Roger Penrose and Brian Cox on the Big Bang, the multiverse and physics' greatest lesson | Q&A

[00:00:00]Some advice for a future Nobel Prize winner.

[00:00:02]>> Oh, gosh.

[00:00:04]The trouble is when people ask me this sort of question, I say the most important thing that I find when I look back at my life and the great sort of good ideas I've had from time to time, the best thing to be is lucky.

[00:00:18]I couldn't share an office with anybody, but it happened to be with Engelbart.

[00:00:22]>> [music] >> And it was two things I learned from him that I happened to put together, and they were really important in later life.

[00:00:35]>> Hello. Uh thank you very much for this talk. My name is Daniel Hermel. Um I'm just wondering uh in your theory um what happens at what kicks off this chain of eons, and what ends this chain of eons, or is that the wrong question?

[00:00:49]>> No, it's good to say call it chain of eons, it's fine.

[00:00:52]Well, you see, there needn't be anything.

[00:00:55]Maybe it keeps on going forever.

[00:00:58]I don't know. I have no answer to that question. But it's perfectly reasonable within this picture to say this chain is just eternal.

[00:01:06]There is no beginning, there will be no end.

[00:01:09]>> What what's the what's the um how do you dodge We talked about Stephen's singularity theorem based on your singularity theorem earlier. What how does how is that dodged? What why does there not have to be a singularity in our past?

[00:01:24]>> Well, you see, the singularities that particular one, you see, is only You have to distinguish the ones in black holes.

[00:01:33]Because the singularities in black holes basically uh irrelevant in the sense that they're in the black holes.

[00:01:42]The black holes evaporate away. Okay, there might be a little tiny singularity when the black hole goes pop at the end.

[00:01:51]But that's so tiny. I mean, it all gets a bit of a pop, it might not be good to be too close to that pop. But But it's not >> It's quite a big pop, isn't it?

[00:02:00]>> Yes.

[00:02:00]Um well, depends on >> [laughter] >> what kind of scale you're using. It's been a nasty one to go off in this room, that's true.

[00:02:07]>> Yeah.

[00:02:07]>> But um but it's a pop on the sort of cosmic scale. Yeah.

[00:02:12]But um it's not important from this point of view. There is a different It's a interesting question.

[00:02:20]And it's not even clear they happen. You see, that does depend on the on the uh Hawking evaporation, which I do believe in. I think it's correct. But you could take a negative view to Hawking evaporation and say that it doesn't really happen.

[00:02:34]There's no direct evidence for it.

[00:02:36]It's just the theoretical evidence. I think the theory is pretty good. I think it does. I agree with Hawking that there should be that radiation. But it doesn't come in until Well, look, think about the the temperature. You see, there's a Hawking temperature to a black hole, which is ridiculously cold.

[00:02:53]The bigger the black hole, the colder is this ridiculous Hawking temperature.

[00:02:59]Okay, we're talking about black holes which are much bigger than any we've ever observed. I mean, already now most of the material in the universe is in black holes.

[00:03:09]They're pretty big, but they're trivial but compared with these things start swallowing each other up and the whole galac- galactic clusters form these huge black holes.

[00:03:20]And they sit around and they sit around and they sit around.

[00:03:24]And that Hawking temperature is ridiculously cold, much colder than the temperature in the universe. And it sits there and it waits and it waits and it waits until the temperature of the universe gets colder and colder and colder until it's colder than that ridiculously cold temperature of the black hole. And then it starts to radiate away and radiate away for something like 10 to the hundred years.

[00:03:50]Think of one followed a hundred zeros that number of years.

[00:03:56]More than that, actually, before this effect kicks in.

[00:04:00]Pretty long time.

[00:04:02]>> [laughter] >> But that is the argument that after that length of time, the Hawking evaporation takes it to black holes where and they're gone after that time.

[00:04:11]It doesn't make much difference whether that's right or wrong in my picture.

[00:04:16]I mean, it's just true. I wrote a paper with some Hungarian uh Polish, I should say, Polish colleagues where we talk about what we call Hawking points.

[00:04:26]And these are these little points coming through from the previous eon.

[00:04:30]And they're the spots.

[00:04:32]We call them Hawking points because they probably are the Hawking radiation. So late, but they're little tiny points.

[00:04:39]And then by the time you see them, they spread out to about Well, I'm forgetting if it's 4° or 8° across in the sky. So, it's a little little spot in the sky. Not all that small, actually.

