Brian Greene: Quantum Gravity, The Big Bang, Aliens, Death, and Meaning | Lex Fridman Podcast #232
the following is a conversation with brian greene theoretical physicist at columbia and author of many amazing books on physics including his latest until the end of time mind matter and our search for meaning in an evolving universe this is the lex friedman podcast to support it please check out our sponsors in the description and now here's my conversation with brian green in your most recent book until the end of time you quote bertrand russell from a debate he had about god in 1948 he says quote so far as scientific evidence goes the universe has crawled by slow stages to somewhat pitiful result on this earth and is going to crawl by still more pitiful stages to a condition of universal death if this is to be taken as evidence of purpose i can only say that the purpose is one that does not appeal to me i see no reason therefore to believe in any sort of god that's quite a depressing statement as you say this is a bleak outlook on our universe and the emergence of human consciousness so let me ask what is the more hopeful perspective to take on the story well i think the more hopeful perspective is to more fully understand what was driving bertrand russell to this perspective and then to see it within a broader context and really that's in some sense what what my book until the end the time is all about but in brief i would say that there's a lot of truth to what bertrand russell was saying there when you look at the second law of thermodynamics which is the underlying scientific idea that's driving this notion that everything's going to wither decay fall apart yeah that's true second law of thermodynamics establishes that disorder entropy in aggregate is always on the rise and that is indeed interpretable as disintegration and destruction over sufficiently long time scales but my view is when you recognize how special that makes us that we are these exquisitely ordered configurations of particles that only will last for a blink of an eye in cosmological time like terms the fact that we're here and we can do what we do to me that's just really something that inspires gratitude and wonder and and a sense of of deep purpose by virtue of being these unique collections of entities that happen to rise up look around and try to figure out where we are and what the heck we should do with our time so it's not that i would disagree with burch and russell in terms of the basic physics and the basic unfolding but i think it's really a matter of the slant that you take on what it means for us so maybe we'll skip around a bit but let me ask the biggest possible question then you said purpose so what's the meaning of it all then is uh is there a meaning to life that we can take from this from this brief emergence of complexity that arises from simple things and then goes into a heat death that is once again returns to simple things as the march of the second law the thermodynamics goes on i think there is but i don't think it's a universal answer and so i think throughout the ages there has been a kind of quest for some final way of articulating meaning and purpose whether it's god whether it's love whether it's companionship i mean many people put forward different ways of taking this question on and there is no one right answer when you recognize deeply that the universe doesn't care there is nothing out there that is the final answer it's not as though we need a more powerful telescope and somehow if we can look deeply into the universe all will become clear in fact the deeper we've looked both literally and metaphorically into the universe and into the structure of reality the more it's become clear that we are just a momentary byproduct of laws of physics that don't have any emotional content they don't have any intrinsic sense of meaning or purpose and when you recognize that you realize that searching for the universal for this kind of a question is a fool's errand every individual has the capacity to make their own meaning to set their own purpose and that's not some platitude that is what we are because there is no fundamental answer it's what you make of it and however much that may sound like a hallmark card this really is the deep lesson of physics and science more generally over the past few hundred years well there's some level where you can objectively say that whatever we've got going on here is kind of peculiar it's kind of um special in in in in terms of complexity and maybe you can even begin to measure it and like come up with metrics where whatever we got going on on earth these like uh interesting hierarchical complexities that form more and more sophisticated biological system that seems kind of unique when you look at the entire universe the um the observable part that we can see with our tools i mean so i have to ask as you described in your book once again uh schroedinger wrote the book what is life based on the few lectures he gave in 1944 so let me ask the fundamental question here what is life this particular thing we got going on here this pocket of complexity that emerged from such simple things yeah it's a tough question i asked that question even to richard dawkins once and i already have my preconceived notion which he pretty much confirmed which is if one could give an answer to that question that allowed you to sort of draw a line in the sand between the not living and the living then perhaps we would have the insight that we yearn for and trying to say what is so special about life but the fact of the matter is it's a continuum there's a continuum from the things that we would typically call non-living inanimate to the things that we obviously call adamant and full of the currents of life somewhere in there it is a question of the complexity of the structure the ability of the structure to take in raw material from the environment and process it through a metabolism that allows the structure to extract energy and to release entropy to the wider environment somewhere in those collections of biological processes is the necessity or the necessary ingredients and processes for life but drawing that line in the sand is not something that we're able to do but i would agree with you it's deeply peculiar it may in fact be unique but it may not it could be that the universe is such that under fairly typical conditions a star that's a well-ordered source of low entropy energy that's what the sun is together with a planet being bathed by that low entropy energy together with a surface that has enough of the raw constituents that we recognize are fairly commonplace result of supernova explosions where star spews forth the result of the nuclear furnace that is the core of a star it could be that all you need are those fairly commonplace conditions and maybe life naturally forms like the james webb space telescope right is going up hopefully in december and one of the one of the goals of that mission is to look at atmospheres around distant planets and perhaps come to some sense of how special or not life or leaf life as we know it is in the universe which part of the story of life let's stick to earth for a second do you think is the uh is the hardest if you were like uh a betting man like which part is the hardest to uh make happen is it the origin of life again we haven't drawn the line of worth as you say uh the line between a rock and a rabbit um that part is it uh complex organisms like multicellular organisms is it uh crawling out of the ocean where the fish somehow figured out how to crawl around is it then the uh us homo sapiens as we like to think of ourselves special and intelligent uh or is it somewhere in between as you also talk about again very hard to know at which point this consciousness yeah emerge like if you if you were to sort of took us a survey and made bets about other earth-like planets in the universe where do you think they get stuck the most well i would certainly see if we're going to go all the way to conscious beings like ourselves i would put it at the onset of consciousness which again i think is a continuum i don't think it is something that you can draw the line in the sand but there are obvious circumstances there are obvious creatures such as ourselves where we do recognize a certain kind of self-reflective conscious awareness and if we think about what it would require for a system of living beings to acquire consciousness i think that's probably the hardest part because look take earth and recognize that it weren't for you know some singular event 65 million years ago where this large rock slams into planet earth and wipes out the dinosaurs maybe the dinosaurs would still rule the planet and they may well have not developed the kind of conscious awareness that we have so for billions of years on this planet there was life that didn't have the kind of conscious awareness that we have and it was an accidental event in astrophysical history that allowed a mammalian species like us to ultimately be the end product and so yeah i could imagine there's a lot of life out there but perhaps none of it's wondering what's the meaning of life or trying to make sense of it just going about its business of survival which of course is the dominant activity that life on this planet has practice we are a rare exception to that and i really appreciate that you lean into some of these unanswerable questions to me today but the so you think about consciousness not as like a phase shift the binary zero one you think uh it was a continuum that humans somehow are maybe some of the most conscious beings on earth so you're so i mean people will dispute that yes i mean whoa and it's a very hard argument people will dispute that rocks probably will stay quiet on the matter maybe not right for the moment they're waiting for their opportunity but but but i i i agree that um look even when you and i look at each other i am not fully convinced that you're a conscious being right i mean i think that you are on to me i mean your behavior is such that that's the best explanation for what's going on but of course we're all in the position of only having direct awareness of our own conscious being and therefore when it comes to other creatures in the world we're in a similar state of ignorance regarding what's actually happening inside of their head if they have a head and so it's hard to know how singular we are but i would say based on the best available data and the best explanations we can make yeah there is something special about us i don't think that there are fish walking around and you know coming up with you know existentialism i don't know that there are you know dogs walking around who've developed an understanding the general theory of relativity i mean maybe we're wrong but that seems the best explanation what do you think is more special intelligence or consciousness i think consciousness and i think that there's a deep connection between these ideas they are distinct but they're deeply connected but look i mean to me and to of course many philosophers actually coined a name for this the heart problem of consciousness you know david chalmers and others as a physicist i look at the world and i see it's particles governed by physical law we can name them you know we've got electrons we've got quarks that come in various flavors and so forth we have a list of ingredients that science has revealed and we have a list of laws that seemingly govern those ingredients and and nowhere in there is