Ensuring Humanity's Survival w/ Lord Martin Rees

Oct 28

EPISODE #27

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Astronomer Royal Lord Martin Rees shares his insights into the existential threats facing humanity, what it means to be a techno-optimist, and how we can plan for the long-term future.

Lord Martin Rees is a leading astrophysicist as well as a senior figure in UK science. He has conducted influential theoretical work on subjects as diverse as black hole formation and extragalactic radio sources, and provided key evidence to contradict the Steady State theory of the evolution of the Universe.

Martin was also one of the first to predict the uneven distribution of matter in the Universe, and proposed observational tests to determine the clustering of stars and galaxies. Much of his most valuable research has focused on the end of the so-called cosmic dark ages — a period shortly after the Big Bang when the Universe was as yet without light sources.

As Astronomer Royal and a Past President of the Royal Society, Martin is a prominent scientific spokesperson and the author of seven books of popular science. After receiving a knighthood in 1992 for his services to science, he was elevated to the title of Baron Rees of Ludlow in 2005.

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Transcript

Luke Robert Mason: You're listening to the FUTURES Podcast with me, Luke Robert Mason.

On this episode I speak to Astronomer Royal, Lord Martin Rees.

"This is the first century when human beings - one species - are sufficiently empowered that they can determine the future of the entire planet and the entire biosphere." - Lord Martin Rees, excerpt from interview.

Martin shared his insights into the existential threats facing humanity, what it means to be a techno-optimist, and how we can plan for the long term future.

This episode is an edited version of a recent live stream event. You can view the full, unedited video of this conversation at FUTURES Podcast dot net.

Luke Robert Mason: Now according to Lord Martin Rees, humanity has reached a critical juncture. During the next century we're likely to face a number of existential threats from cyber attacks, biotechnology, artificial intelligence and climate change. Surviving these scenarios will depend on our collective ability to adapt to new ideas and to plan accordingly for tomorrow. In his recent book, On the Future, he outlines some of the ways we might leverage science to solve our greatest problems, whilst avoiding the dystopian risks. To do this, we might learn to think rationally, globally, and optimistically about the future. So, Martin, I want to kick off by asking: What is so special about this century?

Lord Martin Rees: Well Luke, first, thank you very much for having me on your show. I'll try and not be too irredeemably gloomy and say some cheerful things during the time. To answer your question, this century is special - even to an astronomer who is aware that the Earth has been around for 45 million centuries. This is still a special century, because it's the first of those 45 million when one species - namely the human species - has the power to determine the future of the planet.

This is for a number of reasons. Firstly, there are more of us; the population is far higher than it ever was. Secondly, we are more interconnected. If something goes wrong in one part of the world, it may spread globally. That's certainly what we're seeing with COVID-19 at the moment. Thirdly, we are empowered by technology, so that even a few people have the power to cause massive disruption through cyber and bio attacks. First it's the environmental effect of so many people on the planet, secondly cascading globally because we're so interconnected, and thirdly the empowerment of even small groups by these new technologies.

Mason: You describe yourself, Martin, as a techno-optimist, but a political pessimist. What do you mean by that?

Rees: Well I'm a techno-optimist because of course, we know how wonderful these technologies are. They've made everyone in the world healthier and living longer. They've reduced infant mortality and all of these things. They've enriched our lives in amazing ways. Certainly, the population of the world now - which is about 7.8 billion - couldn't all be fed had we not developed far better technology and better agriculture over the last 50 years. Certainly, it's very positive that we have these developments.

The problem is that they can be misused. The stakes get higher because of these technologies being so powerful. As far as the population is concerned, we are in nation states which compete with each other. If we want to avoid the downsides - let's take climate change for example. We all know that if we go on as we are now, there will be dangerous climate change in the second half of the century and we've got to do something about it, everyone knows this. It's very hard to get politicians to take actions now when the benefit accrues mainly to people in remote parts of the world, decades ahead. They've got an urgent agenda, they care about getting votes in the next election, etcetera. When I say I'm a political pessimist, it's because nation states don't agree and also that politicians tend to think short term. Those are the two main worries I have.

Mason: Now in the book, you focus on some very specific technologies. You look at biotechnology, cybertechnology, and artificial intelligence. Why do you focus so heavily on these particular, novel technologies?

Rees: Well I think they are the most qualitatively new and fast moving technologies. When you say bio, that includes a lot of things. It includes viruses, it also includes genetic modification, plant breeding and things like that. Bio is a very broad category. AI - artificial intelligence - is also very broad, and that meshes into cyber. But also, I do discuss environmental issues because we are, as I said, for the first time numerous enough and empowered enough to change the whole global environment, causing mass extinctions, drastic climate change, etcetera.

Mason: The book spends a lot of time looking at this thing called existential threats. It would be quite easy to spend this entire podcast outlining the multitude of misfortunes that humanity might potentially face. I want to look more broadly at this concept of risk. You're very careful to differentiate between this idea of existential threats and extreme risks. Why is it often better to talk about extreme rather than existential risks?

Rees: I think existential has the connotations of something that's going to wipe ourselves out completely. It's very hard to think of any kind of catastrophe that would wipe out every human being. There are some that could, but they're not the likely ones. I think it's better to talk about extreme risks. In my book, I don't say much about the rather rare scenarios that could wipe everyone out, but I do discuss the kind of scenarios which could be setbacks to civilisation. If you ask me for my prognosis, it's that we will have a bumpy ride through this century because there will be episodes where a few people cause something like a massive cyber attack or an engineered pandemic which cascades globally. Or, we'll create very severe climate change. These will be setbacks to civilisation, so I think we'll have a bumpy ride. I prefer to use the word extreme threats because that doesn't mean you have to imagine everyone being wiped out. You have to imagine, simply, that there will be an end to the steady progress that we've got used to. One of my main themes is that we shouldn't be complacent. We should worry about events which haven't yet happened, but which would be so serious that even one occurrence is too many. There's a very good mantra which I like to quote which is: The unfamiliar is not the same as the improbable. That's too, for instance, the pandemics.

Mason: The pandemic is a good example, and perhaps we'll get to that a little bit later. I do want to touch upon this idea of risk. When we talk about this idea of existential risks, an existential risk can be seen as a collective noun. It can describe a multitude of things that can potentially happen. But, risks can also be used as a verb; certain things that are worth doing. As you say in the book, any innovation is initially risky, but if we don't take risks as humanity, we might end up foregoing certain benefits. For you personally, what risks do you believe might be worth actually taking to ensure the survival of humanity?

