i'm stephen sackur. one of the key drivers of human thought and behaviour throughout history has been knowledge of our own mortality. from childhood, each of us knows we will die. religion, philosophy and science all wrestle with that fact and have, in different ways, embraced the quest for immortality. my guest today, stephen cave, director of the cambridge institute for humanity and technology, is at the centre of a growing debate about the merits of extending human longevity. is it wise to seek to live forever?

stephen cave, welcome to hardtalk. thank you for having me. it's a great pleasure. you believe that our human awareness of our own mortality is absolutely central to the human story. why? well, all creatures strive to live on, to keep going. they wouldn't be around us any more if they didn't. the mouse that didn't care about surviving wouldn't pass on its genes. so we come from a long line of creatures that are determined to keep going. but we have these big brains, that's part of our survival mechanism, if you like, that allow us to see the future, to generalise. and we're conscious of ourselves as individuals, and that means we're conscious of our own deaths. and of all the billions of creatures on earth, very few creatures have to live with that terrible awareness that, one day, all of their efforts will come to nothing.

and so, if we look back through human history, what we see is humanity struggling to make sense of this. some of the earliest archaeological evidence we find of human development is grave goods, for example, suggesting people very early believed in an afterlife. the oldest work of human literature, the epic of gilgamesh, is about the quest for immortality and wrestling to come to terms with mortality. of course, we have religions and cultural artefacts that are ways of projecting ourselves into the future. of course, we try very hard to stay alive in this world. right. so what you are saying is that we are trying to make sense of our own mortality, but we're also sort of wrestling against it, trying somehow or other to find a recipe to avoid it, to avert this ultimate finish? yeah. there are lots of ways in which we can come to terms with mortality.

we can tell ourselves that this life isjust the beginning, that the real life is in another realm somewhere else. but the basic plan is to stay alive today for as long as we can. religions, of course, they have their own belief systems. and whether it be western or eastern religions, they have different forms of an afterlife. let'sjust, at the beginning of this conversation, be clear about you yourself. you have no belief whatsoever in an afterlife. that's true. i grew up in a christian culture here in in england, but i was sceptical of the stories i was being told, you know, when my grandparents died when i was quite young. i wasn't even convinced the people telling those stories really believed in them. i think we live in something of a time of crisis for these kinds of belief systems, at least in the west. you talk about the death of your father and that giving you a whole new sort of awareness of... ..the self being something which has a physicalform,

in terms of the brain, and that, when the brain dies, that self is terminated. why was the death of a loved one so central to that deeper understanding you gained? well, a lot of people have this experience that, you know, when... children don't think much about death, but then, when they experience it, it could be the death of a pet, but it could be often the death of a grandparent or some other loved one. then they think, "0k, where have they gone?" and then they realise, "well, hang on, if it could happen "to them, it could happen to me." and that moment is a terrifying one. but with my father, it was a little bit different because i was trained as a philosopher in the western tradition, which is very dualist. that means a separation of mind and body. and we're used to the idea, prevalent in christianity and other religions, that the mind, the spirit, the soul will go off to some other realm. but when you see someone suffering from brain cancer, as was the case with my father, then you realise that, actually, the mind, the true self is very much bound up with this physical body and,

of course, in particular, the brain. now, before we get into detail of your analysis of different ways in which human beings right now are pursuing longevity, i just want to sort of address what i see as a basic contradiction in your work. you seem to be saying that we humans are immature, in the sense we fear death, and that's why we are so attracted to belief systems which tell us we don't necessarily die. on the other hand, you seem to be saying it is extraordinarily positive and useful that we've developed all these different ways of coping with death, and with the fear of death, because it's motivated so much creativity, so much that's positive in human development. so are you essentially selling us a negative story or a positive story? well, you know, i wouldn't say we're immature in being unable to face death and having to tell ourselves these stories.

