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Fabric of the Cosmos (part 3)

May 13, 2012     Time: 00:21:27


Dr. Craig concludes his discussion of the PBS series by examining aspects of the "multi-verse". And, what in the world is a "Boltzmann Brain?"

Transcript Fabric of the Cosmos Part 3


Kevin Harris: Thanks for joining us on Reasonable Faith with Dr. William Lane Craig. Dr. Craig, we've been looking at The Fabric of the Cosmos with Brian Greene, produced by Nova for PBS, really well-done, and, yet, we've also tried to uncover some of the hidden agendas and assumptions of this series. When we look today at this particular segment of the series – universe or multiverse? – what are some of the overriding views that are held that flavor and color this one?

Dr. Craig: Well, what this program is really about, Kevin, is the problem of the fine-tuning of the universe for intelligent, interactive, embodied agents, like ourselves. I don't believe the word fine-tuning is actually mentioned in the program, but instead he talks about the dark energy that pervades the cosmos and which has a very precise life-permitting value, and how can you explain this apart from some sort of cosmic intelligence which has designed the universe to be life-permitting? So that would be the cash value, theologically, for the question that he's asking – universe or multiverse? – because those are, in a sense, the options for explaining the fine-tuning. He might have entitled this: universe, multiverse, or God? But God doesn't get into the pool of explanatory options in this program.

Kevin Harris: Well, this is the newest kid on the block – multiverse. And I think that, not only does this series embrace it, but Brian Greene certainly does – the multiverse.

Dr. Craig: Yes, this has become the center of the debate over fine-tuning today. The principle alternative to a cosmic designer is some sort of multiverse or world ensemble or many worlds hypothesis in order to give you the probabilistic resources for our highly improbable fine-tuned universe to exist. If you have many roulette wheels rolling at once then you'll increase the probability that one will come up in a particular number than if there's just one wheel that's turning. And so the multiverse is an attempt to get as many roulette wheels turning as possible in order to get this highly, highly, improbable result that we observe.

Kevin Harris: I see that move, and that would be fine and dandy if it were true.

Dr. Craig: Yes, that's right. It would work if it were true.

Kevin Harris: Stephen Weinberg says, “if the multiverse is indeed infinite then one is going to have to confront a lot of possibilities that are very hard to imagine.” So he's captured our imagination there, an infinite multiverse?

Dr. Craig: That the multiverse is infinite is not something that's required by the multiverse hypothesis. That's a sort of ad hoc adjustment that needs to be made by hand. You've got to get an infinite number of these universes in order to guarantee that our universe will come up by chance somewhere in the multiverse. If there's only a finite number of universes in the multiverse then it's not guaranteed that ours would appear anywhere by chance. So many times theorists will say, well, there's an infinite number of multiverses. Now that is a breathtaking metaphysical hypothesis, Kevin, that there's an infinite number of multiverses.

Now, how they get that is very interesting, too, because it involves, again, a commitment to a certain metaphysical view of time. What they do is they interpret universes which are future relative to us to be actually real and existent. So that if these universes keep on coming into existence into the future then all of those can be counted as equally real and existent. And that's how you get your infinite number of universes – by counting these ones that are in the future as though they actually exist. Well, the problem is that presupposes this view of time according to which there is no objective distinction between past, present, and future. If you say that temporal becoming is real then universes that will form in the future are pure possibilities. [1] They're mere potentialities. They in no sense exist. Therefore you would not have your infinite number of roulette wheels spinning right now, and therefore there would be no guarantee that we would exist right now.

The point that I'm making here, Kevin, is that the postulate has to be a lot more than just saying there are other worlds, there are other universes. This has got to be adjusted so, number one, they've got to be infinite in number if you're going to guarantee that our universe will appear some place, you've got to postulate a certain number of these; but then also you need to postulate that they're randomly ordered in their constants and quantities, because if they're just all the same, or, say, if there are only three kinds of universes in the multiverse then there's, again, no guarantee that ours would appear anywhere by chance. So the hypothesis is a lot more finessed than just saying, 'maybe there are other worlds.' You're postulating the existence of this infinite number of randomly ordered unseen universes out there just in order to explain away the fine-tuning of our universe that we observe.

Kevin Harris: Andreas Albrecht of the University of California says in this series, “I'm very uncomfortable with the multiverse. To become solid science it's got a lot of growing up to do.”

Dr. Craig: Yeah, it looks very metaphysical at this point. It's a metaphysical hypothesis because there isn't any physical evidence that there are other universes. Now, I think it would be good at this point to say, Kevin, that the theist doesn't have any objection in principle to there being a multiverse and there being other universes. We would say that even that multiverse was brought into being by God. In fact, I think, Kevin, and this will emerge in the course of this podcast, really, the best hope for the existence of a multiverse is theism. I don't see much hope for thinking that there is a multiverse if naturalism is true. I think the best hope of saying that there is a multiverse is that God has created it and brought into being many worlds. So there's nothing inherently anti-theistic about this. We have no ax to grind in this discussion. We can be open to follow the evidence where it leads.

