Welcome to a talkcast. I'm Brett Hall and this is episode 215 of Talkcast. Today I'm doing one of those quite rare episodes where I actually talk to someone else rather than having a soliloquy. And today I'm speaking with someone I've known for over 25 years. He was once a lecturer of mine at the University of New South Wales where he lectured me on physics. Actually it was more an astrobiology course. We'll get to that. But even after I graduated from the first degree that I did, I became fascinated by his back catalogue and he's been mentioned before on talkcast many times. Just because there are so many parts of his research that in fact come to bear on the kind of things that David Deutsch talks about because in both cases although they're coming from quite different philosophical traditions and worldviews, nonetheless because they're interested in fundamental aspects of what it is that life is about and the laws of physics and the place of human beings within all of this stuff or people as we might say. There is some overlap between what Charlie Lineweaver and David Deutsch talk about and perhaps just as importantly they both follow the fun. Charlie seems to have no exhaustive way of figuring out what it is he wants to do next. He seems to effortlessly change his area of interest or what he's curious about from one year to the next and you'll hear a little bit about his life story there in the first part of the chat. And you'll also hear that, well, Charlie and I don't always agree, or do we? We don't. And because Charlie and I have spoken at length about the issues on which we disagree in real life, I haven't recapitulated much of any of those disagreements here, although you'll hear a taste of that. Anyway, the areas where we disagree aren't as interesting as those areas where I just wanted to find out from Charlie. Here's particular views where I happen to align with him because he can explain so much of these areas of astrobiology and cosmology in a way which, well, I think the average listener will find great value in. Not least because he is a communicator as well as a scientist of the first rate. He should be more well known but he's just not out there on social media. Importantly, although we cover many interesting topics, there is one elephant in the room, which doesn't really get a mention at all, Charlie's atavistic cancer hypothesis he developed with Paul Davies. And one of the reasons that I have been vocal recently in trying to bring to the world's attention the existence of Charlie line with, and not that he needs much help from me because he already is famous in certain circles. He needs to be more famous because of this completely new way of trying to understand cancer. It's a new approach to curing cancer. Now, might it file? Of course, everything could file, but this approach is worth looking into. I, as I say in this interview, don't really touch on that because a wonderful interview was done recently between Charlie and another podcaster on that stuff. And by the way, I will be releasing a talk. I had the privilege of being a part of with Charlie recently as well, where he talks about the technical details of some of this stuff. So just wait for that to come in the top cast feed too soon. I talked by Charlie line, we were about atavistic cancer. And I've told this story on top cast before. I don't want to drop names, but it just happens to be the case. It was a curious little part of my life where I happen to be working as a science communicator for the University of New South Wales, where Charlie was my professor. And I was organizing this event, it was called Science in the Pub, and they just happened to be debating a panel of astronomers what the meaning of the word planet was all about. And so anyway, they were having this fun debate and whatever else. And I was just organizing the event and who should walk into the event, but the great Paul Davies. Paul Davies was remember and he fans out there, they're up to be listening to me. He was my science hero before I knew anything about David Deutsch. I was reading Paul Davies books from like the year 1992. And when I exhausted all of Paul Davies back catalog of books, well, what was sitting on the shelf there was a book that had been blurbed on the back by Paul Davies, which said something to the effect of, I have not been so inspired since I read Girdle Eshabak. And that was a quote by Paul Davies. And that was on the back of the book called The Fabric of Reality by David Deutsch. And so to have Paul Davies walk into this pub at an event that happened to be hosting, and to see Paul Davies come in there was like, I don't know, a teenager who happens to love the latest pop sensation seeing Taylor Swift walking into the venue where they happen to be. So I was so excited. And I remember going up, you know, gingerly as the age of 21 or something like that, maybe younger. And saying to Professor Paul Davies, you know, you're my scientific hero. I don't have one of your books here with me. But could you sign, could you autograph my lecture notes, which I happen to be carrying with me? And the lecture notes were for this subject that Charlie Lineweaver happened to be teaching. And Paul looked on the front cover and he said, Oh, Charlie Lineweaver, do you know Charlie Lineweaver? I said, do you know him? He happens to be one of my lecturers. Oh, well, here's my card. And so I got Paul Davies card. I got two cards. I said, could I have another one, please? Professor Davies and I'll keep one as a souvenir for myself. But I will pass on as you've just asked the other one to Charlie Lineweaver. And so I like to regard myself as a very small footnote to a footnote in the history of the collaboration that began that evening between Paul Davies and Charlie Lineweaver, who have worked on a number of different papers. And we'll talk about some of those throughout this episode with Charlie. But importantly, and recently, the stuff they've been doing on atavistic cancer research, but they also did stuff on cosmology and black holes, the shadow biosphere, we will hear about it all. I have been endlessly fascinated by the back catalogue of papers that Charlie has written ever since. We will hear here about what he's working on now, what his latest interests are, as well as how he got into physics, his contribution to Nobel Prize winning research, and what he happens to think about some of my ideas with which he thinks he disagrees, but I'm not sure that he really does, although we don't explore it all here. So, optimists out there everywhere have fun with this chat between myself and the iconic Charlie Lineweaver. Hello again, Charlie, and welcome this time to Topcast, which is my podcast, The Theory of Knowledge podcast, which actually has a K and a C juxtaposed there, and I always emphasise the K and the C next to each other as knowledge creation. So it's a knowledge creation podcast, and I think that creators of knowledge are a force in the universe, something akin to gravity almost in the way they're able to transform matter around us. That's what people are, and you yourself are emblematic of the kind of scientist who has contributed across the board to so many diverse fields, and that's where I wanted to begin the conversation today, because I hear from people quite often who say, "If only I had have studied more chemistry or mathematics or physics when I was at high school or if I had have gone to university and done one of those degrees, then my life would be more enriched now." But there is a lesson in your own life story, because you didn't follow the traditional trajectory that people are assumed to go through in order to become a professional scientist, a cosmologist, who is contributing to some really groundbreaking fundamental research. You found yourself in soccer boots at some point, and then teaching Japanese people English. So explain to me how those things somehow led you to working on research that actually led to a Nobel Prize. Okay, that's a long question. You're asking my entire history of my life. How about we just stick to the fact that you didn't to undergraduate physics straight out of high school? You went to Dean? It goes back to, I guess, an identity crisis. I think everybody has at least some version of an identity crisis. I had a strong one in high school. I didn't know what I wanted to become, except that I had a sense of cultural claustrophobia. I knew I was being fed a bunch of stuff about America. I grew up in New York. I was born in North Carolina, grew up in New York and a place called Northport, New York, and I just had the feeling that I was claustrophobic culturally. So I wanted to travel. As a matter of fact, when I first applied to Brown University as an undergraduate, they said, "Oh, look at this. We were the state champions in soccer." And I was the center, not the center for this, the midfielder. And so I was going to go to Brown University based on a soccer scholarship, but they asked me, "Oh, so what do you want to study, by the way?" And I said, "Well, I'm not sure, but I know I want to take a junior year abroad." And they heard that and they said, "Okay, we don't need this guy." He's obviously more committed to traveling abroad than to the soccer. Anyway, so I always had this strong sense of a cultural identity crisis and not knowing who I was, but I wanted to be a man of a world somehow. And I was always good at school, but I never paid much attention to it in high school. I was one of these people who thought it was cool not to study and do really well on exams without studying. So that was my misguided youth until I got to university when I said, "Hey, I like this stuff, find out stuff." But I did do a junior year abroad. I was an old American soccer player at the State University of New