Interview with Lord Martin Rees — Transcript

Thomas:

Sometimes in this game, you get to do an interview where you can genuinely say, “The person I’m about to interview needs no introduction.” This is one of those occasions, but if I were to do that, it would wreck the fun of getting to introduce the interview. And why would I deprive myself of that? So, this episode we’re interviewing Lord Martin Rees, the Astronomer Royal. Martin Rees is one of the foremost cosmologists and astrophysicists of our time. He was made the Astronomer Royal in 1995. He’s been the Master of Trinity College Cambridge, President of the Royal Society. He’s written more than 500 research papers across various areas of astrophysics and cosmology, including contributions to the origin of the cosmic microwave background radiation, the final proofs of the Big Bang Theory, through studying quasars and gamma ray bursts.

Thomas:

In the latter part of his career, he has been an immensely influential popularizer of science, writing books on cosmologies such as Just Six Numbers, and Our Cosmic Habitat. And he has also devoted himself to considering grand problems of the future of humanity, and the existential risks that we face. His book, Our Final Century, helped to kick off the field of existential risk studies, and he co-founded the Center for the Study of Existential Risks at the University of Cambridge in 2012. It is no exaggeration to say that a great many of the ideas that we’ve discussed on this show, and my own personal inspiration to study physics in the first place, owes to the work of Lord Rees, both in discovering much of the science in the first place, and then again in popularizing and explaining the ideas so wonderfully in his books.

Thomas:

I was extremely grateful that he was willing to be so generous with his time, and respond to such a large range of my questions. Our interview touches on existential risks, the current pandemic, extraterrestrial life, cosmology in general, and the history of cosmology, and the nature of fundamental physics and what is still left to find out. Without further ado then, the interview.

Thomas:

First of all, Lord Rees, I want to thank you very much for being so generous with your time and coming on the show today. And we’d like to start by talking about the field of catastrophic risks. So in 2003 you published this book, Our Final Century, which helped to kick off a flurry of academic activity in this field, and you co-founded the Center for the Study of Existential Risks a few years ago. Similar organizations have sprung up all over the place. Reflecting on this effort to get people to take these risks seriously, have you had the impact that you’ve hoped so far?

Martin Rees:

Well, ironically the COVID-19 pandemic has made us more relevant, and people take these serious global threats more seriously. But the history that I’ve always realized is that this century is special. It’s the first when one species, named the human species, has the power and number to actually affect the whole world. We’re collectively changing the world’s climate and its biodiversity by our actions, and also we are able, through our technology, to cause runaway catastrophes. And so things are special this century. And as you say, my book in 2003 I address this question. I have a more recent book, which is called On The Future: Prospects for Humanity. And the main point is that we do need to worry about the dangers, which we can cause by error or by design, and of course the COVID-19 pandemic is an event which does have global consequences. And that’s a wake up call, as it were, and makes us aware that we do need to plan and be prepared for a new class of catastrophe which couldn’t have happened in a less empowered and less interconnected world.

Thomas:

At the time when you wrote Our Final Century, you had a rough estimate of the odds of making it to the end of the century at around 50/50. So I wanted to start with an optimistic approach. Let’s say that we make it to the end of the century. What did we get right, and therefore what do we still need to do?

Martin Rees:

Well I think we will have a bumpy ride through this century. I think one can imagine that we could’ve wiped ourselves out, but I think that’s pretty unlikely. But I think events worse than the present pandemic are almost certain to occur during this century, and also there’s a new class of threats from, for instance, cyber attacks which knock down the electricity grids in a whole country, or bio-threats, engineered pandemics rather than natural ones. So I think there’s a growing range for things we need to worry about. So we’d be very lucky if we get to the end of the century without having had a fairly bumpy ride. That’s all I would say. I wouldn’t want to put any firm probabilities on these things.

Martin Rees:

All I would say is that there’s a very important maxim that the unfamiliar is not the same as the improbable. And of course, we’ve never had a pandemic quite like the present one, and there are other possible dangers that may emerge, which are so serious that one occurrence is too many, and we need to prepare for them. I think one thing that has been learned in the last year is that we ought to think a bit more in advance about these scenarios, so that we are better prepared for them.

Thomas:

Coming onto the COVID-19 pandemic, then, when I ask about the impact of it, I’m reminded of the old historians’ joke when asked about the legacy of the French Revolution. “Please ask me in a few hundred years.” You had this famous wager that there would be a mass casualty event from bio-terror or bio-error by the end of this year. Now, COVID is a natural pandemic, but it’s not dissimilar to the kind of catastrophe that you warned of and envisioned. Reflecting on it, it feels like some parts of our response held up better than we expected, while others were much worse. So I want to ask, given that you’ve thought about this in advance, do you think this pandemic has unfolded as you expected? And what has and hasn’t surprised you about how we’ve responded to it?

Martin Rees:

Well, I hadn’t thought through the scenario of what the response would be, and I have to say I was thinking already of some, not natural but engineered pandemic, because I was very worried when I read that back in 2011 two research groups had been able to modify the influenza virus to make it more transmissible. And of course, if that can be done with some viruses, simple ones, then it won’t be very long before it can be done with things like the coronavirus. So I’d been thinking that the first real global pandemic would be an engineered one. I know there’s some people that think this pandemic started with a leakage from the lab. I don’t think many people think that’s correct. So they think it’s a natural one. But we were, I think, prepared for an influenza pandemic because there had been bird flu and things like that in the past.

Martin Rees:

But what we weren’t prepared for at all were the special features of a coronavirus, in particular the fact that we would be unlikely to quickly get a vaccine against it, and also that it would require protective clothing, et cetera, because of the way it was transmitted. And so we were not prepared in those two respects. And this is, in a way, surprising because there had been two similar types of virus, SARS and MERS, in Asia within the last 20 years. So we couldn’t say it was a very improbable event. And incidentally, perhaps it’s because there had been these precursors in Asia that the countries of East Asia handled the present pandemic far better than we have.

