can still wonder why there is something rather than nothing, but that's quite different.

    To be honest, I don't think that the anthropic principle, and the acceptance of many planets or many universes, is a necessary solution to the question of life's existence as it isn't really a problem. If it is a problem, it's only a problem in precisely the same way that the existence of hydrogen is.

    1. "I don't acknowledge a distinction between asking why we exist on this planet, and asking why the universe seems tuned for life at all"

      I don't see that distinction either, Callum.

      But if you think that the existence of life in this universe is the same kind of proposition as the existence of life on earth, then you're tacitly agreeing with my conclusion that there are many universes.

      The only reason our existence on earth is unsurprising is because there are trillions of other less suitable planets in the universe from which earth is selected.

      If earth were the only planet in the universe, and it was just right for life, then that would be a much stranger situation.

      I also disagree with you that the existence of life is not a problem. The existence of life is a much more complex and non-arbitrary phenomenon than the existence of hydrogen. It's certainly more significant to us. And this significance makes its existence against all odds a curious thing.

      For example, if you looked up into the sky and saw the clouds spelling out C A LLu M then you would be surprised and wonder if there were some explanation (e.g. some sky-writer was responsible). This is because these letters are significant to you, while the vast majority of ways that clouds could be arranged in the sky are not significant at all.

      If we simulated a lot of mathematical constructs (e.g. Conway's Life and other cellular automata) then we would routinely see emergent substructures which are no more complex than a hydrogen atom.

      The emergence of anything as complex, surprising and beautiful as life would, I suspect, be several orders of magnitude more rare.

    2. Although I think there may be reasons to believe that we do find ourselves in a multi-verse, the anthropic principle is not one of them. In fact, I think using the anthropic principle as the basis for such an argument could turn out to be quite ironically hubristic! Our non-specialness is not so special that we must postulate many planets and universes to account for it!

      In my rejection of the anthropic principle as useful (emphasis on "useful"; the anthropic principle is true, but I think it is so trivial now that it shouldn't be used as the basis of cosmological arguments), I wouldn't say that the only reason our existence on earth is unsurprising is because there are trillions of other less suitable planets. If our solar system was our entire universe, we could not find recourse in such arguments; instead, we might find that there is something about the laws of physics which necessitates life being unique (indeed, although it seems tremendously unlikely, life could be unique in this universe. That would not mean it is miraculous, it would just mean that there is some as yet undiscovered aspect of the laws of physics that relegates life to supreme rarity).

      The reason our existence on earth ought to be unsurprising is quite simply because it is an expected consequence of the laws of physics. In this sense, I find it surprising that you should say it is more of a problem than hydrogen, especially given the MUH. As Edward Harrison said, "Hydrogen is an odorless, colourless gas which, given enough time, turns into people." Give me a universe with certain laws, and there's the explanation for life. No anthropic principle required. Again, that just leaves us with the question of the universe's particular existence in the first place.

      I also more forcefully reject the notion that the significance we assign to life makes its existence "against all odds" a curious thing. First, our assignment of significance is utterly arbitrary and self-serving. There is no essence to life that makes it qualitatively more important and compelling than anything else we see in the world. Second, its appearance was not "against all odds", in fact, as you should well know, it was inevitable!

      When comparing our universe to the potential emergence of life in something like Conway's Life, I think you're almost making Paley's watchmaker fallacy. As you well know, if we simulate any mathematical construct, its output is thoroughly determined and will be identical every time we run it. For want of a less contentious phrasing given some of our current disagreements, life is a property of the algorithm; not a chance happening when we start watching the simulation. Although the absolute numerical occurrences of self-aware creatures would be far less than the absolute number of quarks, that does not mean that it poses a harder explanatory problem any more than we should consider the existence of atomic nuclei a degree more stupefying than the existence of protons and neutrons.

      Thus, life in our universe is precisely as predictable and unsurprising as hydrogen. With that perspective in mind, the existence of hydrogen itself is not something to be ruled out; we should absolutely question why hydrogen rather than something else currently unimaginable exists, but we must not get so carried away as to think that life is a harder problem.

    3. EDIT: It wasn't Paley's watchmaker argument I was thinking of, it was Hoyle's Boeing 747.

    4. If our solar system was our whole universe, we would have no recourse to the anthropic principle. You suggest that we should conclude then that there is something about the laws of physics which necessitates life.

      If that was your conclusion in that scenario, you would be dead wrong.

      My conclusion would probably either that there are other planets which we cannot observe, or that our universe had been designed. And this latter explanation would be right, because you have just designed it by proposing it.

      The laws of physics as understood already seem to relegate life to great rarity, although this is far from certain. In any case, it would not be terribly surprising if this were the case. But then our existence can only be accounted for if there are a great number of planets.

      "Give me a universe with certain laws, and there's the explanation for life. No anthropic principle required."

      That seems to miss the point of the question. If we consider life to be significant, and if the vast majority of possible universes could not contain life (as seems probable), then it is very unlikely that the single universe that actually exists should happen to be just right for life. The only way this becomes unsurprising is if we consider the possibility of the existence of a vast number of universes.

      Significance is key. It might be arbitrary in some sense, but that doesn't mean we can disregard it. Suppose I wrote a piece of software that had as its purpose the generation of a random number between zero and a billion. Now, suppose the first number I see that piece of software generate is the number one. I believe I would be quite right to conclude that the software must be faulty, simply because the number one is significant to me and the chances of it arising by chance are tiny.

      If the software generated the same number twice, I would conclude that it must be faulty. If the software generated the number 500,000,000, then I would think it was faulty. If it generated the digits of my birthday I would think I was hallucinating or that somebody was playing a practical joke on me.

      Unless of course I let it run for a tremendously long time and then "mined" the results. Finding something of great personal significance in a small sample of results may be staggeringly unlikely, but finding it in a large sample of results is inevitable. That's why the anthropic principle is important in understanding why it is that the one universe we know exists is capable of supporting life, which is of great significance to us.

      Life is a harder problem to solve than hyrdogen because life is incredibly more complex, interesting, improbable and significant to us. Life may be a property of the algorithm of the universe, but what needs explanation is not why life arises in this universe, but why the one universe we know exists happens to be one of those rare possible universes that support life. The only answer that makes sense to me is that there are multiple universes, and so of course we must find ourselves in one that supports life.

      You haven't provided an alternative explanation. To me, it looks like you're just shrugging your shoulders and incuriously declaring "that's just the way it is".

    5. Wherever there is life, we must conclude that the laws of physics necessitate life. That's a trivially true statement. In a universe that constituted our single solar system, you couldn't postulate at all that it had to be designed - it's quite possible (who really knows?) that one of the infinite number of possible universes is such a universe and, with the multi-verse theory, we do not need to postulate designers for each one. In that one universe comprising a single solar system with life, that is simply an inevitable consequence of the initial state.

      On the rarity of life, it depends what you mean by rare. Even though I concede it is tremendously rare compared to other things we know of in the universe, I would again make the comparison with increasingly rare kinds of matter. I do not think it would be rational to imagine that atomic nuclei are a little more special than protons and neutrons, or that helium is more special than hydrogen, or, as we go up the scale of complexity, that life is more special than anything less complex. Each of these things are all precisely as unspecial as each other because they are all natural consequences of each other.

