Space, Time, and the Universe with Brian Cox | 1 Hour NO MUSIC Sleep Remix (NO AI)

Añadido: 2026-05-17

[00:00:15]I think it's right to say that Einstein really felt I think that that initially that an eternal universe was more natural but it is also true to say that his theory general relativity really doesn't quite rule that out, but it's strongly suggestive of there being a beginning and or an end. So the theory itself historically speaking strongly suggests that and so he came changed his mind and then we saw the universe was expanding.

[00:00:46]We observed that and then we've now seen the oldest light in the universe, the cosmic microwave background radiation which is the afterglow of the big bang.

[00:00:55]So we know that the universe was hot and dense 13.8 8 billion years ago. We have so much evidence for that, not least that we have a photograph of it 380,000 years after the Big Bang. It's called the cosmic microwave background. That's from the satellite called Plank, a European satellite, and also a satellite called Kobe. So, we have this images of the afterglow of the Big Bang. We also have theories that tell us about the abundance of chemical elements in the universe which match this perfectly. So, there's multiple lines of evidence that tell us the universe was hot and dense.

[00:01:26]But none of that tells us that that was the beginning. That I think that would be widely accepted. It's a beginning in Einstein's theory. If you just take general relativity, there's a singularity there at the beginning of time. We don't know what it is, but it's there. But it absolutely is true to say that we we think that's not complete as a picture. So So there it is. That's the So that is light that was emitted about 380,000 years after the Big Bang. So it's it's a and the key thing there's so many things to say about these images, but one thing is that those colors correspond to regions of very slightly different density that we detected now in in the in the gases of the young universe. So those colors correspond to regions of different density. So in in this young universe 380,000 years after the big bang that's only hydrogen and helium gas basically and a bit of lithium bit of little some of the lighter elements but basically hydrogen and helium. So you've got an almost smooth almost featureless universe then but these little density fluctuations are very important because as the universe expanded and cooled they collapsed to form the galaxies.

[00:02:48]So without those ripples, without that pattern, we would not exist. Nothing of interest would exist. And so you the question is where did that come from?

[00:02:59]That pattern, it's fundamentally important. And the theory of inflation that I mentioned earlier that there's this time before the universe got hot and dense, that theory predicted that pattern before it was observed. So this idea that you've got this very quickly stretching space and by the way so it's so the stretch if I can remember the number is if you consider two points in space during inflation the distance between them was doubling every 10 theus 37 seconds which is 0 0 37 one of a second so it's incredible rate of expansion that draws to a close and those theories so there's inflation there. So those theories predicted slight variations in the rate at which inflation stops. So our universe is accelerating in its expansion which is one of the great mysteries that was discovered in the 1990s by a friend of mine actually Brian Schmidt got the Nobel Prize for this discovery. He told me once, I don't know if I told you the story before, but he told me that he uh he'd uh made this measurement and it wasn't really he was looking at supernova explosions and he'd seen that the suggestion in the data was that the universe is accelerating in its expansion, not slowing down but speeding up in its rate of expansion. And and no one was expecting it. So he thought it was just wrong. He thought but he couldn't find anything wrong with his data. So he published it and thought, "Well, that's the end of my career. Can you just publish it?" He thought, "That's a good scientist, right? I I I don't think this is right, but I can't see anything wrong with it. I'll publish it. Someone else will tell me where my mistake was." And there was no mistake.

[00:04:46]And he won the Nobel Prize for that discovery. That's the 1990s.

[00:04:51]So this idea the universe is accelerating in expansion. The way that it does that is really important. Is it going to carry on doing that? Is whatever's driving that expansion going to change in some way which could actually recolapse the universe again.

[00:05:08]We give it a name by the way, dark energy, this thing, but we don't know what it is. I think it's very fair to say, but it looks a bit like inflation, but it's way slower. So maybe they're linked, maybe it's the same kind of thing. We don't really know. And so it's one of the great mysteries. So, but but the universe, it looks like the universe is going to continue to expand forever and to continue to accelerate.

[00:05:36]Dark matter is in some sense marginally less confusing in the sense that at least we have an idea of what it might be. Dark energy, there are people working on it, so there are theories about what it might be, but I think it it it feels less explicable given what we know than dark matter. But we haven't discovered what we we think dark matter might be some kind of particle that is got certain properties and doesn't interact very strongly. It's like interacts like neutrinos basically that you mentioned earlier. So really doesn't interact very strongly but we thought we might have seen those particles. We're looking for them. They would be passing through this room now. And so we could build a detector in here and we do that and we look for these particles. We haven't seen them. We thought we might make them at the Large Hadron Collider at CERN. I think many people thought that we'd see the signature of these things and we haven't done. So it could be that we're not right with that picture. So yeah, so it's about um 5% matter about 70% dark energy and the rest are 25% dark matter. We're just less than 5% th this us and the stuff we can see. So everything we can see in the sky all the gas and the dust and the galaxies and the stars and the black holes all those things less than 5%.