Thomas:

Yes. I think that’s certainly the case. And one thing that I think is interesting is: In many of your works, when you talked about the threat of a pandemic, you would say that there would be a potential for society to collapse, or for anarchy to happen if hospitals became filled. And I don’t think that any of us really anticipated this level of social restriction being possible or able to be implemented by governments. In some ways, I think we’ve actually shown that we can act collectively when there is a problem like this that arises, at least within societies. But then internationally, the response doesn’t seem to have held up very well and it seems like each country is going their own way. Do you think that’s a fair assessment? And do you think, reflecting on this and how it might relate to other catastrophic risks, there are ways that we should shore up our defenses against things like this happening in the future?

Martin Rees:

Yes indeed. I think we need to be on a wartime level of preparation in a sense to go through these things properly, and the countries that were most successful were, of course, those that were draconian in their early lockdowns, et cetera. And we, and other European countries, were less successful than those in the Far East. And I think we do need to be prepared, and the public need to be prepared, for such events so it doesn’t come as a shock and we don’t have to think things out on the fly, as it were, when the disaster comes.

Thomas:

The pandemic has brought the idea of science policy and the phrase we all hear a lot of, “Following the science,” into the limelight, for better or worse. And I wondered if you’d like to talk about your experience in the House of Lords and discussions with politicians that you’ve had, perhaps before this about these catastrophic threats. And also the role that science should or shouldn’t play in policy making.

Martin Rees:

Well of course it’s clear that in the case of this pandemic, the scientists have been learning as they went along. There were lots of things that were quite unclear back in March which are now clearer. And, of course, when the facts change, then policy changes. And so it’s not surprising there’s been change in policy. But I think the public tends to feel that the scientists do, in effect, know the answers and it’s clear what should be done. But that’s not the case. And of course, even when the scientists can give clear information about the scientistic aspects of a phenomenon, then politicians have to take that into account, but along with other things like the economic and the social and political consequences of the action. And so science is part of the decision making, but it’s not the sole determinant of what actually happens. And scientists should realize that there are other factors that politicians have to take into account where scientists aren’t experts, and where they’re just concerned citizens. So that’s one point.

Martin Rees:

But there are some times, cases, when the scientists are not prepared and don’t know what advice to give. In fact I could give two examples. One was back about 30 years ago, mad cow disease was a very unusual kind of disease which surprised everyone, and at first it was thought that it could not be transmitted to humans, and then it was. And it was so uncertain that one had no idea how serious it would be. In fact, about 100 people died from mad cow disease over a quite long period. But if you’d been the scientist advisor to the government back then, and you been asked, “Is there a 1% chance of a million deaths?” You’d have to have said yes, because you couldn’t rule it out. And so the politicians therefore would be justified in overreacting. And second in a very different case, the unpronounceable volcano, which exploded a few years ago. You may remember that.

Thomas:

Yes. Eyjafjallajökull or whatever it was. I tried.

Martin Rees:

Say it again?

Thomas:

Eyjafjallajökull. Something like that. I apologize for any Icelandic listeners we may have.

Martin Rees:

Yes. Well this is an example where advice was actually an overreaction because there’d be no preparation. Everyone knew that there were explosions of volcanoes in Iceland, et cetera, but what they did was they stopped all flights in Northern Europe. What they would’ve needed to do, really, to be better prepared would be to know better how resilient jet engines are to different kinds of dust, and whether the warranty governing the aero engines would still apply, and also have better ways of tracking where the dust actually was. If a similar eruption happened now, then the reaction would be less extreme because they would know what was dangerous and what was not. Whereas because they didn’t know, the reaction was overcautious and excessive. And so one reason for doing scenarios in advance is not only to be prepared when things happen, but not to overreact when things happen.

Thomas:

I mean it’s an interesting balance between reaction and overreaction. I think those of us who were worried about existential threats before, thanks to warnings like yours, I feel like we took the pandemic perhaps a little more seriously earlier on, as we were motivated by a sense of the fragility of our civilization. And I think now everyone can see that modern humans, our technology has not made us immune from these catastrophic risks, and we can all see the price of the disruption that they can cause. And I wonder if the long-term response to this pandemic will be that if a virus emerges in the future, people will take it much, much more seriously much more early on, and attempt to nip it in the bud where we have that maximum leverage of action to act early on. And you would also hope that our societies in the future would devote more resources to thinking about these problems and trying to work out the most effective ways of being prepared rather than dealing with the rather large expense of trying to deal with the problem after it’s already got out of hand.

Martin Rees:

Well certainly to some extent because estimates of the total cost of this pandemic in money, let alone in lives, are something like 20 trillion pounds. And if you work out the insurance premium by multiplying the cost of an event by its likelihood, then even if you thought that this would only happen once every 50 years, it would be worth spending a few hundred billion pounds in preparation. We didn’t.

Thomas:

And thinking of people like Florian Krammer here, who suggested the idea that you might want to come up with vaccines against the diseases that were most likely to cross over into humanity, even if they haven’t done so yet, this would be an effort that would cost some billions of dollars, but-

Martin Rees:

That’s precisely the kind of thing we should do. We should try to be prepared and have the expertise so we can quickly have a vaccine. And of course politicians need to realize that they may have to sanction the spending of money that may turn out to be wasted if the pandemic doesn’t occur. And back in 2009, I think some politicians were criticized rather unfairly because they stocked up on vaccines against a flu pandemic that didn’t occur. To criticize politicians for taking that precaution that was unnecessary is as unfair as criticizing someone for taking out fire insurance when their house doesn’t burn down. And so we’ve got to accept that some preparation will lead to unnecessary expenditure, but I think you want the safe side. We are going to need to be prepared more. And of course, this is the case for studying diseases in greater detail so that we can work out how transmissible they are, et cetera. And of course let’s not forget that pandemics are only one class of extreme risk we need to worry about.