      To make the point even more obvious, consider the different value we would (I argue, erroneously) perceive between humans and the first self-replicating molecule on earth. Humans may be vastly more complex, but given the planet's conditions, they were absolute bound to arise from that first molecule. They are just as unspecial as that molecule, and that molecule as unspecial as its surrounding chemicals and atoms.

      There is no significance to life whatsoever, we just value it because it belongs to us. Your analogy to the random number generator is absolutely the same as Hoyle's Boeing 747 fallacy. For that to make any sense, you have to postulate that life, even *given* our universe's laws and conditions, is unlikely. That's simply not true. Although you would bestow 500,000,000 with more significance than the other numbers, that does not mean you should find its appearance suspect, even if it's the random number generator's first output. That's like people who would never play 1, 2, 3, 4, 5, 6 on the lottery without realising that it is precisely as likely as every other permutation of 1-49. Such incredulity is totally unfounded and is the basis for the ridiculous pattern seeking of religions and pseudoscience.

      "What needs explanation is not why life arises in this universe, but why the one universe we know exists happens to be one of those rare possible universes that support life." I would argue once again that, given the unspecial nature of life, this question should be reformed to ask why our universe supports hydrogen. Well, to me, that's just a dumb question. What does it matter whether it features hydrogen or something else? So, we got lucky to be alive, that doesn't mean we need to search for some answer as to why our universe is so special and magical and life-giving. Once again, this incredulity is unfounded. It marvels at the fact that OUR existence is the way it is, so surely there must be other universes to account for it. I think that's reverse-hubris. I would agree with you that I'm basically shrugging my shoulders and declaring that's just the way it is - because that may actually be the case. My appraisal of your approach would be that you are yielding to your primate urge to find an explanation for everything.

    6. ""Wherever there is life, we must conclude that the laws of physics necessitate life. "

      True, but beside the point. The question is not why there is life in this universe, but why this universe happens to support life.

      The thing about universes with single solar systems is that such universes are so preposterously unlikely that from the point of view of a person within those universes it would be more reasonable to postulate a designer rather than that they arose by chance. Yes, as it happens I believe such universes must exist, but they are vastly outnumbered by universes such as ours. A consequence of this is that there must be universes where reason and logic would lead to the wrong conclusions. Those universes are fantastically rare so we should not expect to be in such a universe.

      If pefectly random quantum fluctuations caused Elvis to spontaneously appear before you, you would be right to seek another explanation, perhaps suspecting that you were hallucinating, or that this was an imposter, or some other more prosaic explanation. You would be wrong, but you would be reasonable. To believe that he had in fact manifested due to quantum fluctuations would be insane.

      I think you are probably relatively alone in believing that life is an unremarkable or unsurprising phenomenon. It may arise out of the laws of physics, but it's hard to imagine being presented with the laws of physics and then deriving the phenomenon of life from them. Deriving hydrogen, other elements, stars etc seems more feasible.

      Nor are humans bound to derive from that original self-replicating molecule. Mutations are events that are subject to quantum fluctuations, so the process of evolution really is a kind of directed randomness. There was nothing inevitable about the evolution of intelligent life on earth. That same self-replicating molecule may have developed on numerous other worlds with near-identical environments, but we would not expect the life on a typical one of those worlds to evolve along the same paths as the life on this one.

    7. "Although you would bestow 500,000,000 with more significance than the other numbers, that does not mean you should find its appearance suspect, even if it's the random number generator's first output."

      You are simply wrong here. Let's say there are twenty numbers which I will find significant. If I'm randomly selecting one number of a billion possible numbers, then the probability that the number I select will be significant is 20/10^9 or 0.00000002. This probability is sufficiently low that if a suspiciously significant number is the first result of the algorithm, then it is more likely that there is something fishy going on than that we have really selected this number randomly.

      This is why winning lottery numbers do not tend to look significant. That people then think they can increase their odds by deliberately selecting insignificant looking lottery numbers is simply misunderstanding the nature of probability. I can confidently predict that the numbers 1,2,3,4,5,6 will not win the lottery because those numbers are significant. But I can just as confidently predict that 1,4,14,20,23,30 will not win the lottery. One way of explaining this is that having listed these numbers out, I have now conferred upon them a significance that they would not otherwise have had. Before listing those numbers, I would not have been surprised to see them win. After selecting them, I would indeed be shocked.

      I'm really not seeing the connection to the 747 thing. You might need to spell this out for me.

      In conclusion, I want to again assert that you have not succeeded in demonstrating that life is not special. Life is indeed special or significant, and intelligent life is even more so. Given the assumption that most possible universes would not support life, the fact that our universe does support life is indeed surprising and in need of explanation. The anthropic principle works perfectly well but to use that you need to conclude that there are a vast number of universes. So unless there is some other explanation for why this universe supports life, the anthropic principle suggests that our universe is but one in a vast multiverse."

  2. "The thing about universes with single solar systems is that such universes are so preposterously unlikely that from the point of view of a person within those universes it would be more reasonable to postulate a designer rather than that they arose by chance."

    That's not a safe assumption. It's perfectly reasonable to think that people with sufficiently advanced science in such a universe would have the rationale to see that a designer is neither necessary nor logically consistent for other logical reasons (infinite regress, complexity etc.). They wouldn't be compelled to believe in a designer purely because they can't invoke the anthropic principle.

    "To believe that he had in fact manifested due to quantum fluctuations would be insane."

    Not quite as insane as thinking it's a suspension of the laws of physics! It being the result of quantum fluctuations is as naturalistic an explanation as any other; you'd just go with whichever has evidence. Presumably, hallucinations and delusion would have associated cognitive evidence. This isn't a guessing game where you pull the most likely conclusion out of the bag; by positive evidence or process of elimination, you come to a reasonable conclusion.

    "I think you are probably relatively alone in believing that life is an unremarkable or unsurprising phenomenon. It may arise out of the laws of physics, but it's hard to imagine being presented with the laws of physics and then deriving the phenomenon of life from them. Deriving hydrogen, other elements, stars etc seems more feasible."

    I don't think so, and I think you're just saying this to perpetuate your intuition that life is somehow special. Even if it's true that given the laws of the universe it would be harder to derive the existence of life, that doesn't mean it's special. Again, it would be harder to derive the existence of hydrogen than it would leptons; do you think hydrogen is a degree more special? Besides, our ability to derive such things says something only about our ability, not the intrinsic specialness of the things to be derived. In a universe where all the matter we understand constitutes only 4% of the total energy, life is just a lucky contamination.

    1. I think universes which very much appear to be designed would lead rational people to believe in a designer. For example, they might believe they live in a computer simulation (and perhaps that computer simulation arises in an undesigned universe).

      I think the only way out for rational people in that single planet universe would in fact be to invoke the anthropic principle and to assume that there is some reason that they cannot observe other planets.

      "Not quite as insane as thinking it's a suspension of the laws of physics!"

      I didn't propose suspension of the laws of physics as an explanation. This event is so improbable as to be effectively impossible. Thus, to believe that it had occurred would be irrational, no matter what the evidence. Far more likely that you're having a stroke or something. Any other explanation, no matter how improbable, is likely to be more likely than quantum fluctuations. Perhaps this is a clone of Elvis. That may be preposterous but it's still more likely than quantum fluctuations.

