Lord Martin Rees is a cosmologist and astrophysicist at Cambridge University and co-founder of the Centre for the Study of Existential Risk. Please support this podcast by checking out our sponsors:
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OUTLINE:
0:00 - Introduction
0:52 - Understanding the universe
9:22 - Human limitations and AI
18:18 - Dark matter
25:38 - Vast universe
33:19 - Alien life
47:12 - Space exploration
1:11:35 - Future technology
1:22:57 - Newton and Einstein
1:26:59 - Black holes
1:40:40 - Cosmological threats
2:07:44 - Advice for young people
2:10:14 - Mortality

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No reason to think that the ocean ends just beyond your horizon.

And likewise, there's no reason to think that the aftermath of our Big Bang ends just at the boundary of what we can see.

Indeed, there are quite strong arguments that it probably goes on about 100 times further.

And it may even go on so much further that all combinatorials are replicated and there's another set of people like us sitting in a room like this.

The following is a conversation with Lord Martin Rees, Emeritus Professor of Cosmology and Astrophysics at Cambridge University and co-founder of the Center for the Study of Existential Risk.

To support it, please check out our sponsors in the description.

And now, dear friends, here's Martin Rees.

In your 2020 Scientific American article, you write that, quote, "'Today we know that the universe is far bigger "'and stranger than anyone suspected.'" So what do you think are the strangest, maybe the most beautiful, or maybe even the most terrifying things lurking out there in the cosmos?

Well, of course, we're still groping for any detailed understanding of the remote parts of the universe.

But of course, what we've learned in the last few decades is really 2 things.

First, we've understood that the universe had an origin about 13.8 billion years ago in a so-called Big Bang, a hot, dense state whose very beginnings are still shrouded in mystery.

And also we've learned more about the extreme things in it, black holes, neutron stars, explosions of various kinds.

And 1 of the most potentially exciting discoveries in the last 20 years, mainly the last 10, has been the realization that most of the stars in the sky are orbited by retinues of planets, just as the sun is orbited by the Earth and the other familiar planets.

And this, of course, makes the night sky far more interesting.

What you see up there aren't just points of light, but they're planetary systems.

And that raises a question, could there be life out there?

And so that is an exciting problem for the 21st century.

LRS So when you see all those lights out there, you immediately imagine all the planetary worlds that are around them, and they potentially have all kinds of different lives, living organisms, life forms, or

We know that they have masses and orbits rather like the planets of our solar system, but we don't know at all if there's any life on any of them.

I mean, it's entirely logically possible that life is unique to this earth, doesn't exist anywhere.

On the other hand, it could be that the origin of life is something which happens routinely given conditions like the young earth, in which case there could be literally billions of places in our galaxy where some sort of biosphere has evolved.

And settling where the truth lies between those 2 extremes is a challenge for the coming decades.

So certainly we're either lucky to be here or very, very, very lucky to be here?

Where do you fall, your own estimate, your own guess on this question?

I think it would be foolish to give any firm estimate because we just don't know.

And that's just a example of how we are depending on greater observations.

And also incidentally, in the case of life, we've got to take account of the fact that, as I always say to my scientific colleagues, biology is a much harder subject than physics.

And most of the universe, as we know about, could be understood by physics, but we've got to remember that even the smallest living organism, an insect, is far more complicated with layer on layer complexity than the most complicated star or galaxy.

You know, that's the funny thing about physics and biology.

The dream of physicists in the 20th century and maybe this century is to discover the theory of everything.

And there's a sense by, that once you discover that theory, you will understand everything.

If we unlock the mysteries of how the universe works, would we be able to understand how life emerges from that fabric of the universe that we understand?

I think the phrase theory of everything is very misleading because it's used to describe a theory which unifies the 3 laws of microphysics, electromagnetism, and weak interaction with gravity.

So it's an important step forward for particle physicists.

But the lack of such a theory doesn't hold up any other scientists.