Thomas:

So this is a recurring theme in your work really, which is about the perils of short-term thinking, business men who want short-term profits, politicians and democratic establishments that are too concerned about the politics of the next election. What do you think we can do to encourage longer term thinking and planning? Do we need a cultural shift?

Martin Rees:

I think we do. Of course, let’s take the issue of climate change, that’s really in a sense a slow motion version of what we’ve had to deal with now. Now we have a crisis that we have to respond to very quickly. In the case of climate change, we can predict with great confidence that conditions will get very serious, at least in the second half of the century, and that we can prevent these serious consequences only if we change our course now and do something to reduce our dependence on carbon. But it’s very hard to persuade people to devote resources to something when the benefit will accrue 20 or 30 years from now, and moreover, will accrue not to your own nation but to people in remote parts of the world, which will be more affected by climate change. So it’s very hard to get politicians to take account of these long-term threats unless the public does, because the politicians won’t do it if they lose votes by spending money in a way that the public doesn’t support.

Martin Rees:

So I think what we need to do to promote long-term thinking is to go directly to the public. It’s not enough for science advisors to tell politicians what may happen in 30 or 40 years. The politicians need to have this concern fed into their inboxes and see it in the press, and realize the public’s concerned. And so what’s very important is that the public should be aware of the downside of climate change, and think ahead. Most people do care about the life chances of their grandchildren, and baby’s born today will still be alive in the 22nd century. So it shouldn’t be too difficult to persuade people that they should care about what might happen 50 years from now, even though the standard economic discount rate which would apply to particular office building or something, would attenuate your concerns after about 2050. So we need to think long term. And I think here, religion can help. In fact, the Papal encyclical in 2015 called La Darto C, where the pope talked about our obligation to non-human world and the climate and the environment, et cetera.

Martin Rees:

That was very influential. It got a standing ovation at the UN. And he has a billion followers in Latin America, Africa and East Asia. And the fact that politicians knew those followers cared made it easier to get a consensus at the Paris Climate Conference in December of 2015. And a smaller version we had in this country a couple of years ago, which was when Mr. Michael Gove, not perhaps the most enlightened politician, introduced legislation to ban non-reusable plastic drinking straws and things of that kind. Now the reason he was prepared to do that was he knew that the voters would support him. And the reason the voters was that our secular pope, David Attenborough if it were, fronted those TV programs, Blue Planet Two, which shown among other things an albatross returning to its nest and coughing up for its young, not the nourishment, but bits of plastic. And that had made the public aware that accumulation of plastics in the ocean was an environmental concern.

Thomas:

I think it’s interesting this parallel with religion, because once religion did provide a sense of something beyond ourselves and beyond our own lives, which, as you write about in your books, inspired people to build cathedrals that they knew they would never see completed. Do you think that contemplating the long-term future of our species of intelligent life could provide the same motivation today for secular people? And would that be a reason for us to continue speculating on these subjects?

Martin Rees:

Well I think so. It’s true that we do need to think long-term, because the ones we do is that our world has billions of years ahead of it. It’s taken four billion years, or thereabouts, for our biosphere and us to evolve from simple beginnings in the young Earth. But we know that the Earth will last for five or six billion years more before the sun flares up and dies. So we’re not even the halfway stage in the life of our planet. And so we certainly think longer term. And of course, it’s at first quite paradoxical that we don’t think long-term to the extent that the cathedral builders did when they were happy to build an edifice which wouldn’t be finished in their lifetime, but it still inspires us many centuries ahead. But I think the reason for that apparent paradox is that things are changing so fast. The cathedral builders, they thought maybe the world would end in 1000 years.

Martin Rees:

But at the same time, they thought that children and their grand children would live lives rather like their own. And therefore, they would appreciate the finished cathedral. Whereas now, things are changing so fast that I don’t think we can, with the same confidence, say what life will be like for people 50 years from now. And I think that uncertainty is an excuse, as it were, for not thinking long term, because we aren’t quite sure of what people will want then, what the issues will be. So we need to do our best to try and foresee what will happen. And of course, ensure innovation is responsible, and that we avoid developing the kind of technology which will be damaging in the long run. But it is very hard to get people to think long-term when it’s clear that things are changing very fast.

Thomas:

It almost causes us to discount the future because it’s so uncertain of what we might want.

Martin Rees:

Yes, we do apply a certain discount rate to these things, but because of uncertainty as you say we do discount it too much. And we’ve got to realize that irreversible damage can be done if we don’t, for instance, try to control our CO2 emissions.

Thomas:

I would feel bad if I got through this whole conversation without having at least one question about extraterrestrial life. We can see in recent years that the astronomical parameters that are relevant to trying to work out the probability of life, things like how many exoplanets there are, what their atmospheres might be like, are being narrowed down by new studies now. Others like the likelihood for life to develop initially, or for life to become intelligent once it’s started, these things remain elusive because we have just the one data point here on Earth. How do you think astrobiology has shed light on what we might expect? And what would you view as the best prospects for finding evidence of life?