there even a hint that when you put those particles together in the right way an inner world should turn on and it's not only that there's no hint it's insane i mean it's ridiculous how could it be that a thoughtless passionless emotionless particle when grouped together with compatriots somehow can yield something so deeply foreign to the nature of the ingredients themselves so so answering that question i think is among the deepest and most difficult questions that we face do you think it is in fact a really hard problem or is it possible i think you mentioned your book that it's just like almost like a side effect it's an emergent thing that's like oh it's nice it's like a nice little feature yeah well i mean when people use the phrase hard problem i mean they mean in a somewhat technical sense that it's trying to explain something that seems fundamentally unavailable to third party objective analysis right i'm the only one that can get inside my head and i can tell you a lot about what's happening inside my head right now it's reflected in what i'm saying and you can try to deduce things about what's going on inside my head but you don't have access to it in the way that i do and so it seems like a fundamentally different kind of problem from the ones that we have successfully dealt with over the course of centuries in science where we look at the motion of the moon everybody can look everybody can measure it we look at you know the properties of hydrogen when you shine lasers on everybody can look at the data and understand it and so it seems like a fundamentally different problem and in that sense it seems like it is hard relative to the others but i do think ultimately that the explanation will be as you recount i think that a hundred years from now or maybe it's a thousand it's hard to predict the time scale for developments but i think we'll get to a place where we'll look back and kind of smile at those folks in the 20th century and before 21st century and before who thought consciousness was so incredibly mysterious when the reality of it is it's just a thing that happens when particles come together and and however mysterious that feels right now i think for instance when we start to build conscious systems you know things that you know you're more familiar with than i am when we start to build these artificial systems and those systems report to us i'm feeling sad i'm feeling anxious yeah there's a world going on inside here i think the mystery of consciousness will just begin to evaporate well that's first of all beautifully put and i agree with you completely just the way you said it it'll begin to evaporate i have built quite a few robots and have had them do emotion emotional type things and it's immediate that exactly what you're saying this kind of mystery of consciousness starts to evaporate that the kind of need to truly understand to solve the hard problem of consciousness like disappears because well i don't really care if i understand what can solve the hard problem of consciousness that thing sure as heck looks conscious you know i feel like that way when i interact with a dog i don't need to solve the problem of consciousness to to be able to interact and richly enjoy the experience with this other living being obviously same thing with other humans i don't need to fully understand it and there's some aspect maybe this is a little bit too engineering focused but there's some aspect in which it feels like consciousness is just a nice trick to help us communicate with each other it sounds ridiculous to say but sort of uh the ability to experience the world is very useful in a subjective sense it's very useful to put yourself in that world and to be able to describe the experience to others yeah it could be just the social and the emerge obviously animals the sort of more primitive animals might experience consciousness in some more primitive way but this kind of rich subjective experience that we think about as humans i think it's probably deeply coupled like language and poetry yeah that resonates with my view as well i mean there's a scientist maybe you've spoken to michael graziano from princeton yeah he um he's developed ideas of consciousness that look i don't think they solve the problem but i think they do illuminate it in an interesting way where basically we are not aware of all the underlying physiochemical processes that make our brains and our inner worlds tick the way they do and because of that dissociation between sensation and the physics of it and the chemistry of it and the biology of it it feels like our minds and our inner worlds are just untethered like floating somewhere in this gray matter inside of our heads and the way i like to think of it is like look you know if um if if if you're in a dark room right and and i had glow-in-the-dark paint on my fingers so all you saw was my fingers dancing around there'd be something mysterious how how could those fingers be doing that and then you turn a light you realize oh there's this arm underlying it and that's the deep physical connection explains it all and i think that's what we're missing the deep physical connection between what's happening up here and what is responsible for it in a physical chemical biological way and so to me that at least gives me some understanding of why consciousness feels so mysterious because we are suppressing all of the underlying science that ultimately is responsible for it and one day we will reveal that more fully and i think that will help us tether this experience to something quite tangible in the world i wonder if the mystery is uh an important component of enjoying something so once once we know how this thing works maybe we uh will no longer enjoy like this conversation we'll seek other sources of enjoyment but there's uh this is again from an engineering perspective i wonder if the mystery is is an important component well you know there's have you ever seen there's this beautiful interview that richard feynman did you know great nobel laureate physicist responsible for a lot of our understanding of quantum mechanics quantum fields and so forth and he was in a conversation with an interviewer where he noted that some people feel like once the mystery is gone once science explains something it the beauty goes away you know the wonder if it goes away and he was emphasizing in his response to that he's like no that's not the right way of thinking about he says look when i look at a rose he says yeah i can still deeply enjoy the aroma the color the texture he says but what i can do that you can't if you're not a physicist i can look more deeply and understand where the red comes from where the aroma comes from where the structure comes from he says that only augments my wonder it only augments my experience it doesn't flatten it or take away from it so yeah well i sort of take that as a bit of a of a motto in some sense that that there is a wonder that comes from a kind of ignorance and i don't mean that in a derogatory sense but just from not knowing so there is a wonder that comes from mystery there's another kind of wonder that comes from knowing and and and deep knowing and i think that kind of wonder has its own special character that in some ways can be more gratifying i hope he's right i hope you're right and but there's also i remember he he said something about like an like science is an onion or something like that you can peel back you can keep it keep peeling back i mean there is also when you understand something there's always a sense that there's more mystery to understand like you never get to the bottom of the mystery but i think it's also different than you know i don't think you can analogize say to a magician right the magician you know does some trick you learn how it sounds like oh my god that was that's ridiculous when you find but but nature is perhaps the best magician if you want to try to make the analogy there because when you peel things back and you understand how it is that things have color and you have electrons dancing from one orbital to another emitting photons at very particular wavelengths that are described by these beautiful equations of quantum electrodynamics part of which that feynman developed it gives you a greater sense of awe when the curtain is pulled back than what happens in other circumstances where it does flatten it completely yeah it's very possible then say in physics that we arrive at a theory of everything that unifies the laws of physics and has a very strong understanding of the fabric of reality even like from the very for the big bang to today it's possible that that understanding is only going to elevate our appreciation of this whole thing yeah i think it will i think it will i think it has it has so far but the other side of it which you which you emphasize is it's not like science somehow reaches an end right there are certain categories of questions that do reach an end i think we one day we'll close the book on nature's ingredients and the fundamental laws now that can't prove that maybe it goes on forever smaller and smaller maybe they're deeper and deeper laws but i i don't think so i think that there's going to be a collection of ingredients in a collection of basic laws that chapter will close but it's one chapter now we take that knowledge and we try to understand how the world builds the structures that it does you know from planets to people to black holes to the possibility of other universes and every step of the way the collection of questions that we don't know the answer to only blossoms and so there's a there's a deep sense of gratification from understanding certain quantities of the world but i would say that if you take a ratio of what we understand to the things that we know that we don't yet understand that ratio keeps getting smaller and smaller because the things that we know that we don't understand grows larger and larger do you have a hope that we solve that theory of everything puzzle in the next few decades so there's been a bunch of attempts from string theory to all kinds of attempts of trying to solve quantum gravity or basically come up with a theory for quantum gravity there's a lot of uh complexities to this one for experimental validation you have to observe effects that are very difficult to uh measure so you have to build like that's like an engineering challenge and then there's the theory challenge which is like it seems very difficult to connect the laws of gravity to quantum mechanics do you have a hope or are we hopelessly stuck well i have to have to have a hope i mean it's in some sense but i devote at least part of my professional life toward trying to make progress on i'm glad you use the phrase quantum gravity i'm not a great fan of the theory of everything phrase because it does make other scientists feel like if they're not working on this what are they working on man's like you know there's not much left when you're talking about theory of everything biology is just small d yeah right exactly yeah so so it is really trying to put gravity and quantum mechanics together and uh since i was a college kid i was uh deeply fascinated with gravity and as i learned quantum mechanics the the notion of physicists being stumped and trying to blend them together how could one not get fired up about maybe contributing something to that journey and so we've been on this you know i've been on this for 30 years since i was a student we we have made progress we do have ideas you mentioned