      Life is more special than hydrogen because:

      1. It is more significant to us (and I have justified the significance of significance, I feel. More on this in the next response)
      2. It is rarer than hydrogen within the universe
      3. It is likely to be immensely more rare than stuff like hydrogen across universes.
      4. It is more complex and more interesting than hydrogen. There's a lot more you can say about life than you can say about hydrogen.
      5. Intelligent life is the only thing that gives rise to conscious minds, and conscious minds are the only things to which the concept of 'specialness' even means anything.

      But really, it's all about significance. Which might be arbitrary, but that doesn't matter. All that matters is how probable it is a priori that this thing we find significant would result.

      To finally answer your question, then yes, I think significance is probably related to complexity. But what is significant to us varies from person to person. Hydrogen is marginally more special or significant than leptons. It is marginally more interesting, marginally more complex, marginally more improbable, etc.

  3. "Nor are humans bound to derive from that original self-replicating molecule. Mutations are events that are subject to quantum fluctuations, so the process of evolution really is a kind of directed randomness."

    I haven't read anything stating that mutations are events subject to quantum fluctuations; that sounds a bit Deepak Chropraish to me. They're random, yes, but not quantum so far as I know (link me up if you have evidence to the contrary). I'm not saying, though, that *humans* would be a necessary conclusion of evolution; of course not. But the appearance of the self-replicating molecule is an expected occurrence of chemical reactions and the ensuing life, whatever form it takes, would be just as unspecial.

    "One way of explaining this is that having listed these numbers out, I have now conferred upon them a significance that they would not otherwise have had. Before listing those numbers, I would not have been surprised to see them win. After selecting them, I would indeed be shocked."

    Right, but your level of surprise doesn't affect their actual probability of occurring. Perhaps I stated my idea too strongly; you could absolutely suspect that there was something fishy going on, but your arbitrary bestowing of significance is not reason enough to conclude as such.

    "I'm really not seeing the connection to the 747 thing. You might need to spell this out for me."

    You keep saying that life is unlikely. It's not, it's predetermined to the same extent hydrogen is.

    "In conclusion, I want to again assert that you have not succeeded in demonstrating that life is not special. Life is indeed special or significant, and intelligent life is even more so."

    I can just assert that you have not succeeded in demonstrating that life is special. I think it's far safer to conclude that everything within the universe is equally unspecial unless there is some particular reason to believe the contrary. The fact that we view our consciousness as significant is only to be expected given evolutionary history; that is a totally self-serving idea that is not founded on reason. Do you accept that hydrogen is more special than a proton? Either you must accept a scale of specialness correlated with complexity, or you'll have to show me where to draw a magic line. I also think it's nothing but a blatant fallacy to say that the anthropic principle actually, positively means that there must be a multi-verse; that is just an argument from personal incredulity. All the anthropic principle gives is a method of contextual understanding; it's not an actual rigorous empirical observation.

    1. I haven't a source to hand to support the assertion that mutations are subject to quantum mechanics, but it seems obvious to me. Mutations happen on the level of individual molecules. A mutation can occur because a single gamma ray photon hits a strand of DNA. Gamma ray photons are certainly subject to quantum mechanics. If you seriously doubt this, I can try to find more sources to back up my claim, but it seems to be a side issue so it perhaps doesn't matter.

      "... you could absolutely suspect that there was something fishy going on, but your arbitrary bestowing of significance is not reason enough to conclude as such."

      If I presented you with a piece of software that would give you any number from 1 to a Googolplex, and if the first number that software gave you was the number 1, you should be absolutely convinced that this selection was non-random. The significance of the number one is absolutely enough reason to conclude that this was not selected randomly.

      If I presented you with a piece of software that would randomly select letters from the alphabet in sequence for a randomly determined number of iterations, and if the first output of that program were the complete works of Shakespeare, you would be absolutely bonkers crazy to entertain even a shred of a possibility that this software was really working randomly.

      The number 1 is significant to us in ways that a randomly selected integer would not be. The complete works of Shakespeare is significant to us in a way that a randomly selected block of text would not be. A universe with life in it is significant to us in a way that a randomly selected universe would be. You'd have to be bonkers crazy to believe that this was a complete accident if the vast majority of possible universes do not support life. Either there are vast numbers of universes, so that life is inevitable in at least one of them, or there is a designer.

      "it's nothing but a blatant fallacy to say that the anthropic principle actually, positively means that there must be a multi-verse;"

      You seem to be misunderstanding something. If it is true that the explanation for why the universe is fine-tuned for life is anthropic, then that explanation is only applicable if there is a multiverse. If there is not a multiverse then the anthropic principle doesn't apply. If it does apply, that is equivalent to saying that there actually, positively is a multiverse.

    2. I think even molecules are too macro in scale for quantum mechanics to apply to their replicative function, and though gamma rays are subject to QM, the interaction of a gamma ray and a molecule that leads to mutation and cancer is not. But this is unimportant; what matters is that the process is random and we both agree on that.

      Your Shakespeare analogy is compelling. I feel instinctively that I want to go against it, but I can't think of a rationale, so I'll accept it for now! You're right about the random number generator then. However, this is emphatically nothing to do whatsoever with the perceived significance of life in our universe. Again, this is the Boeing 747 fallacy, as it relies on the assumption that the appearance of life is a staggeringly improbable event. The number generator is *random*. The letter generator is *random*. But the occurrence of life is 100% *non-random* in precisely the same way that hydrogen is non-random. Thus the significance we apply to it has wholly different consequences - I would say none.

      We also don't even know if the universe is fine-tuned for life. Life may be possible with all kinds of tunings - that is not a settled subject in physics, despite many speculations. It will also appear on the grand cosmic scale that this universe is *not* fine-tuned for life! We are a short blip clinging to nigh-inhospitable edges of the cosmos, and soon we and all other life-forms will be non-existent as the universe gives way to eternal heat-death. What on earth could be fine-tuned about that? If anything, this universe is fine-tuned to avoid and destroy life as much as possible.

    3. The quantum stuff is a side issue, but I want to try to explain why I think you're wrong in case it comes up again. In conversations with you, it seems to me that your quantum intuitions are a little bit off, so it may be helpful to expound on it a little.

      No, I don't think you're right that molecules are too large. Individual errors in transcription can be due to events at a very small level. Furthermore, if gamma rays are subject to quantum mechanics, then the interaction of gamma rays with DNA is certainly subject to quantum mechanics. (Whether there is a gamma ray there at all may be the result of a quantum event).

      You seem to think that quantum mechanical effects only apply at small scales, but that's simply not true. If it was then we wouldn't be able to see interference patterns when we do the double slit experiment. It's just that quantum effects tend to average out to relatively predictable outcomes in most situations, at least in the short term and where chaos is not a factor.

      But at the level of individual atoms and photons, etc, quantum effects are very relevant. If those events are amplified, e.g. by being replicated as DNA copies itself, or by being detected by a geiger counter, then they can absolutely have large scale effects. Entire galaxies have formed because of quantum fluctuations shortly after the big bang.

      Also, don't underestimate the power of chaos theory. The butterfly effect is a real phenomenon. I would not be surprised to learn that quantum events can have real impact on entire weather systems. In fact, I'd be surprised to learn the opposite. Small changes in a lot of systems really do get magnified more and more over time. There is no reason to believe that there is a lower bound for this effect to apply. This is why I think it is perfectly plausible that in the many worlds interpretation there are worlds where you scratch your nose twice while in others you scratch your nose three times.

