Instant Genius - The origin of the Universe, with Prof Thomas Hertog

Episode Date: April 6, 2023

When the University of Leuven professor of theoretical physics Thomas Hertog first met famed cosmologist Stephen Hawking he found himself confronted with two questions: “Why is the Universe the way it is? Why are we here?”. The two would go onto to seek answers to these profound questions during a close collaboration that lasted for twenty years. In this episode, Prof Hertog tells us about his time working with Hawking, his new book, On the Origin of Time, and the path that led the two of them to hit upon the revolutionary new theory that the laws of physics are born and evolve as the Universe they govern takes shape. Learn more about your ad choices. Visit podcastchoices.com/adchoices

Ambition comes in all shapes and sizes. At First Citizens Bank, we roll with your goals because we're built for what you're building. Fit for your ambition for Citizens Bank. Peak pollination season, and my business is scaling fast. To keep the nectar flowing, I need a phone plan with top priority data speed. That's why I chose GoogleFi wireless. My connections stay strong even when the hive is buzzing.

Plus, unlimited plans started $35 a month. Now that's a deal that doesn't stay. Explore GoogleFi Wireless plans today. Plus taxes and government fees. GoogleFi Wireless is not subject to data traffic deprioritization during times of high network usage. You said this place was steps from the water. We just haven't found the steps yet. How much did we save?

Enough. Enough to get lost! Or you could book a stay with Hilton. Welcome to your oceanfront room. Just steps from the water. The Hilton sale is on now. Book on Hilton.com or the Hilton app and save up to 20% to get the stay you expected.

When you want savings, not surprises. It matters where you stay. Hilton, for the stay. This podcast is sponsored by name, audio and focal. Streaming has made music more accessible than ever, but true listening is about more than ease. It's about quality. British audio experts name audio,

alongside French acoustic specialist focal, combine handcrafted tradition with cutting-edge innovation and high-end materials, delivering digital precision with analogue warmth. So you can experience exceptional sound at home. Music just as the artist intended. Visit name audio.com to learn more. Hello and welcome to Instant Genius,

a bite-sized master class in podcast form. I'm Jason Goethe, commissioning editor at BBC Science Focus magazine. When the University of Leuven, Professor of Theoretical Physics, Thomas Hurtock, first met famed cosmologist Stephen Hawking, he found himself confronted with two questions. Why is the universe the way it is? And why are we here? The two would go on to seek answers to these profound questions during a close collaboration that lasted for 20 years. In this episode, Professor Hurtog tells us about his time working with Hawking,

his new book, On the Origin of Time, and the path that led the two of them to hit upon a revolutionary new idea. The theory that the laws of physics are born and evolve as the universe they govern takes shape. In the book, you mentioned that when you first met Stephen, he said to you, why is the universe the way it is? Why are we here? That's like a really intimidating, like big question to be asked the first time that you meet somebody. So how did you feel in that moment? Were you prepared and what impression did you have with Stephen? Okay, yes, this was at a job interview in a sense. Yes, there was a non-trivial,

a non-trivial job interview. But of course I sort of knew where the question came from. So this was the late 90s. And in the late 90s, the multiverse idea became very popular among cosmologists and theoretical physicists. So that's the idea that there are just many universes, that the Big Bang was not unique, that our Big Bang was just one of many Big Bangs. And perhaps these different universities, universes have different laws of physics. And so, some universes would be fit for life. In some universes, life could develop, and in other universes it couldn't. So this was a whole new idea, a whole new way of thinking about this perennial question

why the universe down at the level of physics appears designed. The whole idea of the multiverse was essentially saying, well, maybe there is no design. Maybe there are so many universes that once in a while you'll find one which is fit for life, a universe in which stars and galaxies can form, in which the right mix of particles exists, a universe that doesn't expand too fast so that gravity can act. There are a whole range of properties that are needed down at the level of physics in order for a universe to become habitable. And so that was the context. That was the context of that first conversation that I had with Hawking

when he was essentially debating whether or not to take me on as his PhD student, right? And it's very different. The multiverse idea was so, I guess, so popular at a time because the alternative explanation seemed to be that there must be some sort of golden mathematical rule that dictates how the universe should be. Clearly, yeah, that was never found. And so I think that was sort of that shift was going on in the late 90s. Still, I could feel that Stephen was not entirely happy with that whole idea of the Maldiviris,