Anyone doing biology or most of physics is not held up at all through not understanding sub-nuclear physics.

They're held up because they're dealing with things that are very complicated.

And that's especially true of anything biological.

So what's holding up biologists is not a lack of a so-called theory of everything.

It's the inability to understand things which are very complicated.

What do you think we'll understand first?

How the universe works or how the human body works?

Deeply, like from a fundamental deep level?

Well, I think, and perhaps we can come back to it later, that there are only limited prospects of ever being able to understand with unaided human brains, the most fundamental theories linking together all the forces of nature.

I think that may be a limitation of the human brains.

But I also think that we can, perhaps aided by computer simulations, understand a bit more of the complexity of nature.

But even understanding a simple organism from the atom up is very, very difficult.

And I think extreme reductionists have a very misleading perception.

They tend to think that in a sense, we are all solutions to Schrodinger's equation, et cetera.

But that isn't the way we'll ever understand anything.

It may be true that we are reductious in the sense that we believe that that's the case.

We don't believe in any special life force in living things, but nonetheless, no 1 thinks that we can understand a living thing by solving Schrodinger's equation.

To take an example which isn't as complicated, Lots of people study the flow of fluids like water.

Why waves break, why flows go turbulent, things like that.

This is a serious branch of applied mathematics and engineering.

And in doing this, you have concepts of viscosity, turbulence, and things like that.

Now, you can understand quite a lot about how water behaves and how waves break in terms of those concepts, but the fact that any breaking wave is a solution of Schrodinger's equation for 10 to 30 particles.

Even if you could solve that, which you clearly can't, would not give you any insight.

So the important thing is that every science has its own irreducible concepts in which you get the best explanation.

So it may be in chemistry, it's things like valence, in biology, the concepts in cell biology, and In ecology, there are concepts like imprinting, et cetera.

And in psychology, there are other concepts.

So in a sense, the sciences are like a tall building where you have basic physics, the most fundamental, then the rest of physics, then chemistry, then cell biology, etc., all the way up to the economists in the penthouse and all that.

That's true in a sense, but it's not true that it's like a building in that it's made unstable by an unstable base.

Because if you're a chemist, biologist, or an economist, you're facing challenging problems, but they're not made any worse by uncertainty about sub-nuclear physics.

And at every level, just because you understand the rules of the game, or have some understanding of the rules of the game, doesn't mean you know what kind of beautiful things that game creates.

Right, so if you're interested in birds and how they fly, then things like imprinting the baby on the mother and all that and things like that are what you need to understand.

You couldn't even in principle solve this vertical equation how an albatross wanders for thousands of miles of the Southern Ocean and comes back and then coughs up food for its young.

That's something we can understand in a sense and predict behavior, but it's not because we can solve it on the atomic scale.

You mentioned that there might be some fundamental limitation to the human brain.

That limits our ability to understand some aspect of how the universe works.

RHT I would simply say that just as a monkey can't understand quantum theory or even Newtonian physics, there's no particular reason why the human brain should evolve to be well-matched to understanding the deepest aspects of reality.

And I suspect that there may be aspects that we are not even aware of and couldn't really fully comprehend.

But as an intermediate step towards that, 1 thing which I think is very interesting possibility is the extent to which AI can help us.

I mean, I think if you take the example of so-called theories of everything, 1 of which is string theory.

String theory involves very complicated geometry and structures in 10 dimensions.

And it's certainly in my view on the cards that the physics of 10 dimensions, very complicated geometry, may be too hard for a human being to work through, but could be worked through by an AI with the advantage of the huge processing power, which enables them to learn World Championship Chess within a few hours just by watching games.

So there's every reason to expect that these machines could help us to solve these problems.

And of course, if that's the way we came to understand whether string theory was right, it should be in a sense frustrating because you wouldn't get the sort of aha insight, which is the greatest satisfaction from doing science.