this is a human constant. well, forgive me, but i'm quoting from you now. "as a species," you say, "we need to outgrow our "fear of death." mm, i think there's something... i talk about the wisdom narrative that can be found in many cultures, looking back throughout recorded history, both in religions like christianity, particularly in the old testament, and in buddhism and in other kinds of belief systems, like ancient greek philosophy, which are about trying to come to terms with death and facing mortality and thinking about the benefits that can come from that. for example, appreciating the time that we have here on earth. in the past, on this programme, i have talked to scientists who have devoted a great deal of time, money and effort to the study of how to... ..block — even reverse — the ageing process in human beings. dr aubrey de grey is one very well—known gerontologist proponent of this effort, and he reckons that,

within our lifetimes, we may see human beings living for hundreds, if not 1,000 years. is that not something to embrace, indeed, to encourage scientists to work upon? well, there are many age—related diseases which are extremely debilitating, and many lives are too short. there are many people right now who would benefit from the kind of technologies that aubrey and others are working on. but if we are going to try to radically extend lives, which is something humans have always dreamt of, then we need to prepare. we're not ready for the consequences of that right now. but are you saying that, if we prepare ourselves — and your think tank and research institute is one of those that talks about this a great deal — you're saying that, if we think about it deeply enough, it would be a good thing? i think it could be. imean, i'm... because i'm sceptical about the possibility of immortality, sceptical about the desirability of immortality, people tend to frame my work as saying

that, you know, 70 or 80 years is enough. now, i hope that, when i'm 70 or 80, i will want to continue to live on. i hope that everyone will feel like that about their lives. so i think the kind of research that's happening now that could help people to live a few decades longer is very welcome. you're at the intersection of sort of philosophy, technology and science. when you look at today's scientific breakthroughs and technological developments, do you believe that real, significant progress is being made in life extension? yes, there is progress. there are reasons to be sceptical and there are reasons to be optimistic, and we have to balance these two. the reasons to be sceptical are, this is something humans have notjust been pursuing for thousands of years, but genuinely believed that they were on the verge of for thousands of years. the ancient egyptians thought they were on the verge of creating an elixir. the ancient chinese thought it. scientists have been thinking it for centuries. but there has been real progress in the last decades

in extending the lives of other organisms, like fruit flies and nematode worms, and even mammals like mice... and if i may... ..that suggest we're getting closer. if i may introduce thejellyfish, we now know there is one species ofjellyfish, some call it the immortaljellyfish, which has the ability — i think it's technically called transdifferentiation — to redevelop itself, to go back to its earliest form and then grow again. we seem now to be able to learn a great deal in terms of genetic engineering from other living organisms. if we can tap the codes that allow that to happen, surely immortality is no longer some sort of myth or dream. well, i think real progress is possible. never before in human history have we put so much talent and so much money into this area of research. and there have been some real breakthroughs. so i've moved from a position of scepticism to one of thinking that this is possible, and if it's possible, then we need to prepare, because we're not ready now.

does it worry you, and you've already talked about the money, that some of the most enthusiastic proponents of developing this research are the richest and arguably the most powerful private—sector businesspeople in the world? thinking ofjeff bezos, peter thiel, elon musk — they all seem somewhat obsessed with this area of scientific research, extending human life. they have the money to do it, but it raises questions about whether the work they do will be open to others or will be reserved for themselves. well, it's such an important question. i mean, if they're donating large sums of money that drive forward basic research for the benefit of all, then that should certainly be welcome. but one of the real concerns about the consequences of life—extension technology is that it will be the privilege of a rich elite, and that, i think, would have disastrous

consequences. a philosopher, who i believe you know, certainly i'm sure you know his work, john davis, he wrote a book called the new methuselahs. he said, "imagine a world in which the wealthy few live "on in endless youth, an elite gerontocracy of near mortals." he said, "it would be a world where they behave like ranchers "watching a herd of cattle," that is the likes of you and me, "whose members change with the years, "while they remain in control." that's dystopian. that is truly scary. yes, it's terrifying. time is the most precious thing that we have, you know? discrepancies in life expectancy now, here in england, for example, might be about ten years between rich and poor, or different areas of the country. and whenever that's reported on, it's rightly with a sense of outrage. you know, something must be done. now, imagine if those differences weren't a decade, but were centuries or thousands of years. i hope we would find that unacceptable. you, in your latest book, entitled should you choose to live forever?, you debate