strength theory is one possible scenario it's not stuck string theory is a vibrant field of research that is making incredible progress but we've not made progress on this issue of experimental verification validation which as you know it is a vital part of the story so i would have hoped that by now we would have made contact with observation if you would have interviewed me back in the 80s when i was you know a wild bright-eyed kid trying to make headway working 18 hours a day on this sort of stuff i would have said yeah by by 2021 yeah we're gonna know whether it's right or wrong we'll make contact i would have said look there may be certain mathematical puzzles that we've got to work out but we'll know enough to make contact with experiment that has not happened on the other hand if you would have interviewed me back then and asked me will we be able to talk about detailed qualities of black holes and understand them at the uh the level of detail that we actually i i would have said no i i don't think that we're going to be able to do that will we have a an exact formulation of strength here in certain circumstances no i don't think we're going to have that and yet we do so it's just to say you don't know where the progress is going to happen but yes i do hold out hope that maybe before i move on to wherever i don't think there is an after but i i would love before i leave this earth to to know the answer but you know science and the universe it's not about pleasing any individual it is what it is and so we just press onward and we'll see where it goes so in terms of string theory if i just look from an outsider's perspective currently at the theoretical physics community string theory is the theory was as a theory has been very popular for for a few decades but has recently fallen out of favor or at least there's been like you know it became more popular to kind of ask the question is string theory really the answer where do you fall on this like how do you make sense of this puzzle why do you think it has fallen out of favor yeah so i don't i would actually challenge the statement that's fallen out of favor i would say that any field of research when it's new and it's the the bright shiny bicycle that no one has yet seen on that block yeah it's going to attract attention and the news outlets are going to cover it and students are going to flock to it sure but as a as a field matures it does shed those qualities because it's no longer as novel as it was when it was first introduced 30 or 40 years ago but you need to judge it by a different standard you need to judge it by is it making progress on foundational issues deepening our understanding of the subject and by that measure string theory is is is scoring very high now at the same time you also need to judge whether it makes contact with experiment as we discussed before too and on that measure we're still challenged so i would say that many strengthers myself included are are very sober about the theory it it has the tremendous progress that it had 30 40 years ago that hasn't gone away but we've become better equipped at assessing the long journey ahead and that was something that we weren't particularly good at back say in the 80s look when i was just starting out in the field there was a sense of physics is about to end string theory is about to be the be-all and end-all final unified theory and that will bring this chapter to a close now i have to say i think it was more the younger physicists who were saying that some of the more seasoned even if they were pro-string theory at the time i don't know if they were rolling their eyes but they knew yeah that was going to be a long long journey i think people like you know john schwartz one of the founders of string theory michael green no relation to me founders of the theory edward whitton you know one of the main people driving the theory back then and today i think they knew that we were in for a long haul and and that's the nature of science quick hits that resolve everything few and far between and so if you were in for the quick solution to the big questions of the world then you would have been disappointed and i think there were people who were disappointed and moved on and work on other subjects if we were in in the way that einstein was in for a lifetime of investigation to try to see where what the answers to the deep questions would be then i think string theory has been a rich source of material that has kept so many people deeply engaged in moving the frontier forward there's a few qualities about string theory which are weird i mean a lot of physics is just weird and beautiful so let me ask the question what do you as most beautiful about string theory well but what attracted me to the theory at the outset beyond its putting gravity and quantum mechanics together which i think is um it's true claim to fame at least on paper it's able to do that what attracted me to here was the fact that it requires extra dimensions of space and this was an idea that intrigued me in a very deep way even before i really understood what it meant i somehow had i mean talk about sort of the emotional part of consciousness and the cognitive part in some perhaps you call it strange in some strange emotional way i was enamored with einstein's general relativity the idea of curved space and time before i really knew what it meant it just spoke to me i don't know how else to say it and then when i subsequently learned that people had thought about more dimensions of space than we can see and how those extra dimensions would be vital to a deep understanding of the things that we do see in this world four five six dimensions might explain why there are certain forces and particles and how they behave to me this was like amazing utterly amazing and then when i learned that strength theory embraced all these ideas embraced the general theory of relativity embraced quantum mechanics embraced the possibility of extra dimensions then i was then i was hooked and so when i was a graduate student we would just spend hours we i mean a couple of other graduate students and myself who had a have sort of worked really well together at oxford in england we would we would work these enormous numbers of hours a day trying to understand the shapes of these extra dimensions the geometry of them what those geometrical shapes for the extra dimensions would imply for things that we see in the world around us and it was a it was a heady heady time and and that kind of excitement has sort of filtered through over the decades but i'd say that's really the the part of the theory that i think really hooked me most wrongly how are we supposed to think about those extra dimensions i was supposed to imagine actual physical reality or is this more in the space of mathematics that allows you to sort of come up with tricks to describe the four-dimensional reality that we more directly perceive no one really knows the answer of course but if i take the most straightforward approach to string theory you really are imagining that these dimensions are there they're real i mean just as you would say that the three space dimensions around us you know left right back forth up down yeah we they're real they're here we are immersed within those dimensions these other dimensions are as real as these with the one difference being their shape and their size differs from the shape and size of the dimensions that we have direct access to through through human experience and one approach imagines that these extra dimensions are tightly coiled up curled up crushed together if you will into a beautiful geometrical form that's all around us but just too small for us to detect with our eyes too small for us to detect even with the most powerful equipment that we have nevertheless according to the mathematics the size and the shape of those extra dimensions leaves an imprint in the world that we do have access to so one of the ways that we have hoped yet to achieve to make contact with experimental physics is to see a signature of those extra dimensions in places like the large hadron collider in geneva switzerland and it hasn't happened yet doesn't mean it won't happen but that would be a stunning moment in the history of the species if data that we acquired in these dimensions gives us kind of incontrovertible evidence that these dimensions are not the only dimensions i mean how mind-blowing would would that be so with a large header and collider it would be something in the movement of the particles or also the gravitational waves potentially be a place where you can detect signs of multiple dimensions like with something called ligo but much more accurate in principle all of these can work so one of the experiments that we had high hopes for but by high hopes i'm actually exaggerating one of the experiments that we imagined might in the best of all circumstances yield some insight we weren't with baited breath waiting for the result we knew it was a long shot when you slam protons together at very high speed as a large hadron collider if there are these extra dimensions and if they have the right form and that's a hypothesis that may not be correct but when the proteins collide they can create debris energetic debris that can in some sense leave our dimensions and insert itself into the other dimensions and the way you'd recognize that is there'd be more energy before the collision than after the collision because the debris would have taken energy away from the place where our detectors can detect it so that's that's one real concrete way that you could find evidence for extra dimensions but yeah since extra dimensions are of space and gravity is something that exists within in fact is associated with the shape of space gravitational waves in principle can provide a kind of you know cat scan of of the extra dimensions if you had sufficient control over those processes we don't yet but perhaps one day we will does it make you sad a little bit or maybe looking out into the future you mentioned edwin that no nobel prizes have been given yet related to string theory do you think they will be do you think you have to have experimental validation or can a nobel prize be given which i don't think has been given for quite a long time for uh purely sort of theoretical contributions yeah it certainly as a matter of historical precedent has been the case that those who win the prize have established investigated illuminated a demonstrably real quality of the world so gravitational waves the prize was awarded after they were detected not not the mathematics of it but the actual detection of it you know the higgs particle you know it was an idea that came from the 1960s peter higgs and others in fact and it wasn't until 2012 on july 4th when the announcement came that this protocol had been detected the large hadron collider that people viewed it as eligible for the nobel prize the idea was there the math was there but you needed to confirm it indeed the prize ultimately was awarded so i'm not surprised in fact i would have been surprised if a nobel prize had been awarded in the arena of string theory because it's far too speculative right now it's far too hypothetical in fact i am sympathetic to the view that it really shouldn't be called string theory it degrades the word theory because theory in science of course means the best available explanation for the things that we observe in the world the things that we measure in experiments about the world and string theory does