Martin Rees:

Well I think you built a very good summary of what is becoming more certain, and what’s still very uncertain. The big exciting development, of course, in the last 20 years in astronomy is realizing that most stars are orbited by planets, just as the sun is orbited by the Earth and the other familiar planets. And there are, in our Milky Way Galaxy, many, many millions of planets, rather like the young Earth, about the size of the Earth, orbiting a star rather like the sun, at a distance where water could exist, neither boiling away nor being frozen all the time. So those are all candidates for life. But what we don’t yet know is how likely it is that life evolved, because we don’t know how it began on Earth. We understand evolution, how simple life evolved by natural selection into the biosphere that we are part of today, but the transition of complex chemistry to the first metabolizing, reproducing entities that we call alive, that is still a mystery.

Martin Rees:

And that’s a fascinating question even to the most Earth-bound biologists. And so I hope that we’ll make progress in the next 20 or 30 years in two ways. One is, we might understand the origin of life, because more people are now working on that problem from a terrestrial perspective. But also, we will perhaps have evidence from data gained by the next generation of even bigger telescopes we now have, for whether any of these planets orbiting nearby stars have any kind of biosphere, because there are spectroscopic signatures of methane and oxygen, et cetera. And so if you got a strong enough signal, which implies a very, very large optical mirror, then you might be able to take a spectrum and get an inference of some sort of biosphere around some of these planets.

Martin Rees:

And that’s something which should be feasible with the next generation of telescopes, in particular there’s a telescope being built in Chile by a European Observatory, it’s a consortium of astronomers in Europe which we belong to in the UK, and fortunately Brexit doesn’t stop us belonging to that. And this would have a 39 meter diameter mirror, and this will collect enough light from planets orbiting nearby stars to be able to get at least a crude spectrum from them. And this will be the first way we can perhaps, if we’re lucky, find evidence for life. And of course, the other thing that will be important would be to look more carefully in our own solar system. Of course, Mars may have some evidence of life there. We don’t know. But other places, not so distant, like the moons of Saturn and Jupiter. Enceladus, a moon of Saturn, which has an ocean with water underneath, and Europa, which is a moon of Jupiter, which also has a frozen surface with water underneath, and it could be that there’s something swimming in those oceans.

Martin Rees:

And within 10 or 20 years, probes will be sent to look for that. And even if it’s very simple life, then finding evidence for it elsewhere in our solar system, particularly in the outer solar system, would be crucially important because if it turned out that life had originated twice independently within our solar system, that immediately says it’s not a rare fluke that’s happened on Earth. And therefore, it would’ve happened on a large fraction of the other Earth-life planets. So finding evidence for life on Enceladus or Europa would immediately say that there’s likely to be life in literally millions of places in our galaxy. What’s important about mentioning Mars, because some people point out that it might be possible for life to be transmitted between Mars and the Earth by meteorite, et cetera, so it could be essentially we’re all Martians and life came from Mars to the Earth. But I think it would not be so likely that it could be transmitted from as far away as Jupiter or Saturn to the Earth. So it would have to be independent.

Thomas:

Philosophical implications of that for things like the Fermi Paradox and trying to understand what else is out there would be truly profound. So you think that these things, these atmospheric detections are far more likely than some of the other things people have suggested such as finding radio waves via sati, or seeing big astroengineering projects out there in space, which advanced civilizations might-

Martin Rees:

Well I think so. It’s obviously less likely that there will be intelligent life, or biological life, than some life of any kind, and indeed biologists who study evolution on the Earth, they debate about whether the emergence of intelligence was fairly automatic, or whether if you were to rerun the clock on the earth, you might end up with a different set of flora and fauna on the Earth today without intelligence. So people wonder about how many contingencies have to be fulfilled for intelligent life to arise on the Earth, even once it got started as simple life. So we don’t know. But my take on this is that we don’t know, but if we were to detect some artifact or some manifested artificial transmission, it would probably come, not from a civilization rather like we have on Earth today trying to send messages to us, but from something electronic.

Martin Rees:

And let me explain why I say this. If you look at the history of life on Earth, then it’s taken three or four billion years to get from the simplest life to us. And for a few thousand years, we’ve had a technological civilization. And it may be that in the next thousand years, this will be usurped by some sort of post-human electronic civilization. If that happens, then those electronic entities may be near-immortal, they may not want to be on a planet, they may become zero G, they won’t need an atmosphere, so they would go up into the blue yonder. So in the far future, there may electronic entities which are, in a sense, our progeny, but they’re not flesh and blood. And they will exist for billions of years, perhaps, even though the rest of the civilization that created them may only exist for a few thousand years. Now, if there was another planet where evolution had gone roughly the same way as on Earth, then of course it wouldn’t be synchronized. It is most unlikely that it will be synchronized within a few thousand years when the ages of the stars differ by billions of years.

Martin Rees:

So if it had lagged behind, then of course we’d see no intelligence. Whereas if it had been a billion, or even a few million years, ahead of us and along the same track, then of course if it had got far beyond the stage when it was a flesh and blood civilization, and so any evidence of it would be in these electronic entities left behind. So my prediction is that we may not find any evidence for intelligent civilization, but if we do it will be something electronic, which would be some artifact left by some long dead civilization. And of course, we then confront, as you mentioned, the Fermi Paradox. This is the issue of whether it’s surprising that we haven’t already been invaded, as it were, by intelligences from elsewhere. The argument there is that some planets will have had a billion or two billion year headstart over the Earth because they’re around older stars, so why haven’t some of them got to us before we got to them if the origin of intelligent life is common?

Martin Rees:

It’s a good argument, obviously, but I think there are many escape clauses. I think the most important one is that post-human evolution is not governed by Darwinian selection. It will be what I call secular intelligent design. It will be us designing machines with superhuman capability, and maybe the machines then designing still more themselves. And so since it would be some sort of design, not just random process like Darwinian evolution, then it’s not going to necessarily have the qualities needed for success in Darwinian competition. Darwinian selection favors intelligence, but it also favors aggression. But this future evolution, which is technologically led, Amy not favor aggression. So it could be that there are super intelligences out there who are living an entirely contemplative life, and showing no expansionist tendencies, and not revealing themselves. So this is really a case when absence of evidence isn’t evidence of absence.