with a us—based philosopher, john martin fischer, who's extremely enthusiastic about this research and about what it could achieve for humanity. you much more sceptical. basically, his message to you is, you are a curmudgeon that, just like, for example, thomas malthus in the 18th century, who couldn't see the transformative effect that technology would have on food production, you can't see the ways in which the human spirit of sort of innovation and development will allow us to live longer and benefit from that rather than suffer from it. well, john is an excellent philosopher, based in sunny california, and he likes to contrast his sunny, californian optimism with my english melancholy. curmudgeon, he calls you. curmudgeon. exactly. and... but i think we need to be cautious and we need to look at the possible downsides. broadly speaking, i'm incredibly excited by new technologies, life—extension technologies and lots of others.

but my mission, and that of the new institute we founded, is to make these transformations go well. and we only do that by thinking also about how these technologies, including this one, life extension, can go wrong and what we need to do to make them go well. you say you're broadly, and in principle, excited. you don't come across as excited. you come across as deeply concerned. you talk about the earth's carrying capacity. that, iguess, means its resource base and what it can...the number of people it can manage to keep alive on this planet. you talk about the carrying capacity being overburdened, and you say that a longevity of 120 to 160 years for the average human would make life pretty much impossible. well, i am very concerned. i think everyone ought to be concerned about the drain on the planet's resources that we're exerting with 8 billion people. and we need to be tackling that. and my worry is when people say, you know, "it would be

"fantastic if we have a breakthrough in life "extension and, sure, there'll be problems, "but we'll solve them." well, fine. but let's. .. show me how you can solve the problems of biodiversity loss and ecosystem collapse and global warming now, and then i'll believe you if you tell me you can do it if everyone is living to 120 and population has doubled. those material challenges are clearly very real. but you go beyond the material challenges. you talk about the philosophical objections that you have as well. you seem to be suggesting that, actually, if we could live much longer and, you know, posit the notion of forever — ie, immortality — it would be extremely bad for us, bad for us because it would drain us of motivation. we would all be bored and we would be unhappy human beings. do you really believe that? the philosophical debate about immortality has been focused on genuinely unending life. and i think, given the prospect of eternity, we would either have to become something very different to the very finite creatures we are now with

a limited set of interests, or we would become terribly bored and fall into ennui. but that doesn't mean that applies to the real prospects of life extension of a few decades. but it is worth bearing in mind that, you know, hundreds of millions of people right now are already depressed. this is worth taking seriously. you know... ..there's an old joke about two ladies in a canteen and one says, "the food here's terrible." and the other one says, "yeah, and the portions are so small." why would you want a larger portion of terrible food? i mean, we have hundreds... i like thejoke, and i get the message. but there are equally many millions of people living around the world who are deeply depressed by the notion that, actually, before very long, they're going to die. and it gives them an overwhelming sense of the pointlessness of everything. hmm. life can be full ofjoy. and i think our priority should be to enable as many people as possible to live in full health for as long as possible. and so, if the focus of this kind of research is on what's called compressing morbidity, you know, making people

who are ageing healthier and extending people's lives that way, i'd be very supportive. but life extension for a few while others are living a life of depression and debilitation wouldn't be right. your debate opponent in this book, john martin fischer, he asks you to indulge in a thought experiment. he says, you, stephen, "imagine that i have an elixir "which can, when you reach the age of 80, can prolong "your life by a week. "and at the age of 80, your life is good. "you're in good physical and mental health. "would you drink that elixir just to ensure "that for the next week you go "on living that good life?" i hope i would. i hope that's what i'd want to do when i'm 80. you hope you would. so if you would drink it for one week, what would you do