But on the other hand, if a machine churns away a 10-dimensional geometry, figuring out all the possible origamis wound up in extra dimensions, if it comes out at the end, spews out the correct mass of the electron, the fact that there are 3 kinds of neutrinos, something like that, you would know that there was some truth in the theory.

And so, we may have a theory which we come to trust because it does predict things that we can observe and check, but we may never really understand the full workings of it to the extent that we do more or less understand how most phenomena can be explained in a fundamental way.

Of course, in the case of quantum theory, many people would say, understandably, there's still some mystery.

But there could be deeper mysteries when we get to these unified theories, where there's a big gap between what a computer can print out for us at the end and what we can actually grasp and think through in our heads.

Yeah, it's interesting that the idea that there could be things a computer could tell us that is true.

And maybe it can even help us understand why it's true a little bit.

But ultimately, it's still a long journey to really deeply understand the whys of it.

Yes, and that's a limitation of our brain.

We can try to sneak up to it in different ways, given the limitations of our brain.

Have you, I've gotten a chance to spend the day at DeepMind, talk to Demis Hassabis.

His big dream is to apply AI to the questions of science, certainly to the questions of physics.

Have you gotten a chance to interact with him?

I remember the first time I met him, he said that he was like me.

He wants to understand the universe, but he thought the best thing to do was to try and develop AI.

And then with the help of AI, he'd stand more chance of understanding the universe.

And of course, although we're familiar with the way his computers play Go and chess, he's already made contributions to science through understanding protein folding better than the best human chemists.

And so already he's on the path to showing ways in which computers have the power to learn and do things by having a bit to analyze enormous samples in a short time to do better than humans.

And so I think he would resonate with what I've just said, that it may be that in these other fundamental questions, the computers will play a crucial role.

Yeah, and they're also doing quantum mechanical simulation of electrons.

They're doing control of high temperature plasmas, fusion reactors.

Yes, that's a new thing, which is very interesting, they can suppress the instabilities in these tokamaks better than any other way, yeah.

progress by AIs in science is making big strides.

Do you think an AI system will win a Nobel Prize in this century?

If I can digress and put in a plug for my next book, it has a chapter saying why Nobel Prizes do more harm than good.

So on a quite separate subject, I think Nobel Prizes do a great deal of damage to the percept of the way science is done.

Of course, if you ask who or what deserves the credit for any scientific discovery, it may be often someone who has an idea, a team of people who work a big experiment, etc.

And of course, it's the quality of the equipment, which is crucial.

And certainly in the subjects I do in astronomy, the huge advances we've had come not from us being more intelligent than Aristotle was, but through us having far, far better data from powerful telescopes on the ground and in space.

And also, incidentally, we've benefited hugely in astronomy from computer simulations.

Because if you are a subatomic physicist, then of course you crash together the particles in the big accelerator like the 1 at CERN and see what happens.

But I can't crash together 2 galaxies or 2 stars and see what happens.

But in the virtual world of a computer, 1 can do simulations like that.

And the power of computers is such that these simulations can yield phenomena and insights which we wouldn't have guessed beforehand.

And the way we can feel we're making progress in trying to understand some of these phenomena, why galaxies have the size and shape they do and all that, is because we can do simulations and tweaking different initial conditions and seeing which gives the best fit to what we actually observe.

And so, that's a way in which we've made progress in using computers.

And incidentally, we also now need to analyze data because 1 thinks of astronomy as being traditionally a rather data-poor subject.

But the European satellite called Gaia has just put online the speeds and colors and properties of nearly 2000000000 stars in the Milky Way, which we do fantastic analyses of.

And that, of course, could not be done at all without just the number of crunchy capacitive computers.

LRW And the new methods of machine learning actually love raw data, the kind that astronomy provides, organized, structured, raw data.

Yeah, well, indeed, because the reason they really have a benefit over us is that they can learn and think so much faster.

That's how they can learn to play chess and go.

That's how they can learn to diagnose lung cancer better than a radiologist.

