Roger Penrose - Why Did Our Universe Begin?

Roger, the Big Bang has now entered common knowledge as the way the

universe

began and everyone always asked how the Big Bang began and what happened before that and philosophers, theologians, physicists are now starting to speculate about it. . I really come to you because you have some very unique ass, uh, ideas about the big bang, well, there's something almost paradoxical about this microwave background, it tells us that there was something like the big bang there, but it also tells us why the observations of the Microwave background allow you to plot the frequency. You can pop the intensity against each frequency and you find this wonderful curve, it's the blackbody spectrum of the Planck curve and it matches that with extraordinary precision, much better than you could produce in the laboratory and this tells us that the early

universe

must have been in what is called thermal equilibrium now thermal equilibrium by definition is the maximum random state it is the state that the second law tells us we are going to get in the future if you want, but there it is in the past, then why?

It's that very special state that has to have been there at the

begin

ning, otherwise we don't have a second law. The second law of thermodynamics tells us that things become more and more random and that tells us that as we go back in time, things become less and less. less random, so it must be very, very special in the initial stage, but what we find is that the matter that we are seeing in this radiation is radiation that is light and that has been in equilibrium with matter, so that is what you're looking at and that's in this maximum random state, maximum entropy state, we say and something special about that was in gravity, what you're not looking at is gravity and the thing is that the universe was very, very uniform. in the early days and we thought about uniforms.

Okay, it's consistent with being random if you want, but that's not true when it's a main ingredient because it tends to group things together. The sun is out there, for example, because it is pooled from a previously uniform distribution of gas and that sun is heated. the sky in the background is cold the sun is hot and it's the difference between the hot sun and the whole sky that we live in and that's where all life comes from so uh, that's the key now so the universe was very special but It was very special just in gravity, somehow gravity was not thermalized with everything else and that is something that needs to be explained, it is the biggest enigma about the big bang now I don't see most of these theories trying to answer.

That question, certainly, the inflationary model doesn't, it just in a sense makes things worse and the argument is that it softens the universe and things like that, but it doesn't do that unless you're already special or even more special. in the early stages, so if you follow the argument you will see that it doesn't really explain this initial specialty and it can't because it's all consistent with the second law of thermodynamics, which says that things become more and more random, so with what clarity? I have become more and more special in the early stages, there has to be something more now for a long time.

If someone had asked me what happened before the Big Bang, I would have given the conventional answer: the Big Bang was this singular state. when all our equations go crazy and time and space you know they don't make any sense, even the question above doesn't mean anything you see, so that's the conventional answer, you say you can't talk about it, they're just questions without sense, there is no before there is no before now I have changed my mind I am not sure it is fair that I have changed my mind but you have another idea that I am following and I think it has a reasonable chance of being correct and this depends on how you characterize the initial state of the universe so what I'm saying is that gravity was special everything else seems to have been as random as it could be now can you characterize that in some geometric way?

Well, a colleague of mine, uh, Paul Todd, who? The mathematics institute here at Oxford has had a particular way of characterizing this. I have been concerned about this for a long time and have formulated something I call the vile curvature hypothesis. Let's not worry about what that means, but about something about the particular. type of space-time curvature that could have been present in the early universe. Now my colleague Paul has a way to put it in a nice geometric way, namely that you could extend the universe to before the big bang. Now this is just a mathematical statement you're not saying you believe in any physics here just saying this mathematical statement you could extend it sooner as long as you're somehow allowed to stretch the universe so I think what's the best way to explain this I think that exists are some nice images that escher has of a whole universe of angels and demons and they are all inside this circular limit and at the edge you see that it is infinity and the entire universe is crushed on this disk now if you forget the size of those angels and demons and you only care about the shapes, then you can, no matter how big they are, the little ones on the edge have the same kind of shape as the ones in the middle, but if you are prepared to stretch out and squash it in an even way , it's okay that you can stretch that limit to infinity or you can squash it back down to this finite limit.

Now there is a universe and the universe in this image stops at the edge which is infinity, but you could imagine extending it to the other side. and preserving this type of geometry is called conformal geometry, which is a mathematical term that means okay, you know about the shapes, the small shapes, but you don't know about the sizes so small and large, the count is the same, but different angles count as different or different small. The shapes are a little bit different, so if you don't mind stretching or squishing, then you could exit this universe somewhere else, so I want you to imagine the same thing here that you have the Big Bang, which somehow stretches out. be a surface like it's a one time surface but you could go before it now this math trick is I'm not saying this is real I'm just thinking it's a math trick this math trick if you express the condition in your universe like this way you say it could extend until before that date that is one way to characterize the initial state of the universe the universe seems to be like this it seems that the gravitational degrees of freedom are eliminated, which is what this image is to express that it is difficult to say This is not getting too technical, but I hope this kind of idea is understood well, now that's one side of the picture and, if you like, the physical justification for this is that in the early universe the temperature was so high, the energies of the particles were so high that it didn't matter at all what their masses were.

See, mass is what you use if you want to build a clock. There is a fundamental one, the two fundamental equations in physics that I am. referring here, one is the famous Planck's law which says that energy equals e equals h nu, so energy is proportional to frequency. The other one is the famous and even more famous Einstein equation which is equal to m c squared, which tells you that energy is proportional to mass, so if we put those two together, it says that mass and frequency are basically the same. same, which means that there is a clock, which is the frequency, it is a measure of mass.