even back then. So you mentioned what you call bio-friendlyness in the book, which is really interesting. So you talk about this perfect mathematical balance. How perfectly balanced exactly is it? Can we even put that into perspective? Sure, you can do a thought experiment and play God, so to speak, and twiddled with the laws of physics, and then you can simulate what would happen. And it turns out that quite a few properties are accurately fine, untuned, so to a percent level and even

even way beyond. There are also a number of discrete properties of the universe which you just can't twiddle a little bit. Think about the number of dimensions we have, for instance. Three dimensions of space

and one dimension of time. If you change any of that to four dimensions of space or two dimensions of time, it would just not work at all. Four dimensions of space. As far as we know, you wouldn't have stable atoms or stable solar systems. So very basic things would just not work. So the list is long and perhaps the most mind-boggling example is a famous one by now. It has to do with what people call the dark energy in the universe.

So the dark energy is essentially an energy which we associate. with empty space. Empty space doesn't seem empty but filled with a sort of uniform pressure and energy. And that leads the universe, that leads the expansion of the universe to accelerate. Well, but the density of dark energy in our universe is extremely, extremely small. It is a huge factor smaller than what you might have thought it could be. And that has been essential in order to get, say, seven or eight billion years time in which the universe was slowing down. And that's what you need to form galaxies and stars and planets and life and so forth. If the dark energy had been a little larger, that whole period of hesitation in the universe would not have happened.

And again, the universe would be lifeless. So, yes, it's seriously mind-boggling. And so the question is, and that's essentially what you were saying earlier, why did the Big Bang get it right? So that billions of years later, the conditions for life would be there. So we've mentioned the Big Bang and a lot of this hangs around that idea. So for people who perhaps don't know what it is, could you explain it simply what the current thinking is? Perhaps naively, we think perhaps of the Big Bang as some sort of extremely hot explosion. But in fact, the Big Bang, as we understand it, is a much more fundamental beginning.

Crucially, it involves also the beginning of time. So the Big Bang in this grand theory of Albert Einstein, the his theory of general relativity, is really the origin of time. and so it's a fundamental beginning where if you think about it and this is the crux of the hypothesis that I developed with Hawking over over the years may signal also the beginning of the laws of physics so it's a really fundamental beginning that's one hypothesis another hypothesis could be well in that multiverse thinking the Big Bang is of course not the ultimate beginning. It would be a sort of yeah transition in an ever-existing giant inflating space

presumably. But that comes with its own paradoxes I should say so I'm leaning more towards the idea and that is essentially central in my book as well that the Big Bang was a genuine genuine origin. To the extent that we always tend to ask well what was there before the Big Bang. In our theory the question doesn't even make sense because the very notion of time and therefore the idea of causality the idea that there should be a cause of the Big Bang doesn't seem to have any support

and that is of course very, very strange but the Big Bang really is something very very strange one of the keys in this puzzle is that the idea that the universe is expanding So how do we know that? How have cosmologists figured that out? Right.

Of course, the whole high, every, it's the central inside of modern cosmologies in Einstein, on which everything rests, right? So there are two things to say here. The expansion of the universe, which you should think of, the expansion of space itself, like a balloon, is something which is predicted by the theory of Einstein. Somehow, so Einstein, what did he do with his theory of relativity? He brought space and time, which for Newton were metaphysical concepts,

he brought his into physics. Space and time became physical entities, the fabric of space time. And the idea of gravitational waves, for instance, ripples of space time is a very tangible manifestation of this. But then people working with Einstein's theory in the 20s realized that space and time cannot just remain fixed, according to Einstein's theory, even though Einstein himself didn't quite like that idea. And so they predicted that space must be expanding. And therefore, of course, that if you go back in time, space must be shrinking. Now, if space expands, it means that the distance between galaxies must be expanding.

as time goes on. So galaxies, even though they don't quite move, because they are sitting in this inflating space, the distance between them increases. And so if you send a signal from one galaxy to another, that signal in a way, yeah, has to catch up with that expansion. It undergoes that expansion, why it's traveling, and that has an effect. A signal, a light signal, a light ray, traveling through an expanding space is going to be shifted. Its color is going to be shifted towards the red of the spectrum. Its wavelength is going to stretch while the light ray travels through space, for instance, from one galaxy to another. And so a very clear manifestation of the expansion of the universe is that we should see distant galaxies, we should see the light from distant galaxies redshift, as we say.