Rees: Well I think everyday life is risky, and doing anything does cause risks. If you think of technology, then of course there is a lot of debate about the risk of new biotech, for instance. Let's take, for instance, genetically modified crops - GM crops. This is a case where many people regard this as too risky. I think they're being ultra-cautious. Mainland Europe has laws which don't allow GM crops, whereas in the United States they're allowed. I think if you want to ensure we can feed the world by climate change, we're going to need GM crops. The point here is that some people take the precautionary principle too far and say that we shouldn't do anything for the first time, because there may be some un-envisioned downside. There's something in that - we've got to be cautious - but I think we can't take it too far. In the case of GM crops, we know that there are 300 million people in North America who have done a big control experiment. They've eaten this stuff for 20 years or so with no manifest downsides. I would have thought we can be fairly sure that there won't be a catastrophe from GM crops. I think the EU regulations on that are too cautious. There is a trade off - we've sometimes got to do things for the first time. One thing I would say is that if something is going to be done which is new and where there are conceivable downsides, it's very important that the decision to go ahead should be the outcome of broad discussion. What naturally would worry people would be if a few scientists tried to assure the politicians that this thing is quite safe and they should go ahead. There's got to be proper discussion so that disinterested views can prevail and decide if the risk is small enough to be worth taking in order to get a manifest benefit.

Mason: Sometimes regardless of the risks - the actual scientific risks - some things can just receive bad PR. The GM crop example that you gave is a very good example. There seem to be so many hidden costs of just outright saying, 'No.' How do you think we collectively take a more proactionary as opposed to precautionary approach to engineering our way out of any potential threats?

Rees: What went wrong with the GM debate in the UK was that there was a standoff that developed between Monsanto, who handle things very insensitively, and environmental campaigners. This standoff had developed and commercial interest got involved before the public was really aware that there was a debate. There should have been engagement between industry and science and politicians, early on. To take another example of when things went better, the UK has guidelines for research on human embryos - which upto 14 days is okay but not after that. These guidelines are being followed by most other countries, and they were developed in the 1980s by a committee chaired by Mary Warnock, a philosopher. She and her committee engaged with parliamentarians and with the public, and with ethicists and religious leaders and all that, trying to get a consensus. That's the way things should be done, and that's a model for how we should deal with any major innovation. It wasn't done with GM crops, it was done for embryos. One issue now is AI and whether there are any uses of AI which are, if not dangerous, then unethical. Here again, there needs to be some public discussion to avoid - in this case not a government but a multinational conglomerate - getting too much power.

Mason: When I think about balancing risk and reward, I always think of nuclear energy. I know you've been heavily involved for many years in the nuclear discussion. Recently, we've seen the rise of something called ecomodernism; the ecomodernist approach to energy. Basically, they make a compelling argument that nuclear creates the greatest yield of energy with the least amount of waste. Obviously, that small amount of waste is a very dangerous amount of waste. They basically argue that this is worth doing despite the risks involved with nuclear reactors. Are you sympathetic to that approach?

Rees: Yes I am, and I think that's a very good example. We know that nuclear energy is risky - we know about Chernobyl and all that. I think the risks have been exaggerated because the number of people killed by radiation doses and leakages is very small. I think there's an exaggerated response to the Fukushima Disaster in Japan. Certainly, there are dangers. We should worry about nuclear power stations spreading worldwide because of the risks of things like Fukushima, and also of course because of the risks around nuclear weapons; proliferation. Unless we have a very powerful international body to control the enrichment of uranium, etcetera.

I do think, myself, that when we think of how we're going to provide energy for the world in a way that doesn't produce carbon dioxide, we're going to make a lot of use of wind and solar energy and one or two niche sources of energy like tidal power around the UK, we do need some base load when there's no wind and no sun. We can have storage in batteries or in hydrogen, for instance, but of course the most obvious base load which is carbon free would be nuclear. I personally think that we should - in this country and many others - go for nuclear. But before any mass production of nuclear reactors, we should do more R&D into so-called fourth generation reactors. The problem is that nuclear power stations which exist now, some are very old and they're all based on 1960s technology. There has been very little R&D for new ideas, but there are lots of possible new designs including what we call small modular reactors which can be flexible - made in a factory and then moved on the back of a lorry to the locations and things like that. I certainly think as part of the energy mix, we ought to have R&D into these forms of fission energy which are cleaner and safer than the ones on which the existing nuclear power stations depend. Of course, I think we should spend up to several billion dollars a year - in my view- on fusion. That's a long way away perhaps, but in the context of energy which the world is spending five trillion dollars a year on, we should surely be spending a few billion dollars a year on ways of exploring how fusion energy could actually work.

Mason: To look at an example closer to home about how we balance this idea of risk and reward, I think to COVID-19 and I look at the UK's originally proposed idea of herd immunity as a way to combat COVID-19. Do you think this was an example of one of those risks worth taking, or is that a very problematic approach to something like a pandemic?

Rees: Well I think you're quite right in saying that obviously there's a balance between ensuring that the number of fatalities stays low, avoiding shutting down the entire economy and everyday life - there's clearly a balance. Right from the start, those in charge were trying to strike this balance. But of course, right at the beginning, they were in the dark about how rapidly it would spread and how it spread most effectively. That's why I think we should be a bit indulgent and shouldn't blame them too much, because in retrospect they didn't get everything right. Now when fortune is in decline in this country, we've got to the stage when we are considering a trade-off. We're saying we could keep the lockdown for longer, but that would be very bad for the economy. More seriously it would be very bad for children if they can't go back to school and have a constrained environment for longer. I think the government is probably doing the right thing in this, and let's just hope that they are proved in retrospect to have made the right judgment, balancing risks and benefits.

There are other examples. There was Mad Cow Disease about 25 years ago which was a completely unknown disease and some people thought it might be a major pandemic. In fact, it wasn't. The government had overreacted, but that was understandable because they couldn't rule out it being a disease that killed hundreds of thousands of people. In fact, it only killed a hundred people. But at the time when they have to make a decision, the government said we shouldn't eat meat on the bone and things like that - which was overcautious - but when people didn't know, it was right to be cautious. That was a case when the precautionary principle was applied realistically, because we didn't know.

Mason: I want to turn to one of the figures that appears quite dominantly in your book and that is the character of the posthuman. What is the posthuman, and what do you think a posthuman existence might actually look like?