York at Binghamton, and then I did a junior year abroad. I went to the University of Ileiife in Nigeria. Why? Because of the sense of cultural claustrophobia. And then I realized that I couldn't speak English. Most Americans think they can speak English. And so I was one of them, and then I realized, "Wait a minute. I can't write very well. I can't speak very well." So I said, "I better study English." So I went back and I majored in history in English at the State University of New York at Binghamton, mostly because they had the best teachers there. The teachers in the history and the English departments were by far better than the ones in science, although I love science. So I studied English in history, and then I went to Brown University and did creative writing after a year. And then when I was in West Africa, oh, I forgot. When I was in Nigeria, I then got kicked out because there was a coup d'etat, and I didn't have a proper visa. I had a tourist visa rather than a student visa. So then I hitchhiked around West Africa with my then girlfriend, went to Dakar and went to Timbuktu and crossed the Sahara in a goat truck. And then I got a scholarship to study Egyptian studies in Alexandria. So that's what I did. I studied a lot of history, and I majored in world history in English, and then I went to graduate school at Brown University in English. But then after a year, I said, "Hey, I want to learn French better because I saw all those people who are speaking French in West Africa, so I'm going to speak French." And so I went to the LA Armstrong says in Paris for a year and then went back to Brown, graduated, and then I went to Dros? No, no. Then I went to Munich and started studying physics. Undergird. Now, why did you pick physics at that time? That seems like a strange sudden turn from languages. Well, I realized this is a profound realization that when you study history, or when you study English, you're studying basically the culture of one small fraction of humanity. And so I wasn't becoming a man of the world. I was becoming a Western man. And I didn't want that to happen. I wanted to study something that everybody in the whole whole world would respect. And I was always good in physics. That was one of the things I loved the most about high school. And so then I said, "I'm going to study physics and play soccer." So that's what I did in Germany. And that's where I began my undergraduate physics career. Then I continued that in Japan. After three years in Germany, I went to Japan for three years, studied Japanese and studied physics. And then I guess an interesting story is that while I was in Japan, I wanted to study for the GRE exam in physics. And so I was teaching English there, almost every Westerner who lives in Japan teaches English for money. And so I did that. But I had the advantage of teaching English to physicists. And what I got was I got the GRE study book, and I said, "You guys are physicists, and I want to learn this stuff, and I can teach you English. So why don't you explain to me in your broken English what the physics of these questions is?" And so basically, I was getting paid to study for the GREs. And I thought that was a very good, it was almost like $100 an hour or something. Because anyways, a lot. And I thought, "This is great. I'm getting paid to study what I'm supposed to do anyway." So then I went to enter the PhD program in physics at Berkeley. And after this is in 1987, two years later, I passed the qualifying exams. And then I saw a notice on the board said, "Hey, something about the cosmic background explorer." And looking at the microwave background, I said, "Oh, that sounds interesting." So I went up to George Smootz Lab and applied. And I was accepted. And then for the next five years or so, we studied the fluctuations in the microwave background. And for that discovery of these fluctuations, when I say fluctuations, in other words, you look at these are the oldest photons you can see. You're essentially looking at the photosphere of the universe, looking at redshift, not of 1, 2, or 10, but redshift of 1,000. And so these are the oldest photons you can see. If you look in any direction, you will see this radiation. It's the background radiation. And essentially, George Smootz said it's like looking at the face of God or something. The idea is that the structure we see in the universe around us had to have had seeds very early on that could grow gravitationally. Those seeds had to have been there at the time of this microwave radiation. No one had seen the hot and cold spots, which would correspond to the seeds until this Kobe satellite, and particularly one instrument on board the Kobe satellite, the differential microwave radiometer. And George Smootz was the principal investigator of that. And I was his only PhD student at that time. So I worked very closely with George, but there was another whole big group that worked on this. And you go ahead. But the basic problem was that we knew that the temperature of the cosmic microwave background was everyone throws around at number 2.7. And it was smooth. It was uniform. But that was known. But the mystery was that the rest of the universe was lumpy. And what you found was, in fact, lumpiness in the CMB, is that right? And you personally were responsible for the processing of the data. And was it you who slipped it under his door or was there some story there? Well, there was quite a big group, and a lot of people deserve credit. And when these people get Nobel prizes, they're often members of groups. But George, really, he got a Nobel prize with John Mather. Both of them deserved the Nobel Prize. But there were big teams behind each of these guys. I was, like I said, the only PhD student that George had. But he had several other people programming, and then he had a whole big team on the East Coast. But I'm talking about Berkeley here. And so, yes, we knew that there was structure locally. We also, so far, the microwave background seemed to be perfectly one temperature. But we knew there had to be fluctuations at a certain level. 10 to the minus 3, or 10 to the minus 4, 10 to the minus 5. And Bingo, we found these fluctuations at 10 to the minus 5. But it required quite a lot of calibration, quite a lot of subtraction of the foreground from our galaxy. There are synchrotron radiation, there's free free radiation. So, basically, my PhD was called the correlation function. So, I made one or two of the diagrams in our most famous 1992 paper in which we announced the discovery of the fluctuations in the background, which Stephen Hawking called the greatest discovery of the century, if not of all time. One way to understand why he said that is because we were looking at angular scales that we saw a structure that was so big that it could not have been causally determined. So, one side of this, let's say there's a big hotspot, that hotspot was so big that one side did not know about the other. So, it had to have been produced in an epic called inflation where you could have causal connection between those two sides of the hotspot. And today, we're still studying the anisotropy in the cosmic microwave background. I mean, after the cosmic background explorer that you worked on, then there was WMAP, the Wilkinson microwave anisotropy probe, and then there was Planck, I don't know if there's a fourth one out there now, each one more high resolution than the last. But can you explain why do we do this? Why are we finding ever more precise temperature differentials between one's cold spot and one warm spot next to each other? What can that tell us about deep mysteries of the universe? Well, just imagine you're an archaeologist and you're looking for the origin of humanity, and what you want is to look at, you know, I guess, Neanderthals and our early ancestors 300,000 years ago, and then you look at Homo erectus, you look at Australopithecines. In other words, if you want to find out how we got here, we need to know the history of how we got here. Now, if you apply that on the largest scale, we're talking about how did the universe get to be here? Why is there something rather than nothing, for example, is one question that sometimes asks. And so you have to find the earliest evidence you can for your model of the universe, and the microwave background is the earliest evidence we have. It's a picture of the universe when it was 380,000 years after the Big Bang, which is less than half a million years. So that's very, very young. Now, there are other ways to probe even deeper, for example, if we had a neutrino telescope, we could see much closer to the Big Bang, and presumably, and maybe, I don't know, 20, 30, 40 years, we will have gravitational telescopes that might be sensitive enough to look even further back in time. The reason why that's important is because we need to probe the earliest epics about 10 to the minus nine seconds after the Big Bang, because that's where we need quantum cosmology. We need to marry quantum theory with general relativity, and we have a very poor understanding of how they meld together. But if we get more and more evidence from these earlier times where we know we need that combination to describe things, well, if we have data from that period, that would just be great. So the earlier the better is a simple answer to your question in terms of evidence. When we talk about the accelerating universe, which comes to us via the Hubble expansion measurements of type 1A supernovae, there's also a way of triangulating or cross-checking the C&B measurements or maps against that. Is that correct? Is there a way of checking to see that you've got an accelerating universe given a more precise map of the anisotropy? You're right that they're interlocking. I mean, whenever, for example, you talked