Thomas:

It’s interesting because there’s this aestivation hypothesis that maybe they are out there waiting for the universe to be cold enough to make it worthwhile to do their calculations.

Martin Rees:

That’s another reason why they might not be concerned with us now, yes.

Thomas:

I also wonder if maybe it is the fact that the civilizations that remain aggressive don’t actually make it past the filter that we’re approaching at the moment, and only the ones that are able to direct their evolution in a more benign way actually do survive.

Martin Rees:

That’s certainly another possibility, because it could be that we will perhaps survive the next century but not much beyond that, and not for long enough to have allowed post-human progeny to get beyond the Earth.

Thomas:

So this is also a physics podcast, and I really wanted to talk about cosmology for a little bit. I think the fact that we can infer so much about the nature of our universe, its history, and its future, essentially just from the starlight that falls on our planet in experiments that we’ve performed on Earth, it stands out for me as one of the greatest stories that we’re able to tell. Our understanding of the cosmos has evolved hugely over the course of your career, and you contributed a lot to some of that. Would you talk about what it was like when you first got involved, cosmology? And some of the subsequent developments that you think have been the most important and the most surprising perhaps?

Martin Rees:

Well I do think that when the history of science is written, what’s happened in cosmology in the last 50 years will be one of the most exciting chapters, because this has really transformed our understanding. If you go back just 50 years, no one knew whether our universe started with Big Bang or not. I mean, my senior professor Fred Hoyle, when I was a student, he believed in so called steady-state universe, which is expanding, but it went on forever and as the galaxies disperse, new ones form in the gaps as it were. So it never started from Big Bang. And that was a controversy and we didn’t know very much about the overall scale of the universe. Whereas since that time, we have learned through very compelling lines of evidence that everything started in a hot dense beginning, what we call the Big Bang, and we can trace properties of the material back to within a billionth of a second of the very beginning of all.

Martin Rees:

As we trace things further back, then everything would’ve got hotter and denser near the beginning, and the reason the first nanosecond is a mystery is that every particle then has higher energies than we can achieve even in a big accelerator like the LHC at CERN. So we can’t understand the physics of the crucial tiny initial incident, which happened. But after that, we can understand what happened, and we have fossils of different stages. We have very good evidence of what happened when the universe was a few seconds old, when helium and deuterium and hydrogen underwent nuclear reactions and emerged in certain proportions, and when we look at the radiation which fills space microwaves, they are a relic of the hot dense beginning. The radiation’s very hot and dense because the universe expanded, the universe cooled down its radiation and diluted it, but it’s still there and it’s observed in microwaves. And this was discovered in the late 1960s.

Martin Rees:

The other thing that we’ve learned is that this early universe was not completely smooth. It had some fluctuations in it, some places where the density is above average, some where density is below average. And the places where density is above average, as the universe expanded, they’d be decelerated more by their own gravity than the average. And they would eventually condense out into bound systems. And that’s, crudely speaking, how galaxies formed. And so we know that the universe does hot and dense, we know by studying the background of radiation that it had these fluctuations, and moreover we now know from computer simulations that those fluctuations have the properties needed to give rise to galaxies of the kind that we observe now grouped together in clusters in the way we observe now. So we have a pretty good outline picture of what happened in the 13.8 billion years since this Big Bang. But, of course, every advance brings into focus a new set of problems.

Martin Rees:

What we’d like to know is why is the universe expanding the way it is? Why does it contain the amount of atoms and radiation it does? Plus also, some other particles, for example dark matter, and why does it expand in a smooth way except a small populations? The answers to all those questions, minus the first tiny fraction of a second, which is still rather mysterious, mysterious because the conditions are so extreme we don’t yet understand the physics. And so that’s a challenge for the future, to try and get clues to the physics that prevailed at these very early stages, which are conditions too extreme for us to do direct experiments. So that is the challenge now, and to understand what happened in the Big Bang, was our Big Bang the only one? And how big is the universe? How much further does it extend beyond the range of the telescopes we can use today?

Martin Rees:

And I should’ve said, that most of the progress has been due to not armchair theorists, but observers using more powerful telescopes, and also telescopes in space able to observe X-rays, infrared, ultraviolet, et cetera. And that’s allowed us to observe galaxies and other objects at very great distances. And of course, we have an advantage over geologists and paleontologists in that we can actually see the past, because when we look at distance galaxies, we’re seeing them as they were when they were younger, and we can look back far enough to see a galaxy when they were newly formed. And so we can check our theories by seeing, do they match the way galaxies are today? Do they match the way they were one billion, two billion, three billion, four billion years ago, et cetera?

Martin Rees:

So we have quite a number of good checks on whether our theories are basically correct. So obviously we can’t be certain. We may be missing some crucial features. But we do have a much clearer picture now of our galaxy, our place within it, and the physical laws that govern it. And the other thing we’ve learned is that Einstein’s theory of gravity does seem to be correct. We had no good test of this 50 years ago, whereas now we find evidence for black holes, which are the most extreme and fascinating predictions of Einstein’s theory. We can study them in detail. So we’ve made tremendous progress in understanding physical laws which govern stars, black holes and galaxies. And most of the Big Bang. That’s a rather long answer to your question, I’m afraid.

Thomas:

No, no. That’s a wonderful overview of cosmology. It’s so interesting. I’m writing a series of episodes at the moment covering the history of cosmology, and I tried to think, “Where should I begin with this story?” And the place I ended up beginning was Fred Hoyle on what is now Radio 4 I suppose, addressing people saying that most of the theories of cosmology have been worked out and that it was in fact the steady-state theory, because that was the moment that he coined the term The Big Bang in an almost slightly derogatory way. At the start of your career, that was a very active debate between the steady-state universe and the Big Bang Theory, which you helped to resolve.