Rees: Well this is taking us beyond this century and towards science fiction. One of the new technologies which we haven't mentioned much yet is, of course, genetics and gene modification and all of that, which can be used not just to tame plants, not just to remove your propensity to Huntington's Disease, but eventually perhaps to make more drastic changes. It's not easy, because most of the characteristics of humans - like the way they look and intelligence - are combinations of tens of thousands of genes. They're not a single gene like what gives you Huntington's Disease. Therefore, you can't - if you wanted to - redesign humans. You can only do that when two things happen which are both far away in the future. One is being able to analyse enough genomes using AI to decide which combination of genes is optimal for a particular characteristic. Secondly, having decided that, being able to synthesise a genome with those qualities. Those are both a long way away. Of course, it'll raise ethical issues around how we do that. Another related thing people talk about is whether we can enhance humans - not by genetics, but by plugging in some extra memory to our brain. A sort of memory store which is electronic. This is talked about, and Elon Musk has this scheme to plug thousands of electrodes into your brain. This is being talked about, and science fiction writers think that this may happen. If you ask me my view, I would hope that these techniques will be pretty heavily regulated. Both prudential grounds - because they will have downsides - and also on ethical grounds. I think it would be a new and fundamental kind of inequality if some people are able to enhance themselves, unethically. But if I can digress into my favourite subject which is space, then I think if we look beyond the Earth, this does become realistic. When you digress a bit into space, then we know that humans have been to the moon, and I think by the end of the century there will be some people establishing a little colony on Mars. I don't think there'll be mass emigration because there's nowhere in our solar system as comfortable as even the South Pole or the top of Everest. I certainly don't agree with Elon Musk and my late colleague, Stephen Hawking, that we should have mass emigration to Mars. I know we want to go, but dealing with climate change on Earth is a doddle compared to terraforming Mars to make it habitable. Mass emigration is off. But on the other hand, I think that there will be some people who will go to Mars and I think they'll be funded not by the government - because governments are risk averse when they're controlling the lives of civilian astronauts, so that makes anything they do expensive. But I think these private companies like Elon Musk's SpaceX and Jeff Bezos' Blue Origin - these companies are going to be able to take high risk by launching adventurers into space, even if there's a 10 or 20 percent chance of failure.

Mason: Do you think it'll be humans? What gives us the original definition of the cyborg is the original essay by Clynes and Kline where they were looking at what we'd need to do to the human body in order to survive an extra-terrestrial environment. They were talking quite specifically about space - redesigning the body for a new environment. Do you think it's actually going to be our biological body as it's evolved here on Earth that's going to go into space, or do you think we're closer to sending robots that we can later use as avatars? What we'll end up doing is not sending our physical bodies into space, but we'll end up sending our minds. We'll communicate with these robotic avatars and control them, getting the experience of being on another planet - but our physical body can stay here on terra-firma.

Rees: Yes. I mean, that's one scenario. What I would say is that supposing a few crazy pioneers form a little colony on Mars and they have a one way ticket so they have to settle there, they will find themselves ill-adapted to living on Mars because we're adapted, as humans, to live on the Earth - which is very different. They will have every incentive to use these techniques which will indeed by genetic modification and as you say, cyborg modification, to adapt to this hostile environment. They'll be away from the regulators, who I hope are going to constrain this being done here on Earth. Within a century or two, then there will be these people on Mars who will be very different from us. As you say, it could be that they will download themselves into robots, or there could be robots of intelligence at least comparable to humans. Then, those robots - or electronic descendants of humans - they won't want an atmosphere. They may prefer zero-G. They will go up into space, and if they're electronic they'll be near-immortal, and so an interstellar void won't be daunting to them. That's a scenario for the far future, I think. There will be electronic entities which will spread through the solar system and beyond.

I think although we want to - in my view - go slow on modifying human beings on the Earth, it probably will happen. One thing I say in my book which I find a slightly sad and scary thought is that the one thing that hasn't changed over several millennia is human nature. That's the reason why we can read classical literature and the Old Testament and all that. We can admire the artefacts left by the Greeks and Romans and all of their literature and feel an affinity with them. Human nature is the same now as it was for them. I think there's a rather low chance that whenever the dominant entity is, say 500 years from now, will have any affinity with us. They may have some algorithmic understanding of how we behaved, but they may be much more different from us than we are from the Romans and Greeks.

Mason: Well if climate change goes the way that most are expecting, the Earth might be so inhospitable anyway that living on Mars might be the better option.

Rees: Mars might be even worse, but I think to go back to climate change, it really is important that we do think long term enough to do something about it before it gets serious. The situation is that there is a huge debate about the details of climate change, but most people agree it's a serious threat. That by the end of the century, we'll have crossed tipping points that will lead to very severe changes in the entire global climate. It's worth paying an insurance premium now in order to avoid that. The trouble is, some people aren't prepared to pay that insurance premium. Those who aren't prepared to do it are people like Bjorn Lomborg, the environmental campaigner from Denmark. He's a bogeyman amongst other environmentalists which is slightly unfair because he doesn't contest the science. What he does, though, is he has a group of economists and they apply quite heavy discount rates to future benefits and future dis-benefits. For that reason, he downplays the priority of doing things that will make the climate safer in the second half of the century, compared to more immediate ways of helping the world's poor. The ethics of applying a discounted rate in this context is very dubious, because most say - and this is the conventional view that leads to policy on climate change - is that you shouldn't discriminate on the grounds of date of birth. You should care about the life chances of a baby born today, who will still be alive in the 22nd century. You shouldn't apply a three and a half percent discount rate which means you don't care about what happens 2050. Probably, it's to get public agreement about policies which do, in effect, provide this insurance that things won't get catastrophically bad later on in the century.

Mason: Let's talk about one of the tipping points that features quite heavily in the book and that you've spoken about a lot which is this idea of population growth, and the fear around population growth. You have a very nuanced perspective on the possibility of this idea that the population is going to grow to an unsustainable rate. You go so far as to say that it's impossible to define an optimum population or the world's ideal carrying capacity, and you have very specific reasons for that. I just wonder if you could explain your position on population growth.

Rees: Well firstly, the world's population has doubled in the last 50 years. About three and a half billion in the 1960s, to 7.8 billion now. The projections are that it's levelling off, and in fact the global birth rate has actually declined over the last few years. Even though that's the case, the population is destined, almost certainly, to rise to about nine billion by the middle of the century. That's really for two reasons. Firstly, the demographic transition hasn't happened in Sub-Saharan Africa. The population is still rising fast there. Secondly, people are living longer. If you've got a histogram of the number of people at different ages, then for Western Europe there are roughly equal numbers in every decade of age up to 70. If you do this for Africa, the young - the under 20s - are about half of the total population. They're going to live longer and so they're going to have two kids and that will push up the population. Nine billion by mid-century is almost inevitable.

What happens after that is unpredictable. The population could go down or it could keep on going up, if say Sub-Saharan Africa continues to have large families. We don't know. I think we shouldn't panic too much about nine billion by mid-century, because we've managed to cope with the doubling of the population in fifty years. In the late 1960s, there was a forecast by the Club of Rome and by people like Paul Ehrlich about mass starvation in the 70s and 80s, and they didn't happen. Food production managed to keep up with population growth during that period. It's true, there are still famines - but they're caused by maldistribution and wars, not by overall shortages. If you look ahead to 2050, then I think especially if we use high density agriculture, minimising water-usage, and GM technology, we can feed nine billion people. I think we have to eat less beef, because if all those nine billion had the diet of present day Americans, that would lead to problems with global warming and land use. If we want to ensure that people can be fed without producing too much Co2 and without encroaching on natural forests anymore, then the average diet has to change. There is, to quote Ghandi, "enough for everyone's need if not for everyone's greed.", and we can feed nine billion people. There's no reason for panic on that.