at the end of that one week? would you want to drink it again? that's much harder to say. why, if you've just had a great week because of the elixir, surely you'd want another great week, and another after that? i mean, his message, beyond the thought experiment, is that, actually, when you drill down into it, if you have a good life, why not want to prolong it for as long as you possibly can? well, i completely understand the impulse, and i'm all for creating a world in which as many people as possible can have that kind of life that they embrace. and that's why i'm very supportive of much of the research that's going into cellular rejuvenation and the other things that will help us to tackle the diseases of ageing. i hope these breakthroughs will come, but as a society, we need to think carefully about what that means for ensuring people have good mental and physical health for as long as possible. what do you think of those people, some of them very, very rich, some of them indeed scientists, who actually, while they wait for the magical forever life solution to be found, they want their own bodies to be frozen, cryogenically, for liquid nitrogen to perhaps give them, albeit a very small chance, of being revived at some later point, when we have found this miraculous answer to forever life ? well, the belief that we can

one day be resurrected, whether by gods or by scientists, is a very ancient one, so i understand the impulse. i think the chances of success are very, very small. freezing someone is very bad for you. as a rule, it would be considered murder. your cells turn to slush and so on. but if you say this to someone who signs up for this practice, they would say the chances might be small, but they're better than coming back from cremation. so, you know, i understand why they're taking the odds. let's leave the freezer to one side. let's think about a different way in which we might, in the future, think of immortality. that is al, artificial intelligence, giving us the capacity to download what is the essence of ourself, that is what happens in our brain. download the memories, the thoughts, the emotions, the material that makes us us onto a computer, to digitise it, to turn ourselves into digital cells which can be kept in a metal box forever.

isn't that going to be a form of immortality? well, it is certainly something that some people believe is a form of immortality, and is already on offer. i mean, there are already companies promising something like this, whether as a way of managing grief — so if it's a loved one that dies — or as a route to immortality when thinking about your own prospects. but i don't think this is a route to immortality. you know, it's notjust a means of maintaining sort of memories, it's not like keeping photos on your phone. this can be generative. this can be the essence of you, which generates new thoughts, new conversations, which keeps you, in a sense, alive. now, your institute works on technology in the future and humanity. is that not something that actually is a realistic possibility? yes, it's a great question, and we're in deeply philosophical territory when thinking about — is that really you? i don't think it is. i think i'm this particular animal, this particular body, this organism, and no organism is transferred when my psychological data is transferred onto a computer.

but there are philosophers who differ, and we do, in fact, have a research project that's thinking about what this will mean for how we grieve, how we think about our own mortality, for religion, if this becomes a common practice, which it might. let's talk a little more about artificial intelligence. i've already referred to colleagues of yours, who, with the greatest of respect, call you a curmudgeon on the issue of prolonging life. they also, i think, call you a curmudgeon when it comes to your attitude to artificial intelligence, because there are so many people out there working on this who are deeply excited and positive about the future. demis hassabis of google deepmind. he says, you know, "things are changing at digital speed. "we are in the renaissance of scientific discovery. "ai has the potential," he says, "to help with "humanity's greatest challenges. "it's going to be transformative. "it's going to be beneficial." you, on the other hand, seem to spend your time talking about the need for global regulation. why are you being,

again, curmudgeonly? well, those two things are definitely not opposed, in global regulation and innovation. 0n the contrary, i think we need regulation in order to make this technology go well. that's my mission with all of these technologies — to ask, how do we make them go well? of course, they have enormous potential to bring prosperity. that's the history of technology. but in the long run, it tends to bring great prosperity, and we enjoy the lives that we do at the moment, and only through technology can we support... it's sort of easy to call for regulation and demand that the international community acts together to achieve meaningful regulation. but isn't the truth of it it's never going to happen, because the key drivers of ai development are vast corporations, driven by greed, i suppose, on one level, and nation states, who are driven to a large part by national security interests and great power rivalries? the idea that those different actors are all going to come together and be collaborative,

