COMPLEXITY: Physics of Life

Complex Conceptions of Time with David Krakauer, Ted Chiang, David Wolpert, & James Gleick

Episode Notes

And now for something completely different!  Last October, The Santa Fe Institute held its third InterPlanetary Festival at SITE Santa Fe, celebrating the immensely long time horizon, deep scientific and philosophical questions, psychological challenges, and engineering problems involved in humankind’s Great Work to extend its understanding and presence into outer space. For our third edition, we turned our attention to visionary projects living generations will likely not live to see completed — interstellar travel, off-world cities, radical new ways of understanding spacetime — as an invitation to engage in science as not merely interesting but deeply fun. For our first panel, we decided to inquire: What is time, really? How has science fiction changed  the way we track and measure, speak about, and live in time? And how do physics and complex systems science pose and answer these most fundamental questions?

Welcome to COMPLEXITY, the official podcast of the Santa Fe Institute. I’m your host, Michael Garfield, and every other week we’ll bring you with us for far-ranging conversations with our worldwide network of rigorous researchers developing new frameworks to explain the deepest mysteries of the universe.

In this week’s episode, we share the Complex Conceptions of Time panel from InterPlanetary Festival 2022, moderated by SFI President David Krakauer and featuring an all-star trinity of panelists: science journalist James Gleick, sci-fi author and SFI Miller Scholar Ted Chiang, and physicist and SFI Professor David Wolpert. In this hour, we play with and dissect some favorite metaphors for time, unroll the history of time’s mathematization, review time travel in science fiction, and examine the arguments between free will and determinism.

Be sure to check out our extensive show notes with links to all our references at — as well as the extensive, interactive web-based “Voyager Golden Record Liner Notes” with links to not only all of the panels from IPFest 2022 but also copious additional resources, including contributor bios, peer-reviewed publications, science fiction and nonfiction science writing, and more…

If you value our research and communication efforts, please subscribe, rate and review us at Apple Podcasts or Spotify, and consider making a donation — or finding other ways to engage with us — at

If you’d like some HD virtual backgrounds of the SFI campus to use on video calls and a chance to win a signed copy of one of our books from the SFI Press, help us improve our science communication by completing a survey about our various scicomm channels. Thanks for your time!

Lastly, we have a bevy of summer programs coming up! Join us June 19-23 for Collective Intelligence: Foundations + Radical Ideas, a first-ever event open to both academics and professionals, with sessions on adaptive matter, animal groups, brains, AI, teams, and more.  Space is limited!  The application deadline has been extended to March 1st.

OR apply to the Graduate Workshop on Complexity in Social Science.

OR the Complexity GAINS UK program for PhD students.

(OR check our open listings for a staff or research job!)

Join our Facebook discussion group to meet like minds and talk about each episode.

Podcast theme music by Mitch Mignano.

Episode cover art by Michael Garfield with the help of Midjourney.

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(SOME) Mentioned & Related Links:

David Krakauer
Mathematical languages shape our understanding of time in physics
by Nicolas Gisin
Does Time Really Flow? New Clues Come From a Century-Old Approach to Math
by Natalie Wolchover
The Principle of Least Action
Path Integral Formulation
Closed Timelike Curve
The Time Machine
by H. G. Wells
Kip Thorne

James Gleick
Genius: The Life and Science of Richard Feynman
The Physicist and The Philosopher
by Jimena Canales

Ted Chiang
“Story of Your Life”
Russian Doll (TV series)
“The Merchant and the Alchemist's Gate”

David Wolpert
Complexity 94 - David Wolpert & Farita Tasnim on The Thermodynamics of Communication
Complexity 45 - David Wolpert on The No Free Lunch Theorems and Why They Undermine The Scientific Method
A Connecticut Yankee in King Arthur’s Court by Mark Twain
Intuitionist Mathematics

Episode Transcription

James Gleick (0s): If time is a river, are you in the river flowing with time or are you standing on the bank watching as time goes by.  We say all of that and we start to speak of time as a quantity. And if it's a quantity, it's a quantity that you can save or waste or put in the bank or spend.

Ted Chiang (17s): Prophecy stories, they are stories about information moving backward in time. It's just that the perspective is different. They're told from the point of view of the person receiving the information from the future. And throughout prophecy stories, they're really old. They go back thousands of years. I think of them as, you know, this sort of antecedent of time travel stories that are almost as old as storytelling. But the thing is, all prophecy stories of old that I'm aware of, someone gets a prophecy of something that'll happen in their future. They take steps to avert it and then they, the steps they've taken can merely bring about the prophecy they cause it to come true.