And those redshifts were observed very soon after the theoretical discovery on the basis of Einstein's theory that our universe is expanding. So in this sort of background hum that's left in the universe, right? Yeah, I'd say so. yeah, ahem, that's a good way of saying it, yeah. Right. So now if you're bold and you trace the idea of the expansion backwards in time all the way or almost all the way, at some point you're going to find that all the matter in the universe is squeezed into a small volume. And if you squeeze matter into a very small volume, it's going to heat up. And so you're quickly driven towards the conclusion. that some time in the far past, the universe must have been hot, must have been very different, must be like, have been like one giant fireball. And now is the crucial point. The heat of that early universe can't just disappear because it's literally all of space

that is heated up in these earliest moments. So the heat of the Big Bang, with the expansion of the universe can cool down, but it can't disappear because the universe is all there is. And so that was a key prediction. If the Big Bang theory were right, we should somehow be immersed right now in the cold afterglow of that primeval heat. decades later in the 60s that afterglow that hum as you say was observed was found in fact it was found by huge radio antennas which were being constructed in the 60s for intercontinental communication why radio antennas because these giant radio disks they are sensitive to cold long wave-length radio radiation and that's what the Big Bang is now. The temperature is about 2.7 Kelvin, so minus 260-something degrees. Whatever bike you're looking for from mountain to road, either pedal-powered or electric,

we've got what you want ready for super-fast delivery. Quality gear at prices you won't find in your average bike shop. Bikeshomline.com. Ride more for less. When you need to build up your team to handle the growing chaos at work, use Indeed-sponsored jobs. It gives your job post. the boost it needs to be seen and helps reach people with the right skills, certifications,

and more. Spend less time searching and more time actually interviewing candidates who check all your boxes. Listeners of this show will get a $75-sponsored job credit at Indeed.com slash podcast. That's Indeed.com slash podcast. Terms and conditions apply. Need a hiring hero? This is a job for Indeed sponsored jobs. This podcast is sponsored by name, audio, and focal. With over 100 years of combined expert name and focal have been bringing music to listeners just as the artist intended. Since day one, this mantra has shaped every innovation in hi-fi design, technology and acoustic engineering, balancing craftsmanship and tradition with pioneering thinking.

Name audio pushes cutting-edge technology to ensure digital precision whilst sustaining Pratt, pace, rhythm and timing. The elusive quality that makes music feel alive and gives us. it emotional texture. Today, in partnership with French acoustic specialist focal, name audio creates systems that deliver exceptional sound and unforgettable listening experiences at home. Try it for yourself at a focal powered by name boutique. Visit focal powered by name.com for more information. So another thing that feeds into this is the idea of this singularity, which I believe came from studying black holes.

So now we go back to the early universe and it's very hot and we have that radiation and now you're really asking, well, what if we go even further back? And then we come to what we were saying a few minutes ago, then we come to the origin of time, to what you call what in Einstein's theory would be a singularity. In fact, there was a key insight. of Hawking in the 60s, and indeed, as you say, he was using the techniques that Roger Penrose had been developing in the context of black holes. Penrose had shown that inside black holes,

time comes to an end. So that fabric of space time, which is this physical thing ever since Einstein, doesn't just go on and on and on. It can really sort of crumble and destroy itself. It's the most crangest thing about Einstein's theory, that it can, that it sort of predict its own downfall, its own demise. It crunches inside black holes and then Hawking ingeniously turned Penrose's argument all the way upside down and showed that the fabric of space time has a beginning, that time has a beginning in a big bang. And so that is the basis. That is the basis. That is the basis of the conundrum that we mentioned earlier, like, okay, why is the universe fit for life? Why did the Big Bang, which is such a fundamental, mind-boggling, unimaginable origin,

namely the origin of time itself? How does it come that? Out of that, Big Bang emerges a bio-friendly universe. So we're talking about space-time, we're talking about relativity. So perhaps some people won't be familiar with exactly what the relationship between time and gravity is and how that's explained by Einstein. I mean, are you able to sum that up briefly for those? Sure, sure, sure, yeah, yeah. We are always talking about time and space here, but really gravity comes along for the right, I would say, right? This theory of Einstein that we're talking about, about space and time, his theory of relativity.