[00:04:51]It's bigger than the full moon.

[00:04:53]>> So, another observable prediction in the cosmic microwave background.

[00:04:56]>> Oh, yeah, but they've been seen.

[00:04:57]>> Undoubtable feature.

[00:04:57]>> We've seen them.

[00:04:59]With a 99.84% confidence level.

[00:05:03]Nobody believes us, of course.

[00:05:05]>> [laughter] >> No, well, in particle physics, that's not good enough, is it? 99% >> [laughter] >> But in cosmology, that's pretty good.

[00:05:14]>> All right. We have another question.

[00:05:16]There's one right at the front here.

[00:05:18]I'm going to do that thing where I make I guess one at the front, one at the back, one at the front, one at the back, and you have to do a lot of exercise.

[00:05:26]>> Um I was just wondering, um so what triggers the Big Bang when everything's photons just floating around and and gravitational waves? What actually triggers that?

[00:05:39]>> Well, the infinity, you see. That's right. I mean, it's a good question to ask, and people do ask that question.

[00:05:45]What is it that triggers the next eon Come on. Well, it's a good place to to trigger it because it's infinity. You see You see, I'm in I'm a bit biased here because a lot of what I used to do in cosmology and general relativity was applying a a nice little trick which was to talk about infinity from the conformal picture. You see, you can draw a nice picture of infinity and I used to draw these pictures. They're called tend to be called Penrose diagrams for some reason. But anyway, I draw these little pictures. Infinity, you can draw it. It's a nice place. It's a And it joins on to something else and it might be joining the future of somebody else's past infinity or something.

[00:06:26]But in these little pictures, it joins on to the Big Bang.

[00:06:29]And you can't say when it is. Well, yeah, it was infinity, but infinity isn't that far off really because you have to think of how do you you have a clock who's saying this is my clock say how long is infinity? Well, the clock it depends on mass because clocks depend on mass being there. If you didn't have any mass, you wouldn't have any clocks.

[00:06:50]So, if the mass sort of fades out you don't have any clocks.

[00:06:55]So, infinity isn't that far along.

[00:06:57]That's not so far off.

[00:06:58]I mean, it's a bit of a stupid thing to say, I agree. But But But it's it's the picture. You have to get used to it.

[00:07:06]And I have got used to it by playing around with these things such a long time that I don't think infinity is that far off, you see. Cuz you draw pictures and it's a good thing to talk about and I just as good a place as singularities really. Would another way of phrasing it be to say how does mass return? So, how do the clocks return? Yes, you do need the mass.

[00:07:27]The mass fades in a way. It has to come back. That's quite right.

[00:07:32]And that needs a good theory of mass and we don't have a good theory.

[00:07:37]You see there's not really a good theory.

[00:07:42]I think I used to have a slightly different argument for that than I do now.

[00:07:47]You see, I used to think that particle physics was important in this what I call the crossover from one eon to the next. And I wrote a book called Cycles of Time.

[00:08:01]And I was quite flattered because a lot of Chinese people wanted to buy Chinese translation of this book. I wouldn't going to say don't read it.

[00:08:09]What I should say is don't read any of the appendices. Read the book, that's fine, but don't read any of the appendices. They're all wrong.

[00:08:19]Well, not so much that they're all wrong, but they're all irrelevant.

[00:08:23]Because I tried to think in particle physics, how do you try to make the mass disappear? I'm just your question here.

[00:08:30]But my view is no, that's the wrong way of thinking about it. Particle physics doesn't come in until much later.

[00:08:37]But the crossover from one eon to the next is is driven by gravitational radiation. That is the main thing which gets through from one to the side to the other.

[00:08:48]There are certain other things which get through.

[00:08:51]Photons get through as long as they're big enough wavelength. So, magnetic fields get through.

[00:08:58]Broad enough electromagnetic photons, ordinary light wouldn't. They would get scattered cuz when they get to the other side, they the the there's so much temperature, so enormous that they just scatter all over the place. They don't but the energy will get through.

[00:09:14]The gravitational waves get through.

[00:09:17]The general energy of a of a galactic cluster as it makes a little point and comes through. Then what we see this points, and I say that with my Polish colleagues, and we have a paper on this which people don't seem to pay much attention to.