    4. I don't think my quantum intuitions are off, I think you're conflating two processes that require delineation, namely causes and interactions.

      As an example, take Schrodinger's Cat. Whether or not the poison is released is fundamentally driven by a quantum event. The mechanism of the cat's inhalation of poison, while determined by a preceding quantum event, is not in itself a quantum event.

      In the same way, my point was that the presence of a gamma ray is of course determined by a quantum event, but, given its presence, the way it interacts with a molecule is not a quantum process.

      Amplification and chaos theory are important, but I think you have to be really careful. Many people play fast and loose with quantum mechanics, like Deepak Chopra, and conclude from its very existence that anything goes. This is not the case, and this is why you have to put limits on the butterfly effect. You can no more say that the existence of quantum mechanics underpinning all of matter leads to significant events in the replication of DNA than you can say that the existence of quantum mechanics affects the trajectory of a thrown ball. The atoms which constitute the ball are experiencing probabilistic quantum events all the time, but these do not amplify to have any perceptible effect on the ball itself. Without further empirical observation, you've got no basis on which to say that DNA is an exception, you just think that it ought to be. I certainly haven't seen any respectable biological theories that use quantum mechanics to explain replication (there are, as far as I can tell, only fringe theories by physicists who have no detailed understanding of the chemistry and biology).

    5. The problem with the 747 argument was that it proposed that the aircraft was randomly assembled all in one go. The reason that analogy does not apply to biological evolution is because evolution is a built up by a series of small random modifications arising one after another where a non-random force of selection is in place.

      No such explanation can account for the staggeringly improbable fact that the universe supports life.

      By the way, I'll freely admit that I can't prove it is staggeringly improbable. I'm assuming that it is. I'm making an argument based on that assumption, an assumption shared by many scientists. I'm not saying that anthropic reasoning proves there are multiple universes, I'm only saying that it is suggestive of that possibility. If an argument can be made (as attempted by Stenger), that support for life is not improbable at all, then anthropic reasoning is not applicable.

      I don't understand why you think that support for life is not random, by which I take it to mean "subject to probabilistic arguments", but computer algorithms are.

      As it happens, it is impossible to write a truly random computer algorithm. True randomness can only be supplied by specialised hardware which reads quantum fluctuations, but even then we have no way of knowing if quantum fluctuations are actually random or just appear that way. Computers instead usually generate pseudorandom numbers. They use complex algorithms that generate chaotic and effectively unpredictable output, but any appearance of randomness is illusory.

      A simple pseudorandom number generator might take as its seed the digits of the decimal expansion of PI . It might perform some function on them to obscure them so that the sequence is not recognised by those who are familiar with these digits. The result should be effectively random enough for most purposes, and the output should be indistinguishable from true random output, but it is nonrandom nevertheless.

      None of this affects my argument that we should be highly suspicious of significant numbers in the output. And if the laws of the universe, including the fine tuning of constants that allow life to exist are also nonrandom, then the argument is similarly unaffected.

      True randomness is unimportant. All that is important is whether it is likely that the significance of something is extreme enough that it would be unreasonable to ascribe it to coincidence. If it turns out that the overwhelming majority of universes we might describe mathematically would not support intelligent life, then it would be unreasonable to ascribe the existence of intelligent life in our universe to coincidence. It must be some force of natural selection from a large population (e.g. the anthropic principle) or intelligent design.

      Finally, the fact that the universe will not support life in the future is totally irrelevant. All that matters is whether the universe supports life long enough for the evolution of life intelligent enough to ponder these questions. We should not expect that it be perfectly optimal in this regard, we should only expect it to be sufficient or typical.

    6. On the quantum question, the initial context of the disagreement was an offhand comment that I made saying that the path evolution takes is not deterministic because of quantum effects. No specific product of evolution is inevitable or predictable well in advance.

      In the same way, whether the cat lives or dies is unpredictable. Neither outcome is inevitable.

      You appeared to disagree with this point of view, which if true would indicate to me that your quantum intuitions are misleading you.

      I think you're wrong that quantum mechanics play no role in the actual process of mutation also. In particular, the way a gamma ray interacts with pretty much anything is basically the definition of a quantum process! Gamma photons are too small to behave predictably.

      In a trivial way, quantum mechanics has to be involved in every chemical reaction because quantum mechanics is the very basis of all chemistry. For most chemical reactions, we see no detectable effects of indeterminism because these process are usually aggregated statistical things which are insensitive to fine detail. As a piece of iron rusts, the precise number of iron oxide molecules that have been formed will be randomly affected by quantum fluctuations, however the approximate number of iron oxide molecules will be predictable to a high degree of accuracy.

      DNA replication is different. All it takes is for one change to happen for that change to be copied and amplified and have profound effects down the line.

    7. You're right, the Boeing 747 argument doesn't apply to the question of why our universe supports life, but it's not always clear that that's what you're talking about. The analogy with a random number generator makes it seem more like you're talking about why life arose in this universe at all. If you're only talking about why our universe supports life, that's different. And you're right that it's an assumption to say it's improbable; I've already made my case that it doesn't require a more special explanation than hydrogen does; and the petty fragility of life appears to me as though the universe is not fine-tuned for life at all. If it were fine-tuned, life would be more stable. I think it's a cop-out to say that it doesn't matter that the universe is fundamentally hostile to our existence - I think that absolutely does relegate the significance of our existence because it opens the possibility for a vast number of possible universes that support life to varying degrees of stability, suggesting that it's not a rare occurrence.

      I've got no idea what you meant by the rest of that post. I suspect it's because we were talking at cross-purposes - I wasn't saying that support for life is non-random (it doesn't seem to me to make sense to talk about it as random or non-random with what little we know), I was talking about the appearance of life in our universe already given its constants.

      Right, the products of evolution are non-deterministic - if I made it seem as though I thought they were, I was confusing myself or said something I didn't mean. I'm still not prepared to accept that the randomness of mutation is quantum though, and if you want to convince me you're just going to have to tell me a respectable book on the subject.

    8. In discussing multiple universes I am really talking about why our universe happens to support life. The anthropic principle is also relevant to how life can have arisen in the first place, which is where the confusion may have come from. In the latter case, the anthropic principle would predict a vast universe and so scientists in a universe which contained only one planet and one sun would be confused.

      We have not yet settled whether life requires an explanation more than hydrogen then. I have explained that it does because it is of an improbable significance, and I have explained why the arbitrary nature of significance is not a problem. As in the example of the Shakespeare example, the significance of one set of characters is not objectively any more than any other, yet the improbable significance we perceive in Shakespeare's text would prevent us from rationally ascribing the result to coincidience. As far as I'm aware, you haven't given a satisfactory rebuttal to this.

      The rest of my post is an attempt to address your contention that my analogies to Shakespeare and random number generation are irrelevant, because these are *random* (which they are not) while the occurrence of life is *non-random* (which I think it probably is, depending what we're talking about).