not do that at least not yet so it really should be the string hypothesis right we're at an earlier stage of development and that's not the kind of thing that nobel prizes should be awarded for what do you think about the critics out there peter white he's from colombia too i think sabine hafenstadter is that a healthy thing or should we sort of focus on sort of the optimism of of these hypotheses yeah it's actually a good way that you frame it because i'm always somewhat repelled by views of the world that start from the negative try to cut down an idea try to say that's the wrong way of thinking about things and so on i'm much more drawn maybe because i'm an optimist i don't know i'm much more drawn to those who go out into the world with new ideas yeah and and don't try to cut down one idea but rather present another one that might be better and so you make the first idea maybe strengthy irrelevant because you've come up with the better approach to the world so do i think it's healthy look i think having a wide range of views and perspectives is generally a healthy thing i think it's good to have arguments within a subject in order that you stay fresh and you stay focused on the things that matter but in the end of the day i think it's a more vital contribution to give us something new rather than to criticize something that's there yeah i'm totally with you um but it could be just the nature of being an optimist i and also just a a love of engineering it's there's it it helps nobody by criticizing the uh the rocket that somebody else built just build a bigger cheaper better rocket exactly yeah and that seems to be how uh human civilization can progress effectively we we've uh mentioned the second law of thermodynamics i got to ask you about time yeah and do you do you think of time as emergent or fundamental to our universe i like to think of it as emergent i don't have a solid reason for that perspective i have a lot of hints of reasons that some of which come out of string theory and quantum gravity that perhaps would be worth talking about but what i would say is time is the most familiar quality of experience because there's nothing that takes place that doesn't take place within an interval of time and yet at the same time it is perhaps the most mysterious quality of the world so it's a wonderful confluence of the familiar and the deeply mysterious all in one little package if you were to ask me what is time i don't i don't really know i don't think anybody does i i can say what time gives us it allows us the language for talking about change it allows us to envision the events of the universe being spread out in this temporal timeline and in that way allows us to see the patterns that unfold within time i mean time allows us the structure and the organization to think about things in that kind of a progression but what actually is it i i don't really know and that's so strange because we can measure it right i mean there are laboratories in the world that measure this thing called time to spectacular precision but you know if you go up to the folks and say like what is it that you're actually measuring i don't know that they can really articulate the kind of answer that you would expect from those who are engineering a device that can measure something called time to that level of precision so it's a very curious combination what do you make of the one-way feeling of causality like is causality a thing or is that too just a human story that we put on top of this emerging phenomena of time i don't know um i can give you my my guess and my intuition about it i do think that at the macroscopic level if we're talking about sort of the human experience of time i do think at the macroscopic level there is a fundamental notion of causality that does emerge from a starting point that may not have causality built in so i certainly would allow that at the deepest description of reality when we finally have that on the table we may not see causality directly at that fundamental level but i do believe that we will understand how to go from that fundamental level to a world where at the macroscopic level there is this notion of a causes b a notion that einstein deeply embraced in his special theory of relativity where he showed that time has qualities that we wouldn't expect based on experience you and i if we move relative to each other our clocks tick off time at different rate and our clocks is just a means of measuring this thing called time so this is really time that we're talking about time for you and time for me are different if we're in relative motion he then shows in the general theory of relativity that if we're experiencing different gravity different gravitational fields or actually more precisely different gravitational potentials time will elapse for us at different rates these are things that are astoundingly strange that give rise to a scientific notion of time travel okay so this is this is how far einstein took us in wiping away the old understanding of time and injecting a new understanding of its qualities so so there's so much about time that's counterintuitive but i do not think that we're ever going to wipe away causality at the macroscopic at the microscope i mean there's so many interesting things at the macroscopic level that may only exist at the microscopic level yeah like we already talked about consciousness that that very well could be one of the things you mentioned time travel so um i mean according to einstein and in general what types of travel do you think our physical universe allows well certainly allows time travel to the future and i'm not talking about the silly thing that you and i are now going into the future second by second second i'm talking about really the diversion that you see in hollywood at least in terms of its net effect whereby an individual can follow an einsteinian strategy and propel themselves into the future in some sense more quickly so if if i wanted to see what's happening on planet earth 1 million years from now einstein tells me how to get 1 million years from now build a ship i got to turn to guys you know who know how to build stuff i can't do it like you build a ship that can go out into the universe near the speed of light turn around and come back let's say it's a six month journey out a six month journey back and einstein tells me how fast i need to travel how close to the speed of light i need to go so that when i step out of my ship it will now be one million years into the future on planet earth and this is not a controversial statement right this is not something where there's differences of opinion in the scientific community any scientist who knows anything about what einstein taught us agrees with what i just said it's it's commonplace it's bread and butter physics and so that kind of travel to the future is absolutely allowed by the laws of physics there are engineering challenges they're they're technological challenges close to the speed of light yeah yeah and they're they're even biological challenges right they're g-forces that you're going to experience you know so there's all sorts of stuff embedded in this but those i will call the details and those details notwithstanding the universe allows this kind of travel to the future and if i could pause real quick you could also at the macro level with biology extend the human lifespan to do a kind of travel forward in time if you expand how long we live yeah that's a way to from a perspective of an observer a conscious observer that is a human being you're essentially traveling forward in time by allowing yourself to live long enough to see the thing yes so that's in the space of biology uh what about traveling back in time yeah that's the um that is a natural next question especially if you uh if you're doing if you're going on one of these journeys is it a one-way journey yeah can you can you come back and the physics community doesn't speak with a unified voice on this as yet but i would say that the dominant perspective is that you cannot get back now having said that there are proposals that serious people have written papers on regarding hypothetical ways in which you could travel to the past and we've seen some of these again hollywood loves to take the most sexy ideas of physics and build narratives around them this idea of a wormhole like jody foster and contact went through a wormhole deep space nine star i'm sure there are many other examples where these ideas that i've probably never even seen but with wormholes there's at least a proposal of how you could take a wormhole tunnel through space-time manipulate the openings of the wormhole in such a way that the openings are no longer synchronous they are out of sync relative to each other which would mean one's ahead and one's behind which means if you go through one direction you travel to the future if you go back you travel to the past now we don't know if there are wormholes possible according to einstein correct they are possible according to einstein but even einstein was very quick to say just because my math allows for something doesn't mean it's real and he famously didn't even believe in black holes yeah didn't believe in the big bang right and yet the big the the black hole issue has really been settled now we have radio telescopic photographs of the black hole in m87 who's in newspapers around the world just a couple of years ago so so it's just to say that just because it's in einstein's math um it doesn't mean it's real but yes it is the case that wormholes are allowed by einstein's equations and in principle you can imagine you know putting electric charges on the openings of the wormhole allowing you to toe them around in a manner that could yield this temporal asymmetry between them maybe you toe one of the mouths to the edge of a black hole in principle you can do this slowing down the passage of time near that black hole and then when you bring it back it will be well out of sync with the other opening and therefore could be a significant temporal gap between one and the other but people have studied this in more detail questioned could you ever keep a wormhole open assuming it does exist could you ever travel through a wormhole or would there be a requirement of some kind of exotic matter to prop it open that perhaps doesn't exist so there are many many issues that people have raised and i would say that the general sentiment is that it's unlikely that this kind of scenario is going to survive our deeper understanding of physics when we finally have it but that doesn't mean that the door is closed so maybe it's a a small possibility that this could one day be ready that's such an interesting way to put it it will not this kind of scenario will not survive deep understanding of physics it's an interesting way to put it because it makes you wonder what kind of scenarios will be created by our deeper understanding of physics maybe uh sorry to go crazy for a second but if you have like the pan psychosome idea that consciousness permeates all matter maybe traveling in that whatever laws of physics the consciousness operates under something like that in that view of the universe if we somehow are able to understand that part maybe traveling is super easy yeah it does not follow the constraints of the speed of light something like this yeah so look i have i have a definite degree of um sympathy with the possibility that consciousness might be more than what we described earlier is just the byproduct of mindless