about the supernova research, they're found an accelerating universe. But when you combine that with the microwave background, you can say that the universe is made out of about 30% matter and about 70% of this lambda, this cosmological constant, which is the source of, we think, the source of the acceleration. So all of the cosmological data has to fit together. And when you put it all together, you get the standard model now. It's called the land CDM. Lambdas means there's dark energy of about 70%. CDM means that there's cold, dark matter at about 25%. And then you have matter like you and me in the periodic table at about 5%. So that is the standard model. There are many, many different ways to check that. The CMB, in particular, what's called the power spectrum of the CMB. That's how much power there is in these fluctuations. So hot spots, cool spots on this scale, hot spots, cool spots on this scale, hot spots, cool spots on that scale. So the whole range of scales, and you put that power together, it creates a power spectrum, that power spectrum can tell us all kinds of things, particular how old the universe is, this 13.8 value that comes up. What, how many, how much dark matter there is, how much lambda there is. And that has to correlate with, that has to be consistent with other observations, like the supernova ones you talked about, or the baryonic acoustic oscillations, or for just simply the age of the universe. If you find something that's 15 billion or 20 billion years old, that is inconsistent with what we know about the age of the universe based on general relativity and all of these observations I just mentioned. And if you find something that's 20 billion years old, you're going to win a Nobel Prize, but you're going to have to convince an awful lot of people why your results are better than the ones that we have so far. Do you have a favored explanation, but it wouldn't be an explanation at the moment, conjecture about what cold, dark matter is, or what the solution might be? Could it be a? No, I, I, I said to disfavor the mind, the modified Newtonian drymatics, because they, they, they invoke it for particular observations, and not all of the ones that you could invoke it for. So I, I'm, I kind of disfavor that one. Axion seems like an interesting character, interesting candidate, the wimps, so weak, weakly interacting, massive particles. I even like the machos, these are massive compact halo objects, and they could be composed of primordial black holes, for example. So my favorite, I guess, would be primordial black holes, but then that basically anything that does not shine, it could be a black dark matter candidate. Also, I want to correct the idea that it's dark matter, it's not dark matter. Dark matter is, dust is dark matter, and it absorbs light. This stuff does not absorb light, so it's more accurately called transparent matter. Yes, yes. I think this is where people can see that you earned your fame, and in Australia for quite a while there, you were the, the go-to guy for media outlets wanting to know what was happening in the sky, you know, some asteroids passing over. Is it going to hit us? Let's go to Charlie Lineweaver. But it shows the flexibility of your mind, I think, in one person to be able to go from soccer to learning linguistics, and then history, and physics, and then you go to cosmology. And now, let's turn to some even more fun stuff. You just seem to enjoy having fun with your career, the planet of the apes hypothesis. And I want this to get into people's minds. This is such a wonderful little heuristic that Charlie has come up with, I think, uniquely, in order to illustrate that the common misconception, what everyone seems to know, is that there are just trillions upon trillions upon trillions of planets out there. So, of course, there is going to be intelligent life out there, but Charlie pushes back on me. It's so powerful, and so well, with the planet of the apes hypothesis. Could we recapitulate that for me here now and for it? So, you, you are familiar, presumably most of your listeners are familiar with the planet of the apes movie. In basically, Charlton Heston has a crew that's been cryogenically preserved for a while, and they crash land on some planet. They don't know where they are. And then, over the course of the movie, they find out that they have landed on earth. And the weird thing about it is that they have a, on this planet, they have watches, so they know that there's a 24-hour day. They can measure the atmosphere. It's 20 percent oxygen and 80 percent nitrogen, like ours is. They have, it has a moon, and it has three species of other apes, and it has corn, it has horses. And the ridiculous idea is that only at the end when the guy, when Charlton Heston's with his squeeze riding a horse, sees a half-buried statue of liberty, he said, "God damn it, this is earth." And so, the idea that somebody could land on a planet and see corn and horses and three species of apes speaking English, and human beings who are mute, that just seems, these guys, I call this one of the largest eras in quirk ommetry. And the idea, they should have known, I mean, if you can measure the exact composition of the, or the length of the day, or the length of the month, or the composition of the air, or the genetic quirkiness of corn, and horses, and three species of ape, you should, any biologist would know this has to be earth, but no, no, this is Charlton Heston only when he sees the half-buried statue of liberty, he says, "Oh, this is earth. God damn it, what have we done?" So, the reason I call that a fallacy is because it's so easy for us to think that we inhabit what you might call the intelligence niche, and that whenever we, if we go through World War III or 4 or 5, and marginalize ourselves, or go extinct, that other species, i.e., the things that are most closely related to us on earth, that is the chimps, the gorillas, and the orangutans, they would necessarily converge on what seems to be this intelligence niche. And I, that's the idea that I'm pushing back on, because humans do not, chimps do not want to become humans, and you, any more than humans, want to become chimps. I mean, every, every organism on earth has evolved mechanisms, its brain, its liver, its lungs, its skin, to stay alive in the niche, in the environment in which it's evolving. And to pretend that, oh, our evolution is so wonderful and great that any other species would want to evolve into it, that's the part that I, that I call the planet of the apes fallacy. And another way to say that is that humans are unique, just like every other species. That's something I repeat again and again and again, because all I hear from people is humans are unique, humans are unique. Why are humans so special? Why are humans so special? And people come up with all kinds of reasons of, we especially because this, it's just an exercise in vanity. But when you say humans are unique, I admit that, but just like every other species, it, it puts it in perspective in a way that I think is important. And when we go looking you wouldn't go looking for a sulfur-crested cock or two on another planet, you wouldn't go looking for an Indian elephant on another planet, you wouldn't go looking for a naked mole rat on another planet, and yet people are looking for other people on other planets. How do I know that? Because they've defined intelligence to be human-like intelligence. An example of that is we have these, we have this big brain, right here, big brain, but our olfactory lobes are tiny. I have a dog that can live in a world of smells and I have absolutely no recognition of the smells that she can smell. And so to pretend that our way of seeing, we're primates and so vision is very, very important, a dog smelling is much more important. So I'm trying to relativize what your brain is for and not pretend that our brain is somehow more general and better and therefore a convergent feature of evolution, no matter which planet you find life on. That's basically the four-minute version of the fallacy of the planet of the apes. That's brilliant, yeah. So another way of putting this is that among various species, we've found wings which are evolved independently, whether it's insects, fish, birds, of course, mammals, but we're not getting these large brains that are able to generate explanations cropping up over and again. Maybe our ancestor species, it seemed to have happened once, but Australia left on its own for however many hundreds of millions or tens of millions of years. The kangaroos, as you like to say, weren't about to start developing radio astronomy or nor should we expect there to be a direction in anywhere in evolution. However, I've also heard people say that life is inevitable or increased complexity is inevitable. Is there any such inevitability given the laws of that question? Let me start up with the continent you mentioned. Now we now have about six or seven continents and we know because of plate tectonics that they have drifted around and you can estimate based on the plate tectonics and the rate at which plates are moving around how long these continents were independent of each other. So Australia, for example, has been independent of other continents about 100 million years. The same thing for South America has been independent until it ran into North America about 3 million years ago. So the evolution of landlocked creatures is not just one experiment on Earth. There are at least six experiments on Earth, but I would also argue that anytime you have sexually reproducing critters, they are essentially evolving separate from each other. So you have a million separate experiments in evolution and when you look at what happened on Australia, for example, now if human-like intelligence