Barr and the multiverse

[Al Moritz]

There is an interesting article about the multiverse in Seed Magazine by Nathan Schneider:

seedmagazine.com/content/print/the_multiverse_problem/

I have a discussion about the multiverse with Stephen Barr, who wrote the book "Modern Physics and Ancient Faith", over at Nathan Schneider's blog:

www.therowboat.com/2009/03/the-multiverse-problem/

[unkleE]

Al,

That is a most interesting discussion you are having with Barr. I think it is a wonderful feature of the internet that I can be in personal contact with you, and with Barr second hand through you, and learn in ways that wouldn't have once been possible. I am especially interested because I have just finished reading his book, and I was very impressed with it.

I will share my ignorance to say that while I think you may be strictly speaking correct, and the multiverse isn't science in the strict sense, I'm inclined to think we should take notice of him. Thus I think we christians should maybe adopt a precautionary principle approach, and address our apologetics to both possibilities - which you have suggested.

I think it may be true, as you say, that, for many, a major attraction of the multiverse is that it keeps a designer God at a distance. But I think this is an ineffective and probably unworthy apologetic tactic, as Barr says.

So thanks for sharing the discussion with us, even though I am probably inclining slightly, though not completely, to Barr.

[humphreyclarke]

That is an interesting discussion you had with Barr. I think that he and Don Page (for more on him, see his lecture on Quantum cosmology here www.st-edmunds.cam.ac.uk/faraday/resources/Short%20Course%206/FAR102%20Page.mp3 ) realise that, in some forms, the multiverse explanation is actually an ally of theistic belief.

1) As George Ellis points out, we would still have to ask 'why this multiverse'?. One can envisage many multiverses which would not give rise to life at all.

2) As Paul Davies points out, a multiverse is going to require meta laws to guide its functioning, within a highly restricted mathematical subset. There is inevitably going to be fine tuning involved at a higher level.

3) The thing that is really impressive about the universe is not so much the actual fine tuning, it is the entire formational structure of the universe. You could vary the constants all you like but without having The Pauli exclusion principle you are not going to get anything interesting.

4) The bishop of Paris in the middle ages said God could perfectly well create as many universes as he wants.

5) One of Dawkins's arguments is that we should be trying to obtain simple explanations for complex phenomena in the manner of evolution. Appealing to the multiverse scuppers this. The bigger the multiverse is, the more complex it is. The infinite (or close to infinite) multiverse needed to explain the fine tuning is going to be unbelievably complex and doesn't even provide an ultimate explanation since it is a contingent object. If such an entity actually existed, you would be justified in positing a non contingent eternal creator God as the cause.

6) The multiverse is a tacit admission that the universe is not self explanatory and we need to appeal to a reality outside our own to explain it, which is also what the Theist wants to say.

I do have some serious doubts about whether a set of infinite objects going back into the past could actually exist. The paradoxes involved give me a headache.

[unkleE]

Humphrey, I thought all of your points were good, especially this one:

The multiverse is a tacit admission that the universe is not self explanatory and we need to appeal to a reality outside our own to explain it, which is also what the Theist wants to say.

Yes, while I am forced to agree with Barr that the multiverse is possible, I still can't help feeling it is an all purpose get-out clause which can prove anything you want (much as atheists accuse about the concept of God). And it is interesting to hear non-theists suggesting that the definition of "universe" should include any physical universe which came before ours, to avoid this idea of needing an explanation beyond our universe.

I do have some serious doubts about whether a set of infinite objects going back into the past could actually exist. The paradoxes involved give me a headache.

Me too, for three reasons:

(1) I don't believe a succession of universes can add up to infinity - we can't count to infinity. I read one mathematician who argued that the only way an infinite number of physical things could occur would not be serially, but to all to be "created" at once!

(2) If there had been an infinite time before now, every possible physical process would have fully run its course long before now. The only way anything could occur would be if some physical processes were perpetual motion, an impossibility in our understanding of the physical world.

(3) The only other way for an infinite time to have not fully exhausted all physical processes would be if there was no time before the big bang - which leaves us with a "world" outside our 3D world and its causality, and outside time. It's starting to sound more "supernatural" than "natural" to me.

There is no way out of it for me. The fine-tuning we see in our universe is too amazing and unlikely to have occurred by chance, as even unbelieving cosmologists admit, and surely God is at least a reasonable, if not probable, explanation. If the multiverse is true, then it had to be finely tuned, which again points to God. And if there was an infinite universe before ours, it had to be even more finely tuned so as to allow perpetual motion, which points even more to God.

[humphreyclarke]

Is there a resolution to the infinite past paradox. This used to bother me enormously until I read that time began at the big bang. Of course if the multiverse hypothesis is true, then presumably other spacetimes existed before the big bang and these have some kind of infinite past in which an infinite number of universes are churned out for no reason. If that is the case then, how am I existing now?, surely that is impossible if there is an infinite past as the present could never come to be?. If the universe did not begin to exist a finite time ago, then the present moment could never arrive.