David Wolpert (50s): Arguably close timeline curves make the case done. Or else you get these silly things like the Grandfather Potter docs. You go back into the past, you destroy your parents, so therefore you could not have existed. And oh, paradox, if you don't have this notion of free will, instead all of reality into all the future and all the past and all of different points in space is all just a solution to the equation, then you just got a solution. It's sitting there, it's a static object. There's no sense in which you could go along a world line and make a decision with some freedom to undo what was there in the past.

Michael Garfield (1m 52s): And now for something completely different. Last October, the Santa Fe Institute held its third Interplanetary Festival at Site Santa Fe, celebrating the immensely longtime horizon, deep scientific and philosophical questions, psychological challenges and engineering problems involved in humankind's great work to extend its understanding and presence into outer space. For our third edition, we turned our attention to visionary projects living generations will likely not live to see completed. Interstellar travel off world cities, radical new ways of understanding space time as an invitation to engage in science as not merely interesting but deeply fun.

For our first panel, we decided to inquire what is time really? How has science fiction changed the way we track and measure, speak about and live in time? And how does complex systems science pose and answer these most fundamental questions? Welcome to 


, the official podcast of the Santa Fe Institute. I'm your host, Michael Garfield. And every other week we'll bring you with us for far ranging conversations with our worldwide network of rigorous researchers developing new frameworks to explain the deepest mysteries of the universe.

In this week's episode, we shared the Complex Conceptions of Time panel from Interplanetary Festival 2022, moderated by SFI President David Krakauer and featuring an all-star trinity of panelists, science journalists, James Gleick, Sci-Fi author and SFI Miller Scholar, Ted Chiang and physicist and SFI Professor David Wolpert. In this hour we play with and dissect some favorite metaphors for time, unroll the history of time's mathematization, review time travel and science fiction, and examine the arguments between free will and determinism.

Be sure to check out our extensive show notes with links to all of ourreferences at

, as well as the extensive interactive web-based voyager golden record liner notes with links to not only all the panels from IP Fest 2022, but also copious additional resources including contributor bios, peer-reviewed publications, science fiction and nonfiction, science writing, and more. If you value our research and communication efforts, please subscribe, rate and review us at Apple Podcasts or Spotify and consider making a donation or finding other ways to engage with us at

.  If you'd like some HD virtual backgrounds of the SFI campus to use on video calls and a chance to win a signed copy of one of our books from the SFI press, help us approve our science communication by completing a survey about our various Sycom channels. Thanks for your time. Lastly, we have a bevy of summer programs coming up. Join us June 19th through the 23rd for collective Intelligence foundations and radical ideas, a first ever event open to both academics and professionals with sessions on adaptive matter, animal groups, brains, AI teams, and more. Space is limited.

But the application deadline has been extended to March 1st or apply to the graduate workshop on complexity in social science or the Complexity Gains UK program for PhD students. Or check our open listings for a staff or research job. Join our Facebook discussion group to meet like minds and talk about each episode. Thanks for listening.

David Krakauer (5m 31s): The basic premise, I guess if I was honest, is what would it take to make science hedonistic? And instead of telling people that they have to do it, you'd have to tell 'em to stop it. And so that's what I would like. So with that, I'm gonna invite up the time panel for our first panel of the day. And they're sitting right here, so why don't you all come up and join me. All right, so you all have mics.

Remember they're physical objects that need to be placed in front of your mouth, not by the side of your ear. So these are things. So let me introduce my panelists. My left, the legendary James Gleick, award-winning author of narrative nonfiction called one of the Greatest Science Writers of All Time. According to him, he's the author of 

Time Travel: A History, Chaos: Making for New Science

The Information

. And he, I think James in his work de limits a lot of the science actually that we do in one way or another and has written really extraordinary book and not, and that doesn't exhaust it.

His biography of Feynman is really a wonder if you've not read it. So I highly recommend James' work. Sitting next to him, the legendary Ted Chiang. It is won just about every single science fiction award you could name Nebula Awards, Hugo Awards, Locus Awards, his 

Short Story of Your Life

. I was made into the really wonderful film 


by Denis Villeneuve, I'm sure most of you seen. He's also a Miller Scholar at the Santa Fe Institute, which is the most important thing he's ever done. Ted is rare, I think in the elegance with which he writes about science.

There's a beautiful filigreed perfection to his stories, which we all very much admire. He actually has a wonderful sentence in his book that we'll get to, 

The Merchant and the Alchemist Gate

, which I think should be the spirit in which we conduct this panel. And he says, “driven by the curiosity that ipel men to inspect the heads of the execute it.” So okay, maybe not. And, and then of course my colleague, Professor at the Santa Fe Institute, David Wolpert, he works on thermodynamics of computation, the foundations of physics, the dynamics of social organizations is a true polymath and David's one of those people who seems to straddle quite effortlessly the world of logic and crystalline worlds and the worlds of machines, which is quite a unique set of skills.