it's really a theory of gravity but gravity according to Einstein is not a force it's not a force that we sort of postulate that exists no gravity is in a sense

an emergent phenomenon it comes about from Einstein's equation and how so well the equation like any equation has two sides so there's space and time the shape space and time on the one hand the evolution of space but on the other side of Einstein's theory Einstein's equation resides the matter and so Einstein's

equation Einstein's theory is really a dialogue it's a dialogue between matter and space and time the shape of space time and the way the dialogue works is that matter will tend to bend will tend to curve space time in its neighborhood and it's that curvature of space time that bending which we experience as gravity. So the mass of the sun for instance will bend the fabric of space in its environment. It will create a little dip, say, and that dip is enough to keep the planets in orbit around the sun. So we say, well, this is gravity, but gravity here is a manifestation of that curvature of space according to Einstein.

Yeah. So you mentioned the multiverse at the start of our conversation. So let's have a look at the multiverse then. What are we talking about there? What exactly does that word mean? It's not clear what exactly the multiverse mean. But surely in the late 90s, around the time that I met Stephen, the multiverse was generally taught of

as an infinite, inflating space, a kind of universe-generating thing. It was generally thought of, a little bit like you imagine it, like different universes would be like bubbles in a giant space, and gradually people realized that these bubbles could be different in all sorts of respects. And so the multiverse became, I would say, an uncontrollable, beast. You might wonder, well, why, what were Hawking's reservations with regard to the multiverse back then? It's not just the fact that, of course, we can't go to another universe to check it out. So you might wonder how you can test this. No, I think the problem with the multiverse is worse.

it's the fact that if you have all these universes, then you're going to have to ask the question, okay, in which of these universes should we find ourselves? In which universe are we? It's again the same question as the one you posed at the start of our conversation. Why are we here? But here means in this universe. And the multiverse theory is ambiguous on that question.

it doesn't say anything about in which universe we should be, and therefore it doesn't make unambiguous predictions for what we should observe. But a scientific theory, which does not make an ambiguous predictions, is not really testable, is not really falsifiable. And so from the start, Hawking was zooming in on this, it's almost like an epistemic problem with the multiverse. It didn't feel like proper science. Having said this, it took many years for us to find our way out of this.

You say that about the kind of the mystery of the multiverse. So obviously the idea came from somewhere. So I'm thinking about quantum physics, I suppose, now. What led physicists to think of this concept? As you say, it came from a kind of half-bacon mixture between gravity, classical Einstein kind of thinking about gravity, about the expanding universe, as we were discussing. But if you add on top of that expansion a little quantum randomness,

then you're sort of let to almost automatically to, well, this quantum randomness can perhaps, we can perhaps extrapolate this a little bit and say that this quantum randomness leads to variations between different regions of this expanding universe. And if you then extrapolate it even further, it's a small step to say, well, maybe this quantum randomness can lead to different kinds of hot big bangs in these different regions. So it was a series of reasonings from naively, I would say, combining Einstein's ideas with quantum theory that led to the multiverse. And it was appealing, it was appealing because of its radical new take on this mystery of design. It was some sort of, yeah, it seemed to resolve that ancient riddle of cosmic design. So there's many different ideas of, there's not one idea of what the multiverse is, right? There's many different ideas.

I guess so. They're all variations of one another, I would say. But sure, sure, there are many different ideas. But of course, the crux of the hypothesis that I developed with Hawking is that this was, that multiverse thinking was, too much of an extrapolation of our sort of mixture of gravity and quantum thinking. So in our hypothesis

our Big Bang is a genuine origin and so you can say well where is the multiverse? The multiverse is in a sense it's sort of dissolved in uncertainty it sort of disappeared from our equations which was an amazing moment really sort of a eureka moment I would say It's a little bit like the Darwinian evolution in biology

and hence also the title of my book is a variation on the origin of time is of course a variation of Darwin's title You could say well Darwin he doesn't need a zillion other planets To do biology on this planet It's a little bit the same with our hypothesis We don't need a zillion other universes they may or may not exist But they don't enter in our equations and in our predictions and in our predictive process to analyze predictions.