was a convergent feature of evolution, you would expect, you know, there's a two kangaroos. This kangaroo over here had three more neurons and it gave it the ability to be a little bit smarter when it came to X, Y, and Z and then et cetera, et cetera, et cetera. It survives a little bit better, et cetera, et cetera, et cetera. So it devolves into a big brain creature. That type of argument is easy to make, but apparently that's not the way evolution works because it hasn't worked that way in every experiment that has been done. In other words, there have been at least six natural experiments for what does evolution do with landlocked vertebrates and those experiments are called Madagascar, India, Australia, New Zealand, South America, and North America. And the point is that we find no evidence for evolution towards human-like intelligence. And that is the best evidence we have to evaluate whether our type of intelligence is a convergent feature or not. And the answer that I think strongly suggested, if not definitive, is that evolution does not try to produce human-like intelligence anywhere. If it did, well, for example, we have a brain this big, but we went from this big to this big in about three, four million years. It tripled in size. Now, okay, so three or four million years is a characteristic timescale for this creating a big brain. Well, I mentioned that Australia had been independent for about 100 million years. So that's 25 times longer than it took our particular species to get this big brain. So obviously, it could have happened in Australia or in New Zealand or in South America. And when you look at the critters that are most similar to big-brained humans, you find out that, hey, they are not big brains. They are some of the primates in South America. They're the kangaroos or wombats. I don't know what you want to call the most human-like critter that evolved in Australia, but it's certainly not many people would think it's likely to become an electrical engineer and start sending out signals to the rest of the universe. Or you could ask the question. It's a very hypothetical question. How long would it take for anything in Australia, the kangaroo, a wombat, or any kidna, a monotreme to evolve into an electrical engineer and start doing what we know how to do humans? And the answer is, who knows? It's probably never. And if that's the answer, then human-like intelligence is not a convergent feature of evolution. It's evidence that humans are unique, just like every other species, and these other unique species are not trying to evolve into what we are any more than we are trying to evolve into a worm or a dog or a, I don't know, the tree outside of my window here. So it's not trying to become a human. We're not trying to become it. And so that's kind of a relativistic way of looking at these things. But I think that is what the lesson of the independent continents and the evolution on these continents during 50, 60, 100 million years is telling us. They should take that seriously, and we should take less seriously our vanity in wanting to believe that we are unique, but we are so great that other life forms elsewhere in the universe will evolve into electrical engineers and starts producing radio telescopes. Yes, so this answers the Fermi Paradox. At least it is one possible solution to the Fermi Paradox. But it's not to say that on those trillions upon trillions of other planets that are out there, they couldn't be covered all in sludge and slime and bacteria and archaea and those kind of things have given that, and your own research has touched upon this, how relatively quickly life seemed to have arose in the geological record here on planet Earth. Did it arise very, very quickly? I don't know, but unusually quickly. That, as a little word, I'm completely foreign to my vocabulary. Well, we can talk about, we have estimates for how quickly it evolved. The Earth in the Sun, the solar system, is about 4.5 billion years old, 4.567 if you're interested in more digits. And the Earth started out hot, and then it had to cool down. And the life, what we call life now, has a thermal limit. It's somewhere between 121, which is the current maximum to, maybe as high as 220, and you might ask the question, wait a minute, doesn't water boil at 100? Yes, it does, but we're talking about water under pressure, and so water can get up to 200, or a few, well, maybe, I'm not sure, maybe even 320 Celsius. No, Cal, is that Celsius? Yes, that's Celsius. And so, where was I on this? Oh, you're asking, how did life start early? Well, I wouldn't say early. I wouldn't say late. I would say it started at a certain time, and there was a slow evolution. And it looks like now, based on research that just came out last month, that it's somewhere between, let's say, 4.3 and 3.9. So, let's say, to round it off, I just often say life has been on the planet Earth for about 4 billion years. The issue about why that's important for the probability of life is imagine that, let's say, imagine that you want to roll a, rolling a dice? Well, let's talk about the German tank problem. I don't know if I've told you about this, and that is, imagine you're in World War II, and you have just captured a tank, and the number on the tank is 5. And your captain says, "Well, can you tell us how many they have? We need to know how big the tank army is of the Germans." And just based on, if you have captured a random number, and it is 5, it's very, very unlikely that they have a billion, or a million, or even 200 tanks. It's much more likely that you have captured a random number, and that would be maybe they have 10, maybe they have 6, maybe they have 50, something like that. In other words, you can infer the number even from just one example. So, applying the same analysis that life on Earth started very quickly, that means that the probability of it starting under those conditions was higher. The earlier something happens, the more probable it was, is the general idea. If you make the assumption that the same or similar conditions were available on other Earth like planets and water elsewhere, then you can infer about the probability of life elsewhere. That basic bottom line is, under those assumptions, the earlier we find that life has evolved on Earth, the more likely life is to have evolved elsewhere. Yes, although people often point to the idea that, well, we've just got an n of 1 when it comes to Earth and observing life, what you've pointed out there, quite right, is no, we have more than just n equals 1. We also have time constraints as well, and those time constraints make a lot of difference about inferring whether or not. Right, so we do have an n of 1, but we also, as you point out, we have information on the timing of that n of 1. So, it might very well still be the case for the optimists that, if the optimists about wanting there to be aliens out there, there could be alien bacteria out there. What are the chances of alien multicellular organisms, alien vertebrates or something like that? Or you could also ask what's the probability of alien viruses? I mean, oh, so we just talked about the origin of life and that you can get a handle, rough handle on the estimate of how probable it is based on how quickly it evolved on Earth. As to what happens after that, I just raise my wave my hands. The reason I wait, this is a very important point because you mentioned earlier that I think you said flight, and many people, Richard Dawkins and many others, including Simon Conway Morris, have made the point that, oh, there are many examples in the history of evolution on Earth in which there has been convergence on certain traits. And I've been pushing back on this for about 20 years. And the reason I push back is because of what I call deep homology. So what I mean by that is, so you will see Richard Dawkins probably in 10 of his books, he says, their vision has evolved multiple times, or the eye, or eyes have evolved multiple times. And I've heard that repeated hundreds of times, and I think it's just wrong. And the reason, excuse me, the reason I think is wrong is the following. He talks about vertebrate and invertebrate eyes. And he says, oh, look at that, that's an independent origin. But like all life on Earth, they have common ancestors. You and I have a common ancestor, maybe 10 generations, maybe 20 generations ago. We and chimpanzees have a common ancestor about six or seven million years ago. Now you can ask the question, when was the common ancestor of vertebrates with this vertebrate eye and invertebrates with this supposedly independent eye? And the answer is something like 600 million, maybe 500 million years. And then you have to ask the question, did that common ancestor have anything that looked like an eye? And the answer is yes, it had what you could call proto eyes or proto proto eyes. So when you say it evolved independently, you're pretending that you don't have a common ancestor which had the prerequisites and a lot of the basic ingredients, including the basic biochemistry that octopus eyes and our eyes currently have. So that's, and so that's what's, I'm invoking what's called deep homology, deep common ancestry, that you need to know about what was already there before you talk about convergence. Another short way to say it is everybody has a common ancestor. And if you want to talk about convergence, you have to talk about divergence. If you want to talk about divergence, you have to know how similar, what fraction of the trait you're converging on was already down here. That aspect is the crucial part of this argument. And it is systematically ignored by all people who are talking about convergence on flight, convergence on eyes, convergence on what other things they talk about. Well, anyway, there are