Perhaps the paradox can be resolved by saying this infinite number of spacetimes exist at the same time, in which case they presumably all came into existence at once.

Interesting how the question 'why is there something rather than nothing?' would then become 'why is there virtually everything rather than nothing?'.

[humphreyclarke]

Apr 14, 2009 23:00:33 GMT unkleE said:

Yes, while I am forced to agree with Barr that the multiverse is possible, I still can't help feeling it is an all purpose get-out clause which can prove anything you want (much as atheists accuse about the concept of God). And it is interesting to hear non-theists suggesting that the definition of "universe" should include any physical universe which came before ours, to avoid this idea of needing an explanation beyond our universe.

Yeah, I liked this interview with Leonard Susskind

www.newscientist.com/article/mg18825305.800-is-string-theory-in-trouble.html

Why are physicists taking the idea of multiple universes seriously now?

First, there was the discovery in the past few years that inflation seems right. This theory that the universe expanded spectacularly in the first fraction of a second fits a lot of data. Inflation tells us that the universe is probably extremely big and necessarily diverse. On sufficiently big scales, and if inflation lasts long enough, this diversity will produce every possible universe. The same process that forged our universe in a big bang will happen over and over. The mathematics are rickety, but that's what inflation implies: a huge universe with patches that are very different from one another. The bottom line is that we no longer have any good reason to believe that our tiny patch of universe is representative of the whole thing.

Second was the discovery that the value of the cosmological constant - the energy of empty space which contributes to the expansion rate of the universe - seems absurdly improbable, and nothing in fundamental physics is able to explain why. I remember when Steven Weinberg first suggested that the cosmological constant might be anthropically determined - that it has to be this way otherwise we would not be here to observe it. I was very impressed with the argument, but troubled by it. Like everybody else, I thought the cosmological constant was probably zero - meaning that all the quantum fluctuations that make up the vacuum energy cancel out, and gravity alone affects the expansion of the universe. It would be much easier to explain if they cancelled out to zero, rather than to nearly zero. The discovery that there is a non-zero cosmological constant changed everything. Still, those two things were not enough to tip the balance for me.

What finally convinced you?

The discovery in string theory of this large landscape of solutions, of different vacuums, which describe very different physical environments, tipped the scales for me. At first, string theorists thought there were about a million solutions. Thinking about Weinberg's argument and about the non-zero cosmological constant, I used to go around asking my mathematician friends: are you sure it's only a million? They all assured me it was the best bet.

But a million is not enough for anthropic explanations - the chances of one of the universes being suitable for life are still too small. When Joe Polchinski and Raphael Bousso wrote their paper in 2000 that revealed there are more like 10 to the power 500 vacuums in string theory, that to me was the tipping point. The three things seemed to be coming together. I felt I couldn't ignore this possibility, so I wrote a paper saying so. The initial reaction was very hostile, but over the past couple of years people are taking it more seriously. They are worried that it might be true.

If we do not accept the landscape idea are we stuck with intelligent design?

I doubt that physicists will see it that way. If, for some unforeseen reason, the landscape turns out to be inconsistent - maybe for mathematical reasons, or because it disagrees with observation - I am pretty sure that physicists will go on searching for natural explanations of the world. But I have to say that if that happens, as things stand now we will be in a very awkward position. Without any explanation of nature's fine-tunings we will be hard pressed to answer the ID critics. One might argue that the hope that a mathematically unique solution will emerge is as faith-based as ID.

Problem is, once you have a theory that predicts 10 to the power 500 different universes its hard to see how it will ever be confirmed or disproved. In this interview with Paul Steinhart he says (regarding eternal inflation):

seedmagazine.com/content/article/seed_salon_paul_steinhardt_peter_galison/

Consider the following problem we have right now in cosmology: The cyclic model predicts that there shouldn’t be a spectrum of large-wavelength gravitational waves, and typical inflation says they should exist. If we see them, as far as I know, the cyclic theory is dead, and the case for inflation is strengthened. That’s normal science.

But suppose we don’t observe them. That would still be consistent with the cyclic picture. But in the inflationary picture, because it allows an infinite number of patches of every possibility, there will always be some patches that actually don’t produce gravitational waves. Since you get an infinite amount of everything, it might be that we are living in one of those patches of the universe. How do we prove or disprove that idea?

It’s a very strange kind of science. To me, the playing field becomes uneven between a theory making testable predictions, versus a theory that is Teflon. From what I can tell, there is no observation that can disprove inflation. Some people even advertise that as an advantage. To me, that’s a new and unacceptable way of thinking.

[unkleE]

The Susskind quote brings out something that Barr's book also makes clear, that there are two basically different types of multiverse hypotheses. I had always thought that the 10^500 or whatever universes were totally separate in space and time, and hence not connected, but that is only one option, and the less likely option in Barr's mind. The other option is that these "universes" are "domains" within this one universe - i.e. they are all connected in space and time because they all grew out of each other by inflation. That is the model Susskind spoke of, so I don't know why it is called multiple universe or multiverse, because it is really (I think) one very large and varied universe that is envisaged.