[00:09:33]>> [laughter] >> Uh what what do we go right to the back for I was [laughter] you went to the back yeah. So someone right in the back corner cuz back corners never get a question, do they?

[00:09:45]>> Can you hear me? Do you believe in the multiverse?

[00:09:49]>> I suppose that you might be which one is >> It's a good It's a good question. If I can remember what the multiverse is. You see the multiverse is that you got lots of different universes sitting around.

[00:09:58]And I think people like it because they want might say in some of them you got different constants of nature. And our particular one has certain values for the constants of nature. I mean very fundamental things like Well, I won't say what they're like, but they're a particular numbers which are a bit mysterious. Dirac points out these things are in his early stages of this discussion.

[00:10:19]And yeah, there's some very puzzles about where these numbers come from. You might say there are different universes which have different numbers. I don't know about that.

[00:10:27]Is the multiverse where you say there are all these different sort of parallel universes sitting around like this?

[00:10:32]That's not my picture. I don't know whether they're around or not. I don't like them very much. I prefer them this way rather than that way if you like.

[00:10:41]When I say this way, I mean in the temporal direction they keep on going. In the spatial direction, no, I don't see why you need other ones.

[00:10:50]My tentative view, and this is just speculation, I don't really know, there really is probably a good theory for why the numbers have to be why they are. And that there is some deep piece of mathematics hiding there which we don't know yet. Which tells us why these strange numbers that we find in physics have to have the values they have.

[00:11:11]>> So that would be the weakness of gravity.

[00:11:13]>> That's one of them. Yes. To say why do we have such a small See, gravity is weak when you're talking about small things and you're putting power, but when you have big things it dominates.

[00:11:24]And it's not just gravity, it's that other part. It's the lambda. It's the thing that people the dark people call dark energy.

[00:11:31]Dreadful term. But they call it dark energy. I just call it the cosmological constant. I mean, that's the term in Einstein.

[00:11:38]>> Okay, we've got time for one more question. Yeah, just one more one more one right in the middle. Why don't we do one right in the middle cuz I haven't done anything in the middle.

[00:11:46]Yeah, and >> Someone in the gallery stood in the middle, no?

[00:11:51]>> Who else could possibly be coming on?

[00:11:54]>> [laughter] >> Yeah.

[00:11:59]>> [laughter] >> Uh I I'm a student and I just wanted to ask like um what was the most important thing you learned in physics that helped you gain the Nobel Prize?

[00:12:16]>> [laughter] >> Some advice for a future Nobel Prize winner.

[00:12:20]>> Oh gosh.

[00:12:22]The trouble is like people ask me this sort of question. I say, the most important thing that I find when I look back in my life with the great sort of good ideas from time the best thing to be is lucky.

[00:12:35]It's not much use to tell people that be lucky. That doesn't help.

[00:12:40]But I realized that a lot of things which were very important and came together because of things which I'd learned at different times in my stages.

[00:12:47]I shared an office with Engelbert Schucking and I learned various things from him. He was a great figure. He He knew uh He was a very important role in my life cuz he knew everything. That was important that He knew everything and everybody. He was also quite original which was unusual.

[00:13:04]People who know everything and everybody don't usually do original things, but he was good in that respect. His original ideas weren't all that great, I have to say.

[00:13:13]But he was a great person to have shared an office with.

[00:13:16]I could have shared an office with anybody, but it happened to be with Engelbert.

[00:13:20]And it was two things I learned from his that I happened to put together and they were really important in later life. I wouldn't have known that otherwise if I hadn't shared this often office with Engelbart.

[00:13:32]How do I tell people to share their office with the right person?

[00:13:36]That's not much of a piece of advice, isn't it?

[00:13:39]I think that perhaps is a important role here is not is to be respectful. You see, you have to be deep and broad at the same time.

[00:13:50]In your specialist area, you have to go deep. So, you have to learn a lot about what your particular area is and learn what's going on, what other people have been doing, and go deep into that. But, at the same time, keep an eye on the breadth of it. So, I like to think of this sort of funnel that goes out like this.

[00:14:08]So, you keep your eye on other topics and learn don't be too single-minded.

[00:14:16]Be Keep keep keep an eye open on what's going on outside your particular topic as well as being deep at the same time.

[00:14:25]It's difficult to do, but that's perhaps the best advice I can give.

[00:14:30]>> I think that's a a wonderful place to finish. So, please thank Roger Penrose.

[00:14:35]>> [applause] [applause]