[00:07:01]as according to the standard model of cosmology. But those are models. I mean it's it's important to say that it's interesting until so we have a hypothesis which is strongly supported by lots of bits of evidence that dark matter is some kind of particle. So it's it's that's the broadly that's what you'll find in the textbooks. But it's true that until you find it, until you see it, then you haven't shown it to be correct. No, they all have problems and most of them have problems with that pattern, the CMV, the cosmic microwave background that we just saw. Because that pattern, what you're looking at actually in that pattern is acoustic. is waves, sound waves essentially in the early universe that go through the plasma of the early universe and and they they go out and we know what speed they go through that plasma. So, it's almost like you're looking at a pond and you're throwing stones into the pond and they all land in the pond at the same time and send ripples out, little little circular ripples in the pond and they all overlap and that's what that pattern is. So, we're looking at sound waves going through this plasma and and those those theories require the dark matter. The dark matter fits well if it's in there in in in this plasma in this kind of soup that this subatomic particle soup that's the early universe and the way the sound waves go through it fit that idea. So, that's one thing. But the idea also came from looking at galaxies and how they rotate and galaxies and how they bend light and and and deform space and time and how they interact together. So there's loads of different bits of information, observations of the universe from the cosmic microwave background all the way through to galaxies and the formation of galaxies and the theories that we have there that suggest there are these particles around that interact very weakly with light. So they don't really interact with light at all, which is why we don't see them, which is why they're dark. That's just like a neutrino, right? So like heavy neutrinos or and actually there was a theory once that maybe they were heavy nutrinos but that's kind of disfavored now. And so so we we have loads of kind of different bits that fit. This is how you do science. You start with a theory and you make a load of observations and you can infer things and you get a consistent picture. But very importantly, until you find it, until you really find that particle, then you don't know. So you might say, how do you know it's there?

[00:09:43]You know, which is a good question, right? I mean, if if if we've not detected this stuff, how do you know?

[00:09:48]And it's from Einstein's theory really.

[00:09:51]So it's from gravity. is is from looking at the way that galaxies rotate and the way that these sound waves moves through the early universe and the way that the universe expands because the way the universe expands is related to the stuff that's in the universe. So we can weigh the universe by and and find out what kind of different things are in there by looking at the way it's expanded and how that expansion history has changed over time.

[00:10:20]So it's all you what what you do with science which is why it's it's true that you can criticize any one bit of it and people will. So online you'll see in the comments under this there'll be people saying but what about this? What about this? What about and it's true that you can you can pluck away and pick away at any piece of it. But the way it tends to work is when you have this kind of consensus view of something. It's because you have multiple observations that all fit a particular hypothesis.

[00:10:49]And by changing one of them, by changing the explanation of one of them, you tend to mess the whole other thing up. You you mess the the wider description of multiple phenomena up. You mess it all up. So, it's quite hard to find other theories at the moment that will fit all of those different observations.

[00:11:11]I mean another example would be the age of things is it it's interesting that you can look at we can measure the age of the earth right and you measure it from geological processes radioactive dating and so on and you can kind of measure the age of the earth you can measure the age of the sun in a different way you can measure it by looking at called helioismology so you can work out you can measure how much helium is in the core of the sun and the sun shines by making helium from hydrogen so by measuring the amount of helium in the core or by looking at basically sound waves. It's like an earthquake but sun quakes. You can measure how much helium's in there. So you can get an estimate of the age of the sun and then you can get an estimate of the age of the universe by measuring how it's expanding and using Einstein's theory. The fact that they all fit with a picture of a universe that's 13.8 billion years old, a sun that's 4 and a half billion years old, a planet that's 4 and a half billion years old. The fact that it all fits is It's quite an intricate model and so you could say well I argue with the the measurements of the age of the earth maybe I don't like the radioactive dating or something and people will say that but the thing is it's a consistent picture with multiple different observations and same with dark matter so the standard model of cosmology is you have I said about 5% matter 25% dark matter 70% dark energy It might be wrong, but it fits loads of different independent observations. So, it's a consistent picture.

[00:12:52]So, Steven Hawking back in the 70s published a paper. Um, the initial one was called Black Hole Explosions, which is a great title for a paper. and and he he calculated he found out that black holes in his in his language he said black holes ain't so black they glow in the sky like coals in the sky and they radiate and so over time they lose energy and and mass and ultimately disappear over huge time scales and that's so important and I I I show this picture in the show that if you go into Westminster Abbey and look on the floor of Westminster Abbey on Steven's memorial stone, then you find his equation for the temperature of a black hole literally chiseled in stone on the floor of an abbey. So you might say why why is it so important? This was the key. This was this Rosetta Stone idea in trying to understand what happens what happens to the stuff that fell in.

[00:14:03]It was it was when you thought these things existed forever, which is prehawking.