On the other hand, if you ask, "What's the optimum population for the world?" then it may be that it is less than nine billion, and so maybe we should hope that the population does start to fall after 2050, and there are some scenarios where it does, because the population is already falling in West Europe, and Japan and places like that. Maybe we should hope that that happens in the future.

Mason: You say in the book that it's not really quantity that's the issue - it's quality of these lives. What's more dangerous than overpopulation is this idea of perceived inequality, as you call it in the book global embitterment. Why is that an even greater threat than the idea of overpopulation, and if it is such a threat, how can we go about tackling it?

Rees: As I say, nine billion can be fed, but it's not clear they will be because that does depend on proper distribution. One big concern as I briefly mentioned is what happens in Africa. If the population of Sub-Saharan Africa goes on growing - for cultural reasons, families remain large - then in some of the UN projections, Africa's population would double again between 2050 and 2100; from two billion to four billion. In that scenario - this is one of the UN projections - Nigeria would, by 2100, have a population of 900 million, which is a population equal to Europe and North America added together. If they are still caught by the poverty trap, they'd be lagging behind the rest of the world, and this is indeed a recipe for maximum embitterment, and would be unacceptable. The reason it would be unacceptable is firstly that the contract between the wealthy world and Africa would be very large and we'd have to minimise it, but secondly, there are two reasons why the situation would be more bitter.

First, the one thing that everyone would have in Africa is knowledge of the rest of the world. They all have the internet and they would know what they're missing, in a way that they didn't a hundred years ago - so that's one thing. Secondly, they can't develop their economy in the way that the East Asian Tigers did, for instance, by cheap manufacturing. With robotics, manufacturing is being re-shored back into prosperous countries. The countries of the Middle East and Africa which need economic development can't track what was done in Vietnam, Taiwan and places like that.

This means that in my opinion, if you want to have a fairly peaceful world in the second half of the century, then we've got to ensure that Africa and other regions don't lag behind. It'd be a mega-version of the Marshall Aid Plan whereby the United States helped out Europe 70 years ago after World War II. I think it's going to be crucial that the wealthy companies ensure that the poor countries in the south don't get left behind. We should do this, and not just for altruistic reasons.

Mason: Now I want to turn to the discussion of nature, and discuss the appropriate relationship that humanity should have with nature. There's so much talk of tech and reengineering the environment, finding technological solutions to things like climate change. Should humanity actually look to nature as a collaborator, rather than something that humanity should be seen to conquer? Is there a way in which we can enhance our understanding of nature and perhaps work with nature?

Rees: Yes, and this is why I was against any sort of drastic genetic modification of humans. I think we ought to ensure that we do preserve the variety of nature. This is not just because plants in the Amazon Rainforest may have genes that are useful to us and not just for other reasons of human benefit, but because the variety of the natural world and the amazing beauty of nature is something which many of us feel has value in its own right, over and above its importance for us as humans. So we should preserve it, and of course as you know one of the consequences of the grave human impact on the environment and potential climate change is going to be mass extinctions. I quote in my book the great Harvard ecologist E.O. Wilson, who says, "If humans' collective action leads to mass extinctions, it's a sin that future generations will least forgive us for." I certainly resonate with that view. I think we want to preserve nature for that reason. I think we ought to not take a science fiction picture where we completely change our planet, completely reform it. Maybe crazy people on Mars can do that out there, but we should leave things as they are. I think that's what people want. If you think of what wealthy people who have the choice do, they tend to like to have a house with a big garden or park and things like that. They like to be among nature. I think they also like to have human beings to help them support that. That's why in my book, I discuss the importance of not using robots to replace human beings as carers. You'd prefer to have a real human being for that, and that's the choice in which people make and we can make that possible for everyone. I think that we want to realise that as human beings, we have certain values and we value the natural world, we value other human beings, and we don't want those things to change too fast.

Mason: Again, would you agree with the eco-modernist perspective that it is better to re-wild the Earth rather than reengineer the environment? It feels like nature is one of those things that already works at a global scale. It works irrespective of geopolitical orders. Do you think that if we just handed back 50 percent of the Earth to Mother Nature, that she would just sort out the rest?

Rees: We could, but that must be too romantic. Of course, many of us chose the British landscape which is very beautiful, but of course that's, in a sense, artificial. 2000 years ago, the British landscape had lots more forests and wasn't in many ways as beautiful as it is now. I think it's not always the case that an artificial landscape is less good than natural landscapes. I think we could say that much of the British landscape which many of us appreciate is, in fact, artificial. What we've got to ensure is that it is one which actually enhances nature, rather than destroys it.

Mason: To take one step further, nature was here long before us and it really understood the networks that were required to allow for this planet to give rise to things like life. Do you think nature does a lot better job at understanding the intricate networks that allow for life to emerge, rather than human beings? Do you think we're always going to be subservient to nature and always have a better understanding of this thing than us?

Rees: I think you're sounding rather like James Lovelock.

Mason: That's not such a bad thing!

Rees: That's right, and of course as he would say, the planet can look after itself. That doesn't mean that what will happen is good for humans. I think as humans, we're entitled to consider our species and our survival, which may not happen in some scenarios which are good for the rest of the natural world. We should surely have the knowledge and empowerment now to create a habitat which doesn't lead to mass extinctions and is something we can admire, and which doesn't destroy all of the forests, etcetera. I think we can have a symbiosis with nature which leaves space for human beings to manage their lives.

Mason: Now I want to turn to a theme that keeps coming up in this podcast and it's the idea of the human subjective understanding of time, and how that really impacts how we, as collective humanity, thinks about our future. To start that off, I want to discuss your own relationship with time - both at a human scale and at a cosmic scale. Starting with that human scale, you've personally spent 78 years on this planet. I want to understand how that passage of time has really impacted the way that you, personally, think about the future.

Rees: Well I mean, I think, obviously, if you get to your seventies, you do have a different perspective on life. You look back at all of your mistakes and realise the extent to which any good luck is pure luck. This is why, incidentally, I've become evermore egalitarian in my views. As I live long enough to follow people's careers, I realised more and more how their success and a sort of commercial or careerist way is always uncorrelated with their ability or the importance of their work. I've just realised that more and more and that has made me even more committed to a more egalitarian world than we have in this country. That's one thing. Of course, we've got to think on longer timescales than ourselves. One thing that we do as human beings is surely appreciate the heritage of centuries past. We benefit from what the Victorians did and their structure, and we ought to ensure that we leave for future generations not a depleted and hostile planet, but one which is at least as good as the one we inherited. We've got to think in terms of multigenerational welfare.