Thomas:

For my generation, I think when I look at cosmology from a historical perspective, the thing we have to appreciate is that all of these things take on an aura of inevitability once we know about them. The narrative of the Big Bang is established for us, and so it almost seems natural to say the universe had a beginning because we’ve always taken this as an assumption. But the actual process of inferring what’s really going on from astronomical observations when you have several different theories that could explain them, is a lot trickier. Would you like to talk a little bit about your experiences being involved in that debate between the steady-state universe and the idea that the universe had a beginning?

Martin Rees:

Well of course, the idea of a Big Bang was first formulated in the 1920s by Lemaitre, who’s a Belgian priest. And he was first because of primordial atom, and this was an idea but there was no way of testing it. And there were two things which happened in the 1960s. The first, which was one that happened in Cambridge which I followed closely, was that radio astronomers led by Martin Ryle, they discovered that some galaxies emitted very strong radio waves. We now know that the radio waves are energized by black holes in their centers. But what Martin Ryle realized was that some of these things were a long way away, even further away than the optical telescopes could probe at that time. And Martin Ryle surveyed the sky and compared the relative numbers of apparently bright and apparently faint ones.

Martin Rees:

And he showed that the number of faint ones was surprisingly high compared to the number of bright ones, and that implied that there were more a long way away than there were closer by, as compared to if they were in Euclidean space. He interpreted this as saying that they were a phenomenon that was more common when the universe was young than today. Turned out he was right, because young galaxies are more prone to have these answers than the present day ones. But of course that was inconsistent with the steady-state theory, which would’ve said that at all eras, on average, things look the same. So this was the first tentative evidence, but it wasn’t completely compelling. There were some ways around it, and what was far more compelling, and made most people take Big Bang seriously, was the discovery that intergalactic space was filled with microwaves seemingly coming from all directions and having no obvious source, and realizing that this radiation was best explained as the afterglow of the hot dense beginning, the radiation that was hot and dense and became diffused and cool to three degrees above absolute zero by the expansion.

Martin Rees:

And this discovery made most people accept the Big Bang. Fred Hoyle never really did. He still had a more complicated idea. He ended up with a compromise, as I recall, of a steady bang, but he never really reconciled himself to the standard Big Bang. Although ironically, he did some of the best work underlying the theory. I mean I mentioned earlier that we can predict what proportions of hydrogen, helium and deuterium would be made in the Big Bang as it cooled down to temperatures of a few billion degrees. And he and colleagues did some of the best calculations on this. And his great achievement which did survive was realizing that, contrary to what Lemaitre had thought, the rest of the periodic table, carbon, oxygen and iron and all the elements that we’re made of, couldn’t be made in the Big Bang. Only hydrogen, helium and deuterium, and a bit of lithium.

Martin Rees:

And he realized that most of the elements which we are made of were synthesized in starts. The idea here is that stars get their fuel by nuclear fusion, they get most of their energy by turning hydrogen to helium, but then they turned helium into carbon and oxygen, and up to iron. When stars end their lives, the heavy ones explode and fling back into space as processed material, and this material then condenses into a new generation of stars. And so according to this wonderful story, our solar system condensed about four and a half billion years ago from a gas cloud already contaminated by the debris from earlier generation of massive stars, which had lived and died, and thrown back processed material into space, including carbon, oxygen and all those elements.

Martin Rees:

So we now know that every atom of carbon in our bodies is made inside a star, and the reaction we have inside us, atoms which had their origin in many hundreds of stars spread through the Milky Way, stars who have lived and died at least four and a half billion years ago, so that their debris was part of what formed our solar system. And that’s a wonderful story, which Hoyle and his collaborators actually outlined back in the 1950s, and that has survived. So Hoyle was a really great figure in this subject.

Thomas:

In recent years, ideas about the multiverse have gained a following in both popular and serious science, and you were one of the people who initially supported and suggested this. One advantage, at least philosophically, is that a multiverse might help to solve this anthropic fine-tuning problem of why the universe appears to be so well-calibrated for complexity and human life. I wondered if you’d like to talk first on your thoughts on this fine-tuning problem, and the parameters that appear to be tuned to allow us to exist, and whether we need a multiverse to help us resolve this.

Martin Rees:

Well, fine-tuning, the point is that you can easily imagine a counterfactual universe, which would not allow complexity in life. I mean, for instance if the properties of atomic nuclei were such that you didn’t get nuclear energy, then you’d have no chemistry. You’d just have a universe of just hydrogen. Or, if gravity was very strong, then stars might exist but they’d be very small and short-lived, et cetera. So it’s clear that there have to be parameters in some particular range in order to stand a chance of having complexity. You want a lot of time, and you want stable stars, et cetera. And it’s easy to imagine the counterfact universe where that didn’t happen. Just how much fine-tuning is needed is a bit controversial, but you certainly need some. But quite apart from that, there are some theories of the very early universe which go under the name of the inflation of the universe ideas, which are mainly put forward as an explanation of why the universe is expanding the way it is, and why it’s more or less the same, on average, everywhere we look.