[00:14:09]Um then you think, well, it's okay. It gets locked up inside. It can never get out. We don't care. But the thing evaporates away. One day it will be gone. So then suddenly you have to be faced with this question. What happened to everything? Then um if I throw a book into a black hole, is it somehow possible in the far future if you collect all this so-called Hawking radiation that comes off, is it possible to reconstruct the information in the book? And that that's been a a question, simple question that's driven this tremendous amount of research for 50 years. And it was pretty much solved in 2019 actually and 2020 pretty much. I mean it's there's still a huge number of questions but roughly we well the statement is everything comes out again all the information comes out. So so everything that fell in in principle in the far future you could reconstruct the information of everything that fell in.

[00:15:12]It's is an astonishing idea because I should the last thing I'll say is that before that before the Hawking papers and before this modern understanding inside a black hole just according to Einstein sits the end of time which is an astonishing thing to say because we can see them. We have a photograph of one of these things in the center of a galaxy too actually now. And you're looking when you look at that photograph you're looking at the end of time in space. So then you think well if things go to the end of time how does everything get out again? And that's the content of the this tremendous work in theoretical physics. And this work studying black holes it's one of those things that a certain kind of person says is useless. Right? You said why?

[00:16:03]Who cares? Right? It turns out that the techniques that have been developed and the understanding that's being gained from looking at these things has got a very strong crossover with building quantum computers, right? Which is a quantum computers are in laboratories now. They have a tremendous potential to revolutionize our civilization.

[00:16:28]Incredibly powerful computing devices.

[00:16:34]So what happens when a star is burning its fuel like the sun is now? What's happening is that the sun is carrying out nuclear reactions in the core.

[00:16:45]They're called nuclear fusion reactions that releases energy and that keeps the star up. But the star is burning a lot of fuel. The sun is burning, let me remember the number, it's uh 500 or 600 million tons of fuel every second.

[00:17:04]Hydrogen fuel can burn it into helium.

[00:17:07]So that can't go on forever. In the sun's case, it'll last for about another four or five billion years. When it runs out of fuel, then gravity will take over and the star will start to collapse. And if the star is big enough, there's no known force, even the the rigidity of matter that will stop it collapsing. So it collapses and collapses and collapses and forms a black hole. And that's how the the so-called stellar mass black holes are formed.

[00:17:43]Now, I should just mention there are black holes, super massive black holes at the center of galaxies, and we don't fully understand how those form, but they're millions of times the mass of a star. So, the Milky Way galaxies got one. How they form and how galaxies formed in the early universe is is a piece of research that's going on now. And I'm going to say this many times, I think, during this this talk, but that might be one of the things you choose to work on. So if if you're interested in that work on galaxy formation because there's a lot of work to do.

[00:18:21]>> There are theories that people try to build where you modify our theory of gravity. So many of these observations not all of them. So the cosmic microwave background are different observations but many of them depend on gravity and how gravity works. Einstein's theory of general relativity.

[00:18:41]So you could try to modify that theory to say well it our observation's wrong may because the way we measure how the expansion of the universe is is to look at light from supernova is one way and see how it stretched over time because the light let's say the you have a supernova uh and it happened a billion years ago then the light has been traveling for a billion years across the universe and so the universe has been expanding for a billion years so the light will be stretched and So you can measure how much stretch there is. So you just measure the color of the light from the supernova.

[00:19:17]So but so you can argue that maybe if you go for light that's been traveling 12 billion years across the universe then maybe there was something different. Maybe the light was emitted a bit different. Maybe the speed of light changes over time or something or you know so you can invent theories to change the the data or the interpretation of the data. But what you always find I think it would be fair to say is that you can change a theory and explain one bit but all the wheels come off the other bits. So that that's why it's quite difficult right? So until you know what it is you don't have a complete theory.

[00:20:01]I I think it what we're seeing is that we don't understand how structures formed in the universe. We we have a reasonable idea but we don't understand the detail. There are several sort of proposed observatories. Um and also by the way gravitational wave detectors which so we've got LIGO which is on the ground. There were proposals to put one in space which is called LISA. One one of the one of the proposals is called LISA which is lasers between satellites.

[00:20:32]So you can have much bigger things. And the reason that's interesting is because there'll be gravitational waves from the big bang. So you know as you mentioned nutrinos you got nutrino observatories which can observe nutrinos from the early universe and you can see things.

[00:20:48]It's just like light in a way but it gives you a different view. You mentioned earlier it's a different way of looking at the universe. So the nutrinos will have information.

[00:20:59]Gravitational waves will have detailed information about the big bang itself but we can't detect them at the moment because we can't detect those really tiny little ripples in space and time and we want to know. It's like you said earlier we're asking very deep questions >> about why the universe is the way it is.

[00:21:18]in maybe why there's a universe at all in the sense that did it have a beginning and if so what does that mean it mean for something like this to begin I I really I find it fascinating because and the most exciting thing of all is that we don't know that's so important by the way and I just to reiterate I think it's often missed when you're talking about the beauty of science and the value of science it's almost not the knowledge it's almost like the opposite of the knowledge is is it's just this idea that I think it goes back to what we were talking about earlier. I haven't really thought about this connection before, but it's that I was pushing back on you saying I don't know I'd like what would it mean to know everything. I don't think I'd like that. And you you you were saying maybe you would maybe that's what it means. Nana, you know, maybe achieving enlightenment.