BTW, if Penrose is right and there were 10^10^123 possible options for the universe, 10^500 universes is only a very small fraction of this number (1/10^120), so the odds against our universe forming were still infinitessimally small and even the multiverse is insufficient to explain things.

[James Hannam]

Gentlemen,

Lee Smolin, for one, is deeply unhappy at Susskind's ideas and thinks they betray the scientific method. He's not against multiple universes per se, but he is against using them as a explanation.

For example, if it turns out multiple universes are predicted by a model, that's fine for Smolin. But postulating them in order to explain the properties of our universe (as Susskind appears to be doing) is out of order. Smolin thinks this is just the same as postulating a God to explain fine tuning (something he is not keen on either).

Anyway, Smolin's "The Trouble with Physics" is essential reading on this debate, IMHO.

Best wishes

James

[Al Moritz]

A lot of interesting replies. I was on vacation last week and busy before that, so my response is delayed. The discussion with Barr made some things more clear to me and allowed me to formulate things in ways that I could not easily have done before that. I think this comment of mine in the discussion now should clarify why the multiverse is an epistemological problem outside science -- or at least, poses a fundamentally different epistemological problem than anything else in science:

Your argumentation on neutrinos and GR relates to practical observability - and again, you raise some interesting and valid points. Yet the issue seems to be rather observability in principle, not just in practical but also in theoretical terms. In principle we can observe the existence of entities within our own cosmological spacetime. Yet outside of our spacetime observation of the existence of entities is not possible, and the discussion then is essentially about whether we can find legitimate substitutes for this or not.

Yes, certain details about entities in within our spacetime may also escape observation, but that is another issue altogether. While, as you say, we can only develop theories about what happens inside a black hole, at least black holes are in principle observable, which now has worked out in practice as well. It does make sense to construct theories on entities that we do know or can know to actually exist! The multiverse however not just may or may not exist, but its very existence may not be testable in principle, and it therefore poses a fundamentally different epistemological problem than the black hole or the neutrino. This epistemological problem goes to the very heart of what constitutes science.

Also, as I discussed, Barr's argument,

One can imagine that eventually we will develop a theory that accounts for all observed experimental and observational facts of cosmology and particle physics, passes many experimental tests, leads to many correct predictions, leaves no loose theoretical ends, and has a very tight structure. There may at that point be good grounds for confidence that it constitutes the correct fundamental theory of physics. Conceivably, the equations of that well-tested future theory may imply that the universe has a multiverse structure. That, in my view, would count as a theoretical demonstration that the multiverse theory is correct,

confuses actualities with potentialities.

I do agree, after discussing with Barr, that we should have a more cautious apologetic approach, and cannot completely dismiss the possibility of a multiverse. We need to make a distinction between the many-universes multiverse (variants of which include ones where Elvis is both dead and alive, each in different universes) and the many-domain multiverse. It is indeed the many-domain multiverse that is apparently taken seriously by scientists (even though ultimately it may lie outside science), and therefore perhaps should be taken seriously in apologetics. That version of the multiverse does not solve the design problem, however, as has been pointed out. It also does not really violate Occam's razor, because it is just one gigantic universe, and not many completely disconnected ones -- hence, it is philosophically not even that absurd.

Like Unklee and others, I am also impressed by Barr's book, and perhaps it is the best book on the science/religion issue, period. I was a bit disappointed that Barr evaded an answer to my challenge:

Also you seemed to be suspicious in your book of the multiverse idea on grounds of world view (p. 156/7):
"It is a very curious circumstance that materialists, in an effort to avoid what LaPlace called the unnecessary hypothesis of God, are frequently driven to hypothesize the existence of an infinity of unobservable entities. We saw this before [...]. We see it now in the idea of a large and possibly infinite number of domains or universes. [...] It seems that to abolish one unobservable God, it takes an infinite number of unobservable substitutes."

(While you made these comments in the context of the many-universe multiverse, you also mention the domains of the many-domains multiverse.)

Since now you embrace the possibility of a multiverse not just scientifically, but also theologically, this appears to signify somewhat of a shift in your position.

***

I agree with James that Smolin's "The Trouble with Physics" is essential reading on this debate. It boils down to a large part if you believe in string theory, which I don't, for all the reasons Smolin lays out in his excellent book (in subsequent debates leading string theorists, including Polchinski, have tried to diffuse his arguments, but in my view they were not even remotely convincing). String theory is essential when it comes to the possibility of as many variants of the laws of nature in a many-domain multiverse as to be able to explain the apparent fine-tuning of the laws of nature that we observe. As Susskind puts it (see quote above):

But a million is not enough for anthropic explanations - the chances of one of the universes being suitable for life are still too small. When Joe Polchinski and Raphael Bousso wrote their paper in 2000 that revealed there are more like 10 to the power 500 vacuums in string theory, that to me was the tipping point.