Martin Rees:

It turns out it is quite a problem why if we look in all directions to 10 or more billion light years, the universe looks the same. How did it homogenize in this way? And the idea of the inflation of the universe, which was put forward nearly 40 years ago, is an idea which is a rather compelling explanation of this. It’s not battle tested as a theory because it’s hard to directly test it, but it’s a very good idea. Moreover, some versions of this have the property that you would get many Big Bangs, you would have the substratum, which is expanding exponentially, and Big Bangs would condense out of it, not as one but many. And the main advocate of this is a Russian cosmologist called Andrei Linde, who works at Stanford. He had a theory called Internal Inflation, which involved the idea of many Big Bangs. And there are other versions like this. And then of course the second question: If there are many Big Bangs, would they all be governed by the same physical laws? Or might it be that the physical laws of nature are different in different ones? So as you say, some could be tuned for life and some not.

Martin Rees:

And here we don’t know, but there are some theorists, particle physicists, who believe in String Theory, who think that there could indeed be many different forms of empty space, many different vacua, each of which the microphysics would be different. So one possibility, the most exciting idea, is that there are many Big Bangs and as each one cools down, it’s governed by different microphysics from the others, and therefore some would be more propitious for emerging complexity than others. But then there would be some which would be tuned so that life can exist. So that’s affected my idea. But the idea of inflation is a popular interpretation of why the universe is so uniform on the large scale, and there’s a debate among particle physicists about whether the laws of nature are unique or whether there could be other possible laws of nature in other kinds of space.

Martin Rees:

So these are on the frontiers, and of course one is hopeful that these problems will be settled in the next 50 years. I’m not all that optimistic about all of them because simple things have been done and when you get to these things which are harder to test, then of course it may be a longer wait. For instance, the Higgs particle was predicted in the 1960s, it was 50 years before the evidence for that was found in the LHC accelerator at CERN. And so it could be that we’d have to wait a long time before we’d have evidence for theories which allow us to address these questions about the very early universe. We don’t know. And of course, to be slightly more philosophical, it’s also possible that there could be a theory, like Super String Theory, which is a unified theory that brings together gravity and Einstein’s theory, which is dominant for some large scale, with the forces in the micro world. There may be such a unified theory.

Martin Rees:

But even if it exists, it could be it’ll be too hard for us to actually understand. No particular reason to think that all the key features of nature are accessible to human minds, any more than Newton’s ideas are accessible to the monkey. And so it could be that we will hit the buffers, and that even though there is a theory, you won’t understand this. And then of course, you might ask the other question: Will AI help us? And it could be quite possible that there are theories like Super String Theory, which involve very complicated geometry in 10 dimensions, and there are lots of variance in these theories, and it may be just too difficult for a human being to actually work through these very complicated concepts, and this complicated geometry.

Martin Rees:

But through the advance of speed, an AI may be able to do this. And so it could be that we will only know if a particular unified theory is correct because it’s being fed into an AI and the AI has done work and just spewed out at the end of its calculation the correct strength of gravity and other important numbers about the universe. That may be one way to go. But I think we’re going to depend on the better instruments, in the lab and in space, and better computers. And already, we depend very much on computer powers to simulate what happened in space because we can’t do experiments crashing black holes together or crashing galaxies together in the way that particle physicists can crash particles together.

Martin Rees:

But we can in the world of our computer do just those things. We can ask what would happen if two galaxies crashed together, if two black holes merged, et cetera. And then we can compare the results of those calculations with what we actually see when we look out into space. And that’s the way we get a feel for whether or theories are on the right lines, whether the simulations, which we can do, are a good match for what we actually see in the sky. And that’s a very important technique in astronomy, where we can’t obviously do direct experiments but can just observe.

Thomas:

It’s fascinating just coming to this question of the end of theoretical physics. Or rather, I suppose, when we look at the history of how physics has developed, there’s this interplay between theorists and experimentalists. Sometimes theorists lead and come up with testable predictions, which are then falsified by experiment. Sometimes experimentalists lead and find and explain phenomenon, which need theories to be modified in order to adapt them. There’s often this interplay between the two. As you point out, in particle physics and in this fundamental high energy physics, we’re reaching the point where we can’t really probe those higher energies anymore, and we’re getting to the stage where we’re confirming things like the Higgs Boson, which was first theorized some years ago. And it seems the theorists have advanced a long way past the experimentalists, at least for the field of high energy physics.

Thomas:

But one of the passages for me in writing that really stuck with me the most was the point that a full understanding of our universe really goes beyond where reductionism can take us. I think there’s this tempting idea in physics that you can just reduce everything down to these fundamental physical laws, and that the main challenge we’re trying to solve here is to write those down, and then once you have them you can just say, “Well I have the Schrödinger equation which describes the atom, and humans are made up of atoms, so of course I can basically derive all of the complex phenomenon just from these fundamental equations.” You can almost see the textbook saying that the universe is left as an exercise to the reader. But it makes you think that perhaps what’s left in a lot of physics is taking different approaches to understand different phenomenon that are occurring in the world and make predictions. Do you think that there may be more room in other areas of science as opposed to endlessly chasing this fundamental thing.

Martin Rees:

Well I’d like to put a gloss on what you said. The phrase “theory of everything” is often used, and that’s a very misleading, hubristic term to use because it is true that we aspire to have a theory that does tie together the four fundamental forces of nature, maybe String Theory, maybe it’s something quite different. But of course, that would give us a fundamental understanding, but it wouldn’t actually help most scientists with their work. If you’re a chemist, an economist, or a biologist, you’re not held up through not understanding enough subnuclear physics. You’re held up because you’re dealing with very complicated things. And so one point I try to make in my book is that the scientists are in a hierarchy, where each one has its own irreducible concepts.

