Even if the multiverse is true, it can't explain fine-tuning

#1

Here, I’m going to test out a thought experiment that I’ve been working out very recently. This topic has specifically to do with the multiverse itself and how it relates to fine-tuning. We all know the fine-tuning arguments, it’s been outlined pretty widely at this point and anyone in this discussion long enough has definitely discussed it or read about it at some point or another. I found earlier today that the Stanford Encyclopedia of Philosophy had published an excellent article outlining fine-tuning and the finely tuned constants, responses to fine-tuning and responses to the responses. It’s really a fantastic article and a great go-to resource on this topic that had been missing.

Anyways, one of the frequent responses to fine-tuning is the possibility of a multiverse. If a multiverse exists, then that explains fine-tuning. I don’t think so. As I’ve been considering this question, I’ve actually come to the conclusion that even if the multiverse does exist, it doesn’t even get us a teensy bit closer to explaining fine-tuning. I’ll hope to test that out here.

First of all, we’re all also familiar with the astronomical probabilities of some of the constants, ranging from things like 1 in 10^30, 1 in 10^50, and even 1 in 10^120. All the ‘multiverse’ means is that there is more than one universe. So if the multiverse exists, why can’t the multiverse only be two universes? If there are only two universes, then these astronomical probabilities remain hopelessly astronomical. Why can’t there be 10 universes instead of any more? Or even 100? Or even 10 billion? Or 10^24 universes? There’s no reason to think that if a multiverse exists, it would be something like the near infinite number of universes required to counter the constants improbability, let alone an infinite number. But let’s grant that there is an infinite number of universe. Explained now? Well … no.

This is because even if an infinite amount of universes existed, whose to say that they aren’t absolutely identical to each other? Or at least, identical in their constants and structure. In this case, even though there is an infinite number of universes, the probability that this multiverse network will have life is still exactly the same as if there was one universe. And so nothing is explained. In fact, if there were some sort of mechanism that just produced an infinite number of universes endlessly, I couldn’t imagine at all that this mechanism would magically shift itself so as to produce different constants each time it made a universe – it’s seems to me that this mechanism would just produce multiverses on mass in the same ‘method’ like a factory produces countless replicas of the exact same item. In other words, even if a multiverse existed, this doesn’t get us a teensy bit closer to explaining the existence of life in spite of the odds.

(David Heddle) #2

I could not possibly disagree more.

Any such calculation is non-sensical. Nobody knows how to calculate the probabilities of the constants. Furthermore it is unrelated to fine tuning. Our universe is fine-tuned (i.e. the habitability is sensitive to small change in the constants) regardless of whether the constants are low probability or unit probability. The philosophical interpretation of the fine tuning likely depends on the probability. But not the fine-tuning itself.

Secondly, you are begging the question by positing multiverse theories with only a small number of universes or identical universes. The multiverses people are invoking, and seem to be a consequence (maybe not a necessary one) of inflationary models and the String Landscape, are infinite (or effectively infinite, e.g. 10^1000) in number with different physics (constants).

You can believe the multiverse models or not, and they at present are “sciency” rather than science, but at face value they adequately explain fine-tuning through big numbers.

Edit: typos and clarity

#3

Well, I also disagree (but I will concede some things, I therefore appreciate your comments). At the very least, I’d like to ask you some questions since I want to see how you defend these claims.

Secondly, you are begging the question by positing multiverse theories with only a small number of universes or identical universes. The multiverses people are invoking, and seem to be a consequence (maybe not a necessary one) of inflationary models and the String Landscape, are infinite (or effectively infinite, e.g. 10^1000) in number with different physics (constants).

I know that they are posing that there are an effective infinite number of universes that all have different constants and it does “at face value” explain fine-tuning. But I’m simply saying there is absolutely no reason to think that if a multiverse did exist, that the number of universes would either be so great so as to cancel out the probabilities, and if they were so numerous, that they would have different constants. I could be wrong about this. Are you aware of an explanation that would show that the different universes would in fact operate under different constants? If not, it seems to be sheer speculation to me.

Any such calculation is non-sensical. Nobody knows how to calculate the probabilities of the constants. Furthermore it is unrelated to fine tuning. Our universe is fine-tuned (i.e. the habitability is sensitive to small change in the constants) regardless of whether the constants are low probability or unit probability. The philosophical interpretation of the fine tuning likely depends on the probability. But not the fine-tuning itself.

Now, as I think about this, you may be correct that the specific probabilities given are impossible to verify. The Stanford Encyclopedia of Philosophy article I mentioned, much more rigorous than the usual sources, does not mention specific odds. So I guess we agree then, on this point?

(Matthew Pevarnik) #4

We can of course model changing different constants but do not know what values they can even take or what the odds are of getting each particular value.

This goes hand in hand with @heddle saying any probability calculations are meaningless.

I would mildly disagree beyond this however in that while we can model what ranges and combinations of constants permit life like ours (or even getting rocks in a universe) we cannot say that such are ‘Fine-tuned’ since we are really just comparing it to precision that we are familiar with and can achieve via modern science— compared to our best technology, such ranges are indeed ‘fine’ and ‘god-like’ so to speak. And hence it’s a good argument for God these days. Perhaps the strings of string theory are indeed real, and maybe we will be able to manipulate them someday. And then, the “fine – tuning” becomes a little less god-like. Or maybe, we will never know – and probably won’t in our lifetimes so I could be completely wrong!