A book is they can look at 100,000 scans in a few days, whereas no human radiologist sees that many in a lifetime.

Well, there's still a magic to the human intelligence, to the intuition, to the common sense reasoning.

The book I mentioned is called, If Science Is to Save Us, it's coming out in September.

And it's on the big challenges of science, climate, dealing with bio safety and dealing with cyber safety.

And also it's got chapters on the way science is organized, universities and academies, et cetera.

Well, let me actually just stroll around the beautiful and the strange of the universe.

Over 20 years ago, you hypothesized that we would solve the mystery of dark matter by now.

First, what is dark matter and why has it been so tough to figure out?

Well, I mean, we learned that galaxies and other large-scale structures, which are moving around but prevent from flying apart by gravity, would be flying apart if they only contained the stuff we see, if everything in them was shining.

And to understand how galaxies formed and why they do remain confined to the same size, 1 has to infer that there's about 5 times as much stuff producing gravitational forces than the total amount of stuff in the gas and stars that we see.

It's not dark, it's just transparent, et cetera.

And the most likely interpretation is that it's a swarm of microscopic particles which have no electric charge and the very small cross-sections were hitting each other and hitting anything else.

So they swarm around and we can detect their collective effects.

And when we do computer simulations of how galaxies form and evolve and how they emerge from the Big Bang, then we get a nice consistent picture if we put in 5 times as much mass in the form of these mysterious dark particles.

And for instance, it works better if you think they're non-interacting particles than if you think they're a gas, which would have shock waves and things.

So we know something about the properties of these, but we don't know what they are.

And the disappointment compared to my guess 20 years ago is that particles answering this description have not yet been found.

It was thought that the big accelerator, the Large Hadron Collider at CERN, which is the world's biggest, might've found a new class of particles, which would have been the obvious candidates, and it hasn't.

And some people say, well, dark matter can't be there, etc.

But what I would argue is that there's a huge amount of parameter space that hasn't been explored.

There are other kinds of particles called axions, which behave slightly differently, which are a good candidate.

And there's a factor of 10 powers of 10 between the heaviest particles that could be created by the Large Hadron Collider and the heaviest particles which on theoretical grounds could exist without turning into black holes.

So there's a huge amount of possible particles which could be out there as remnants of the Big Bang but which we wouldn't be able to detect so easily.

So the fact that we've got new constraints on what the dark matter could be doesn't diminish my belief that it's there in the form of particles because we've only explored a small fraction of parameter space.

So there's this search, you're literally, upon an unintended earth, searching in the dark here in this giant parameter space of possible particles.

You're searching for, I mean, there could be all kinds of particles.

It could be, and There's some which may be very, very hard to detect, but I think we can hope for some new theoretical ideas.

Because 1 point which perhaps we'd like to discuss more is about the very early stage of the Big Bang.

And the situation now is that we have an outline picture for how the universe has evolved from the time when it was expanding in just a nanosecond right up to the present.

And we could do that because after nanosecond, the physics of the material is in the same range that we can test in the lab.

After a nanosecond, the particles move around like those in the Large Hadron Collider.

If you wait for 1 second, they're rather like in the centers of the hottest stars and nuclear reactions produce hydrogen, helium, etc., which fit the data.

So we can with confidence extrapolate back to when the universe was a nanosecond old.

Indeed, I think we can do it with as much confidence as anything a geologist tells you about the early history of the Earth.

And that's huge progress in the last 50 years.

But any progress puts in sharper focus new mysteries.

And of course, the new mysteries in this context are why is the universe expanding the way it is?

Why does it contain this mixture of atoms and dark matter and radiation?

And why does it have the properties which allow galaxies to form, being fairly smooth but not completely smooth?

And the answer to those questions are generally believed to lie in a much, much earlier stage of the universe when conditions were much more extreme, and therefore far beyond the stage where we had the foothold in experiments.

And So we don't have a convincing theory.