particles you just made the rock happy exactly you know so so it isn't the approach that feels to me the the most likely but i i see the logic if you've got the puzzle how do mindless particles build mind one resolution might be the particles are not mindless the particles have some kind of proto-conscious quality so there's there's something appealing about that straightforward solution to the puzzle and if that's the case if we do live in a pan-psychist world where there's a degree of consciousness residing in everything in the world around us then yes i do think some interesting possibilities might emerge where maybe there's a way of communing with physical reality in a in a deeper way than we have so far i mean we as human beings a vital part of our existence is human to human communication contact we live in social groups and that's what it's allowed us to get to the place where we've gotten imagine that we have long missed that there's other consciousness out there and some kind of relationship or communion with that larger conscious possibility would take us to a different place now do i do i buy into this yet i don't i don't see any evidence for it but do i have an open mind and allow for the possibility in the future yeah i do so if that's not the case and you have these simple particles that at the macro level emerges some interesting stuff like consciousness another thing you write about in the until the end of time book is the the thing that seems to emerge at the macro level is the feeling like uh that like there's a free will like we decide to do stuff and you have a really interesting take here which is no there's not a free will i'm just going to speak for you and then you should correct me no there's not a free will but there is an experience of freedom yeah yeah which i i really love so where does the experience where does freedom come from if we don't have any kind of physics based free will yeah and and so the idea follows naturally from all that we've been talking about let's make the assumption that all there is in the physical universe is stuff governed by laws we may not have those laws may may not know what the fundamental stuff is yet but everything we know in science points in the direction that it's physical stuff governed by universal laws and that being the case or that being the assumption then you come to a particular collection of those ingredients called a human being and that human being has particles that are fully governed by physical law and when you then recognize that every thought that we have every action that we undertake is just the motion of particles when i'm thinking thoughts right now of course at this level of description it is the motion of particles cascading down various neurons inside of my head and so on and every single one of those motions collectively and individually is fully governed by these laws that we perhaps don't have yet but we imagine one day we will that leaves no opportunity for any kind of freedom to break free from the constraint of physical law and that is the end of the story so the traditional intuitive notion of free will that we're the ultimate authors of our actions that we were the buck stops that there is no antecedent that is the cause for our decided to go left or right choose vanilla or chocolate live or die that intuitive sensation does not have a basis in our understanding of the physical world so that's the end of the free will of the traditional sort but then your question is what about this other kind of freedom i talk about and the other kind of freedom if you focus on it intently i think is actually the true version of freedom that we feel and that freedom is this you look at inanimate objects in the world rocks bottles of water whatever they have a very limited behavioral repertoire why their internal organization is too coarse for them to do very much right you have to you try to have a conversation with a glass of water you send sound waves it doesn't do much it may vibrate a little bit but the repertoire of responses are incredibly limited the difference between us and a rock or a bottle of water is that our inner organization by virtue of eons of evolution by natural selection is so refined so spectacularly ordered that we have a huge repertoire of behaviors that are finely attuned to stimuli from the external world you ask me a question that's a stimulus and all of a sudden these particle processes go into action and this is the result this answer that i'm giving you so the freedom that we have is not from the control of physical law the freedom that we have is from the constrained behavior that has long since governed inanimate objects we are liberated from the limited behavioral repertoire of rocks and bottles of water to have this broad spectrum of responses do we pick them we do not do we freely choose them we do not but yet we have them and we can marvel at those behaviors and that's the freedom that we have the complexity and the breadth of that repertoire is is where the freedom is is there something to be said about emergence i don't know if you know i've looked at much about objects that i seem to uh love way more than anyone else which is cellular yeah like game of life type of stuff there you know from simple things emerges beautiful complexities and so that's that repertoire it's like it seems if you have enough stuff just beautiful complexity emerges that sure as heck to our human eyes looks like there's consciousness there there's free will there's little objects moving about and making decisions i mean all of that you can say it's anthropomorphization but it sure as heck feels like their organisms making decisions um what what is that that emergence thing is is that within the realm of physics to understand is it uh is it within the realm of poetry where because what is that like complex systems emergencies what is that will that ever be understood by science so here's here's the way that i think about it so there are clearly qualities of the world that emerge on macroscopic scales our sense of beauty wonder consciousness all these kinds of qualities do i feel that they ultimately are explainable from the laws of physics i do there is nothing that's not ultimately ultimately explainable with the laws of physics from this physicalist perspective which is what i take so you got the particles you got the laws and you have things that emerge from the choreographed motions of those particles but is that the best language for talking about these emergent qualities usually not if i was to take something even more mundane like a baseball flying through the air if i was to describe it in terms of the quarks and the electrons i'd give you this mountain of data with you know 10 to the 28 particles and all of their coordinates in space as a function of time i hand you this mountain of data to be like i don't know what this is and then if you really were clever and looking oh it's a baseball just described in the in the least economical way possible it is much more useful and insightful to talk about the baseball flying through the air similarly there are things at the macroscopic level like human experience and human emotion and human action and the sensation of free will that we undeniably all have even if it itself doesn't have a basis in our understanding of the physical world it's useful to talk about things in this very human language and so yes it's vital to talk about things in the poetic language of human experience but do not lose sight of the fact and some people do they say oh it's just an emerging phenomenon don't lose sight of the fact that emergent phenomena are emerging from this deeper understanding that comes from the reductionist account of physical law and there's a lot of insight to come from that such as the freedom that you thought that you had the freedom of will that you thought you had it doesn't have a basis in that reductionist account so it's not real so speaking of the poetry of human experience you mentioned the images of the black holes how did it make you feel a few years ago when that first image came out it's truly amazing a sense of well i guess the feeling was both amazing and and there's a little sense of um jealousy is not quite the right word but a sense of longing yeah i think that's a better word because here's a subject that started with einstein back in 1915 writes down the equations of the general theory of relativity and then there are scores of individuals over the decades you know starting with people like carl schwarzschild who analyze the equation see the possibility of black holes people develop these ideas john wheeler all these greats of physics it's still a hypothetical subject it gets closer to reality through observations of the center of our galaxy stars whipping around in a manner that could only really be explained by there being a black hole in the center of our galaxy but it was still indirect to actually have a direct image that you can look at what a beautiful arc narrative arc from the theoretical to the absolutely established and that's what we hope will happen with other areas for instance string theory right i mean holy mathematical subject at the outset and still pretty much a holy mathematical subject today yeah do we long for that image where we can look at it and say string it's real i mean you know i mean how thrilling how thrilling to be part of that journey to be part of that that step that moves things from the abstract to the concrete yeah uh so like the image of the dna the early images of the dna for example uh but there is something especially so the problem with strings is they're tiny so it's harder to take a picture i in in the following sense when you think of a black hole i mean you have a swirl of i guess what is i i don't even know it's dust to go whatever light creeding onto the uh event horizon and then there's darkness yeah center and you you just imagine so that picture in particular i guess is of a gigantic black hole so you just i mean it's 10 million billion billions of times the mass of the sun yeah so it's both exciting and terrifying i mean i don't i don't know where you fall on the spectrum i think it's exciting at first like the longer i think about it every time i think about it the more terrifying it becomes so it always starts exciting and then it goes to terrifying and both are feelings very human feelings that i appreciate it's like terrified aw somehow it's still beautiful that's a good way of saying it i think i kind of share that that reaction because there is a way in which when you work on this subject like all the time i teach it i teach about black holes write the equations on the blackboard the ideas reside in a very cognitive i don't know mathematical portion of the brain or at least for me and it's only when you like sit down and it's quiet and you start to contemplate wait wait wait wait this is just like a mathematical game there are these monsters out there now i don't not in it in a sense of i fear for my life but it's a sense of how extraordinary is this universe and so it is breathtaking how powerful nature is yeah how stupendously powerful nature is um and so there is a deep sense of humility that i think this instills if you really allow the ideas to sink in well i have to ask about the most stupendously powerful thing to have ever happened in our universe which is the big bang yeah what's up with the big bang so we can i mean with gravitational waves the hope is when you have more and more accurate