Now, if you don't have mass or if mass becomes irrelevant, you can't build a clock, so in the early universe the universe didn't know how to keep time, you see, it just lost track of how fast things were going, and if you take that seriously, you can imagine going sooner than now, it's a hard idea to understand, but that's mathematical, it makes mathematical sense, but it's hard to think that this is real physics, but okay, that's one side, Now the other side is to think about a very remote future, what do we expect? the universe is expanding without limits, it is accelerating and it is expensive, which is important for this whole picture, otherwise it would not work and this is a mysterious thing that worries people, they call it dark energy, maybe it is just the Einstein's cosmological constant, which is the way I would see it, but we don't know yet why it should be there if you want it, but in this image you need it, so I mean what is the remote future in this image.

Well, the universe. it expands, it expands exponentially, um and okay, there are black holes out there that have a lot of mass according to Stephen Hawking, these things in the very remote future the universe will cool down to a temperature lower than that of any black hole, even the most big. that have a very low temperature, even the big ones that have a very low temperature and will evaporate, get smaller and smaller and eventually explode with a bang, that's the choice, now I'm accepting that I think it's probably true, although there are some conjectural aspects in this, um and eventually all the matter in the universe will disappear, apart from the very scattered radiation, that's right, there are certain assumptions that go into this, but let's accept that there is nothing left but very scattered radiation, how do you talk about that? the very distant future, in fact, the image I'm trying to describe is kind of a result of my worrying about how boring the universe is, you see, it's going to get pretty boring, see, and I can't think of anything more boring than waiting. around for a black hole to finally disappear, you see, it sounds incredibly boring to me, but then I thought: well, who's there to be bored, not us?, the only things around will be these photons and stuff, and it's pretty hard to get bored a photon.

The photon doesn't experience any passage of time, so eternity, eternity is no big deal to a photon, it just screams, there you see it, and this is kind of a mathematical trick, another mathematical trick that I've certainly been involved in. for a long time. time, how do we talk about infinity in relativity in Einstein's theory, united states, general relativity, how do we talk about infinity? Well, you would use the same conformal trick, but now, instead of stretching, which is what I did for the big bang before crushing it, so I'm saying that in the remote future there will be nothing left that has mass, if that's the case , somehow the universe doesn't know how to keep time in remote view, it doesn't know how big it is, see? so the universe forgets how big this sense is and it could also be a small new universe, so the picture is fine, it's crazy, I followed everything until the last step where we have a complete expansion, a complete scattering, no photon radiations of dough. and that and the similarity is that there is no clock because you have no mass, that is correct and that is the same characteristic of the early universe when it was very small, but you have this very large universe that has no clock and now how do you get to that small universe that does not have a clock and the point is that it does not know the difference between big and small because it does not have a group, it does not have a clock, you see, you have the speed of light that allows you to transform from time. into space, but since it has no clocks, it also has no way of measuring distance, so spatial distance becomes irrelevant, temporal distance becomes irrelevant or time, so the universe forgets how big it is, forgets how big it is. great that it is and therefore loses track of it. and it is and becomes the next big bang now of course this must be completed with some honest mathematics and it must also be related to observation and the thing is you might think it's useless how would you ever know if there was a universe above, you see, but it's not that desperate and the first point is that I mentioned inflation.

The inflationary universe is that in the early stages there was this exponential expansion, but in this model the exponential expansion took place in the very remote future and that is quite consistent with our current view, the universe will expand exponentially and therefore you will get the same characteristics that you get with inflation but without inflation, so the idea is that, that exponentially expanding universe, you forget how big it is and it is and it becomes the big bang of the next scale now, how do you observe ? I mean, like I say, can you, it's observation, in addition to agreeing with the well, there are these things called scale invariants, which is one of the observational supports for inflation, so I'm saying.

I think that will carry over to this particular model now. The other thing is that there will actually be some small disturbances that occur, I would say that in the distant future, there will be many black holes before they finally appear. They disappear with bursts, they will be there for a long time and in the process, okay, in the middle of galaxies, our own galaxy, for example, has a black hole in the middle of something like three million times the mass of the sun, okay, that's pretty common in a galaxy in galaxies and clusters, you know that they run into each other, their black holes twist around each other and swallow each other in that process, they will emit gravitational waves, ripples in space-time , this kind of gravitational analogue of light, these waves will leave their mark in infinity, it's a bit difficult to explain that too, butAlthough they spread out infinitely, still because you have to smash them again to see what is happening, they are still there and will have an influence on the next stage of the universe and will, in principle, require delicate analysis.

You should be able to see that if I can use an analogy here, think of a pond and it rains on the pond every day. When a drop of water hits the pond a wave arises which is like these black holes collide and the wave disappears due to the disturbance and gravitational waves so you get these waves after some time the rain stops and there it is when all the black holes have disappeared. You see that after a while the rain stops but you still see the messy waves, it looks like a mess, but in principle you should be able to figure out that these waves are made up of individual places where the raindrops have fallen.

In the same way that I would say that you can observe this background radiation and now there is a lot of information from these new satellites and so on that have been looking at the very detailed structure of this background radiation, we should be able to analyze it and see if it is made up of these individual events that are distributed in this way now that is something for the future could completely destroy the whole idea on the other hand it could turn out that this is an obstacle I find it absolutely fascinating that it is even possible to consider what happened before the Big Bang.

Well, it's not that scandalous. Okay, it's scandalous, but not that scandalous. It is conceivable that this works. Yes, and it explains the very special nature of the Big Bang. Things don't work without that, so I think it's a positive feature that other theories don't seem to give us.