many things. One, two of the most important ones are the flight and eyeballs. So Avatar was basically set on Earth, obviously, because there's just so much there. Okay, we're going to go from four-legged creatures. This is an interesting debate about whether dragons have four legs and wings, or just have hind legs and wings kind of like, and also bats. We talk about flight, for example, let's talk about flight. Birds and bats, bats are mammals, birds are reptiles, they have a common ancestor about 30, 320, 340 million years ago. The question is, did the common ancestor have flight? Well, not really, but it did have four legs. Birds go like this with their front legs, and bats do the same thing with their front legs. So obviously, the ability to go like this was in the common ancestor of bats and birds. So that's another example of one of the more fundamental aspects of the trait you're talking about was already in the common ancestor, and that's why I keep on invoking, you have to talk about what was in the common ancestor before you talk about convergence. So, deep homology is usually ignored, and convergence is always, oh, it looks wonderful, it's converging on the same thing. Another example, oh, here's another example, dolphins and humans. We have big brains, dolphins have big brains, but we know that our common ancestor with dolphins was more like a cow-like thing, and this would have been 95 million years ago. We know these timings from the genetic proximities to each other, and so here we start out a creature. Now, let's say here's four billion years ago, and here's today. We have a common ancestor with dolphins 95 million years ago. That's less than the thickness of my finger up here. So we were identical, identical, identical, identical, identical, revolving all kinds of the same gene hierarchies, the same organs, the same eyes, the same bilateral symmetry, and then 95 million years ago, we diverged. Now, although the common ancestor had a small brain, we know that the things that regulate how big your ears are, big any, your chin is, or big your heart is, or small. Those are things that have turned into toggle switches that you have the same gene regulatory networks that the dolphins have. So you flip a switch very easily, and then, oh, your nose gets bigger, or your brain gets bigger, and so that's not convergence on something. It's a result of an identical system of wiring that evolved during three, the four billion years, minus 95 million. So that's that thickness of it. So it's a little like, another example would be, you know, identical twins. Let's say you two twins are born, and let's say they grow up as carpenters, and they get taught the same things, and then, suppose then at the age of, I don't know, 15, they're separated for three years, and then you find out, oh my gosh, they've been separated, they've converged on the same type of cabinet. And so, of course, they have, because they had for four billion years, or for, you know, the first part of their lifetimes, they were identical twins with the same genes and the same environment, and that sets you up to be able to produce money of the same things that, although they might not be there when they were separated, they converged on it only because of these prerequisites and depomology. That would be my argument against the invocation of convergence that seems to be in style among most biologists today. Well, I think you're disappointing a lot of people who really want to believe, you know, the whole X-Files thing that the UAPs really are from the other side of the galaxy, there's not going to be convergence on intelligence. Never mind that, there's not even going to be a convergence on-- Well, wait a minute, you must know me well enough now that I don't care whether I disappoint people or not. I'm not in the business of of disappointing them, or appointing them. I'm just trying to follow the evidence. Well, let's throw them a bone. I won't let throw anybody a bone, I'll just shut them. I will-- Whatever bone you're talking about, I refuse to throw a point. Go ahead, though. The Shadow Biosphere, this is a cool one. This is a paper you wrote, I think with Paul Davies as well, another one co-authored with Davies, about the aliens might already be here, but we might just not recognize them. So tell us a little bit about the Shadow Biosphere. You know, DNA was discovered by 1953, 1954, and over the past 70 years, we've found out more and more, we've learned how to sequence genomes. Actually, after 2001, when we had the human genome, was the first full genome to be sequenced, and since then, the number of species for which we have the whole genome has just got skyrocketed, exponential, even more than super exponential. So that's because the technology has gotten cheaper, and do we know more and more about other critters? So what was the question again? Oh, the Shadow Biosphere. So as we have-- Now, when you have dozens and dozens and hundreds and now thousands, even tens of thousands of species whose whole genomes have been sequenced, you can compare them. Just like we talked, we can compare humans and chimps and find out, "Whoa, this is the creature that's in the whole world, is closest to us." And then we thought, "Oh, what's the second most?" And then you find out it's a gorilla. Then what's the third most? Then it's the rangutan. What's the fourth most? There's gibbons. And you create this whole tree, not just of humans, our lineage, but of every lineage. You have a tree out there of-- I don't know. Let's say it's a plum tree. And then you say, "Oh, that's a hard fruit." And then you figure out what's the closest one to the plum tree. And you do the same thing, and you go back and back and back. And so you're creating, for the first time, we have what's called the tree of life based on just zillions and zillions of-- well, not zillions. I want you to-- let's just say tens of thousands, if not hundreds of thousands of species whose genomes have been compared, and then we're creating this whole branch tree of life. And the question was, "Oh, the shadow--" Now, when you're creating this tree, every once in a while, you will find something that is a comma-- that is deeper than another branch. For example, let's suppose you only knew about humans, chimps, and gorillas. And then you say, "Ooh, I found something deeper. It's an rangutan." So then you go deeper. Then come and answer this one even deeper. "Ooh, I found a dog." That goes even deeper. "Oh, I found a jawless fish." That goes even deeper. So the history of this-- the progress that we're making in genetics is finding deeper and deeper branches in the tree of life. Now, for example, in 1976, a guy named Carl Woz found archaea. Essentially, that was an even deeper branch. You used to think there's archaea-- there's, you know, bacteria, and then somehow one branch of bacteria became eukaryotes. But now we know that eukaryotes, you, me, plants, fungi, grew out most of it from a type of archaea. And so there was an even deeper branch when he found that out. But what we said was the history of defining deeper branches, let's just hypothesize that we're going to find some more deep branches. And then you say, "Well, wait a minute. What kind of things would they be? How would we recognize them?" And you recognize them in the same way that Carl Woz recognized archaea. And that is you do very careful analysis of their DNA to find out whoa, this is completely different than anything we had before. And that, therefore, it has an ancestor that has a common ancestor with us and with all life on earth that is even deeper. That common ancestor, the most recent-- it's called Luca, the last universal common ancestor of all life. And so the hypothesis that we made was that that Luca keeps on receding into the past as we find out more and more about life that is weirder and different from the existing life that we know about. And so we predicted that on earth there are these other life forms. We call it the shadow biosphere or something that you call dark life. In other words, life forms that we don't know about yet but would have a deeper branching and therefore they would be a new type of life. I should say it's not just one type of life. You get a different type of life for each one that you attach to a deeper branch of the tree of life. And you can get that Luca, the last universal common ancestor, deeper and deeper and deeper. And each one of those separate branches would be what you might call alien life or dark life or life we do not yet know about. In the same way that we did not yet know about the archaea until 1976. So, and archaea are an interesting example. I think many strands of archaea are there. Thermophilic, am I correct? So they're heat-loving life forms. And so even places that were thought previously to be completely inhospitable, in fact, could be replete with archaea. And so, therefore, you could have, perhaps under the surface of even Venus or something like that. Well, I wouldn't go into that far but I wouldn't. The basic point you're making is right, but also not just archaea but there are some species of bacteria which are thermophilic and even hyperthermophilic. These are the ones that can live at temperatures above 90 Celsius. I assume that you took a shower this morning or last night. And if you did, the temperature of that shower I can guarantee was less than 60 degrees because we are not hyperthermophilic or thermophilic. We are mesophilic and that means that, as a matter of fact, all eukaryotes have this limit of about 60 degrees. And what happens is that when you go to temperatures higher than that, your protein denatures like boiling an egg. And so that's why you get burns. But bacteria, some bacteria can love that 60 degree of water, 70, 80. Hey, I like my