      As for a source for quantum influence on mutations, a quick google turns up lots of academic papers. I don't think it's terribly controversial. This paper seems appropriate:'Does%20quantum%20mechanics%20play%20a%20non%20trivial%20role%20in%20life'%20BioSystems%20paper.pdf

    9. Actually, I'd say a good book for you to read is The Emperor's New Mind by Roger Penrose. It covers a lot of the ground that is relevant for the arguments I like to make. The thesis of the book is that quantum events may have some key role to play in consciousness, a position I actually oppose, but a lot of the science he covers to explain his position is the same kind of stuff I would be using in my arguments.

    10. Oh, also, I'm not suggesting that all mutations are decided by quantum fluctuations. I'm just saying that you can't take the state of all the atoms in a nucleus before a cell division and predict with much certainty whether there will be a mutation or not. Even with a perfect model and infinitely powerful computer, you could only assign probabilities. More than one outcome is going to be possible due to quantum noise and chaos.

      If you actually look at a mutation happening in slow motion it probably won't look much like anything particularly mysterious is going on.

      I also think it is likely that quantum effects make it impossible to predict what lottery numbers will be chosen even if you know the positions of all the balls and mechanical parts perfectly before they're mixed together. Quantum mechanics means you just can't make predictions in chaotic systems.

    11. Actually, I suspect the whole quantum conversation is the result of a misunderstanding. I don't mean to imply that the randomness of mutations depends on quantum mechanics. Even if molecules behaved perfectly classically we would see apparent randomness which would be arising out of classical chaos, not quantum mechanics.

      In this picture, you could in principle predict exactly what mutations would occur and when, it's just impossible in practice so it has the appearance of randomness.

      I was just making the point that it isn't even pseudo-random, it turns out it's actually really random. I said this to oppose the view you appeared to be expressing (which I recognise you weren't) that there was nothing random about our genesis.

    12. "We have not yet settled whether life requires an explanation more than hydrogen then. I have explained that it does because it is of an improbable significance" - you haven't explained it, you've only asserted it, and you admitted it was an assertion. It happens to be an assertion I don't accept because, looking around us, I do not see the magical fine-tuning that our intuition suggests so strongly to us. You go back to Shakespeare, but again you're conflating two separate arguments. Either you're talking about life arising in this universe, which is easily explicable through chemistry and evolution, or you're talking about the universe's fundamental constants, in which case you've got no empirical basis on which to assert the randomness of the fine-tuning, which may not even be finely tuned!

      The paper you linked to was self-admittedly speculative with observational techniques only suggested at; not performed - the fact that conjecture exists is hardly reason to go believing in it. I'd also rather see a collaboration between biologists and physicists as opposed to one side making prejudiced conjectures about the other. As for "quantum mechanics means you just can't make predictions in chaotic systems", I think the fact that the system is chaotic is explanation enough for non-determinism; we don't need (and should be wary of trying) to invoke quantum mechanics for the sake of it wherever it sounds reasonably plausible without rigorous application.

    13. Yeah, the whole argument assumes that there is fine tuning. Now, assuming that there is fine tuning, then life demands an explanation while hydrogen does not. That's the argument you haven't refuted, and that is not a bald assertion. The Shakespeare argument explains why significance is important even if it's arbitrary.

      I'm not really interested in getting into whether there is fine tuning or not because I'm happy to leave that debate up to the physicists. The general opinion in physics is that there is fine tuning, but it is not quite a consensus, so it is up for grabs.

      Yup, that paper was speculative. Doesn't really matter though, it is not really of much importance whether quantum mechanics plays a part or not - all that matters is that we agree that evolution is effectively non-deterministic.

    14. I can't comment on the explanations required for a universe with fine-tuning because I've never been in one and can't imagine what it would be like. :P

      The Shakespeare argument still doesn't seem to apply because you can't take such a broad thing as "significance" and apply the analogy across the board with vastly different things. The significance we assign to randomly arranged letters is not sufficiently comparable to the sense of awe we feel at self-awareness. I think where it most fundamentally breaks down is that the significance we assign to life, though misplaced, is *not* arbitrary. We could assign significance to Shakespeare, or to hydrogen atoms, or to brown dwarf stars, or to apples that are 3 inches in diameter - none of these have anything about them that necessitate our assignment of significance. The significance we assign to life, however, is precisely because we are alive. It is an expected consequence of our evolutionary history - *of course* we think life is significant, we *are* life! That's not arbitrary, it's just illusory.

    15. "I can't comment on the explanations required for a universe with fine-tuning because I've never been in one and can't imagine what it would be like. :P"

      Again, *IF* there is fine tuning, *THEN* that fine tuning demands explanation.

      Suppose that the vast majority of possible universes have no life in them at all. Now suppose we have powerful computers that allow us to simulate and observe these universes. All that I need to show real relevant significance is to convince you that we would all be much more interested in the rare universes with life than we would be in those without life.

      Anything which is both improbable and significant requires an explanation. In this regard, our awe at our self-awareness is absolutely comparable to the significance we assign to randomly assigned letters, at least for this purpose. All that is required for the argument is for the result of some purposeless event to result in something surprising or interesting apparently by coincidence.

      There can be a few different types of explanations for this.

      One explanation is that you are too willing to read significance into random features. In this case, the set of results you would find significant is comparable to the set of results you would not find significant. In extreme cases of paranoid delusion, some meaning is arbitrarily read into every result. This is basically how prophets and psychics work. In these cases no explanation is required, you were bound to find something profound in whatever garbage the result contained. This is where you might argue that we are paranoid to see life as more significant than for example the existence of hydrogen in this universe, or the existence of gliders in the Conway's Life universe. I disagree because I think life is orders of magnitude more surprising, complex, beautiful, etc. It doesn't matter that these criteria are arbitrary or subjective. All that matters is that I persuade you that I really would find these features profoundly more interesting than whatever emergent properties I would find in a randomly selected universe.

      Another way to explain it is that the supposedly improbable event is not improbable at all. This would be the case if the emergence of self-aware creatures were a very common property of mathematical constructs with more than a rudimentary level of complexity. This is possible, but I assume that it is not true for the sake of the argument, so there's no point discussing this for now.

      Finally, we might be unsurprised to find significant results if we are simply selecting from a massive pool of possible results. If Google had indexed all the possible combinations of characters less than 2000 characters long, you could find any of Shakespeare's sonnets within that mass of garbage simply by typing the sonnet into Google's search box. This is the explanation that the anthropic principle argues for. Generate enough crap, you'll get something interesting eventually.

      So it seems to me that either intelligent self-awareness is a very common phenomenon which we will find supported in many mathematical constructs corresponding to possible universes, or else it isn't in which case it seems we must conclude that there are a large number of universes.

    16. "Again, *IF* there is fine tuning, *THEN* that fine tuning demands explanation."

      Yes, *fine tuning* demands an explanation, but I was being facetious with the way you worded it like this:

      "Now, assuming that there is fine tuning, then life demands an explanation while hydrogen does not."

      That depends how ubiquitous hydrogen is, and also on something I'll elaborate on below.

      "Anything which is both improbable and significant requires an explanation." I think it's better and cleaner to simply say that anything which is improbable requires an explanation, and this goes more in your favour than mine as the set of things which are improbable is larger than the set of things which are improbable and significant. Significance often tends to be a reformulation of improbability anyway, so I think it's a bunk concept to be avoided.