[00:22:10]But I find the the most the most human I feel I think is when I'm when I'm on the edge of the known. So it's that that that the fact that there are mysteries in the universe, profound mysteries to me is is one of the things that makes life worth living.

[00:22:35]Yeah. I mean it's it's always a a cliche but it's true. a friend of mine um an astronomer always says when people criticize these spacecraft and they say you know the web let's say the James web space telescope is what $6 billion or so um but it's appropriate to point out that nobody put $6 billion in a suitcase and launched it on the rock kit and the $6 billion didn't go into space it was spent on Earth and what is often the case so putting aside the the glory and wonder of the discoveries that are made.

[00:23:12]You are paying people to do high-tech jobs and do research and build machines that operate at the the edge of the possible. And history tells us that that tends to be extremely useful. You're inventing things and trying to do things that are difficult. And that that that expertise never stays in one place. It then spreads out across our civilization in ways that you can't really predict or even quantify.

[00:23:45]How will the universe end? Well, the current best guess or best um estimate is that it will carry on expanding forever.

[00:23:57]And the reason I say that is because actually one of one of your great scientists in Australia, Brian Schmidt, got the Nobel Prize for discovering that the universe is accelerating in its expansion, which is a great mystery because before that discovery, we thought, well, gravity is always attractive and so it should be we've got all these galaxies in the universe and the universe has been expanding since the Big Bang and so it should at least be slowing down and there was even a question as is there enough matter in it to slow it down so much that it stops and recolapses again.

[00:24:34]But this new discovery it's only a decade old or so that the universe is accelerating in its expansion suggests that it will continue to accelerate unless some new physics appears that we don't understand and so it will just continue to expand forever.

[00:24:55]in cosmology. I say this in the show as well. It's one of the most challenging subjects because at one level it makes us feel very very small and insignificant. And it's true, you know, physically. I mean, the Earth is one planet around one star amongst 400 billion stars in one galaxy amongst two trillion galaxies in the part of the universe we can see. But but you're you're right. If you ask the question about life, um the answer is we don't know. We found nothing nothing alive beyond the earth. But admittedly, we haven't been very far or looked tremendously hard. Although we are looking hard now on Mars because we suspect there might have been microbes on Mars because there was once water on Mars and it was geologically active and all the things that we think led to the origin of life on Earth were present on Mars around the same time about 3 and 12 to 4 billion years ago. So, we wouldn't be surprised if we find that microbes existed probably subsurface on Mars or maybe on some of the moons of Jupiter or Saturn where there's water today. Uh, however, nobody expects anything more complicated than a microbe. And it's interesting if so, if you look at the history of life on Earth, you have microbes around 3.8 8 billion years ago, pretty much not long after the Earth formed in geological time. But if you look for evidence of complex life on Earth, then really there isn't any in the fossil record until about 600 million years ago or so. So on this planet for most of the history of the planet there was slime basically single cellled things doing interesting stuff photosynthesis and things but nothing more complicated than a single cell and it's only in the last half a billion years or so that you get this explosion of life on Earth and and only as I said it's only in the last uh less than a million years that we've had homo sapiens on Earth and in the last few tens of thousands of years we've had a civilization. So here it took pretty much 4 billion years to go from cell to civilization. And that's a third of the age of the universe. And so that leads many biologists that I speak to uh to suggest that whilst microbes might be common, civilizations might be rare.

[00:27:35]Actually, I asked a friend of mine, a great physicist Sean Carroll, um, how many civilizations do you think there would be in a Milky Way galaxy, a typical galaxy? And he said none, right? I I tend to say one, but that that's a guess. I would love there to be. And actually, because it worries me, and I this is the way that I end my show, actually. It worries me. Let's take that position. Let let's imagine that in in our galaxy 400 billion suns there's just us that thinks right there may microbes all over the place but in terms of things that think and can feel and in a very real sense bring meaning to the universe. All these things we've talked about the beauty of these galaxies. They're not beautiful if there's nothing there to perceive them, right? They're just galaxies. So if that's it in this galaxy, then the decisions that we make now as as a civilization have a galactic implications, right? If we destroy ourselves, for example, deliberately or through inaction, then it's possible that we eliminate meaning perhaps forever in a galaxy of 400 billion stars. And so that's a I think that leads you to it's it's a good working assumption that we have a tremendous responsibility in a sense not to do that. So I I would be much more comfortable with our current predicament. If if the galaxy was filled with civilizations, then I'd say, well, okay. Um, it would be rather stupid of us to eliminate all this beautiful culture and science and art and music that we've built up, but at least there's someone else that's doing that, but I I'm not actually sure there is.