measurements of the gravitational waves you can crawl back further and further back in time towards the big bang do you ever hope that we'll be able to understand the the early spark that created our universe yeah you know that and the deep interior of a black hole i think the the biggest mysteries that we hope the melding of quantum mechanics and gravity will reveal will illuminate and you know what question could be more captivating than why is there something rather than nothing right why is there a universe at all and will the theories that we're developing take us to an answer to that i don't know even if we truly knew what the big bang is that's a big question it's own right one would still be left with the question well okay so you've explained the process by which a tiny nugget of a universe a kind of nugget of space-time can undergo some kind of growth to yield the world around us but presumably in that explanation you're going to involve mathematics and some ingredients like quantum fields or or matter or energy or something where did that stuff come from you know can we get to that level of explanation i don't know but it is remarkable that if you ask what happened a millionth of a second after the big bang it's not really that controversial any longer right even though there's a lot of argument in the field and it's very heated right now i should say regarding what is the right theory of the big bang what is the right theory of early universe cosmology where i mean early much earlier than a millionth of a second a lot of dissent a lot of uh heated arguments about that no pun intended yeah right exactly um but but but you go like a millionth of a second after that yeah and and we're on pretty firm ground isn't that amazing right yeah to understand you know what happened from that point forward but to go back is is is controversial so there is this theory called inflationary cosmology which i would say has been the dominant paradigm since uh early 1980s so what does that mean roughly 40 years now it's been the dominant cosmological paradigm and it makes use of a curious feature of einstein's general theory of relativity his fear of gravity where einstein shows us mathematically that gravity can not only be attractive you know the kind of gravity that we're used to things pull together but it can also be repulsive and that fact is then leveraged by people like alan guth and and andre linday and at the time paul steinhardt and andres albrecht and others to say okay if we had a little nugget in the earlier universe which was filled with the stuff that yields this repulsive gravity well that would have blown everything apart it would cause everything to swell beautiful explanation for what the bang in the big bang was and then people mathematically analyze the consequences of this idea and they make predictions for tiny temperature differences across the night sky that in principle could be measured you send up balloons you set up satellites with very refined thermometers and they measured the temperature of the night sky and the statistical distribution of the temperature differences agrees with the mathematical predictions yeah i mean it's amazing you just sort of have to stand in awe of this insight so you think aha the theory has been established but scientists are an incredibly skeptical bunch and some scientists including one of the people who helped develop the theory at the outset paul steinhardt comes along and says well yeah it's done this theory's done pretty well so far but there are aspects of this theory that are making me lose confidence for instance this theory seems to suggest that there might be other universes like how do you make sense of a theory that suggests other universes or or there are others who come along and say this theory seems to um talk about length scales that are minuscule even by the so-called plank length the sort of shortest length that we can imagine making sense of in a theory of quantum gravity how do you make sense of that and so and so they develop a list of of things that they consider to be chinks in the inflationary cosmological theories armor and they develop other ideas which they claim yield the same predictions as inflation and cosmology for those temperature differences across space but don't suffer from these problems and then the inflationary cosmology folks say no no no hang on you know your theories suffers from different problems and so the arguments goes it's a healthy debate talk about real debates and science so when you ask what's up with the big bang i don't know right now um if you would have asked me five years ago maybe even less than that three or four years ago i've said look inflation on cosmology has some issues but the package of explanations it provides is so potent and the issues that beset it are seemingly solvable to me that i would imagine it's going to in the end win out i would still say that today but i wouldn't say it as loudly i wouldn't say it as confidently i think it's worth thinking about alternate ideas and it could be the case that the paradigm at some point shifts does dark matter and dark energy fit into the shifting of the explanations for those yeah certainly so so dark energy has uh in in the inflationary theory is kind of a big mystery so dark energy is the observational realization in the last 20 years that not only is the universe expanding it's expanding ever more quickly something is still pushing things outward and the explanation is that there's like a residual version of the repulsive gravity from the early universe but it's such a strange number when you write that amount of dark energy using the relevant units in the theory of quantum gravity it's a decimal point followed by like 120 zeros and then a one we're not used to those kinds of numbers in physics we're used to a half one pi e square to two those are the kinds of fundamental numbers that emerge in our explanations of the world and we look at this bizarre number decimal point all these zeros and one we say something's wrong there like where would that number have come from now there are people who suggest resolution to it so it's not like we're totally in the dark on it but those people like paul steinhardt who have alternate cosmological theories cyclic cosmologies as they call it claim that they have a more natural explanation of the dark energy that it naturally feeds into a cyclical process that is their cosmological paradigm so yeah if the cosmology should change it's conceivable our view of dark energy may change from deeply mysterious to deeply integrate it into a different paradigm that is possible i think it's roger penrose that think that information can bleed through from before the big bang to the after the big bang yeah is that uh is the big bang uh like a full erasure of the hard drive or is there some information that could bleed through yeah i mean so sir roger is among the most creative thinkers of the last 100 years rightly won the nobel prize for his insights into singularities in space time that we know to afflict our mathematical solutions of black holes in the big bang and so forth and um he has an enormously fertile imagination and and i mean that in the most positive sense and um so he has put forward this idea this conformal cyclic cosmology i think is the uh the official title although i could be getting that wrong i can't say that i've studied it i have seen lectures on it i don't find it convincing as yet it feels like it's being built to find a solution as opposed to sort of more naturally emerging maybe roger would say otherwise and i don't mean to in any way cast aspersions on the work it's vital and interesting and people are thinking about it i don't consider it as close a competitor to say the inflationary theory as for instance the stuff that paul steinhardt has put forward but again you've got you got to keep an open mind in this in this business when there's so much that we don't yet understand i mean it is wild to think that information can survive something like that just like it is wild to imagine that information could escape a black hole for example or it just seems like by construction these things are supposed to not bleed out anything but one of the challenges in all these theories is when we talk about a singularity has this really sexy term the singularity yeah but a singularity is is in more ordinary language a physical system where the mathematics breaks down it's nonsensical it's like taking one divided by zero you put that into a calculator and it says e error right it does not make sense doesn't compute and and so it's very hard to make definitive statements about things like the big bang or about black holes until we cure the mathematical singularities and there are some who claim that in certain regimes the singularities have been cured i don't by any means think that there's consensus on these ideas so when one talks about information sort of bleeding through the big bang you've really got to make sure that the equations have no singularity you talk about cyclic cosmology you've got to make sure that the equations don't have any singularities as you go from say one cycle to the next now some of the proponents of these theories claim that they have resolved these issues i i don't think that there's a general sense that that is the case as yet but it could be that look i life is so short that i i haven't had the time to deeply delve into all the mathematical intricacies of all the ideas that have been put forward if i did that i'd never do anything else but that that's what the issue is and of course it's just math there may be holes there may be uh there may be gaps in our our understanding in the way we're modeling physical variables well that's the point in fact when you said i was about to jump in and say modeling but you got there first and it's exactly the right point you're talking about the universe here right and the how do you how do you talk about the universe with a straight face mathematically and the way you do it is you you simplify you throw away those characteristics of the universe that you don't think are vital to a full understanding and so we're going to get to a point people are starting to where we've got to go beyond those simplifications and so cosmology has for a long time modeled the universe in the most simplest terms homogeneous isotropic it has just a few parameters that describe it the average density of mass and energy and so forth we have to go beyond those simplifications and that will require putting these things on computers we're not going to be able to do calculations there so much as astrophysics has gone beyond many simplifications to now give really detailed simulations of star systems and galaxies and so forth we're going to have to do that with cosmology and people are starting to do that today yeah i've seen some interesting work on uh simulation most simulation cosmology by the way is just awesome but you know just like simulation of the early formation of our solar system to understand how the like the ore cloud and just i don't know the the whole of it the how earth came to be yeah like how jupiter just protects us protects us and then there's like weird like moons and volcanoes and and like modeling all of that the formation of all that uh is fascinating yeah because that naturally is the question of how does life emerge and these kinds of rocks how does a rock become a rabbit yeah uh but speaking of models uh there's an equation called the drake equation