      Now, let me do something more methodical and say that life requires a special explanation given the four following assumptions:

      1) There is more than one universe.
      2) These universes have different fundamental constants.
      3) Some of these constants allow life, others do not.
      4) There are more ways for constants to disallow life than to allow life.

      So, what are the problems with these assumptions?

      1) Although this is a prevalent idea in physics today, we don't know that there is more than one universe. We've said that this is an assumption anyway, so that doesn't really matter, but we have to be aware that we need more evidence before deducing this, and the anthropic principle is not enough to deduce it because the anthropic principle also relies on assumptions rather than facts. For reasons expounded on below, it also needn't be a conundrum if the universe is fine-tuned and there is only one universe.

    17. 2) Imagining that we have some other evidence for the existence of multiple universes, this assumption suggests that the fundamental constants of these universes can be different to the constants of our universe. Perhaps, however, there is more than one universe, but they all share the same constants. Although we can theorise quite easily about the consequences of a universe with different constants, we do not actually know from current physics that these differences are permitted, let alone actual. If we were to discover that only one set of fundamental constants is permissible for some as yet undiscovered foundational reason, then the nature of our universe is not so mind-boggling. Whether or not there is more than one copy, with quantum indeterminacy meaning that the contents of each universe appear different, they're all fundamentally the same, so it's really only one universe. With this, we wouldn't need the anthropic principle to account for life because we could state that life is allowed in our universe and therefore all universes. Here, the perception of fine-tuning would be based on the correct assumption that different tunings would disallow life, but on the incorrect assumption that these different tunings are even possible.

      3&4) Ignoring the above concerns, we could say instead that different universes can have different constants, but we do not know which configurations of constants are permissible or which of the permissible configurations would give rise to life. As I already suggested, the fact that life in this universe clings to a paltry 4% of understood matter and will be obliterated in the blink of an eye suggests that there may indeed be many other configurations which allow life, many of them more or less hostile. Perhaps there are equal numbers of configurations which do and do not allow life to occur - we have no way of putting a probability on that, particularly because we also do not know to what extent the constants can change. At the moment, our hypothetical approach poses that the constants can literally be anything, and, if so, then of course more universes will allow life than not. But perhaps instead of them being either anything or only one thing, they may be constrained to a narrow range of configurations, and many of these, or perhaps all or few of them, could give rise to life.

      These are the key problems that strike me with a multi-verse theory that invokes the anthropic principle at the moment. These are concerns that have gone unpacked so far, as people just assume that you can have different constants, and if you can have different constants, then you can have any constants. We simply don't know either of those things.

    18. I think you've lost track of the argument somewhat, so most of your post is kind of missing the point.

      I'm not assuming that other universes exist. I'm not even assuming that other configurations of constants are permitted. I'm saying that even if there is only one universe and only one possible configuration of constants, then it is surprising and suspicious that that configuration of constants and laws supports life.

      Going back to my random number generator again, the first number that program will pick is absolutely determined by the logic within it. If the state is cleaned and the program is run in the same environment again, it will pick the same number. If that number happens to be the number one, we have cause to be suspicious, even though as it happens it is the only permitted number that could have arisen as the first choice according to the logic of the program.

      The fact that the only possible configuration of the universe and constants supports life is surprising if it seems that other (illegal) configurations would not. This is because, whatever the laws are that determine which configurations are legal and which are not, they are surely nothing to do with life. Life is an irrelevant side-effect. It thus remains an unexplained coincidence that life is possible in this universe.

      Unless there are lots of universes or that most conceivable universes would end up supporting life (which you seem to doubt yourself if universes are allowed to have any configuration at all).

    19. That falls under point 2. We would have every cause to be suspicious, but neither a designer nor the anthropic principle are necessary, because we may yet discover for some fundamental physical reason that the constants could never have been anything else.

    20. The constants could never have been anything else doesn't explain the coincidence. Unless life has something to do with the explanation for why these are the necessary values of the constants (e.g. a designer chose them so as to enable life), then there is a coincidence. If we assume that life-support is improbable given other hypothetical (though possibly illegal) values for the constants, then the coincidence is massive.

      Now, since we don't know that only one set of constants is possible, this should lead us to suspect that in fact more than one set of constants are possible, and that there are many universes.

    21. The supposed significance of the coincidence presumes that life is improbable. We have no cause for saying life is improbable without knowledge of the way constants can change, if at all, and what the consequences of those changes are. And if there is some fundamental law that means the universe couldn't have been different, then we're lucky. It's not a huge unlikelihood that needs explaining; it's an inevitability. It's like a number generator that always say 5,000,000 and you always know will say 5,000,000 - you don't go looking for a reason why it doesn't say 4,286,426 because 5,000,000 is too significant. You have a reason why it only says the significant number.

      It's also dubious to state that because we don't know one thing we should therefore actively suspect something else.

    22. And pre-empting you'll say the 5,000,000 generator is designed, we do not know the nature of the law that would necessitate our universe's constants, and so we cannot draw an analogy and claim that those must have been designed too.

    23. (If there's anything we learned from 19th century science, it's that, while humankind's creations are the products of designers, things in nature which appear superficially designed and must necessarily seem to have a designer can eventually be explained by some simple natural process. There could be something similar underlying the formation of the only configuration of constants that explains their apparent design).

    24. We don't need to know the way constants can change. Well, actually, we know they can't change. What you mean is we need to know the statistical distribution of the possible values of the constants.

      But we don't need to know that. If it so happens that constants are much more likely to be arranged so as to support life, then there is a coincidence that they way constants are distributed - the way constants are likely to be - supports life. Instead now of the improbable convenience of the physical laws, we now have to explain the improbable convenience of the metaphysical or logical laws that drive the selection of the physical laws.

      "if there is some fundamental law that means the universe couldn't have been different, then we're lucky."

      Exactly. Potentially very lucky. Potentially so very suspiciously lucky that we should doubt that this is the case.

      "It's also dubious to state that because we don't know one thing we should therefore actively suspect something else."

      Not at all. We don't know if God exists or not. We have no good reason to suspect that he does. Therefore, we should suspect that Jesus did not rise from the dead.

      We don't know if there is some underlying principle that drives the selection of constants and physical laws according to some deeper metaphysical laws. We have no good reason to suspect that there is. Therefore, we should suspect that the laws are chosen arbitrarily.

      But that's not quite what I'm saying. I'm just trying to phrase two analogies similarly to make it clear. In actual fact, it is quite reasonable to postulate some metaphysical principle which helps to define the physical laws and constants. However then it is this principle which is suspiciously convenient and in need of an explanation.

      Your example of the number generator I would address as follows. Let's say I have programmed it myself, so I know I did not deliberately set out for it to generate such an even number, and furthermore the number exactly half-way through the distribution of possible numbers.

      Knowing that this is a massive coincidence, I should then suspect that I have made some programming error resulting in getting the half-way number rather than writing a good algorithm for generating unpredictable numbers.

      It is both an inevitability and a huge unlikelihood that needs explaining. It's a false dichotomy.

    25. "There could be something similar underlying the formation of the only configuration of constants that explains their apparent design"

      Exactly my point. The same explanation that covers biological "design", namely selection from a population. The anthropic principle.

    26. Again you're appealing to improbable convenience, but you're not following the simple point that if there is only one possible configuration of the physical constants, it is not an improbable convenience because there are no other possible configurations - it couldn't have been any other way.

