Jim Fleming: Are alternative universes purely the stuff of make believe or could they actually exist? There was a time when universe meant all there is, the sum total of everything in creation. But recent discoveries in physics and cosmology have lead a number of scientists to conclude that our universe may be just one among many. One of those scientists is physicist Brian Greene. He is a string theorist at Columbia University, author of numerous award winning books for the general public and even an opera with music composed by Philip Glass. His new book is called The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos. Steve Paulson finds this new science a little puzzling.
Steve Paulson: I have to say it's hard to know how seriously to take the idea of parallel universes. So if you had to bet on it, do you think there are other universes out there?
Brian Greene: Well, rather than betting I like to recognize that we should be skeptical but the fact that our mathematical investigations in an attempt to understand things that we can see test, data and observations, many of them bump into one or another version of our universe being one of many universes. So that doesn't mean it's right. We shouldn't believe it until it has experimental support but it's an idea that naturally comes to us. We don't have to go and seek it out.
Paulson: So what's wrong with the idea that there's just one universe? The one that started with the big bang nearly 14 billion years ago?
Greene: Nothing wrong with that idea at all but when we study the big bang theory in detail we are led to this other possibility of many universes in a very simple way. It just could be one flavor of multiverse that emerges from our mathematical studies. The big bang tells us how the universe evolved from a split second after whatever brought it into existence but the big bang theory, many people don't realize is completely silent on what happened at time zero itself, the very beginning. And when we try to fill in that gap as we have been for a number of decades now we find that there is a good chance that there wasn't a single big bang event, that there were possibly many big bang events at various and far flung places throughout a larger cosmos giving rise to universe upon universe upon universe, our universe being the aftermath of one of those bangs. There are other universes which are the aftermaths of the other bangs.
Paulson: So what's the best evidence that there are these multiple universes?
Greene: Well, it depends on which of the various multiverse theories one is talking about. The easiest to test is one that comes out of string theory, the brain multiverse. It envisions that our universe is sort of like one slice of bread in a giant cosmic loaf which would have other slices in principle, other universes parallel to ours. The reason I bring that one up is because the large [? 03:05] this big accelerator in Geneva Switzerland, in the next few years there's at least a chance, a long shot possibility, but at least a chance that this multiverse could be tested by experiments taking place at that machine.
Paulson: Okay, so can you describe this a little bit more? If there's this slice of the universe, paint me a picture of what this would look like.
Greene: Well, everything that we've long thought to be the universe, I mean look around on a dark night and you see the stars, the galaxies, everything that's out there, we imagine is taking place on this slice of bread, on this slab if you will with other slabs that would be out there. The way the large [? 03:47] can potentially test this is the collider slams protons against protons at very high speed and the math shows that there's a chance that debris from those collisions could be ejected off of our slice, off of our membrane, into the wider cosmos. If that happens, the debris would carry away energy with it which would mean that our detectors here on our slice would register less energy after the collision than before missing energy and if we find those missing energy signals this could be evidence that there are these other brains potentially out there, other universes parallel to ours.
Paulson: You said that there are actually a number of different versions of the multiverse or as some people would describe it parallel universes. What are some other scenarios? One of the easiest to imagine is that space might go on forever. Space might be infinitely large and there's a pretty breathtaking conclusion that again follows mathematically which is this. You find from quantum physics that there are only a finite number of distinct configurations of matter in any given region of space that are possible. The configurations of matter from place to place necessarily must repeat. For instance, if you had, and a metaphor I like is we have a deck of cards - you shuffle the deck, you get different orderings, but if you shuffle that deck enough the times, the orderings necessarily will repeat because there are only a finite number of different orderings, shuffle the deck enough times, the orderings have to repeat. Similarly the configurations of matter have to repeat somewhere out there in the cosmos which means for instance the configuration of matter that describes you and me now having this conversation, it must be repeating somewhere out there in an infinite cosmos. We're having that conversation, the one that we're having right now, some place out there in the universe.
Paulson: Hm. Now is this the idea that Hugh Everett put forward in the 1950s that there are these infinite number of universes? In other words, there might be many different versions of me in these parallel universes?