Incidentally, there's an interesting paradox here which I discuss in my book. I talk about the cathedral thinking. I go to Ely Cathedral which is about 12 miles from where I live, and think of the people who built that about 800 years ago. They were people who, on the whole, had never travelled much beyond the Fenns. That was their world. They knew of nothing beyond Europe. They thought the world would only last another thousand years. Nonetheless, they built a cathedral that wasn't finished in their lifetime, and which still inspires us nearly a millennium later.

In contrast, we don't think very much about leaving a legacy for future generations. Even though our horizon is measured in billions of years and we have a global conception which they didn't have. The reason for this, actually, and the reason it's not so paradoxical is that the Middle Ages were an era of slow change. Even though the people didn't expect that the world would last more than a thousand years, they thought nonetheless that their children and their grandchildren would have lives rather like theirs, and they'd therefore appreciate the finished cathedral. So they were prepared to plan long term. The problem now is that even though we're all aware of the billions of years that lie ahead, we can't predict with confidence what things will be like 50 years from now, because change is so rapid. Some of us, therefore, take that as an excuse for not ensuring that there's a good life for people in 50 years from now, because we don't quite know what we should do to ensure it. The change is something which makes long term planning harder now than it was for the Middle Ages.

Mason: Well it does feel like this idea of cathedral thinking is beginning to re-emerge, especially under the climate movement - but it has a new neologism - it's called intergenerational obligations. This idea that we have to consider the rights of those who aren't yet born; the possible people. How do we do that?

Rees: Well, I think ethically we shouldn't. We're saying that if we do that and if we care that the life chance of a baby born today will be alive at the beginning of the 22nd century, then we ought to be prepared to be a big insurance premium to eliminate the probability of a serious climatic disaster by the end of the century. I think we've got to do what we can to reinstate long term thinking, certainly as you say, in the context of climate. If we do things wrong in the next 20 years, then future generations will curse us because it'll be too late for them to reverse the overall heating that will be happening then. I think we do have to instill as far as we can, and draw on religions to help us with this long term concern. This is really a consequence of what I said at the beginning which is that this is the first century when human beings - one species - are sufficiently empowered that they can determine the future of the entire planet and the entire biosphere. We have a huge responsibility.

Mason: I wonder if there's something that we can learn from religion here. I look at your accommodationist approach to religion, where although you don't necessarily believe in a God, you're happy to engage with the culture of Christianity. I wonder if religion had something there, I wonder whether your accommodationist approach to religion is because you recognise religions' ability to garner some form of consensus when it comes to thinking about the future. In other words, do you think we could all do with a little more faith that we're going to make it through?

Rees: Well I think so. I think the point about religion...I quote in my book the papal encyclical which was a big influence on the 2015 Paris Climate Conference, which got a consensus. The papal encyclical which was inspired by The Papal Academy was important. He got a standing ovation at the UN and this had an influence on his billion followers in Latin America, Africa and East Asia. Whatever one thinks of the Catholic church, and the many things we may not support, there's no denying its long term reach, its global view, and its care for the world's poor. I think religions do remind us that we are just one generation of many, and they do instil long term thinking so that we don't discount the future in the way that communists normally do. They also make us, perhaps, care about the rest of nature.

Mason: I want to return to these concepts of time and how our thinking about time really does affect our thinking about the future. It feels like in the modern world today we have this dominant narrative - this dominant concept - of linear time. Linear time has really informed our modern understanding of progress. With linear time, there's the past, the present and a potential future. That future, in the case of linear time, always feels like it's going to be better than today. Also, linear time really has informed our belief that there is an inevitability of an endpoint; the story has to end at some point. What do you think the effect of this concept of linear time has had on our perception of how we think about the future?

Rees: Well I think there are two separate things. One is we are lulled into complacency if we think that there will be continuing improvements. There can be steady improvements for a decade or two, or more, and then some sudden catastrophe. We've had a version of this in the stock market where it goes up by 10 or 20 years and then a sudden decline. We have disasters like the present pandemic which are a setback by a few years. We've got to realise that there are these setbacks and we can't expect continuing improvements for more than a decade or two. The main theme of my book is that the stakes are getting higher because there's a new class of disasters that cascade globally.

The other point - and again, speaking as an astronomer - is that the timeline ahead is enormous. We know that we are the outcome of nearly four billion years of biological evolution - from the first protozoa, as it were, by Darwinian selection. Astronomers know that the Earth's got six billion more years before the sun flares up and dies. The entire universe may go on forever. To quote Woody Allen: Eternity is very long, especially towards the end. Astronomers would never think of us humans as being the culmination of evolution. We may not even be at the half-way stage, because there's more time ahead.

Now of course, it could be that life is unique to the Earth, but on the other hand it's possible that evolution will continue into the future for billions of years more. If that happens, evolution is going to happen much faster. It won't be Darwinian selection which takes hundreds of thousands of years to change one species into another. It will be what I call secular intelligent design. It'll be us or more intelligent successors who will redesign entities. This could lead to changes here on Earth and far beyond, on timescales of only centuries. The timeline ahead is longer than the time that's elapsed up until now. Moreover, the pace of change is going to be faster because it's going to be a technological time scale rather than the slow Darwinian timescale. That means it's utterly hopeless to conceive or attempt to predict what's going to happen in the really far future. Certainly, as astronomers, we're aware that there is this far future for our galaxy and our universe, whatever happens to us down here on the Earth.

Mason: Do you think we should just get rid of the notion of linear time altogether? Should we be embracing a more cyclical notion of time? Would this be useful? Basically, an understanding of time that emphasises repetition and is influenced by the cycles that are apparent in the natural world. At the end of the day, what is wrong with a little bit of creative destruction every now and then if it gives us these new opportunities to find new avenues of exploration?

Rees: Well it might, but in the long run - if you look over billions of years - of course, there, Darwinian evolution has not proceeded smoothly. The dinosaurs could tell you that. But, there has been a gradual emergence of complexity over those millions of billions of years. We are now in a special state when - as I say - future evolution is not going to be Darwinian selection. It's going to be up to us how it happens. So I don't think we can recycle things in the way that might have happened in the past.

Mason: Just to hear me out once more on the idea of cyclical time: do you think the cyclical understanding could also be applied to the cosmic scale? What are your thoughts on the idea that the universe is not just expanding infinitely, but soon it might also contract? In other words, what expands contracts. We've had the Big Bang and this may lead to the Big Crunch, and that will lead to, potentially, another Big Bang. I think that concept is better known as loop quantum cosmology. If it is to be proven that in actual fact, maybe this is the way the universe is going to go - there's going to be this constant expansion and contraction and this more cyclical process - do you think that would spark a copernican style revolution when it comes to thinking about the passing of time?