      Your reworking of the number generator isn't applicable - the whole point is that it was purposely set to generate 5,000,000, it wasn't supposed to generate anything else, and we know that that is what it's going to generate.

      Your Jesus analogy isn't an adequate rebuttal. The reason for disbelieving in Jesus is that there is no evidence for his divinity. That doesn't give us cause to believe in Mohammed or anything else. You can choose to not think that there is only one universe because there's no evidence, but that is not a reason to positively believe something else for which, you already know, there is also no evidence. To state that this means we have good reason to suspect the laws are chosen arbitrarily is just fallacious.

      The anthropic principle is not in the least bit analogous to the evolutionary explanation of complex life, and it takes a great deal of metaphorical casuistry to jump between the two by using the phrase "selection from a population". You can also push the buck back a step and say that if there is only one configuration, then why *that* configuration, or why the metaphysical reasons for there being only one configuration, but you're already presuming that the explanation wouldn't have a satisfying answer - we don't know that because we don't know what the explanation would look like. To make such a claim is similar, I think, to people who accept evolution and then go in search of a deistic cause for abiogenesis - always finding something to force a preconceived idea in somewhere.

  4. I'll get back to your other responses later as I have to work, but I was just listening to Steven Weinberg briefly talking about the potentially unsatisfying answers to the kinds of questions you pose. The analogy he gives is with Kepler's attempt to describe the orbits of the planets with some appealing geometric explanation because we used to think that they were somehow essential to the description of the universe. Yet, when Newton came along, we realised that the orbits were insignificant and arbitrary, they were purely historical accidents.

    For example, the fact that the Earth is 93 million miles away from the sun does not require the kind of explanation Kepler envisioned. That's just the way the solar system formed. To account for it, we do not need to postulate that this is the case because there are many other planets which are not 93 million miles away from their star. Similarly, Weinberg says it could quite possibly be the case that the fundamental constants of the universe are historical accidents. To think that they require a special explanation arises out of your incredulity, but this is to make Kepler's mistake.

    The anthropic principle is not absolutely necessary to account for these things; there may be deeply unsatisfying observational answers waiting for us in future science. As Weinberg says, science is not just a process of discovering answers, it's about discovering the right questions to ask. Kepler got it wrong, and I suspect you might too. Even if you're not, I certainly would not accept that there's an a priori reason to believe that your questions must absolutely be valid. Kepler thought there was for his ideas; I'm not falling into that trap. ;)

    1. If there was some pattern to the orbits of the planets, then it would be reasonable to seek an explanation. For example, if the ratio of the radius of each orbit to the next was the golden ratio, then it would be reasonable to assume that there must be some deep principle at work, not that it had happened that way by chance.

      Kepler seemed to notice a correlation between the sizes of planets and the period of their orbit, but later realised that this correlation was not particularly close and so correctly abandoned the idea. If the correlation were real and very precise, he would have been absolutely right to suspect that there was an explanation for it.

      Similarly, if randomly selected permutations of the laws of nature very rarely allow life to develop, then the laws of this universe would appear to have a very precisely designed pattern to them which enables life. It is then reasonable to assume that there is some deep principle at work in explaining our observation of life in this universe, either anthropic or design or some other idea.

      If 93 million miles is the only radius that will allow life to exist in our solar system, then the anthropic principle is absolutely the explanation for why our planet is 93 miles away from the sun. It's not a coincidence that we find ourselves on such a planet. The orbits of other planets show no particular pattern as far as I'm aware and look pretty insignificant. They look pretty much as we would expect them to look if they happened by chance. That's why Kepler was wrong (as he himself realised). That's why it is reasonable to assume that these orbits are a historical accident.

      It seems to me that any question that is not obviously nonsensical or trivial is a good question to ask. The answer to that question might explain why that question is actually inconsistent or based on untrue assumptions, but if that isn't clear from the outset then even arriving at this conclusion will have provided valuable new insights, as Kepler found when the data disproved his hypothesis.

      And so the attempt to answer the question is a worthwhile endeavour.

    2. If there was some pattern to the orbits of the planets, then yes it would be reasonable to seek an explanation. Kepler did not observe a pattern, either real or false; he was working on the assumption that the cosmos is geometrically perfect in the same way it was previously thought that all planets must be inhabited by life or God's creation would be wasteful. He was working with the numbers to try to force them to a preconceived idea rather than working towards a conclusion from the data.

      My comment about the distance of the earth was not related to life. Yes, if 93 million miles were the only permissible radius, we might have to invoke the anthropic principle. I was talking about the distance regardless of the existence of life. We could imbue the 93 million miles with significance - Kepler certainly wanted to - but we know now that it isn't significant. It's dangerous to think that there is something special and then seek to find answers that fit our assumptions. We are better off assuming nothing and only coming to conclusions from observations.

      It seemed to Kepler that his obviously non-nonsensical and non-trivial question was a good question to ask. He was wrong.

    3. Kepler thought he saw a correlation and investigated it. His question was well posed and he got a well defined answer. I don't really know what I'm talking about with regard to Kepler, admittedly, so it's possible he was motivated by a suspicion that there was something fundamental about the orbits of the planets.

      Nevertheless I think Kepler's investigations were far from poor science. He had a hypothesis, investigated it and found that it was wrong. I find it hard to fault him for that.

  5. Anyway, I've totally forgotten what central point was at stake in our most recent digressions! I should make it clear that I am not wedded to any particular conclusion; yours could well be true. I'm just trying to make the case that yours is not obviously true, and that there are other possible solutions, so your level of conviction seems unwarranted to me. If your argument were a knock-down, I think the opinions of cosmologists, who think about this stuff day in day out, would be a little more uniform. The fact that they're not suggests that us laymen are pontificating on limited information.

  6. Well, the crux of my post was that if the anthropic principle is the explanation for fine tuning, then there must be multiple universes.

    Personally, I believe the anthropic principle is very likely to be that explanation, and this leads me to suspect that there are multiple universes. I'm not sure I'd characterise this as a conviction.

    Where I think you're absolutely wrong is to insist that we don't need an explanation because we're just assigning an arbitrary significance to life. And I think most cosmologists would agree with me there.

    1. I wouldn't state with certainty that life doesn't need an explanation, I just wish to abandon this idea that it needs an explanation because it is "significant". What I care about is whether or not it is *improbable*. If it is improbable, then we could call it significant, but I think it's just better to talk about probability because significance is a word that creates much obfuscation. If it does turn out to be improbable, then it does require an explanation (though the anthropic principle isn't the only possible one).

    2. Improbability is not sufficient to describe the problem. Selecting 34589574 at random would not surprise us if it had no particular meaning, yet it is just as improbable as any other number.

      Results that need explanations are not results that are improbable (all results selected from a large population of possible results are equally improbable). Results that need explanations are surprising results. Surprising results are those where if we divide the possible results into two sets, one much smaller than the other, the result we get is from the smaller set.

      Let's call the much smaller set "significant" and the much larger set "insignificant". We can now describe the result in terms of whether it is significant or not. And these two properties are not all equally improbable. We should expect the result to be insignificant simply because that is the larger subset, even though every individual possible result is equally improbable.

      "To be or not to be" is just as likely a priori as "Asd sdftr4 ergg". Both are equally improbable. We need the concept of significance to explain our surprise.