#5

Yes, I do admit that calculating the probability is meaningless. Will string theory ever challenge fine tuning? Hard to say, we’ll have to see. I would like to ask you though about this;

We can of course model changing different constants but do not know what values they can even take or what the odds are of getting each particular value.

You’re the physics guy here (you and @heddle). I know we can model it, but when we say that we can model is occurring, does this translate to the claim that if a multiverse did indeed exist, the universes would in fact have different constants, or we just speculate that they could have different constants? I’ve seen it claim in some arguments against fine-tuning that the existence of different constants is all together impossible (Colyvan M., J. L. Garfield, and G. Priest, 2005, “Problems with the argument from fine-tuning”, Synthese, 145(39): 325–338).

(Matthew Pevarnik) #6

Here’s an example of a group that does large scale universe simulations for example. They have several different papers like one where they vary the cosmological constant from 0 to 300 times higher and found out universe would do just fine in those simulations:
http://icc.dur.ac.uk/Eagle/

But none of those actual simulations have much of anything to do with the multiverse. I’m not sure where exactly the idea that a string landscape can tweak the fundamental constants as I know as much as you do (or perhaps even less) about string theory.

(David Heddle) #7

I found the paper here. (Try to provide a link, if possible, when you reference an article.)

This is not a physics paper. It is a rather clumsy philosophy-probability paper.

They make so many mistakes by the second page that I can hardly believe what I am reading. They begin by stating the fine-tuning argument with “precision”:

(1) The boundary conditions and laws of physics could not have been too
different from the way they actually are if the Universe is to contain
(carbon-based) life.

(2) The Universe does contain (carbon-based) life

Fine-tuning makes no such claim as (1). The claim is that our universe’s constants could not change much from their given values without destroying habitability. It is the claim that in the multi-dimensional parameter space of constants, we are sitting on an unstable equilibrium–like a mountain peak. It does not does not claim that there are no other mountain peaks, or stable equilibria (valleys), or vast plateaus of stabilityit only claims that a small step from our position in this parameter space is calamitous.

They then give the unsubstantiated and dreaded probability claim as a hence:

Hence:
(3)The Universe as we find it is improbable.

There is no such hence. The fine-tuning argument makes no claim with regard to the probability of our universe. It only makes a claim, be it right or wrong, about the sensitivity of the habitability of our universe to small changes to the constants.

Worse, they make the horrible mistake, usually associated with ignorant blog commenters, of making a gratuitous connection to the religious co-opting of the fine-tuning argument:

(4) The best explanation for this improbable fact is that the Universe was
created by some intelligence.

Hence:
(5) A Universe-creating intelligence exists.

With seemingly no regards to the fact that the fine-tuning problem is viewed as a serious physics puzzle by secular scientists who do not connect it to a religious argument. You could easily replace, with as much legitimacy, (4) and (5) by

(4’) The best explanation for this improbable fact is the multiverse
(5’) No universe-creating intelligence exists.

Their paper has the goal of showing that (3), above, does not follow from (1) or (2). Which is an exercise in irrelevancy. We can readily stipulate that (3) is not a consequence of (1) and (2). But by demonstrating that that (3) is not a consequence of (1) and (2) they have, in their own minds, neutered fine-tuning.

OK… let’s roll with it. Maybe they can provide some value to the community by proving that (3) does not follow. It won’t make any difference to the fine-tuning argument, but it would be at least interesting in its own right. Can they provide a convincing argument?

They have an argument, and it leads to the stunning conclusion:

The fine tuning argument, on its most plausible interpretation, hence not
only shows that life-permitting universes are improbable, but, arguably,
that they are impossible!

Now that would be something! (Although again, it is not an argument at all relevant to fine tuning.) How did they prove such a stunning result in a mere two paragraphs on p. 327?

With some of the worst analysis I have ever seen published. To paraphrase (read it if you think I am being uncharitable) they argue that if a constant k can have any real value (which, by the way, nobody claims, but OK) , then any finite range of possible values (even big ranges, let alone the small ranges demanded by fine-tuning) has effectively a zero probability. Therefore improbable habitable universes are, in fact, impossible.

I’m not kidding, that’s their argument.

I’m pretty sure that they don’t relealize that a high probability universe (esp. P = 1) with fine-tuning (sensitivity) is a much stronger religious apologetic than a low probability universe.

Edit: typos

#8

With some of the worst analysis I have ever seen published. To paraphrase (read it if you think I am being uncharitable) they argue that if a constant k can have any real value (which, by the way, nobody claims, but OK) , then any finite range of possible values (even big ranges, let alone the small ranges demanded by fine-tuning) has effectively a zero probability. Therefore improbable habitable universes are, in fact, impossible.

I’m not kidding, that’s their argument.

Wait, isn’t their argument a total non-sequitur?

NOTE: I just found the paper myself here and began reading it. I apologize, heddle, for having to put you through that. Tell me if I’m wrong – even if there were an infinite set of possible values (which, as you note, is not even the claim), then the probability of any finite range is … not zero at all. It infinitely approaches zero. But it’s not zero. Am I right? If it’s logically possible for a constant to have k value, then by definition its probability can’t be 0 since then it would be logically impossible – you’d have to argue that it’s both logically possible and logically impossible at the same time.

@pevaquark Thanks for that reference. You definitely know more about string theory than me, my only education on this topic is a bit of google and one of Brian Greene’s books. I do think we shouldn’t say string theory can make fine-tuning obsolete until 1) we obtain real evidence of string theory and 2) string theory can actually be shown to affect fine-tuning premises. I know literally nothing about loop quantum gravity besides the name, but don’t jump the gun too quickly!

(system) #9

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