[00:29:36]What's interesting is to me is I I've got interested in uh in Oenheimimer's writing postwar and I've been interested in it. The BBC asked me to look at um there's a thing called the BBC wreath lectures that are very famous in in the UK and every year someone gives these lectures um after Lord Rereath who founded the BBC and Oenheimer did them in 1953 I think it is 53 or 54 and they were considered a failure because no one understood what he was talking about but in there he was concerned with the fact of course that he felt he delivered the means by which we would destroy ourselves. And he felt our technology, our scientific knowhow exceeded our wisdom and our political skill, which is arguably true. So he thought in the 50s he couldn't see how we'd avoid destroying ourselves, but he thought about it a lot, feeling partly personally responsible for it. And he and he he describes this um if there's any lessons that science teaches us that the exploration of nature teaches us that we could move into other fields that we could transfer into politics for example and one of them is this picture that complex systems put it this way complex systems are complicated.

[00:30:59]So, so he's talking about looking at quantum mechanics for example and it gets complicated and you say what is an electron? It's this thing. It's a particle like point light thing or a big extended wavy thing that what is it? It behaves in all these strange ways. We don't really have the language or the mental capacity to picture it. And so he said any attempt to say this thing is this or it is that it is like this thing. It is is doomed. Right? What you have to understand is that you have to develop this rather complex and nuanced picture of the way that nature works and quantum mechanics is a good example. But he said so it is with human societies.

[00:31:40]So in a society what is it? It's a it is at one level a load of individuals like little particles and they have their own needs and desires and they have their views and strongly held views and so should they. By the way, there's a great quote from I think early 60s from Oppenheimer where he says that to be a person of substance, you need an anchor. So you need to believe things and you need to argue for things. You need to take positions. You have to have a morality.

[00:32:12]You have to have a politics, right?

[00:32:13]Basically otherwise you're not a person of substance. But he says at the same time of course you have to recognize there's a society.

[00:32:22]So there are lots of people with anchors and you might strongly disagree with that anchor and they might be wrong, right? Their anchor might be nonsense.

[00:32:32]But the challenge of politics is to avoid war. It's a I read somewhere recently someone said I can't remember it was but said that democracy is a technology to avoid civil war. That's what it is.

[00:32:48]So you've got to understand that whilst you have your and should have your firmly held position, you you have to find a way and it it feels almost contradictory, you have to find a way of understanding that the society as a whole is a complex mixture of all these different little particles with their own anchors and their own positions. And what is the goal? So it is the goal. It often feels to me that politics at the moment the goal is to win an argument. It often feels like to to convince enough people that your view is the right view and that obviously is part of democracy, right? It's the way it works, right? You you argue for your position and then you get you get four or five years to do your thing and then someone else can take over. But also I think the thing we're missing at the moment is that is perhaps more fundamental function of democracy which is to avoid war because if you can avoid war especially with the power that we have now you have the time to sort the rest out but if we can't avoid war we don't. And I think that and oftenheimer wrote that he knew that in the 50s and it feels to me more that we're back full circle now. It feels to me we've almost forgotten. We seem to have forgotten that the primary function of democracy is not to ensure that your side wins.

[00:34:23]The primary function of democracy is to ensure there's a chance for the other side to win at some point in the future.

[00:34:35]There's a theory um and it's actually an um someone I've met several times, Neil Turk, he's one of the physicists who works on this who's a cosmologist who's now in Canada at the perimeter institute and he talks about the fact that there may be extra dimensions in the universe.

[00:34:53]So we we could think of not just our imagine that we forget you can't picture four or five or six dimensions. So imagine that we're just living on a sheet of paper, let's say. Then there are theories where here's our universe floating around and there can be another universe floating around in a big room like this. So there are more spatial dimensions and we're just on a sheet floating around in this bigger multiverse. And then you can ask the question, well, what happens when they collide together? And one of the theories about what caused the big bang is that actually what it was was two of these sheets or brains they're called colliding together after membranes not brains in the head but brain. So they collide together and separate and when they collide together they heat themselves up and you get something that looks like a big bang on that on that sheet of space and time if you like. So that's another different theory for what happened before the big bang is that the universe may have been around forever with all these sheets of different universes if you like floating around and they could sometimes bump into each other. We're making measurements now. I should say that the the the experimental basis for all this is something called the cosmic microwave background radiation or the CMBB. So, we can look up into the sky and we can see the oldest light in the universe. It was released um at 380,000 years after the big bang when the universe cooled down sufficiently for atoms to form. And at that point, the universe became transparent and that light has been traveling through the universe ever since. And we have a satellite up at the moment called Plank. It's a European satellite that's been taking detailed pictures of this light. And in that light, it's like a baby picture of the universe, like a scan, a baby scan of the universe in a sense. And so you can look to the universe as it was in its very earliest days and see different structures and different properties of that light. And they give you the clue as to what happened right back at the at the beginning of time, the beginning of the universe. And that's where these theories are getting their experimental support.

[00:37:14]um it comes up as a question because cosmology is the it's a science of origins and actually with the the study of black holes as I mentioned we're even beginning now to think about what space and time are so naturally the I say it in the show actually I say when we talking about this it's it's the moment of creation if there was so we're asking Was there a moment of creation? And that's the correct language to use, I think. Or it's evocative language, but it's really what we're talking about.

[00:37:50]Did everything come into being or has it always been here? We actually don't even know the answer to that question really.