we were talking about life have to ask when you're at the highest level first when you look out there how many alien civilizations do you think are out there zero one or many so if you say civilization i would bring my number way down it could be zero if you talk about life i think it could be many as we were saying before i think the move from life to consciousness the kinds of beings that would build what we would recognize as a civilization that may be extraordinarily rare i hope it's not you know as a kid i love star trek i i just love the idea that we would be part of some universal community where look experience on planet earth suggests it doesn't always go so well when groups who are separated try to come together and and live in some larger collective but again as an optimist how amazing would it be to converse with an alien civilization and and learn what they've figured out about physics and cosmology and and compare notes and and and learn from each other in in some some wonderful way i i love that idea but if you ask me the likelihood of it i i would err on saying it may be so improbable that the conditions conspire to allow life to move to this place of of consciousness that it might be rare it might be oversimplifying things but just observing the power of the evolutionary process i tend to believe and like you read different theories of how we went uh how homo sapiens evolved it seems like the evolutionary process naturally leads to to homo sapiens or creatures like that or much better than that so to me the there's several scary scenarios so okay the positive scenario is life itself is really difficult so that origin of life is difficult that's exciting for many reasons because we might be able to prove that wrong easily in the near term by finding life elsewhere sure the scary thing to me is if uh life is easy and there's plenty of conscious intelligent civilizations out there and we have not obviously made contact which means with intelligence and consciousness comes responsibility and ultimately destruction so with power comes great responsibility and then we end up destroying ourselves that's the uh the scariest the the positive i guess version is that maybe we're being watched uh sort of like there's a transition to where you don't want to ruin uh the primitive villages out there and so there's a protective layer around us yeah they're they're watching so where where do you and these possible explanations to the fermi paradox why haven't we contacted aliens do you land on well i think the most straightforward explanation is that there aren't any now there are many other explanations too so i you can't be dogmatic about things that are just sort of gut feel but you know one of my favorite twilight zone episodes i don't ever saw this one where this alien civilization finally comes to planet earth and gives us this book that they really want us to to have and to hold and it's in this foreign you know language you don't understand the cryptographers they desperately try to decipher it as humans are going to visit this other alien planet and they're all sending back postcards how wonderful it is and so forth and they they finally decipher the title it's to serve man and everyone's so thrilled oh they're here to service it all makes sense and then just as one of the final cryptographers is going on to the alien ship his his helper runs and says i've deciphered the rest of the book to serve man it's a cookbook you know so you know so yeah is that is that a possibility sure you know and and so could they be watching us and just sort of waiting for us to uh get to a mature enough level i don't know it strikes me well you know i think it'd be better to have this conversation after the james webb telescope i mean i do think that um if we look at the atmospheres of many planets i mean there's now an estimate now that there's on order of one planet per star on average so we've long known that you know the galaxy hundreds of billions of stars numbers of galaxies hundreds of billions of galaxies so we're talking about hundreds of billions of hundreds of billions of planets i'm like you know and if we start to survey some of these planets and one after the other after the other we just sort of find no evidence for any of the biological markers it could be of course maybe life takes a radically different form it'd be hard to know that but i think you know that would at least give us some insight on the life question but i just don't see how we get insight on the civilization or consciousness question without you know the direct connection and and it strikes me that if consciousness is ubiquitous let's say life is i'm willing to grant that if consciousness is also ubiquitous then i don't understand why they haven't been here or why there hasn't been separate because presumably they should be much further ahead of us how unlikely would it be that we're like of all consciousness in the universe we're the most advanced that would be such a special place for human beings that it's hard for me to grant that as a likely possibility rather i think we're kind of running the mill and there are many who are far more advanced than us and i don't think that they would expend the energy to hide themselves so i don't think they care enough and so i see that's actually what i i believe that there's uh a very large number of civilizations that are far more advanced than us but my sense is the humans are exceptionally limited both in our direct sensory capabilities and our physics our tools of sensing that just like with the string theory and the multiple dimensions we're just not like it's like i honestly believe there could be stuff in front of our nose that we're just not seeing what because we're too dumb too uh too much hubris and i mean it's a bunch of stuff and too ignorant as a to the fabric of reality all of those things yeah we're young yeah in terms of intelligence but i guess what i'd say is like i'm on board with all of that as a real possibility but then it does strike me that we are sufficiently able to observe the unit look we can look back to you know a fraction of the duration from here to just a fraction is left that we are unable to see um so however young we are we have been able to sort of pierce the universe and it just strikes me that there would be some signature but maybe maybe that that's coming but but look having said that i do look i i i certainly note the fact that it's rare that i stoop down while walking in manhattan and sort of dig up some ants in the bushes on the side of the street and talk to the ants right because it's just not interesting to me so if we're like the ants on the cosmological landscape then yeah i can imagine that the super advanced aliens would be like like whoever you know but but i feel like we're sufficiently advanced that there should be some signal signature of that but maybe it's coming i think the deeper fundamental problem between us and the ants is that we don't have a common language it's not it's not the interest it's that we don't even have a common language and so the the alien civilizations don't even know how to communicate like we humans have convinced ourselves we're special because we developed the language you talked about you talk about the importance of language to intelligence but it makes you wonder like how very niche is that like club that we've like tried we've created of language and linguistic type of systems that are very specific to our particular kinds of brains and we share ideas together are all super excited that we can understand the universe because we came up with some notation yeah and math i wonder if there's some totally other kinds of language that communicates on a different time scale with different very different mechanisms in a space of information that just is not it's everything everything is lost in translation yeah and it could well be it's a look i mean i think part of the reason i go toward the possibility of the soul intelligence is there's a certain kind of romantic appeal to looking out in the cosmos and it's just quiet and it's just eternal silence there's some there's something that appeals to me at an emotional level that way but yeah i mean um nobody nobody knows and uh it's certainly um conceivable that we're there's just a radical mismatch between the kinds of things that we are able to observe and sensitive to versus the kinds of structures that permeate the universe in a manner that simply we're unable to detect well if we are alone that is exciting in one of the ways it's exciting is um that it's up to us to become to expand out into the universe to um permeate consciousness out into the universe so that's where space exploration comes in let me ask you as somebody who's a screen theorist a physicist do you think space exploration a colonizing space is a physics or an engineering problem what would you say yeah i think it's fundamentally an engineering problem if we're not trying to do things like build wormholes the way they did say an interstellar to get to a different place or trying to travel near the speed of light so that we would actually be able to traverse interstellar distances i mean without that our colonization will happen in a very very slow rate right um but one of the beauties of relativity is if you do travel near the speed of light you you can actually go arbitrarily far in a human lifetime people say how's that possible you can't go billions of light years well you can actually because as you can do this bleed of light the way in which space and time change allows you to go in principle arbitrarily far that's that's very exciting but if we put that physics side of the issue in the manipulation space and time to the side yeah i think it's a deep engineering problem you know how do you terraform other planets i mean uh how do you go beyond our local neighborhood say without you know using the ideas of relativity so i think it's all quite exciting and i think the idea is you know using solar sails that you know people have developed and uh you know trying to take that first step to mars i think that's a vital and valuable step to take but yeah i think these are fundamentally engineering challenges or extending the human lifespan through biology research or um maybe reducing what it means to be a human being into information and uploading certain parts of it maybe not all the full resolution of a human life but maybe the essential things like the dna and be able to reconstruct that human being but you know i have to ask about mars you know do you find the the dream of humans stepping on mars stepping foot first but also colonizing mars um one that's worth us fighting for yeah usually so i mean i think what we have long been not always in the best way is a species of explorers in the literal sense of traveling from one part of the world to another or in the more metaphorical sense of trying to travel through our minds to the quantum realm or back to the big bang or to the center of black holes so i think that's fundamentally part of of the human spirit so i do think that's a vital part of our heritage brought forward into its next incarnation that's who we are do you think there'll be a day in the future where a human being is born on mars and has to learn about his or her human origins on earth like they'll have to read in the book yeah i don't think it'll be a book at that stage it'll probably just be uploaded into the head or something or you know imprinted into the dna and then they just