Greene: It certainly sounds like it but it's actually distinct. Hugh Everett was thinking about a very deep problem in quantum physics. Quantum physics broke the old mold of classical physics by saying that whereas Issac Newton would have said to you tell me how things are now and I will predict with absolute certainty how they will be in five minutes or an hour or ten days from now using my mathematics. Quantum physics came along and said actually Issac Newton that's only an approximation. The best you can do according to quantum physics is the probability the universe will be one way or another based upon how it is now. Now the weird thing is if quantum physics say predicts that an electron has a 50% chance of being over here and a 50% chance of being over there, when we do an experiment that measures the position of the electron, we always find it with absolute certainty at one or another of those locations. We never find it sort of half there and half in the other place. Now, the puzzle is how do we go from the mathematical quantum physics that speaks to a fuzzy, hazy, probabilistic reality, how do we go from that to the definite reality that you observe when you do a measurement? Nobody has been able to fill in that mathematical detail. Hugh Everett suggested the following. He said look, if the math is saying that there are two possible outcomes and say they're all on equal footing then both of them happen. There are two universes, one in which the electron is over here, one in which the electron is over there and there's a copy of you in each universe thinking incorrectly that the reality you are measuring is the unique reality, the unique position of that particle but in reality there are two such universes and two such yous having those thoughts, two parallel universes coming out of quantum physics.
Paulson: Let me step back for a moment and get at the larger question you're raising. This huge hunger among theoretical physicists for a final theory, one theory to rule them all to reconcile the quantum world with the laws of relativity. Of course, as you said, Einstein obsessed about this. Many others have as well. I guess I'm wondering if there really is anything wrong with the idea that we may live in a universe where there is no final all encompassing theory that perhaps different aspects of reality simply cannot be reconciled by science.
Greene: It's conceivable. I find it very hard to believe. I mean for instance with quantum mechanics in general I think the natural response of some people aligns with what you're saying. They would say look, generaltivity is for stars and galaxies, only use if for stars and galaxies. Quantum physics, you say it's good for molecules and atoms, only use it for molecules and atoms and just be happy. Have two theories, each that works in it's own domain. The problem with that kind of perspective is that there are some extreme realms in the universe in which the dividing line between big and small is not so clear. For instance, at a black hole, typically what happens in a black hole, an entire star collapses to a very small size. Now a star is big and massive so you need a theory of gravity, general relativity. When that star collapses to a very small size, you need a theory of small things, quantum physics. You can't use one or the other of these theories, you need to use both. The thing is when they come together in the traditional formulation the math completely breaks down, we are left completely uncertain about what happens at the center of a black hole. The attempt to unify, to reconcile these theories, is the attempt to understand the universe in all realms however extreme, however esoteric. And that goal can't be achieved by imagining two separate theories that don't talk to each other.
Paulson: I know you have a passion for the arts as well as for science and I guess I'm wondering whether the possibility of living in a reality with multiple universes creates some imaginative space for you. I mean I don't know. Does a reality look more exciting, more creative, more full of possibilities?
Greene: Well, I would say all of the above really. I mean what excites me about this kind of science, it really steps beyond the everyday in a fairly dramatic profound way. I mean these ideas of multiple universes is highly, highly speculative. It could be completely wrong so in some sense this could ultimately be a waste of time pursuing these mathematical leads. On the other hand if this idea is right what a fantastic upheaval in our understanding of reality. This would be one of the greatest breaks in how we consider the universe to be constructed if we are one of many universes and that possibility I find so exciting that I'm willing to take the risk and work on something that is on the edge that could be wrong, could be spectacularly wrong. But at the same time it could be spectacularly right.
Fleming: Brian Greene talking with Steve Paulson. Greene is a theoretical physicists and string theorist at Columbia University. His books for the general public include The Elegant Universe, The Fabric of the Cosmos, and most recently, The Hidden Reality. The music we're listening to is from an opera Greene wrote with composer Phillip Glass called Icarus at the Edge of Time.