favorite is 90 degree. So some bacteria are called hyperthermophiles and they're also archaea like this. And so we call them extremophiles but there is some evidence that the first life on Earth was hyperthermophilic. And so for them, we are the ones who are extremophiles because we love these ridiculously cold temperatures of less than 60 centigrade. Yeah, and so like that, along with what you did about the statistics of life arising early on in the Earth that could perhaps be sort of spread out, as it were, from this one n equals one place of Earth to other planets and perhaps it arises there early, perhaps in places which are otherwise considered inhospitable, life could arise there. But, and I was talking to you about this recently, and I'm still unclear, milliuretype experiments, when they're done over and again in the laboratory, what they seem to be able to produce are amino acids. Now you were impressed by the existence of amino acids. I was less impressed because I thought, well, don't we already see spectra of amino acids in interstellar space anyway. But is there a contradiction here between on the one hand, it seems like life arose early on the Earth, therefore it's easy to produce. But on the other, professional scientists working in labs trying to create artificial life are unable to do so. Is life easy to make? Oh, isn't it? Well, you know what? There's another paper that I wrote called, "We have not detected extraterrestrial life or have we." And the point of this article was that we do not know what life is. Now, to back this up, I did a survey of biologists and I asked them, "Are viruses alive?" And just to remind you, viruses are the most common organisms on Earth. And my first survey result was half of them said, "Yes, half of them said no." And I concluded from that that we don't know what life is. But then I said, "Charlie, do a better job of this analysis, please." So I asked about 10 times more biologists and I broke them down into answers and a quarter of them said, "Yes." A quarter of them said, "No." A quarter of them said, "The question doesn't make sense." And the quarter of them said, "It doesn't matter." So that's how much biologists know about life. Now, and I concluded from that that we don't know what life is. But I recently changed my mind completely on this. I said, "That doesn't tell us that we don't know what life is. That tells us that we do know what life is." Why is that? Because the fact that what we consider to be life gets deconstructed, as you go earlier and earlier, and maybe viruses are at the base of the tree of life, that this thing called life should disappear is exactly what you expect if you have a naturalistic explanation for the origin of life. If that's the case, you have to start out with non-life. You have to evolve into something and something and something, and then we have something today which we call life. That means as we look deeper and deeper into the tree, we should start to see our ancestors who are less and less lifelike, and therefore we don't know whether they're life or not. And that's exactly what the model of a naturalistic origin predicts. And so, I've completely reversed my opinion on that saying these results tell us that we do know what life is and that it has changed, and it's consistent with the idea of evolving from non-life, basically what I want to say. Is that clear that point? I think it's a profound point. Try to concretize that a little bit more. What is your answer to the simple question, what is life? Okay, my answer to that question is, what is your answer to what is a human being? I can give an answer to that. No, you can't. I will deconstruct any answer you think you have, but here's my thoughts on this. You can ask the question, are Neanderthals human beings? And you and I have about 2% Neanderthal genes. So, by the criteria that if you can have fertile offspring, you are the same species, then we and the Neanderthals are the same species. That means we are homo sapiens sapiens, and the Neanderthals are homo sapiens Neanderthal lenses. In other words, we are not two different species. We are two different subspecies that can interbreed. And interestingly, the only museum I've ever found that acknowledged this, what I consider a blatant fact, was in the University of, no, it's in Zurich, the university, not the university, it was a museum, the Natural History Museum of Zurich, in which they had the words homo sapiens Neanderthal lenses and homo sapiens, and they were distinguishing between these subspecies. Now, so then we ask, well, what about homo erectus? Notice that we have, it's not homo sapiens erectus. However, there is some components in our genes and in the Neanderthal genes that looks like it might be erectus genes. In other words, and also, I should also mention the Denisovans. So these Denisovans, the Neanderthals, and homo sapiens, they're all mixed up in the genes, and so they're the same species, and so they're different subspecies. But then the question comes, what about homo erectus? Is that of the same species? Well, we've said homo erectus, not homo sapiens, so therefore we're assuming they're the different species, but I suspect that in our genomes, and that you will find some homo erectus genes, which would mean it would be homo sapiens erectus. The bottom line is that any current species has evolved, and has evolved from something that wasn't itself. In other words, there is no time in which there was a mother that gave birth to a child, that child was a homo sapiens, and the mother wasn't. That's just a silly idea, a revolution is gradual like that. That graduality is what prevents you from saying, "I know what a human being is," because there is no boundary there in which the mother is not a homo sapiens, and the child is. So push back on that. Yeah, so if we go to the Star Trek universe, we have, you know, the alien species out there who are clean ones, and whoever, and you have the humans, and you have commander data, and they are the three kinds of people, I would say. They're on a par, commander data. He pretends not to have emotions, but he would, in the real life case, he'd be regarded as artificial general intelligence. He would have a mind that is effectively able to do anything that a human mind could do. And as to for the Klingons and for other alien type species that are able to generate explanations of the rest of physical reality. Let me stop that Parparian explanation. I'm older than you, and so I'm with Captain Kirk, the first generation of Star Trek. And so now you know Spock, right? Spock had a mother who was human and a father who was a Vulcan. Superman had a mother, well, actually, no, he had two parents that were from Krypton. He came to Earth, he was able to have sex with Lois Lane, at least in some comic books, and then they had child. So here's a species, this is an example of how easily we pretend, we project homo sapiens onto the universe, pretending that Vulcan, some species that evolved on another planet, could have sex and be fertile with an earthling. And that's just a ridiculous idea. You can't even have something that evolved on one continent and independently of another one, and then saying, oh, they're going to have sex, it just doesn't work that way. So that's the degree to which in our brains, we pretend that human-like intelligence and human-like genes are convergent, and we should expect homo sapiens elsewhere. Carl Sagan was guilty of this, he talked about the functional equivalent of homo sapiens, but I don't think he went so far as to support the idea that Vulcans could intermarry with human beings. Your point, whoever- No, I agree with you. That's ridiculous. You wanted to say- Well, my point's more about the explanatory power. So what you're doing when you say- Yeah, not mating and not nothing to do with genetics, but rather to do it. It has everything to do with genetics, this is where I disagree with you. You talk about explanatory power as if you pretend that humans on earth are the things that have this ability to do explanatory power, and I wouldn't necessarily disagree with you on that. That means you're talking about a species-specific characteristic. Then you're pretending that that species-specific characteristic belongs to a more general group called any creature in the universe that has explanatory power, and I would say that's just pretending that there's a naked mole rat. We should go looking for naked mole rats. You should go looking for Indian elephants. No, you cannot generalize something that you admit is unique to earth and then pretend that it's a member of a general set elsewhere. So in other words, I believe our closest relatives in the entire universe are here on planet earth, and they're called chimpanzees. And- Genetically, yes. No, no, I mean- I mean- I mean- I mean- I say- I not only genetically, phenotypically, behaviorally, every any way you think of, and you want to say, no, explanatory power is such a convergent feature that any creature that evolved under selection pressure elsewhere will evolve explanatory power, and I said, there's no evidence for that, and there's evidence against it because- lastly, ask kangaroos whether they can- that's in another example that we talked about earlier of explanatory power evolving independently on Australia, and the answer is no. And when you say explanatory power, I think you need to admit that this is a uniquely human thing- at least you can define it that way- and if that's the case, you do not- it makes zero sense to go looking for uniquely human things elsewhere in the universe. At least that's what I would argue. Yet, no, I absolutely agree. As I say, I buy and I'm a great supporter of the planet of the apes hypothesis. I don't think that there are intelligent species