Martin Rees:

So if you’re a chemist, you talk about valency and things. And if you’re a biologist you talk about cells, or maybe organism, et cetera. Or higher up the chain, you may talk about systems in sociology and et cetera. So every science has its own concepts, and it’s valency in chemistry perhaps, and it’s imprinting an animal behavior, et cetera. Let me give you some simple example of the sense in which reductionism does and doesn’t occur. Let’s take a subject like fluid mechanics, fluid flow, which is a serious academic subject, and you can understand when flows go turbulence and what happens when you get a breaking wave and things like that. Okay? And this is a serious subject. And people who work on this subject, they don’t care at all if water is H2O. They treat it as a continuous fluid, and they use concepts like turbulence and viscosity, which are emergent properties. And they can calculate when things are turbulent and et cetera, and it’s a predictive science.

Martin Rees:

But having said that, they wouldn’t deny a breaking wave is a solution to Schrödinger’s equation, if you could solve Schrödinger’s equation to 10 to the 30 atoms, then this would be a solution. No one’s denying that. You’re not saying anything mysterious about a breaking wave. But the main point is that, even though one is reductionist in the sense that one believes these things are solutions to Schrödinger’s equations, simply saying that is not a way to understand the phenomenon you’re trying to describe. It wouldn’t give you any enlightenment if you could do some monster computer program and end up with a breaking wave at the end. We understand it in terms of the concept of fluid mechanics. And I use that example because no one thinks anything mysterious about the way water flows, but if you go higher up the hierarchy to living things, because some people in the past thought there was something special, vitalism, et cetera, which enter different things, and made reductionism even less credible.

Martin Rees:

But my view is that in principle it’s just the same, just as in the case of the breaking wave and the water flow, it is a solution of Schrödinger equation, but just even in the case of the water flow, it’s pretty useless to try and solve Schrödinger equation. That is even more the case for something as complicated as a living thing.

Thomas:

You might be able to write down the Hamiltonian for a human being, but you won’t be able to predict what they’ll say to you next.

Martin Rees:

You have to write it down because it would involve about 10 to 30 particles, but the point is even if you could compute this, it wouldn’t give you the insight we want. Human beings, the insight is in terms of emotions and all that, just as for a chemist it’s not subnuclear physics that matters.

Thomas:

So as our understanding concludes, we’re pushing up against the limits of what we can know, as we’ve touched on here. In cosmological terms, we’re pretty confident we can predict what the universe was a billionth of a second after it began, and trillions of years into the future as well. But let’s say you could ask some omniscient being anything. Is there a major open question in cosmology or in science more generally that you would love to have an answer to? And if so, do you think there would be a prospect for us to answer it?

Martin Rees:

Well I mean I think the very beginning of our universe, where the conditions are so extreme that we clearly need some unified theory of gravity and quantum theory. That is something which is still a mystery. There are ideas, but we have no idea which are correct, or whether we could understand them. So I would say that to understand those sort of things would be one of the challenges, which may or may not be within the capacity of human beings and their intellect. And of course, at the other end of complexity, it’s to understand the human brain. I mean it could be that the human brain is so complication it could never understand itself. That’s a possibility.

Martin Rees:

So there are certainly challenges at every level in science, and they stem from where the mysteries are part of physics as it were to the other extreme, where they’re part of biology or psychology. The thing about science is it’s an unending quest, and as the frontiers advance, their periphery gets longer so that the range of uncertainties and new questions is getting ever larger. And we talked about cosmology, and if I think back to when I was a student in the 1960s, the questions that we were posing then have, in many cases, been settled. But the questions we are addressing now couldn’t even been posed back then. And that’s the nature of science. We settle some things, but that opens up new questions we couldn’t have posed before.

Thomas:

And we have to expect the horizons always to recede, which is a good thing because it means that we’ll never get bored. Lord Martin, I want to thank you so much for being so generous with your time, and for your dedication to science communication as well, which helped to inspire many people, including me, to study physics. So thank you.

Martin Rees:

Thank you very much for the chat. I much enjoyed talking with you. Thank you.

Thomas:

I just want to add here that even after the interview was finished, Lord Rees was still happy to send me some of his recent papers and articles over email, and we’ll probably do a bonus episode at some point covering some of the themes that are brought out in those articles as well. I wanted to mention it simply to say getting to do this interview was a real honor, and although Lord Rees’s reputation for kindness did precede him, it was so lovely to get to have a conversation with someone who has dedicated their life both to science and to the communication of science, and the intersections between scientists and policy and all this sort of thing. And I really hope that you enjoyed listening to the interview half as much as I enjoyed getting to conduct it. We will return soon with more episodes.

Thomas:

In the meantime, Lord Rees is a new user of Twitter where he has mainly assembled his new articles and interviews that he’s contributed to lately. You can find him at @LordMartinRees, and you will find many more of his talks and interviews there. I would also strongly recommend Just Six Numbers and Our Cosmos Habitat for this incredibly concise yet wonderfully detailed and well-explained history of cosmology, the fine-tuning problem, and also his book on the future, which is his most recent book, for some of his work on existential risks and his theorizations about post-humanity and all this sort of thing. There are few with a clearer and more unique voice who manage to pack so much detail and insight into something that’s still very readable and comprehensible, and fewer still, of course, who was actually involved at the forefront of a lot of these discoveries. So I highly recommend these books if you’re looking for some New Year reading. You’ve been listening to Physical Attraction.

Thomas:

You can find us on the web at physicspodcast.com, and please direct and comments, questions or concerns you may have at the contact form there. I try to respond to all of the emails that I can get a hold of. You will also find there the about section, which will tell you the full list of episodes that we’ve done so far, and will summarize and the different series we’ve done on everything from Newton, Stalin and the scientists, the birth of stars, the end of the world, all that sort of thing. So if you are looking for which episode to listen to next, that would be a good place to start and find out what we’ve covered so far. You’ll also find ways to support the show via Patreon or PayPal. This is a solo effort, and all of your help is greatly appreciated. Many thanks to the listeners and the patrons who have contributed already. Until next time then, on the cusp of a new year, please do take care.