Kevin Harris: And we would also be in line with Genesis 1:1, in the beginning God created the heavens and the earth, in that the multiverse would also require a beginning, according to the models.

Dr. Craig: Yes, we've talked about that in other podcasts, that the theorem that was developed by Alexander Vilenkin and Alan Guth and Arvind Borde applies to this multiverse, not just to our universe. And the multiverse itself would have to have a finite past and therefore a past spacetime boundary. It cannot be eternal in the past; it too came into existence. So Vilenkin has recently said that all the evidence says that the universe has a beginning, and by that he means all that exists spatial-temporally.

Kevin Harris: You can always count on Star Trek to have examined some of this on the TV series. But I seem to recall one episode in which there was a universe in which an evil Spock existed, and he had a goatee, you know, kind of sinister looking, and he was mean, and he encountered the good Spock without the goatee. And really that's a simplified version of what this speculation is on multiverses, that somewhere there is a Bill Craig who was a dentist as opposed to a philosopher in a universe somewhere.

Dr. Craig: Yes, the idea there, Kevin, is that if you have a finite number of possibilities and you have an infinite number of universes then every possibility will be actualized some place. I don't think that that at all follows because for someone who believes in freedom of the will, events don't happen just by random chance. Events happen because people choose things for good reasons. And so there may be no world, no universe, in which, for example, Adolf Hitler delivers the Nuremberg Address standing on his head. There's no reason he would do such a thing. So even though that's physically possible, there's no reason to think that even in an infinite multiverse that that event takes place somewhere. Why? Because events don't just happen according to random chance if there are libertarian agents who make significant choices that's going to mess up the calculations. [2]

Kevin Harris: Well, Bill, this program seems to hint at the multiverse being eternal, and we've said that Vilenkin has shown that that's not right. It then goes to dark energy. What do we mean by dark energy?

Dr. Craig: The dark energy is postulated to explain the recently observed acceleration of the universe. Rather then slowing down the expansion of the universe actually seems to be speeding up. There seems to be a repulsive force or dark energy that is blowing the universe apart at ever more rapid speed. And this dark energy is finely-tuned to our existence to the measure of about one part out of ten to the hundred and twentieth power, an inconceivable precision. If it were slightly greater then everything would blow apart so quickly that galaxies and stars and planets would never even have formed. So the dark energy is fine-tuned for the universe to permit intelligent, interactive, embodied agents to a degree that is literally incomprehensible. This is just on example of many examples of fine-tuning of the universe, and this program appeals to dark energy as one reason to adopt a multiverse hypothesis. Now, that's really interesting, Kevin, because they don't call it fine-tuning, but that's really what it is. This is just an instance or an illustration of fine-tuning. What they're really saying is that to explain the fine-tuning of the universe for life we need to appeal to this multiverse hypothesis in order to multiply the probabilistic resources so that somewhere in this world ensemble of universes one with just this value of the dark energy would turn up by chance alone.

Kevin Harris: Yeah, and Brian Greene says it. He says in this series:

The value of the dark energy wouldn't allow the formation of galaxies, stars, and planets. Universes with much less dark energy than ours would just collapse in on themselves. And universes with much more dark energy than ours would expand so fast that matter would never have a chance to coalesce into clumps and form stars and galaxies.

So that is the fine-tuning, isn't it? We're in a Goldilocks region of dark energy.

Dr. Craig: Yes.

Kevin Harris: Now, was dark energy predicted? Because I guess you would think that the expansion of the universe would slow down after the Big Bang.

Dr. Craig: Yes, for years scientists were trying to measure what's called the deceleration parameter of the universe. They thought that they could show that as the expansion moves out that it would slow down, and instead it's speeding up.

Kevin Harris: And so we have to say, okay, now why, against what we would think, is it speeding up? You'd have to postulate something like dark energy.

Dr. Craig: Yes, that's right. And this dark energy is then fine-tuned for life, for life to exist.

Kevin Harris: Is dark energy a tool or is there really experiential evidence that the dark energy is there and is pushing galaxies away?

Dr. Craig: Well, it's a name. Dark energy, in the sense that you can't observe it visually. But it's a name, but there is a real repulsive force that is blowing the universe apart at ever-accelerating speed.

Kevin Harris: By the way, that seems to indicate that we're not going to experience a big crunch.

Dr. Craig: That's what it seems to indicate. It seems to indicate that as time goes on the universe will just expand forever and will never re-collapse.