out there. The point was that if- if there was, you know, whatever chance that happens to be, another alien species out there, they would count as people. They- of course, they would not count as nor be able to interbreed with homo sapiens sapiens. That doesn't make any sense. But they would be a person by virtue of the fact that they can come to an understanding of the rest of physical reality. And so they would be able to presumably, in the distant future, build a spacecraft that could travel across the universes. Perhaps one day, we will be able to, and so if we encounter these other people, we will share our ideas. And this is the kind of thing that we will be able to uniquely do, unlike, you know, elephants coming across giraffes- something they're not really going to share. Ideas, but we will share ideas. So what you're doing is saying that this ability to be creative or have explanatory power is something that I think you would identify on earth only with homo sapiens, and then you're proposing and imagining that it would evolve elsewhere. In other words- No, I don't think- as I say, I don't think that it will. For the planet of the apes hypothesis reason, I don't think that it will happen. If it did, however, if big, big, then yes. I see. Well, then I think we agree mostly, but maybe we have a difference in emphasis. Yeah, I think so. Yeah, it's the only difference in emphasis, and it just comes out. Because one thing animating people right now is, are we going to get to artificial general intelligence? People think that, you know, chat GPT, it's just so impressive that any moment now it's going to become alive, it's going to become able to create knowledge and take over your job or my job or anyone else's job. And I don't buy this idea. I don't think you're going to be able to extrapolate from more and more processing power inside of the hardware to what the hardware is programmed to do. You know, you have to program the thing to do something, and we are not programmed to do something. We are programmed to, if anything, write our own projects to be creative. In fact, much, much harder against this idea of artificial general intelligence in a way that was reminiscent of the argument I made earlier. And that is, brains, this brain that you have and I have, these are the result of our, lots of our ancestors dying and the ones with this type of brain survive. So what we call, we pretend that our type of intel, I think our type of intelligence, I call it human-like intelligence, I should just call it human intelligence, just like a dog has dog intelligence and a cat has cat intelligence and a tree has tree intelligence. And it's, this word intelligence is very hard to define. Some people say, wait a minute, there's emotional intelligence and mathematical intelligence and then there's, you know, the ability to dance intelligence, then there's, you know, maybe sports intelligence. Anyway, you could define an end dimensional thing and call it intelligence, but whatever humans have, I would call it unique to humans, but it has common, we have common ancestors, other things. For example, dogs and us have a common ancestors 95 million years ago and you can see that dogs have olfactory lobes and their brains have about the, their bilaterally symmetric and all kinds of similarities. But what was, wait, I've lost the point here. Remind me of this question we're talking about. The universality of our capacity to create explanations of the universe. Yeah, I wouldn't say the universe. I think, well, let's talk about substrate independent intelligence. Now, a lot of people believe in that. I have, I do not believe in it for one second. And the reason is, is I'm not a Cartesian Cart, the cart says, oh, there's brain and then there's body. And I said, no, your brain is part of your body. You cannot reify it. You cannot pretend that it is not integrally integrated into your body. And it would be crazy to take a brain out and say, okay, we're going to put it in the computer. That makes no sense to me at all. And yet I'm a materialistic reductionist and say, hey, it's all there's nothing special about the type of meat we have in the processing except for the fact that it has four billion years of evolving inside of something whose environment has been like this, this, this, this, this, it has hormone all kinds of exchanges with your body that's going on right now. And to pretend that you can pull that out of its environment and say, oh, this is, this is somehow isolated is the big mistake that I think people are making. It's kind of like there's zero environmental consciousness. As a matter of fact, some people would think that, well, talk about, let's talk about asteroids coming and impacting Earth. If asteroid lands and coming out of the blind spot and kills all kinds of things, one of the things that's going to survive are bacteria and archaea and simple things. So if you create all kinds of scenarios in which life goes extinct, you know, global warming or global cooling or whatever, what comes out on top are the things that were came out earlier that have been around for four billion years that have survived such things for four billion years. And that is not us, but it is things like the bacteria and archaea. So from if you're going to talk about you have a brain to survive, and if you don't survive, then your brain has not done a good job. And so your type of intelligence is not very good, but the type of intelligence that the bacteria have is better for this situation that eventually they we will get into. So I don't, what was the question again? I don't believe in this. I don't even believe in that word. I think that the word general is kind of like saying our intelligence is the best kind. It's the most general. And therefore, that's the one that's we have to be concerned with. And I just think that's ridiculous that you cannot take a human brain and put it into a computer. And you will not be the same person. It will be a different thing. And it will be totally completely, I don't want to use the word autistic, but it'll be isolated in a way that is so unnatural that it's going to die. Because everything is everything in there is meant to be inside and integrated into eyeballs and ears and hormones and heartbeat and etc. So it's kind of like, it's just that makes no sense to me at all this word artificial in general intelligence. I think if you want to talk about human intelligence and you can make something that plays go, you can make something that drives a car, and you can imagine the future of self-driving cars. They will get better and better and better at driving a car, but you wouldn't call that general intelligence. You'd call that car driving intelligence. You could have a robot that was really good at dancing. And the better it gets a dance. Hey, that's not general intelligence. That's dancing intelligence. So the intelligence that evolves depends on the environment that you put something into. What we call general is simply because we pretend that we're not ants. We're not ants. We're not dogs. We're not bacteria. And so our intelligence, we pretend, is general. And it's just not that way. It's very specific. Humans are unique, just like every other species. And so we should not use this word general, artificial general intelligence. Jaron Lanier, he's a computer scientist. He's one of a father's of virtual reality. He had this ship of Theseus idea when it came to trying to delve into the mysteries of consciousness and that kind of thing. And he thought about the thought experiment of, well, what if one day the doctor tells you in a distant future, you're starting to get dementia. Your neurons are starting to decay. What we'll do is we are going to replace your neurons one at a time, very slowly, with a wire, with fiber optic or whatever it happens to be in order to do the functionality of whatever it is that the neuron does. And we're not there yet, but maybe one day in the future, you know, Elon Musk is working on this neurolink thing. If we were to do that neuron by neuron by neuron, at what point do you think that would cease to be a person? Because on your account, it seems to be impossible because I can imagine a fully metal plastic glass person at the end of that process, maybe your entire body gets transformed and you would call it a robot. But because we've done this piecemeal, you could do it an atom at a time, if you like, with advanced technology. We could have a person that didn't technically evolve, but rather they were built at a moment. Right. So first of all, your example is exactly what you're doing right now. And that is your neurons are being replaced. You know, one goes bad and then you gets replaced. And sometimes it doesn't get replaced. And that's not so great. But replacement is something that your body knows how to do in general. So you are in a very real sense a ship of thesis in which almost all parts of all cells in your body have been replaced. Now, interestingly, you can study which cells in your body get replaced more often. And the linings of your intestine, for example, and liver cells and skin cells, these are places that have a natural ability to get replaced because naturally they, for example, the lining of your gastrointestinal tract is digesting meat. Now, you are made out of meat. So essentially that lining is getting digested. And so you have to replace it. And that replacement is mitosis that goes on. And one of the reasons that organs that are highly mitotic in the normal way are closer to cancer is because they have replacements that they have ability to turn on mitosis that's much closer to the surface than the more mature differentiated cells that don't might toast as much during its natural lifetime. So matter of fact, there's something called bomb biology. 