Rees: I don't think so. As you say, long range forecasts are never reliable. With the entire cosmos, there are ideas that it will eventually be collapsed to a Big Crunch. The most likely thing is that it will go expanding on forever. In any case, we're talking there about timescales billions of times longer than human history. Not, I think, relevant to the way we think of ourselves as humans. There's such a big disjunction between the timescales that cosmologists think about, and the ones that even the most farsighted politician or priest thinks. It doesn't really help. I think we've just got to say we don't know what will happen on that very long timescale. We do think of ourselves as an important stage. It's been 45 million centuries and we visit the Earth and this one is special. There'll be another 50 million or 60 centuries before the Earth dies, and we don't know what's going to happen in those.

Mason: Before we turn to some of the questions that we have from the audience, I want to talk about some of the current methods of thinking about tomorrow, and how they're hampered by short term thinking; by polarising debate; by alarmist rhetoric; by pessimism. I want to ask you, Martin, why is the public still in so much denial about the harm we're causing both to the biosphere and the threats posed by our interconnected world?

Rees: Well I think for the biosphere, it's a question that they don't think long term enough. Politicians in particular don't think long term, because they worry about the next election. I quote Mr Jean-Claude Juncker in my book who says: Politicians know what to do, but they don't know how to get re-elected after they've done it. Politicians tend to react on short timeframes. You shouldn't blame them; that's because the public are like that. One thing which I would say in my book is that it's very important for scientists or any charismatic people who speak for them to make people aware of these things. In the 19060s there were people like Rachel Carson who made people care about the environment. We've got David Attenborough now. They can make a big difference.

Just to give one example in the UK recently: Mr Michael Gove is not, perhaps, the most inspirational long term thinker, but he did - when he was in his previous role - introduce legislation to ban non reusable plastic straws and things like that. He did that because he thought - probably rightly - that the voters would support it. The reason that was the case was that millions of them had watched the Attenborough Blue Planet 2 programme - particularly the one showing the albatross returning to its nest and coughing up food for its young. Not coughing up nourishment, but bits of plastic. That's an iconic picture rather like the polar bear on the melting ice-cap, highlighting climate change.

That's an example where a charismatic, inspirational figure like David Attenborough was able to make people think about a long-term issue which wasn't on their radar at all until two or three years ago. People didn't talk about plastic in the ocean, whereas that's become a serious issue. The same is happening - but not enough - for climate change. The campaigns and demonstrations, especially by young people, are welcome because they're making people think long-term. Scientists themselves can't do it without getting the public onside, and the politician will only respond if they think the public and voters will support them. That's why the Pope, in 2015, and our secular Pope, David Attenborough - more recently - have been so important in raising public consciousness of these long-term issues.

Mason: But the public has to make an informed decision, don't they? It's one thing to appeal to their emotions but it's another thing to actually educate them on real science. How do we enhance both the public and the political discourse over long-term scientific and global trends? Even if we just look at what happened with COVID-19 and some of the response that the public - especially in the US - has had, it often seems like despite the science, people just follow the route that they want to take.

Rees: Well I think that's true. There is widespread ignorance of even basic science. You don't need to be an expert in science to understand these things but you need to have a feel for science. Incidentally, I think scientists sometimes complain too much, because we should bemoan ignorance in all areas. It's sad if people don't know the difference between a proton and a protein and don't understand basic things of climate or anatomy, or disease and things like that. It's equally sad if they don't know the history of their country, because that's important if you want to make an informed judgment. I think we've got to hope that basic knowledge is more widespread, so that public debate - which is crucial in a democracy - gets above Daily Mail slogans. We can only do that if the public has at least some feel for science but as I say, it's equally important that the public should have some feel for the history of our nation, and should be able to find South Korea, or Libya, or Oman - which many can't.

Mason: How do we apply that thinking about technologies and the decisions about which technologies we should accelerate, and which technologies we should responsibly constrain? Again, it feels like the ability to make an informed decision is often hampered by monetary incentives, for example. Those monetary incentives, of shareholders of certain technological companies often outweigh the greater good for humanity. How do we make those sorts of informed decisions when it comes to the application of some of the science

Rees: I think we do need regulation. Going back to biotech, for instance, we do need regulations on grounds of safety and on grounds of ethics of certain technologies. My worry about that is that some technologies are dangerous, and we want regulations globally, but enforcing regulations globally in biotech, for instance, is as hopeless as enforcing drug or tax laws, globally. That's why I do worry about the misuse of biotech, etcetera. Also, we need powerful international bodies which can enforce all these regulations, and of course in dealing with large multinational conglomerates as we have in the IT arena. Clearly there's got to be some international regulation of them. We don't yet have that, but that's what we need if we want to minimise the risk of really disastrous downsides of new technology. It is difficult, because in the case of nuclear which we talked about earlier...nuclear facilities to make nuclear bombs are a large and special purpose. It's possible for the International Atomic Energy Agency to regulate them. But of course, the kinds of experiments that could be dangerous or unethical in biology can be done in a small, dual-purpose lab, of which there are many. It's harder to enforce regulations in that arena. Similarly, cyber-attacks of growing impact can be carried out just by a few people or even a loner. I do think we have a bumpy ride, because it'd be hard to prevent a few people misusing these powerful technologies. I'd like to say that the global village will have its village idiots, and they have a global rage. If you want to cope with that, we have to contend with the tension between three things we want to observe: liberty, security and privacy. One of those has to give. In China, it's privacy that's going to give. In the West, it may be something else. I think if you want to ensure that when the stakes are so high, we bring down to a reasonably low level the probability of some bad actor causing catastrophe, we do have to worry about how we can have adequate surveillance.

Mason: Do you think there's a methods issue here when it comes to thinking about and trying to predict the future? I should probably just make it very, very clear to our audience that you're an astronomer, not an astrologer. Those are two entirely different things and one happens to do quite a lot with trying to predict the future. In the current century, it feels like futurism has become a data based science. We seem to be obsessed with modelling the present and the past to try and work out what might happen in the future. What if we end up making false assumptions about our future based on very limited data in both the past and present? Do you think there's an underlying issue here with our methods for how we try to understand, look at and eventually predict the future?

Rees: Well of course, I'm a scientist, not an astrologer - and scientists are pretty rotten forecasters. All I'd say is that they're not as bad as economists, but they can't be reliable and even with very good data - as you say - one can't make confident forecasts very far ahead. We do have to live with uncertainty and do our best to cope with it, and we've got to, in my view, explore scenarios for things that might happen - things that might go wrong - and prepare against them. The Centre I'm involved with in Cambridge - called the Centre for the Study of Existential Risks - is concerned to give more attention to these high consequence, low probability threats, which tend to be not studied enough. There's lots of studies of risks of carcinogenic food, cutting down risk of road accidents and things of that kind, but not enough to these major events. We saw in the case of COVID-19 that we weren't adequately prepared. We didn't have the adequate equipment to deal with it. In retrospect, it would have been a reasonable investment given that no reasonable person would have thought the probability of such an event was lower than, say, once per 20 years.