Until we have something like string theory or some other clues to the ultra-early universe, that's going to remain speculative.

To say how big the gap is, if we take the observable universe out to a bit more than 10 billion light years, then when the universe was a nanosecond old, that would have been squeezed down to the size of our solar system, or compressed into that volume.

But the times we're talking about when the key properties of the universe were first imprinted were times when that entire universe was squeezed down to the size of a tennis ball, or baseball if you prefer, and to emerge from something microscopic.

And it's not surprising that since it's so far from our experimental range of detectability, we are still groping for ideas.

But you think first theory will reach into that place and then experiment will perhaps 1 day catch up.

Well, I think in a sense it's a combination.

I think what we hope for is that there'll be a theory which applies to the early universe, but which also has consequences which we can test in our present-day universe, like discovering why neutrinos exist or things like that.

And that's the thing which, as I mentioned, we may perhaps need a bit of AI to help us to calculate.

But I think the hope would be that we will have a theory which applies under the very, very extreme early stages of the universe, but which gains credibility and gains confidence, because it also manages to account for otherwise unexplained features of the low energy world, and what people call a standard model of particle physics, where there are lots of undetermined numbers.

So we're dancing between physics and philosophy a little bit, but what do you think, what do you think happened before the Big Bang?

So this seems, this feels like something that's out of the reach of science.

RHT It's out of the reach of present science, because science develops and as the front is advanced, then new problems come into focus that couldn't even be postulated before.

I mean, if I think of my own career, when I was a student, the evidence for the Big Bang was pretty weak, whereas now it's extremely strong.

But we are now thinking about the reason why the universe is the way it is and all that.

So I would put all these things we've just mentioned in the category of speculative science, and I don't see a bifurcation between that and philosophy.

But of course, to answer your question, if we do want to understand the very early universe, then we've got to realize that it may involve even more counterintuitive concepts than quantum theory does because it's a condition even further away from everyday world than quantum theory is.

And remember, our brains evolved and haven't changed much since our ancestors roamed the African savanna and looked at the everyday world.

And it's rather amazing that we've been able to make some sense of the quantum micro world and of the cosmos.

But there may be some things which are beyond us.

And certainly, as we implied, there are things that we don't yet understand at all.

And of course, 1 concept we might have to jettison is the idea of 3 dimensions of space and time just ticking away.

I mean, I think Stephen Hawking had an idea that talking about what's what happened before the Big Bang, it's like asking what happens if you go north from the North Pole?

I don't like that idea, but that's a possible 1.

And so, we just don't know what happened at the very beginning of the Big Bang.

Were there many big bangs rather than 1, etc.

Those are issues which we may be able to get some foothold on from some new theory.

But even then, we won't be able to directly test the theories.

But I think it's a heresy to think you have to be able to test every prediction of a theory.

We take seriously what Einstein's theory says about the inside of black holes, even though we can't observe them.

Because that theory has been vindicated in many other places, in cosmology, in black holes, gravitational waves, and all those things.

Likewise, if we had a theory which explains some things about the early history of our Big Bang and the present universe, then we would take seriously the inference if it predicted many Big Bangs, not 1, even though we can't predict the other ones.

So the example is that we can take seriously a prediction if it's the consequence of a theory that we believe on other grounds.

We don't need to be able to detect another big bang in order to take it seriously.

It may not be a proof, but it's a good indication that this is the direction where the truth lies.

Yeah, if the theory is getting confidence in other ways.

Do you think there's other universes besides our own?

There are sort of well-defined theories which make assumptions about the physics at the relevant time.

And this time, incidentally, is 10 to the power minus 36 seconds or earlier than that.

And there were some theories, a famous 1 due to Andrei Linde, the Russian cosmologist now at Stanford, called eternal inflation, which did predict an eternal production of new Big Bangs, as it were.

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Martin Rees: Black Holes, Alien Life, Dark Matter, and the Big Bang | Lex Fridman Podcast #305