    3. OK that's true, but then we need a solid rationale for claiming that life is significant enough to be surprising. As I pointed out earlier, the significance we attach to life is not arbitrary in the same way that a line of Shakespeare is, and this poses problems.

    4. I just have to show that life has a priori rather than a posteriori significance.

      Universe A has gliders (Conway's Life, say)
      Universe B has an infinite highway (Langton's Ant)
      Universe C has an empty infinite featureless void
      Universe D has a finite empty featureless void.
      Universe E has a finite space containing particles which bounce off each other
      Universe F has two kinds of particles which are attracted to each other (say, forming something like hydrogen) and bounce off each other
      Universe Z has intelligent life

      All I need to convince you of is that when presented with all these possibilities, I would find universe Z most fascinating. In other words I'm not simply saying a posteriori that life is fascinating simply because I happen to have already observed a universe that contains life.

      Previously your objection to my logic was that significance is arbitrary, and now your objection is that significance is not arbitrary.

      I would put it to you that arbitrariness is absolutely irrelevant. All that matters is that there are two sets. One set would contain universes which we would consider incredibly fascinating and would be front page news if they were discovered in a simulation (as would any simulation of a universe in which we discovered intelligent life), and the other set would contain universes which may be interesting to some people but would not blow the mind of the public should they be discovered (e.g. Conway's Life).

      If you would not be any more excited by the discovery of intelligent life arising out of a simulation of relatively simple mathematical rules than you would be of discovering hydrogen, then I just can't comprehend how your mind works because it is utterly alien to me.

      If you admit the subjective difference between the two, then you admit that you have no problem assigning hypothetical universes to one of these two sets of "universes significance to Callum" and "universes insignificant to Callum". If one set is much much smaller than the other, then finding we have with a single choice selected a universe from the smaller set is surprising.

    5. I'm still waiting for the reasoned argument because that was a thinly veiled appeal to emotion! :P

      "All I need to convince you of is that when presented with all these possibilities, I would find universe Z most fascinating. In other words I'm not simply saying a posteriori that life is fascinating simply because I happen to have already observed a universe that contains life."

      No, you don't have to demonstrate that you find universe Z fascinating, you have to demonstrate that you *should* find universe Z fascinating, otherwise we could get various people or life-forms that find the other universes equally fascinating - as much as you think they're strange - and then the whole thing is pointless.

      You're right that I was tying myself in knots over arbitrariness, so let's abandon that. Look at it like this instead. The reason for the significance of Shakespeare appearing in a random sentence generator is that Shakespeare's words entered the cultural consciousness in an event independent of the random sentence generator. What's the reason for the significance of life? It's not because of an event independent of the creation of the universe. I've said that it's because we are evolved to be egocentric, but that's not a good enough reason - you haven't advanced an actual reason, you've just said that you find it significant, so there.

      You can't make the argument from arbitrary intrigue because we've abandoned arbitrariness - neither the significance of Shakespeare nor life is arbitrary; there has to be a reason. If you're going to compare our universe to universes without life, you're making an argument from improbability which you've already refuted yourself. You can't make an argument from rarity because there are some apparently not-quite-so interesting things that could be rarer (extremely heavy elements or some exotic things I don't know about). You can't make an argument from complexity because that necessitates degrees of significance, and evolution pushes life down to an initial chemical reaction.

      I would find the universe with life more interesting, but I've got no valid reason to find it more interesting than the infinite featureless void, and nor do you. Or do you?

    6. I don't think it's an appeal to emotion at all. The fact that you have emotions about it proves that there are two categories that we can split potential universes into - those which get you excited and those that don't. It then becomes mathematically improbable for us to find that this universe is a member of the smaller group, especially if it is much smaller.

      Whether you or I *should* find universe Z fascinating is actually irrelevant. All that matters is that we *do* find it orders of magnitude more fascinating than a typical universe. This in itself marks it out as special. It doesn't matter what the reason is for this fascination.

      This is unintuitive, but it doesn't matter from our point of view that there are other hypothetical people who would be unimpressed by life and would be more interested in hydrogen. All that matters is whether you and I find life meaningful.

      I'm going to try to illustrate this. Suppose there is some insane mathematician that just happens for some inexpressible reason to believe that the most significant and beautiful number is 1/137.036.

      Decades later, after many experiments, science has determined that the approximate value of a fundamental constant of nature (the fine structure constant) is 1/137.036.

      The appropriate attitude of that mathematician would be to be dumbfounded. Whatever crazy unsound logic he had in coming up with that number, he should suspect that he is on to something and that there is a reason why this number has cropped up. Let's say he is wrong, but he is wrong for the right reasons.

      Now, suppose that lots of crazy mathematicians have obscure favourite numbers. The correct attitude of the general public should be to be relatively unimpressed. Given the number of crazy mathematicians out there, it's not too surprising that one of them should have picked a favourite number that corresponds to a constant of nature by pure coincidence.

      So your assessment of the probabilities in any given situation depends on your perspective. If you got a phone call informing you that your mother had won the national lottery, you would probably take some convincing that it wasn't a joke. You would find it incredible. However if you heard on the news that some stranger's mother had won the lottery, you wouldn't be a bit surprised.

      Your attitude to this question is precisely analogous to being unimpressed and unsurprised if I tell you that I have won the lottery simply because somebody has to win the lottery.

      No. Me winning the lottery would be amazing to us because it has much greater significance than some stranger winning the lottery. It doesn't matter that there exist other people who would be unimpressed.

      If there is any other more probable explanation for my apparent success than that it had happened by chance (e.g. I'm lying to you) then it would be rational to disbelieve that it had happened by chance.

      That's the scenario we're in. We find life to be incredibly significant. I could justify this by appealing to complexity, self-organization, evolution, parts being shaped by selection for particular purposes, etc, but really it doesn't matter. Once we find it incredibly and (crucially) uniquely significant, we owe ourselves an explanation for how this significant result could have appeared apparently against all odds. If we found hydrogen uniquely significant, we would owe ourselves an explanation of that.

    7. You're using so many different definitions of significance and jumping between them that I don't have the time or interest this evening to pick them apart. I may come back to it some other time, but I'm not sure I want to pursue this topic any further.

    8. Awww... :(

      By the way, I want to compliment you on coming up with an extremely convincing argument. It's very hard to refute. I just happen to think it's wrong. The ingenuity and subtlety of the argument means it's very hard to rebut convincingly.

      I'm not conscious of jumping between different definitions of "significant", but I am jumping wildly between analogies and thought experiments, which is a problem.

      One final thing I want to say on the subject:

      I think your attitude comes from the absolutely justified heuristic that we should not be overly impressed by coincidences. Stuff happens to us all the time - given enough time some truly impressive coincidences are bound to happen to us sooner or later. Most non-skeptics tend to respond to such coincidences by seeking deeper meaning where there is none.

      Where I think this heuristic might fail us is when there is a coincidence which is extremely impressive but which has a reasonable uncoincidental explanation. In those cases it might be more reasonable to be suspicious of the coincidence, depending on the relative probabilities of the two explanations.

    9. If I sounded flippant, I think it's just because I'm unusually tired this evening so feel a bit crappy. I could do with sleeping on the question and no doubt my interest will come back tomorrow. :)