Big Bang Was Not the Beginning | Roger Penrose

But then your model isn't. Is it a Big Bang model with an initial emergence out of nothing, and then eventually a collapse back to that? No. Okay. So how do you conceptualize that? Well, first of all, it is a Big Bang model. In other words, there is a Big Bang, but the Big Bang was not the beginning. The model… The reason people have trouble with this model, I think, is… You're probably going to have trouble with it, and you're not unique in this. You see, people tend to think that if you have a model in which it keeps on going in some sense, and your Big Bang is not the beginning, that you've got to collapse back. So it expands, and then it comes back, and then you're back with… But this model… It seems simpler that way. Yes. But this model is not like that. And that's where you've got to get your mind around. And people have trouble, and I agree with it. It is a crazy idea, and I admit it's a crazy idea. The trouble is, it seems quite likely it's true from certain observational things, but it's crazy, too. It can be crazy and true at the same time. Yeah. That's like a definition of light. Yes. But you see, in this model, the universe expands, and it expands, and this exponential expansion we seem to see, the stars seem to be starting to go away from us, these very distant stars that people look at, with an increasing speed, and there seems to be this exponential expansion. And I agree with that. That's what's driven the dark energy hypothesis, I presume. That's what they call it. Well, I claim it is absolutely nothing inconsistent with Einstein's 1917, was it, modification of his… He regards his biggest mistake, which is probably actually right, that's to say the introduction of a cosmological constant. Right, right. Yeah. He introduced it for the wrong reason, that's true. But he was right to introduce it, even though he regarded it as his biggest mistake. Right. Well, he needed it to make things work, but he didn't have any real practical reason for assuming that it was true, apart from… He wanted a static universe. He didn't like the expansion. No, he didn't. No, this was at a time before… I think Hubble had already seen the expansion, but it hadn't quite got through to Einstein how convincing these results were. So he wanted a universe which was just static and stayed there forever. Right, right. And then he needed the cosmological constant to do that. That's correct. He would need that. However, he was wrong. When he got convinced, oh no, the universe is expanding, sorry, he said, that was a mistake, my biggest blunder, he said. The trouble is, his biggest blunder turned out to be true. Apparently. I mean, this is an argument. People don't necessarily think it was. People might not think it's the cosmological constant. I think it was. I think it's right. I have reasons, you know, internal reasons for that. But let's say that this is right, it's a cosmological constant, the universe expands and expands, exponential expansion. Now you might ask, who's in this universe, essentially? Not us. The black holes will all have evaporated away by Hawking evaporation. There's swallowed galactic clusters. What's left in the universe? Pretty well, photons. Now I'm giving you the simplified version of the theory because there's some questions about it still. But let's say it's dominated by photons, which is pretty well true, but let's take that. Now the trouble with photons is that they don't feel the passage of time. More importantly, the equations governing light are the wonderful equations due to James Clark Maxwell, the Maxwell equations. The Maxwell equations have a very interesting property. They can't tell big from small. They're what's called conformally invariant. If you have a system in which you've got some electromagnetic field and you could stretch this system to bigger or smaller, it doesn't notice the difference. The equations work just as well. You can squash them here and stretch them here. Is that in part because space really doesn't mean anything to a photon? In a sense. Well, it's the scale. You see, it's what we call, there's a term which I'll use here, it's called conformal. Conformal means big and small. I very much like, we talked about Escher a minute ago, there are these Escher pictures called circle limits, where he describes what's called hyperbolic geometry, but don't worry about that. The most famous one is these angels and devils. You see, there's a circular boundary, and they look as though they get smaller and smaller and smaller as they get to the edge. Now as far as those angels and devils are concerned, the little ones are just the same as the big ones. They don't know that they're smaller towards the edge, and that to them is an infinite universe. To us, we can see, no, there's this infinity which is just sitting there. These angels and devils, if they don't know big from small—I'm not sure I have a bit of trouble using this to explain things because the angels and devils do have a size in the picture—but you see, if they were made of massless material, that wouldn't know big from small. So if they were made of just electromagnetism, then big and small are equivalent, and so you wouldn't know when you got to the edge of this universe. So that infinity is just like anywhere else. That's the difficult concept in this thing, that the photons reach infinity without realizing anything funny has happened, if you put it like that. Infinity in this conformal picture is just like anywhere else. It's only mass that knows the difference. If you want to build a clock, you need mass. This comes from the two most famous equations of twentieth-century physics, and the two most famous equations, one of them is Einstein's E equals mc squared, of course, which tells us that energy and mass are equivalent, and the earlier one was Max Planck's E equals h nu, or E equals hf, whatever you call the frequency, which tells you that energy and frequency are equivalent. Put the two together, that tells you mass and frequency are equivalent. That means that if you have a mass, it is a clock. It has a frequency simply determined by its mass, and this fact is really the basis of modern clocks, which are extraordinarily precise. They don't directly give this, because the frequency is much too high, you have to scale it down, but roughly it's the same idea. A mass is a clock, but the other side of that coin is if you don't have any mass, you don't have any clocks. You don't have any time scale, you don't have any distance measure. If the world is inhabited only by massless things, say photons, then it doesn't know big from small, it doesn't know hot from cold. The idea is, and this is where you have to take a deep breath, the idea is that the remote future is indistinguishable from a Big Bang, so long as there is no mass around. The remote future, the reason you have no mass around is basically, well, listen, there's a complicated part of the argument, but let's say it's because there's mainly photons. That's good enough. What about the other way? What about the Big Bang? Well, there's lots of mass there, surely, but the thing is that at the Big Bang, things get so hot, things are moving around so fast, if you like, that the energy, or the mass energy, mass-energy, the concept of mass, according to Einstein, is almost entirely in their motion, and that the mass becomes more and more irrelevant the closer you get to the Big Bang. So again, you have a situation where mass is effectively zero. So are you, is it your claim, belief, theory, that when things ground out in a universe that only consists of electromagnetic radiation, that that is now a precondition for an event like the Big Bang? In a sense, yes. I'm saying that the physics which is going on at the very remote future is extraordinarily like the physics going on at the very beginning. I'm going to end there. And when I say beginning, I only mean the Big Bang, because it's not really the beginning. Yes.