1960, 61, 62, there were bombs going off and they produced very rare isotopes. They got incorporated into the cells that were being produced in a body at that time. And so by looking at, by searching for these rare isotopes in people of different ages and they're different organs, you can tell which organs have been completely rejuvenated since those last bombs and which of them have a remnant of those isotopes. And so it's called bomb biology and it helps you know how quickly would different organs get their cells replaced. You got dangerously close there to mentioning the Autovistic Theory of Cancer. The thing, the one thing I won't talk to you about here because our wonderful podcast was produced and I'll link to that that you did recently discussing the Autovistic Model of Cancer. Absolutely brilliant. So I'll finish because you've been very generous with your time. We're just a question that's completely left field about the potato radius which is just such a fun paper that I used to direct my own students to as to why objects that exist out there in nature have the shapes they do. Could you explain a little what is the potato radius and what does it solve because you're bringing together empirical science, observing stuff, with calculating stuff as well. You're marrying up these two sides of theoretical science and experimental science. So about 20 years ago you may have heard of the Pluto crisis in which people were trying to figure out whether Pluto is a planet or not. The reason was Mike Brown at Caltech had discovered something that was something that's now called Eris that seemed to be possibly was larger than Pluto. And so you know we have these planets Mercury, Venus, Earth, etc. Mars. And as you go further out you get lots and lots of bodies. Asteroid for example asteroids if you look at the asteroid belt between Mars and Jupiter you will see some of the small things look like kind of weird shapes and then the bigger ones are always spherical like the Sun for example is spherical the Earth and Mercury. All these things are spherical but then as you look at the asteroids the biggest ones like Ceres for example is really spherical and then you get smaller and smaller and they start to look not like a sphere but more like a potato. And then when they get even smaller they look like weirder shapes you know it looks like I don't know like this or like this. And the point is that large objects the shape when you have a spherical shape that means that gravity self-gravity has been able to overcome the molecular forces that hold things together. For example this pen if I made this pen a million times bigger it would start to become rounder and rounder. Why? Because the gravity on this thing would be pulled towards the center and the same thing over here I'm gonna get round and rounder. So if I made me bigger and bigger I start to look like one of those thanks giving day balloons and puffier and rounder and then if I got even bigger it would be round and rounder. So in other words self-gravity makes things into spheres because that's the minimum energy configuration. But when you get smaller and smaller you don't have as much self-gravity. Gravity starts to lose compared to molecular forces. Molecular forces are things that just hold the neighboring things together and there's no constraint on it to be spherical. And so you can see this transition between sphere to potato at a certain radius. And the reason why this was important was because in the definition of a planet you have this thing saying you have to be a sphere or there's a fancy term for a type of if you rotate a sphere gets flatter and flatter like an M&M or a smarty. So that's consistent with being spherical but you just have a spin to it. And so the question is when does a body lose itself? When does self-gravity become so weak that the molecular forces start to win over and you get pieces of rock that look like well the potatoes they're kind of roundish but then they get smaller and they become more like arbitrarily shaped rocks. And then at the even lower end you get something like dust. You get all kinds of crazy shapes and that's where gravity almost plays zero role. And so because the the radius at which something became a planet was used to define a planet we thought what does this mean that when when is this that you get to become a sphere. And so we wrote a paper called the potato radius which is the the radius at which a potato turns into a sphere and we looked at the data from all the just that much data to look at you just look at the asteroids and see how big are things that are spherical and how smaller things that are potatoes and how even smaller do they get even weirder shapes. And so we identified this radius and did some physics about how how much stress you know different objects have different stress abilities. So for example you imagine if there's a bowl of water that it is spherical or snow it's not able to maintain mountains or different size shapes it kind of just falls in on itself because self-gravity is more important than the weaker molecular forces. But if you have stronger molecular forces like in a rock or a steel or something then the self-gravity has a harder time making it spherical. So the analysis of that problem when is this transition we called it the potato radius and it's important if you're interested in this distinction between objects that are large enough to be spherical and planetary and ones that are not. That's excellent fantastic and it brings together your deep knowledge on chemistry physics geology you're spoken about biology and just a final question what are you working on now what is the the thing that's animating you're on now. I thought they were going to ask us. What one is let's see. Well I just put out a paper I don't know a couple of months ago on all objects and some questions and this is with a PhD student oh no a master student I had and we're working together on trying to figure out if here's our universe and we have an accelerating universe we're going to end up as an island universe and what that means is that their closest relative Andromeda and our galaxy are going to come together and form a local group universe and beyond that eventually after many billions of years all of the other galaxies that we can now see in our observable universe will disappear in the sense that they'll get redshifted beyond our ability to see them. So we will then be in a universe that will have a center. Now you may have thought you know cosmology cosmologists would never tire of saying the universe does not have a center. We are not the center of the universe we're the center of our observable universe in the same sense that a boat on the Pacific Ocean is the center of its horizon. The horizon is at a certain distance from it but that's arbitrary but in the far far future we there the center will be a giant black hole of about let's see how many 10 to the 10 solar masses to a million maybe maybe a hundred million solar masses and and that will be the center of the universe our universe and so our universe will go from evolve from one that does not have a center to one that does and so we're trying to figure out based on what we know about the large scale structure of the universe and and structures that will collapse into their own island universe how many fragments will our current universe evolve into. So that's one thing another is let's see I mean I'm interested in in free will my wife is a lawyer and she goes on and on about the injustices of law and they seem to be based on the belief in human free will so I've become interested in that problem because I've actually there's one theme that goes through most of my work and that is embedding connections things are connected to other things and you make a giant mistake when you pretend that things are isolated and when you say to somebody you know who committed to crime you say you could have done otherwise you say oh yeah you could have done what where did that come from so the belief in human free will somehow is a belief in a superstitious idea that you can have an electron here that you can decide to move over there and so I guess the belief the non-belief in free will people like Sam Harrison and Robert Sapolsky have written books about this but it's a giant debate that's been going on for two thousand years but I think in law it's particularly important because right now we're saying you could have done otherwise therefore you're guilty rather than looking carefully at the background of this person in front of you who used to be a baby who grew up in an environment that produced this crime and I would say it's the environment that produced the crime rather than the free will of the individual so I'm looking at free will as a so we're trying to write a book on that but that's that's another that's another kettle of worms yes well I'm waiting for the Charlie line we have a book that is that is something we need to see so rather me continue questioning you now because I could question you for another hour and 15 minutes I won't I will thank you politely for your time thank you so much this is where we've been a dream of mine you were one of the greatest lecturers I had at the University of New South Wales doing the life I think it's called what's called my elsewhere in the universal life that we learn something like that are we alone maybe it was are we alone yeah fizz two one seven zero I think yeah absolutely fantastic course where it would cover geology we covered physics we covered astronomy everything was brought together and it was just emblematic of the style of scientists that you are a polymath of the first order so thank you for your time thank you for inviting hope that has been fun. you [BLANK_AUDIO]