[00:37:58]Um, so yeah, I get asked it a lot because I think cosmology is a challenging science that challenges us to think about these things that we we often you know we associate that with theology or philosophy and I think that's that's a good thing because uh something I very strongly believe in is that segmenting or or making little canisters and putting different bits of human experience or different, you know, music and art and theology and philosophy and science and segmenting them all is just the wrong way to look at it. What what we're doing is um a deep level trying to understand what it means to be human in this tremendous potentially infinite universe. And and so I I I those questions get asked and ultimately I I say I'm quite straightforward. I say I don't um I'm not a religious person myself. But um but the correct thing to say even about the question, did the universe have a beginning in time is we don't know. We don't know. That's it.

[00:39:19]To me, that's one of the defining characteristics of being human, trying to make sense of the world.

[00:39:26]>> And that's why by the way I don't like to get into sort of arguments with with pe people who have different different views, different belief systems. My my sort of baseline position is if you're curious and you're interested and you want to know how things happened. That to me is common ground that we can share. The people I don't really understand are people who are not curious and don't have questions because I think Carl Sean wrote a great book called The Demon Haunted World where he says that story about a taxi driver when he got in the taxi at the start and and he's asking him all these questions about Atlantis or whatever it is and this and he realizes he doesn't think this guy is is is an idiot. He thinks this guy has a curious mind. He he's someone who who should be we we can have a wonderful conversation. But he also says that he felt that he'd perhaps been failed by society, by education in that his curiosity had not been somehow channeled to the real mysteries, but he got sidetracked into all this strange stuff. By the way, that that that idea that I think one of the problems we have communicating science and getting young people into science is that idea that you have to somehow be really clever, which is not true at all. It's um it's goes back to what I said before that the it's more you have to be comfortable with not knowing. So that's a big step to say I'm not going to guess and and I'm okay if you ask me a question about the the origin of the universe. The answer is don't know. So I think it's as you said if if you can be comfortable with not having to have a simple intelligible explanation for something then you'll make more progress.

[00:41:27]So it's easy to just go there's a simpler that thing. So there's a simpler explanation there. Yeah. I mean going going back to Richard Feman, he said um what the the great there's a great essay I've probably talked to you about before called the value of science that he wrote 1955. You can get it online and in there he says the most valuable thing is scientists bring this transferable skill to life and it's that you have a great experience with being wrong. The nature is brutal and most of the time you come up with some really great theory and you're really sure about it. You do the experiment and you're just wrong. And so you get so used to it that you come to enjoy it because you're learning. But it's a process. You can't you that's why science is so important in schools and experiments are so important. It's not that you just swing a pendulum and there's nothing interesting about that, but it's just that you're learning that there is there's a gold standard of knowledge which is nature. And as Feman said, it doesn't care who you are or what your title is or what your name is or you may have been elected with 99% votes in the whatever it is, it doesn't matter. Nature just doesn't care. And so the the more you interrogate nature, even as a little a kid at school with a little experiment with a battery and a light or something, you learn that there's a reality and you learn what it takes to acquire reliable knowledge about the world and reliable knowledge is important.

[00:43:05]How do we form a a view of and it can be very important questions. It can be questions like what happens if we carry on putting greenhouse gases into the atmosphere for example whatever your politics are. It's a legitimate question a good question. And so how do we then address that? You can't do it by going back to your political affiliation or your belief system. You've got to try and understand this complicated system which is the climate of a planet. So you make measurements of the thing and you build some models and computer models and there's a very famous saying that all models are wrong because they're models, right? So but they're the best you can do. So you have a go and you come up with some information and and and a model that kind of works and you say this is the best version of our knowledge at the time and then you can try to act on it and you refine the model and that's the process. But the that idea of how can we acquire reliable knowledge that we can trust which might not be right and is very likely not completely right but it's the best we can do at the time. That's what my definition of science would be. It's it's it's nothing more or less than the best picture we can manage of how nature works at any given moment.

[00:44:31]It's not a truth. It's not something by its very nature. The way that science works is it will it may be shown to be incorrect or not particularly great a model tomorrow. But it I would define it as the best we and by we I mean our civilization the best we can do. And so we act on that. I I don't see any other way to act as a civilization other than with that the best we can do.

[00:45:00]Yeah, it's a remarkable instrument and you think of the predecessor which is the Hubble Space Telescope. I think it's almost impossible to imagine a world without that even if you you don't know the the images that we're familiar with of the universe. many of them the spectacular galaxies and star forming regions they're from Hubble but the web is a significant step forward and and technically um one of the most important things is it can see what we call longer wavelength light or infrared light and that's important because if you think about we want to see the first galaxies forming so we want to understand how the first stars and galaxies form med in the universe. And so what you do is you look far out into the universe. And because light travels quite slowly across cosmic distances, let's say you have a galaxy that's um the the most distant one you can see with the naked eye is about 2 million light years away. So that means that the light has been traveling for 2 million years to reach us. And I it's a remarkable thing actually to think when you look it's called the Andromeda galaxy and if you know where you're looking you can just catch it out of the corner of your eye. If you think about it you're seeing that as it was 2 million years ago. It's remarkable. I mean it began its journey before we had evolved on Earth. So in the time it took and that's the nearest neighboring galaxy. The web looks so far out that it's capturing light that's been traveling for over 13 billion years. Um, but the universe has been expanding and so the light has been stretching.