it defies what we know about human history and human nature, doesn't it? well, there's no denying it's incredibly hard. and at the moment, researchers in my institute and across the world are looking at what kind of precedents are the best to follow for al. is it something like the way we manage nuclear weapons? is it something like the way we manage chemical weapons? or is it more like climate change, for example? what do you think? well, i don't think the nuclear weapon analogy is a good one, because there we're talking about one very specific technology, that's very hard to build. whereas ai, it isn't one problem, it's something that's going to impact on every aspect of life, and it's something that we're all going to have access to. so we need to think of it as a very broad range of problems — ai in health care, ai in weapon systems, ai and misinformation, for example, and use different regulatory mechanisms, different ways of cooperating in order to manage those. but this conversation has been, again, a fascinating mix of philosophy, history,

science and technology. what makes you think viewing humanity over a span of time, that human beings are going to find the ways to turn our ever—deepening knowledge of ai and its capacities into something positive, rather than something that sows the seeds of our own destruction? well, we might not. well, now you're the curmudgeon. i mean, i'm trying to be optimistic and suggest that that some kind of collaboration is possible. there are real precedents for coming together to solve urgent problems. often it takes too long, as it is with climate change. but i think we should be optimistic that people have started thinking about the impacts of ai and how to contain it relatively early. i mean, with other technologies like printing or cars and so on, it took centuries or decades to come up with meaningful regulation. so i think we should be optimistic about the many initiatives that are already springing up. stephen cave, it's been fascinating.

thanks for being on hardtalk. thank you very much. inaudible hello there. on wednesday, we were all in the same area of high pressure. but despite that, the amount of cloud we saw from place to place varied a lot. the cloud was at its thickest across eastern scotland and north—east england, where we saw drizzle move in from this sheet of cloud from the north sea. but there was some sunshine. western scotland did 0k, and for east anglia and southern england also there was quite a bit of sunshine around on wednesday, and what a difference the sunshine made to how the weather looked. for example, here in cornwall, barely a cloud in the sky.

now, we're going to have the same kind of weather picture with us for thursday, with the cloud varying a lot from place to place. still got a bit of drizzle falling from it, mind you, east scotland around these eastern coastal counties of england, otherwise dry start to thursday, still some frost slowly melting away for southern england and western scotland initially. but it is across these colder parts of the country where we will have the best of the early morning sunshine. and the cloud across the north sea, i think it's going to thin through the day, so i would expect any drizzle to die away, the afternoon looking dry for all of us. cloud will tend to encroach across the midlands east anglia into parts of south—east england, leaving the best of the sunshine probably across central southern england, south west england, southern wales and probably western scotland. again, not doing too badly for some sunny spells. you might see a bit of sunshine as well in northern ireland. 0n into friday's forecast, that cloud comes further south again. so east anglia, southern england, a lot cloudier this time, probably more in the way of breaks generally across scotland, northern ireland and probably north—west parts of both england and wales. temperatures give or take

around about six degrees, so it is still on the cold side for the time of year. and the weekend has more of the same, really. high pressure stilljust about clinging on. so some cold and frosty mornings, largely dry weather picture with some of you seeing some sunshine, others staying a little on the cloudy side, but it will remain on the cold side. now, beyond that, next week, we get northerly winds diving southwards. they will bring some snow to scotland, i'm sure about that. we could see a weather system move into the cold air, which could bring some snowfall on its northern edge as well across parts of england and wales. but there's still a little bit more uncertainty about that. however, there is plenty of potential to see some disruptive weather with cold, icy and maybe snowy conditions next week.

live from london, this is bbc news. the public inquiry into one of the uk's worst miscarriages of justice resumes later, as hundreds of sub—postmasters wrongly convicted of fraud are to have their convictions overturned. two contenders vying for the republican presidential nomination go head to head — but without frontrunner donald trump on stage.

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