Kevin Harris: I don't want to be crunched, so I'm glad. [laughter] Of course, I know how it turns out. So the dark energy is used as an evidence that there might be a multiverse. What else do they go to here?

Dr. Craig: Well, he not only appeals to the fine-tuning of the universe but he also appeals to inflationary models of the universe and to string theory. Now both of these are extremely speculative and underdeveloped areas of science but that doesn't stop him from appealing to these to generate the multiverse. Here's the problem. In string theory it doesn't predict that the universe should have the precise values of these various constants that we observe, like the gravitational constant or the electromagnetic force. In fact it is consistent with the laws of physics and with string theory that there would be around ten to the five-hundredth power different possibilities for universes governed by our laws of nature. [3] So string theory doesn't do anything to make the observed values of these constants necessary. That would seem to be friendly to the fine-tuning argument. It would show that fine-tuning is not due to physical necessity. String theory does not predict that these constants will have the values they have by physical necessity. It permits a wide range of values, ten to the five-hundredth power different sorts of universes. And this has come to be called the cosmic landscape, which has become a sort of phenom in it's own right. Now, it's important to understand, this cosmic landscape is just a landscape of possibilities, Kevin. These aren’t real worlds or real universes out there, it's just possibilities. But the attempt, then, is to marry string theory with inflationary theory, which says that our universe may be a bubble within a wider universe which is blowing up, which is expanding, a sort of mother universe. And in this mother universe that is blowing up different bubbles will form here and there and these represent different universes. So if you marry string theory with inflationary theory you can say that inflation gives you the many bubbles – right? – and the string theory gives you the random variation of the universes among the ten to the five-hundredth possibilities. And so this is how you'll get your multiverse, based upon string theory and inflation. And the problem, of course, is that this is all conjectural. Nobody has any idea whether or not this is true. There's no evidence that there is such a world ensemble out there. But this is the attempt to generate the multiverse that could then give you the probabilistic resources to explain the observed fine-tuning.

Kevin Harris: Bill, let's conclude today with some evidence against this whole multiverse notion.

Dr. Craig: Yes, I think that is important to rehearse because a number of physicists, such as Roger Penrose at Oxford University, have been highly critical of these attempts to explain fine-tuning by appealing to a multiverse hypothesis. And one of the most critical problems is the problem that's been called the invasion of the Boltzmann brains. Boltzmann brains are brains named after the famous German physicist Ludwig Boltzmann which just fluctuate into existence out of the quantum vacuum. They represent random fluctuations of the vacuum. And these fluctuation-formed brains, then, are observers. This would be an observable universe. A Boltzmann brain could have an observation of the universe in which it exists for a fleeting amount of time. What that means, therefore, Kevin, is that in order for universes to be observable they don't have to be fine-tuned for agents like ourselves. Indeed the most probable sort of observer that would form by chance in a multiverse scenario would be these Boltzmann brains, so that they would dominate the proportion of observable universes. If there is a multiverse then the most probable sort of observable universe by far would be a universe that has a single Boltzmann brain that fluctuates into existence.

What that means, therefore, Kevin, is that the fine-tuning of the universe that we observe for intelligent, embodied, interactive agents cannot be explained away by just saying, “Well, in a multiverse it would have to happen somewhere.” Because given a multiverse hypothesis, it is vastly more probable that what would exist would be a Boltzmann brain observable universe, and not a universe like ours. So the fine-tuning cannot be explained away as simply a self-selection effect of observable universes. There are observable universes that are not fine-tuned like ours, indeed they are vastly, vastly more probable, and therefore should exist if there is a multiverse.

So what that means, I think, is that the evidence indicates that in all probability there is no multiverse out there because we don't have a Boltzmann brain universe, [4] we've got a different kind of observable universe, and therefore that disconfirms very strongly the multiverse hypothesis.

Kevin Harris: So when you say observable universe, the observable universes that exist, are you talking about possible universes?

Dr. Craig: Yes, universes that would have observers in them.

Kevin Harris: There you go; there you go; okay.

Dr. Craig: Think of the multiverse. Most of the multiverse is dead – right? Most of the multiverse has no observes. But by chance alone there will appear observers in some of these universes. And the point I'm making here, and that others have made, is that the incomprehensible majority of those observable universes will be Boltzmann brain worlds, and therefore you can’t explain away the fine-tuning by just saying, “Well, if the universe weren't fine-tuned then it wouldn't be observable. We wouldn’t be here to observe it.” That's not the case. You would have Boltzmann brain universes. So the fact that we don't have a Boltzmann brain universe – unless you think that you're a Boltzmann brain and everything else is an illusion of your consciousness, which would really be scientifically outrageous – you should think that in fact the multiverse does not in all probability exist. [5]