[00:46:50]And so for the most distant galaxies, we're looking back in time almost to the big bang. Then that the Hubble was not sensitive to that light. so that the web can see the formation of the first galaxies. It's it's essentially looking all the way back to very close to the beginning of time. And that's very important because we're not entirely sure exactly how those first galaxies formed.

[00:47:22]Um, we know it's there. We're absolutely sure now it's there from many different measurements from the way that galaxies rotate, the way that galaxies interact with each other and the whole evolution of the universe actually requires there to be dark matter. About five times as much dark matter as there is matter. So it it completely outweighs the stuff out of which we are made and all the stars we can see in the sky are made. So it doesn't glow. It's not stars which is why it's called dark matter. What is it?

[00:47:54]It is as a particle physicist I would say it's probably but this that's an unscientific thing to say but if I had to guess it it's a new kind of particle I would guess. So it one of a particle which we haven't discovered yet um that there are theories many theories in particle physics that suggest that there are other particles out there that are waiting to be discovered at places like the Large Hadron Collider. And um so I I think the evidence tends to suggest there should be some new kind of particle and we may discover it. We have experiments in underground laboratories that are literally looking for the dark matter that we fly through as the earth orbits around the sun and this solar system goes around the galaxy and the galaxy passes through the universe.

[00:48:43]We're flying through this dark matter.

[00:48:45]So it does come through. It should be it should be in this room now and in the room where you're sitting now.

[00:48:51]But it interacts very weakly with normal matter. So we have experiments looking for the very rare times when those dark matter particles might bump in to some matter. So we can look for it that way or we can try and make these new particles at particle accelerators like large collider. So that's what that would be my guess. It's a new kind of particle.

[00:49:14]So I think when I when I think about this I I tend to confine it to our galaxy because I can't conceive of travel between galaxies.

[00:49:26]I think it's too far. Although it is true that the laws of physics do not prevent that. So relativity I teach relativity in the at Manchester University right to the first years the 18y olds and the first thing we do in special relativity is talk about the fact that if you travel close to the speed of light so if you had a spacecraft traveling close to the speed of light then distances shrink from your perspective.

[00:49:54]So, and the one number I always have in my mind is at the Large Hadron Collider at CERN, the protons go around the ring, which is 27 kilometers in circumference and they go around at 99.99999% the speed of light. So, close to the speed of light. At that speed, distances shrink by a factor of 7,000.

[00:50:18]And so that ring is something like four meters in diameter to to the to the protons. So according to laws of physics, if you can build a spacecraft that goes very close to the speed of light, you can shrink the distance to the Andromeda galaxy and therefore the time it takes to get there by a an arbitrary amount.

[00:50:42]Actually, the closer you get to speed of light, the more you can shrink it. And so you can make those two million lighty years. You could traverse across that distance in principle in a minute according to physic. However, the downside is that you you couldn't come back to tell if you came back to the earth at that speed to tell everybody what you'd found at least 4 million years would have passed on the earth. So there's kind of a downside to it.

[00:51:14]We could in principle explore the galaxy and beyond, but getting to chat to everybody about what you found is forbidden. Well, it's a time machine in the sense that we could go arbitrarily far into the future by flying around in a rocket very close to speed of light.

[00:51:36]So, we could come back a million years in the future and and look at the Earth and find out what had happened. You can't go back as far as we can tell. You can't build a time machine to go backwards. So these are time machines.

[00:51:50]The the the world is built such that a time machine, a way to think about it, the way that we teach it in in undergraduate physics is that so in Einstein's theory, there are events which are things that happen in spaceime.

[00:52:07]So that would be an event. It's something that happens. Our conversation now is a thing that happens. spacetime and what Einstein's theory tells you is it's about the relationship between events.

[00:52:19]So, so let's say that we wanted to come back here tomorrow. That would be another event. We meet again tomorrow.

[00:52:27]And you can say how much time has passed between those events. In Einstein's theory, the amount of time that has passed is the length of the path you take over spaceime between the events.

[00:52:42]So it's just like saying in in a sense, what's the distance between Austin and Dallas, right? And you'd say, okay, well, it depends what route you go.

[00:52:50]Well, what's interesting in Einstein's theory, the only complication is the length of the path you take between events is the time measured by a clock that's carried along that path. So that's that's how much if you're the carrying your watch with you and you go between here and tomorrow, you go this way, you go off and maybe you fly to Dallas and back or something and then come back again. there's a particular length. Someone else can take a different path obviously and so that a different amount of time will pass for them between those two things that happen just because of that one fact.