Mason: Talking about exploring the multitude of possible scenarios for the future, do you think science fiction has an important role to play in preparing the public for what could potentially be possible?

Rees: I think it does, and I tell my students that they'd do far better to read first rate science fiction than second rate science. It's more fun, and no one likes to be wrong. It does loads to the imagination, so I certainly recommend that. When you were talking earlier about cyclic events, I was reminded of a book by Olaf Stapledon - he was an under-appreciated science fiction writer. He wrote a book called Last and First Men. He wrote this book in the mid 1930s and it's about 15 species of intelligences and brains that emerge and decay over the next few billion years; he was very imaginative. Of course we all know Arthur C. Clarke, and Stapledon wrote another book called Star Maker. Star Maker is about creative universes and we have a multiverse, and different dimensions and all of that. That's a long way of saying that I think it's very inspiring to read some science fiction.

In fact, I always recommend a book by two people I knew called Stewart and Cohen called Aliens. It's a digest of about 50 science fiction novels, because science fiction is not always the most excellent literature, but it's lovely to have the digest of the ideas in it. This particular book digested the ideas of about 50 books. That's a long way of saying that science fiction writers have a lot to teach us and to nourish our imagination.

Mason: Do you think we'll ever see a Lord Martin Rees science fiction book?

Rees: I don't think I've got the imagination, actually. I'm going to write books about science and the future, and the inanimate universe. I like to say that the inanimate world of atoms and stars and galaxies is simple compared to the biological world. Even an insect is far more complicated - in its layer upon layer structure - than a star or galaxy. I will stick to simple things; the inanimate world. But, I will enjoy reading books by people with more imagination than I can possess.

Mason: Well, if you'll indulge me just for a second. You mention in the book, very briefly, possible ways we might overcome the extinction level event, or how we might recover from the extinction level event. You point at what James Lovelock has been talking about which is this idea of a handbook for survival. What would you include in a James Locklock-esque handbook for the survival of humanity after the extinction event?

Rees: Well of course, going back to what I said about our lack of education in the basic sciences, I think we'd all be completely helpless in even simple agriculture. We are further from nature than any other generation was. What I think I would do is make sure that everyone in school learns a bit more about how to grow food, basic human anatomy and things like that - which they will need. Lovelock had this idea of having this handbook and distributing robust copies all around the world, so it existed. If I could plug another book by Lewis Dartnell called The Knowledge, which again I've got in my book. He summarises the kind of things we'd need to know, if we were to revert to a sudden Stone Age culture and have to start again from there.

Mason: We have a question from Youtube - about education actually - from Eva Pascoe of Cybersalon who asks: Should we be teaching astronomy and perspectives on long term thinking in schools?

Rees: I think we should be teaching basic astronomy. I think it's sad if people don't understand what causes the tides, or what the sun is made of and things like that. I think people ought to understand history. Our civilisation is the outcome of an imprint that goes back for thousands of years, and also they should understand the natural world. What is very sad is that young people are more cut off from the natural world than ever before. Incidentally, I gave a talk at a science festival recently, where I made the point that the fact the technology young people use today is so elaborate, is itself an impediment to get people keen on science. When I was young, you could take apart a motorbike engine or simple radio - something like that - and put it together again to understand how it works. The gadgets that young people use now - smartphones and things like that - you can't possibly understand how they work. If you take them apart you can't put them together again. I think if you look at the careers of most people of early generations who ended up being science engineers, they were tinkerers when they were young. Going right back to Newton, who made models of windmills and clocks; the high tech of his time. Also, biologists looked at bird nests and things like that. Young people now can't understand the technology their everyday life depends on, and they've probably never seen a birds nest, in many cases. I think it's rather sad that education doesn't give people the opportunity to engage with the natural world now. Of course, if they did, then they might value it more and think longer term.

Mason: As expected, we've had questions from our Youtube audience specifically on space. I guess I would certainly be remiss if I didn't ask you about space. One of those questions is from Lisa Petibone who asks: Could a settlement on the moon help us develop innovative solutions to our problems here on Earth, and be a stepping stone to living and traveling in space?

Rees: Well, the answer is that it could be a stepping stone - but as I say, I'm not enthusiastic about mass evacuation of the Earth to live in space, because we're not suited to it. We should realise that as robots and militarisation get better, the practical need for people in space - even to do mining or build out structures on the moon - is getting weaker. As an astronomer, I hope there will be a big radio telescope on the far side of the moon. But, there's no radio background from the Earth. That could be assembled by robots. So, I think we can make use of space for technology, but we could also do industry in space, and we could have huge telescopes in space. Gossamer thin, built under Zero G. I hope that we will use these to get a really detailed image of distant parts of the universe.

Just to mention one thing: one of the most exciting things as an astronomer in the last 20 years has been realising that most of the other stars in the sky are orbited by retinue planets, just like the Earth is orbited by the familiar planets. We can only detect these as little points; we can't image one of them. If we had a huge telescope in space, we could perhaps get an image of another Earth - maybe with a biosphere - orbiting another star. That's a big challenge, and it needs a really big telescope. I say in my book that this is a challenge to achieve by the year 2068. Why do I say 2068? That's a centenary of the famous Earthrise picture showing the Earth as viewed by astronauts orbiting the moon, which was iconic among environmentalists. Let's hope that sometime - maybe a century later - we will have an image of another Earth orbiting another sun.

Mason: We have a telescope that's due to go up very soon - I think it's as soon as 2021 - which is the James Webb telescope. What do you hope that the James Webb telescope might discover?

Rees: Well, it won't do that. It will do a lot more. It will be able to analyse the light from very distant objects and therefore look back far into the past. Even better than that, it's going to be a telescope on the ground built by a European consortium which Britain belongs to, which is a telescope being built in Chile with a mirror 39 metres across. A mosaic of 800 bits of glass. It's got the name 'The ELT' - extremely large telescope. The Europeans aren't very imaginative in their nomenclature. Anyway, that telescope should be able to analyse the light from planets around other stars. It's a challenge because you're looking for a firefly next to a search light, as it were. You're looking at another star which is like the sun, and you're looking at a planet which is fainter to it in the same way that the Earth is fainter than the sun. You need a big telescope, but when we have this telescope it'll be possible to perhaps learn whether there's oxygen, or chlorophyll or things like that on some of the other planets orbiting other stars. The James Webb telescope will be a step towards that, but the big ones on the ground will be more important.

Mason: I had a special request from an audience member, Ben Greenaway, who wanted me to ask you about your opinion on both Donald Trump's idea of a Space Force, and Elon Musk's distracting array of Starlink satellites. I just wanted your opinion on both of those things.