Please tell me more about this idea, this Darwinian idea of the evolution. Right, okay. So that's a bit of the crux of our hypothesis, say. I think it sort of offers a third possible explanation for the apparent design of the cosmos. The first explanation was there must be like a fundamental equation, like a theory of everything, a mathematical rule which dictates how the universe should be. The second explanation is what we discussed, the multiverse. All possible universes are out there and we happen to be inhabitable one.

The third explanation which I developed with Hawking is, well, maybe it's in a sense of fundamentally evolutionary explanation. It's an explanation in which when we go back, into the hot big bang and to the earliest stages of it, there where time begins to behave quantum mechanically, that we hit on a deeper level of evolution, a level of evolution in which even the laws of physics, as we know them, begin to co-evolve with the universe that is taking shape. So in other words, we drive home,

the idea that the Big Bang is not just an explosion, not just the origin of time, but also the origin of the notions of physical laws. And so that is some sort of a third explanation. But of course, it comes with a price because that very early stage of evolution, in which the physical laws themselves were forged, so to say. could have turned out completely differently. So just like the tree of life could have turned out completely differently, my tree of laws could also have turned out completely differently. So it is not an a priori explanation as we were long looking for, in fact.

That's obviously a really, really interesting idea. But how did you reach that conclusion? If you can even summarize that for me, obviously it's years. years of what? Yes, yes, it took a long time. I'm sorry. It's a very good question. How did we reach that conclusion? It's impossible to say we were trying to figure out these paradoxes to do with the multiverse. So the fact that any predictions in the multiverse were ambiguous, we felt was pointing towards a fundamental problem with it. And so we were trying to, we were literally simply trying to construct through thought experiments, to try to get a coherent picture.

We were trying to construct a better theory, a theory which would allow us to make unamigris predictions and that we could test. And so the point is that the heart of our theory is really a mechanism, if you wish. A new kind of law. of physical law, which is not a law of evolution. All laws we know are always laws of evolution. The law of Newton is a law that dictates how things evolve. And the same with any other law of physics that we know.

But the origin of time at the Big Bang necessitated a different kind of law, we felt. A law that in a controllable way describes its own limitations, its own end, it's more like a final or an initial condition, a different kind of law. We found a mechanism for the laws of physics to disappear. And then, once you have that, you look at this formula and you try to interpret them and what is this telling us? Oh, it's telling us a different, it's a little bit of a sort of an epistemic readjustment, right? We were always looking for a foundation and now I'm telling you, hmm, maybe there isn't a foundation. It's just like the laws of biology. When we go back to the earliest life forms, the laws of

biology disappear. No one is saying that the laws of Mendel exist before their life. Their emergent properties. We're essentially saying, well, the laws of physics are similar, except that the evolution that forged the laws of physics happened, of course, way, way back in the heat of the Big Bang. And so they appear to us as eternal truths. But that's just because we're living in the remnants of that evolution. That's the hypothesis. That was the University of Leuven's Professor Thomas Hurtock. Thank you for listening to this episode of Instant Genius.

Brought to you from the team behind BBC Science Focus magazine. The current issue of BBC Science Focus is out now. Pick up a copy wherever you buy your favourite magazines or download a digital copy from your preferred app store. You can of course also find us online at sciencefocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music can be lost through digital sources or poor signal.

Name Audio believes you can have digital precision with analog warmth. Alongside French acoustic specialist vocal, Name creates high-end audio systems combining innovation with craftsmanship, so you can listen to music, just as the artist intended. Discover more at name audio.com. Relax and let Ralph's delivery handle your grocery shopping this week. We start with only the freshest items, then review your list and carefully choose each one. Then we pack it all up and deliver it in as little as 30 minutes so you can feel

confident it's what you ordered. Fresh groceries, your way, with Ralph's delivery and pickup. And right now, you can save $20 on your first delivery or pickup order. Ralph's, fresh for everyone.