[00:53:29]It's a tiny amount unless you travel someone goes close to the speed of light or someone goes near a black hole or something where the where the spacetime is all distorted then you can get big effects but it's still completely measurable. I mean they are quite big effects these in the sense that for the satellite navigation system for example GPS the clocks on the satellites tick at a different rate to the clocks on the ground and it's a quite a big effect I think from memory it's something like 30 over 30,000 nan per day difference because of they're in a weaker gravitational field and they're moving and all sorts of things. It's the same thing, but 30,000 nanose.

[00:54:15]Light travels 1 foot per nancond, which is great. I always say that God used imperial units cuz there 30.8 cm.

[00:54:24]It's 1 foot, right? It's good. It's one foot per nancond. So that's 30,000 ft of position measurement if you drift your clock out by 30,000 nconds.

[00:54:35]So it wouldn't work.

[00:54:37]So, so it's a big effect when you start using time to measure distance, which is what we do in satellite navigation, GPS.

[00:54:46]So, we have to correct. So, the clocks have to be corrected for that effect.

[00:54:51]So, so it's an effect that we can easily measure with atomic clocks, but it doesn't make much difference to us as humans.

[00:54:58]But just that the point is that the laws of nature would allow you to do it if you could go close to speed of light.

[00:55:06]The by the way the last thing I'll say is the the limiting factor. You might say well what what happens if you go really close to the speed of light? What happens if you go at the speed of light?

[00:55:15]Well special relativity Einstein's theory is built such that uh that the distance between any two events in the universe along the path of a beam of light between the events is zero.

[00:55:27]No time at all. So so that's the way that Einstein's theory is built. So he asked the question when he was younger famously, what would the universe look like if I traveled alongside a beam of light? And the answer is that you wouldn't perceive any time. You can't if you've got any mass at all, you can't do that. You can't go at the speed of light. So according to our model, which is a good model, and it seems to work, but if you've got no mass, you go at the speed of light. So if you're a photon, you go at the speed of light. And and no time If you look at Einstein's theory, both his theories of relativity which are our best description of space and time, then the speed of light plays a very specific and important role in those theories. And what it does is it enforces what a physicist would call causality. So it's kind of a big word.

[00:56:28]What does that mean? Well, it's actually meaning that cause and effect are always respected. So, so if I if I throw a ball of paint, let's say, at that wall over there, and it smashes into the wall and all the paint smears over the wall, then you would think, well, it'd be a funny kind of universe if I could arrange things so I would see all the paint appear on the wall before I threw the paintball at the wall. Indeed, it would.

[00:56:54]doesn't seem like a universe that would be logically possible. But if you can travel faster than the speed of light in Einstein's theory, then that's what can happen. You can reverse cause and effect. So the speed of light, it's actually I should say it's kind of a bit of a red herring because people often ask me, well, why why what's special about light? The answer is there's nothing particularly special about light. In in Einstein's theory, it's not really the speed of light. It's the speed of things that have no mass. So, if you have no mass in Einstein's theory, you travel through space and time at the speed of light. And if you have mass, you travel slower than the speed of light. And light happens to be massless.

[00:57:44]So the photons, the particles of light that streaming around in the room now, those things are massless particles, why are they massless? Well, we actually know the answer to that now from the large collider because they don't interact with something called Higs bosons.

[00:58:02]So we even know the answer to that. But that's the thing. So So basically, if you could travel faster than the speed of light, you could do silly things like reverse cause and effect. You could t time travel into the past. You could do all sorts of nasty things like prevent your parents ever meeting and therefore seemingly preventing your own birth which would be a paradox. So it's very important. It's built into the fabric of the universe.

[00:58:31]So I talk about cosmology.

[00:58:33]We spoken about you know the what we call the large scale structure of the universe. So the galaxies and how they formed, how the universe has evolved since the big bang, but also I've got very interested in in my academic work in in black holes. And black holes, they're really evocative things. I think everyone's heard of these strange things, these totally collapsed stars uh from which nothing apparently can escape. But in the past few years, past few decades really, um, beginning work that Stephen Hawking really began back in the 1970s and many others, um, we've begun to suspect there's a lot more to them. And they've started forcing us to reassess our understanding of what space and time are. And that's a really weird sentence. You might think, well, space is the the arena in which we live and time just ticks. But it really isn't. It looks like from studying these things, there are building blocks of space and building blocks of time. And and what I say in the show is that's a mind-blowing idea and I talk about that. But the key point is there's a great quote from Einstein, a beautiful story that Einstein told about when he was a little boy. He was six or seven years old and his dad gave him a compass. And so he looked at the compass and and he saw well there's this thing this needle and it always points north points in this direction. So there's something invisible that I can't see that underlies our reality that's making this needle point north. And he said later in life, it was my first encounter with with an idea which is if you look at nature carefully and really pay attention and you're lucky, you can catch a glimpse of something deeply hidden. Beautiful phrase, something deeply hidden, which is the deep structure of reality. It's what our reality is. And so black holes, I they're kind of a metaphor in a way. I talk about them as Rosetta stones in the sky. They're the things that by studying them and you and you say why why would we study these things? Well, in studying these things, we're beginning to get a deep a deep picture of what our reality actually is. And that's that's a remarkable idea, but it's a beautiful idea that runs through all of science.