Rees: Well, obviously Donald Trump's motivation is to emphasise the use of space as an arena for war. Not only to launch weapons from, but also to attack other satellites. I think any expansion of that effort is something we should deplore. The Musk system of having thousands of satellites...the intention is good. It's to bring the internet to Africa and other places where they don't have broadband internet. But of course, the downside is that these objects will be in very low orbit and they will be a bit of a distraction to astronomers. The good thing, I would say, is that the people at SpaceX are mindful of these concerns and they're trying to avoid these small space crafts having shiny surfaces, etcetera. But still, they will be a bit of an impediment to observations just after sunset and before sunrise, because they're in lower orbits so there's no sun shining on them in the middle of the night.

Mason: If, say, in the next 10 to 20 years, we finally crack commercial spaceflight and it becomes viable, would you consider going to space?

Rees: Elon Musk has said that he wants to die on Mars but not on impact, and he's 49 years old now so he might make it. I think I'd want to be even more old and decayed before I took the risk. I say that because I personally think that there'll never be a case for Europe or America funding massive space exploits. This is because, as I say, robots do everything better and much more cheaply. If the government does something, it's got to have high safety standards. To indicate that, the shuttle NASA has was launched 135 times. It had two spectacular failures. Each of those was a national trauma, but that was less than a two percent failure rate which is fine for most test pilots or astronauts and adventurers. My view is that man spaceflight should be left to the private sector, which means Musk and Bezos and people like that. They can launch adventurers who are prepared to accept high risks and they can therefore have cut-price risky ventures, and we can cheer them on. I don't think I'd go myself.

Mason: We have one last question from Youtube, and it's a two part question really. It's from Eva Pascoe, who asks: What or who inspired you to study astronomy, and what are the big unanswered questions left in astronomy that you think are a priority to answer?

Rees: As I say, my own path into it was an accident. I was good at maths and school and bad at languages, so I specialised in maths in my last years and studied it in university as an undergraduate. I rather wish I had studied science instead; I would have done better if I'd have done more science. By lucky accident, I got into astronomy to do a PhD. This was the mid 60s - a very good time - because that's when studying was opening up. The first evidence for black holes; the first evidence for Big Bang and things like that.

I advise young people listening now - if you're thinking about going into science - pick a subject where new things are happening. Where you can get new data, use new techniques or more powerful computers. You can tackle the problems that the old guys never got a chance to tackle. If you go into a more slowly developing subject, then you have to do the things that the old guys got stuck on. That's less likely to lead to success.

The good thing, I would say, is that although the 60s were an exciting time, the most recent five years have been just as exciting. We've had very exciting developments in planets and other stars - as I mentioned - more evidence on the Big Bang, and more on dark matter. I would say that the subject has developed very, very fast. As in all of science, as the frontiers advance, then old questions get settled and new questions come into view, which couldn't have been posed beforehand. The periphery gets longer, so there's more and more to do. It's a great subject, and it now links together with geology and biology if you think about exoplanets. That's a long answer to say that I got to astronomy just by a chain of accidents, and I've been lucky that it's been a subject which has developed. Also, it's a subject which has a wide attraction to the public, and also an unambiguously positive image. People are slightly ambivalent about nuclear science and genetics, but I think if you do astronomy or evolutionary biology, the public is surprisingly interested. I'm always gratified that the public is interested in these subjects. The question that I'm most often asked which we haven't got around to in this conversation: Is there life out there already? That really grabs people's interest, but that's indeed a very important question.

Mason: It feels like we're understanding more and more about the world through science, and about the nature of reality itself. But, there are some challenges that come with imagining the unimaginable. Part of it is a built in human limit to our understanding. Do you think there are some things that we'll just never know because they're beyond the power of the human mind to grasp, or will these concepts eventually be grasped by things like artificial intelligence, for example?

Rees: Well I'm sure there are things that we're unaware of which may be far too hard for us to grasp. Just like a monkey can't understand quantum theory, there may be things that we can never grasp. With AI, I think there's a bit too much hype about what AI can do, but it can certainly do very complicated calculations and do them very fast. If you think of understanding string theory which involves geometry in 10 or 11 dimensions, and which may help us to understand the very early states of the Big Bang, I can certainly see that there may be a possibility that a machine - a beefed up version of the DeepMind machine that beat the world champion at the game of Go - might be able to calculate 11 dimensional geometry, and explore the consequences of string theory in a way that is just too difficult or long for a human to do. If the machine then spews out, at the end, the correct mass for a proton or correct strength of gravity, we'd know that there was something in the theory.

You wouldn't have this a-ha insight which is the main bonus you get if you make a scientific discovery, because you wouldn't have the insight. But, you would at least know through this idea aided by a machine whether a particular string theory was correct. There may be some things which are even too hard for the machine.

Mason: I keep arguing that the next Einstein will be an AI-nstein.

Rees: I don't think so, because I think the ideas will still come from humans whereas the machines have the advantage of speed and processing power so they can do things far faster than us. The computer that beat the world champion in Go learnt in three hours by playing against itself, and became better than any human. That's the kind of success they have. The thing that machines can't learn is common sense about humans, because they can only do that by watching real humans in real situations. The problem is twofold. The first is that we don't have sensors; they can't sense the world as well as we do. Secondly, everything that we do is very slow by design. You can't give the machine a dataset of real human beings. It's like us watching trees grow. You can't learn very much just in a lifetime. That's why there's a big concern about the extent to which machines will ever acquire common sense. That's relevant to how much we should be prepared to delegate routine choices to machines without being sure that there are humans in the loop.

Mason: So Martin, you do such a wonderful job in this book of balancing your optimism with your anxiety; with balancing speculation and science. For our audience, how do they - and how do we all - become evangelists for new technologists without looking blissfully naive and looking too techno-optimist? How do we do that ourselves? What is your message for our audience?

Rees: Well I think we do need to be cautious in the way we apply these powerful technologies. That's certainly a theme of my book. On the other hand we want to make sure that we develop these technologies. Obviously, they have huge benefits for health and also for monitoring complex systems like electricity grids and traffic flows, etcetera. The Chinese could have a plan to have an economy we could only dream of because they can register and process every transaction made in an entire country. There are things which machines can do but there are also downsides to what they can do. I think the main point is that people shouldn't be too starry eyed about science. They should be like the experts and have enough fear for what science can and cannot do. Only then can we have an informed debate - which we should be having in democracy - about how to deploy these new techniques.

Mason: And on that very level headed endnote, Lord Martin Rees, I just wanted to say thank you for joining us today.

Rees: Thank you very much.

Mason: Thank you to Martin for sharing his thoughts on the challenges that humanity faces in the near future. You can find out more by purchasing his new book, 'On the Future: Prospects for Humanity' - available now.

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