sort of sense it but yeah i think there's there's well look the the issue you raised before is the vital one is it the case that any sufficiently advanced civilization destroys itself is that sort of a a commonplace quality i mean that's the other potential answer to the fermi paradox uh why aren't they here because by the time they got to the technological development where they could travel here they blew themselves up they destroyed themselves and that's a you know you know an unfortunate but you know not a hard to imagine possibility based on things that have happened here on planet earth but but putting that to the side i think it um you know that's the big obstacle but putting it to the side we will resolve the engineering challenges and and you know i should probably um modify my answer from before when you said is it engineering or physics it's really both right so so we will surmount the engineering challenges and that will then make the physics challenges relevant it'll make it relevant to figure out how to travel near the speed of light it'll make it relevant to learn how to manipulate the shape of space-time and so forth so so i think it's a multi-stage process where it is engineering and ultimately physics and if we stick around long enough those are the kinds of challenges i think that we're ultimately going to surmount and then the physics side is figuring out how to harness energy enough to travel outside the solar system which seems like a heck of a difficult journey but even mars itself of um i don't know maybe because i i was born in the soviet union and was born with the you know looking up at the stars and that dream of like the highest of human achievement his ability to fly out there to you know to join the stars i i really like the idea of going to mars of and not just stepping foot on mars and it wasn't until maybe um misinformed but for me personally uh it wasn't until elon musk started talking about the colonization of mars did i realize like we humans can actually do that and the first of all the importance of somebody saying that we can do these seemingly impossible things is um immeasurable because uh you know the fact that he he placed that into my mind and into the minds of millions of others maybe hundreds of millions maybe billions of others young kids today i mean that that's going to make it a reality i for some reason i'm deeply excited even though my work isn't ai that echoes all of this i'm excited by the idea that somebody would be born as we were saying on mars and sort of look up and be able to see with the telescope earth and say that's where i came from i don't know that that idea scale to other planets to other solar systems yeah that's really exciting hugely exciting i i think you're absolutely right i mean the vital thing is to dream right i mean and it sound hackney but it is so important for for young kids for the next generation to to think about the things that are seemingly impossible i mean that's what makes them possible and this is one which is concrete enough i mean this is something that's going to happen soon in terms of actually going to mars and then the next step of establishing some presence some semi-permanent or permanent presence this is this is not something that's gonna wait to the 25th century i mean this is something that's going to happen relatively soon so i mean it could well be in your lifetime unlikely mind but possibly in your lifetime that that kid will be born and and and have the experience that that you describe so yeah it's spectacularly exciting and i actually i would love to go on mars and one of the early you would yeah what if it's one way i was i'm happy really wow yeah and i'm i'm single if there's ladies out there that want to start that family let's go let's go out to mars no i think uh see i have to tell you something you spoke about terror thinking about like black holes if i actually think about going to mars and being on mars and put myself in there fully that's terror inducing the idea of to be in this foreign world where you can't come back where you've made this this choice that can't be reversed or you know at some point it may be but but in that guys that to me carries a deep sense of terror hmm you know i i feel that sense of terror every time kerouac jack carrack talked about this and on the road is you know when you leave a place if you're honest about it like life is short and when you leave a place you move to a new place and you think of all the friends maybe family you're leaving behind as you drive over the hill that that really is goodbye like we sometimes don't think of it that way when we're moving but that really is goodbye to that life to the person you were to all the people maybe if it's close friends you'll see them maybe 10 15 more times in your life and that's it yeah and you're saying goodbye to all of that and so in the same way i i see it as way more dramatic when you're flying away from earth and it's like it's goodbye to dunkin donuts and starbucks and it's goodbye to whatever i don't know why i picked those but some all the things that are special to earth it's goodbye but that's that's life i i suppose more what excites me about that kind of journey is it's a distinct contemplation of your mortality acceptance of your mortality you're saying just like when you take on any difficult journey it's accepting that you're going to die one day and might as well do something truly exciting yes i mean i will you know i'm with you on that i uh i'm a strong believer that deep underneath human motivation is this this terror of our own mortality you know there's this wonderful book that had a great influence in me called the denial of death by ernest becker and when you are aware of the ways in which our mortality influences our behaviors it really does add a different slant a different kind of color to the interpretation of human behavior yeah it's funny um that that book had a big influence on me as well is that right right and terror management theory and and i again from an engineering perspective i don't know how many people that book influenced because i talk to people about the fear of death and it doesn't seem to be that fundamental to their experience and i don't think on the surface is fundamental to my experience but it seems like an awfully in terms of we talk about models and strength theory and theories in terms of theories of this macro experience of human life it seems like a heck of a good theory that the fear of death is that the kind of is the warm at the core yeah well i mean and the terror management theories that you make reference to i mean the this is a group of you know psychologists social psychologists who devise these very clever experiments real world experiments with real people where you can directly measure the hidden influence of the recognition of our own mortality i mean they've done these experiments where they have group of people a group of people b and the only difference between the two groups is that group b they somehow reminded them in some subtle way of their own mortality sometimes it's nothing more than interviewing them with a funeral home across the street you know an influence is there but it's but it's subtle you don't even think you take note of and they can find measurable effects that differentiate the two groups to a high degree of statistical significance and how they respond to certain challenges or certain kinds of questions that shows a direct influence of the reminder of their own mortality and i've read a number of these studies and they are really convincing and so yeah i would say that the reason why so many people would say that yeah fear of mortality it's not front and center in my world view yeah i don't really think about it much doesn't really matter too much the reason why they're able to say that is because this thing called culture has emerged over the course of the last 10 000 years and part of the role of culture is to give us a means of not thinking about our mortality all the time of not living in terror of the inevitable end which faces us all so it's completely understandable that that's the response because that's what culture is at least in part four it's at least possible that uh the fear of death the terror of your mortality is the creative force that created all of the things around us at this human civilization and i think about from an engineering perspective this is where i lose all of my robotics colleagues is i feel like if you want to create intelligence you have to also engineer in some kind of echoes of this kind of fear of uh and not you know fear is such a complicated word but it's kind of like a scarcity a scarcity of time a scarcity of resources that creates a kind of anxiety like deadlines get you to do stuff yeah and there's something almost fundamental to that in terms of uh human experience yeah well that's an interesting thought so you're basically in order to create a kind of structure that mirrors what we call consciousness yes you'd better have that structure confront the same kinds of issues and terrorism that we do consciousness and suffering only makes sense in the context of death if you want to i feel like if you want to fit into human society if you if you're a robot if you want to fit into human society you better have the same kind of existential dread the same kind of fear of mortality otherwise you're not going to fit in [Laughter] it might be it might be wild but it's at least like we're talking about all the theories that are at least worth consideration i think that's a really powerful one and definitely one has uh resonated with me and um definitely seems to capture something beautifully like real about the human condition and i i wonder it's of course sucks to think that we need death to appreciate life but that just may be the way it is well it's interesting if this robotic or artificially intelligent system understands the world and understands the second law of thermodynamics and entropy even in artificial intelligence will realize that even if its parts are really robust ultimately it will disintegrate yeah i mean so the time scales may be different but in a way when you think about it doesn't matter once you know that you are mortal in the sense that you are not eternal the time scale hardly matters because it's it's either the whole thing or not because on the scales of eternity any finite duration however large is effectively zero on the scales of eternity and so maybe it won't be so hard for an artificial system to feel that sense of mortality because it will recognize the underlying physical laws and recognize its own finitude and then it'll be us and robots drinking beers looking up at the stars and just uh you know uh having a good laugh in awe of the whole thing yeah i think that's a pretty good way to end it talking about the fear of death we started talking about the meaning of life and ended on the fear of death brian it's just an incredible conversation pleasure thank you i really really enjoyed it it's been a long time coming i'm a huge fan of your work a huge fan of your writing thanks for talking about thank you thanks for listening to this conversation with brian green to support this podcast please check out our sponsors in the description and now let me leave you with some words from bill bryson physics is really nothing more than a search for ultimate simplicity but so far all we have is a kind of elegant messiness thank you for listening and hope to see you next time you