So let me, today's panel is not about time per se, but the representation of time and time is a river. Time is space. Time is feedback loops. And our thinking about this topic is only as strong as our representations of it and often we get locked into actually our representations and we'll talk about that and maybe in relation to the Einstein/Bergson debate in 1922. But the first thing I wanted to ask you quickly, and they're not really expecting this, is do you have an instinctual aesthetic sense of time?

Do you have a favorite model and metaphor for time that you think about? James, since you're closest to me? I'll ask you first.

James Gleick (8m 33s): Metaphors there. Time is all about metaphors. You've already mentioned river, that's everybody's favorite time is a river that you can't step into the same place twice. That's a butchered version of a butchered translation of a non-existent memory of something Heraclitis is supposed to said. Jorge said, time is a tiger. People talk about time as a thread or a ladder. Apparently we can't talk about time except in metaphors. What's fantastic about the river metaphor is it makes no sense whatsoever.

That is, if time is a river, are you in the river floating along, flowing with time or are you standing on the bank watching as time goes by? We say all of that and we say we, we start to speak of time as a quantity. And if it's a quantity, it's a quantity that you can save or waste or put in the bank or spend or pass. So many science fiction writers, philosophers, and now physicists are struggling with it and that's what makes it so much fun for me.

I have the luxury not being a scientist of not having to be too anxious about what I see as sciences failure really to come to any final answer. Not that I believe science should attempt a final answer for that. I think that's enough metaphors.

David Krakauer (9m 54s): Good, they're good, they're strong. Ted, how about you? Do you have afavorite?

Ted Chiang (9m 57s): So I guess one metaphor that I'd like to mention, which is not to say that like I actually viewed the world through it, but I read about the Amhara culture where their perception of time runs counter to the ones that sort of we are most commonly familiar with in the West. Cuz in the west we think of, you know, the future lies ahead of us and the past lies behind us. But apparently the Amhara, they have it the other way round. They think the metaphor in their language is that the future is this way and the past is this way. And you know, at one level this actually makes a lot more sense because you can see what's ahead of you and we know the past, whereas we can't see what's behind us and we don't know the future.

In that sense, that metaphor actually makes a lot more sense than our metaphor. To most of us when we first hear this, we like, that's weird cuz it seems like we're then you're like walking backwards or something. But again, you know, like that's because we associate movement through time as being, you know, analogous to physical movement. The fact that we even call it movement through time is a physical analogy. And so when I try and time that way, you know, it's like maybe I'm standing still and time is flowing past me and like as more of it comes into view that sort of makes sense. But again, you know, it runs very counter to the standard metaphors that we have in western society in the languages that we are most familiar with.

So like I said, you know, it's not a metaphor that I am really able to internalize, but it's one that I think is really interesting and worth thinking about as a way of reminding us of how culturally bound our sort of common conception of time is.

David Krakauer (11m 30s): Thank you.

David Wolpert (11m 31s): I would try to dig deeper there. There's a huge number of metaphors. So what is the commonality? What is the hidden seed underneath from which all of these sprout to elaborate part of what we know from general relativity, this lock model concerning this, I would actually start by disentangling a little bit. Two of the metaphors that Ted mentioned that you know the past and not the future and it appears as though you're moving across time.

Time does not move. That's very simple physics. For you to move one variable across another when you graph something on a piece of paper, you need to have two dimensions. The movement is that this one is changing at this particular rate of speed or what have you compared to that one down there. So there you've got two variables, position versus in that case position. Time is something with a single variable. So there's got to be something so there's no such notion of time we don't have, here is a present and here is time.

We don't have the two variables. So what might cause us to distort our understanding so that we are forced to rely on metaphors. And I think that Ted actually touched on what is in many ways the fundamental answer. We know the past and not the future. Build on that. We have memories to be a little bit more precise. Sometimes they're called records in the literature of the past. None in the future. Dig further.

What do we mean when we say a memory versus something like a prediction? A memory, both of them are just statistical probabilistic assessments of something in the past, your memories could be wrong. I'm not talking about a brain, the that kind of a thing. I'm just saying in general, it's a statistical inference you're making, you're viewing something here, a footprint on a beach, a photograph on a piece of film, a crater on the moon. And from that you're making some statistical prediction about something that was in the past based upon what you're seeing right now.

And it's got some probably of being wrong. We also make predictions about the future based upon what we see now and I'll leave it here. But I think that a large part of the reason that we are forced to resort to so many different metaphors which vary across all these cultures, actually if you dig down, is got to do with why our memory of the past, our retrodiction, rather than our prediction is so much more accurate than our memory of the future.

There are reasons to believe that physics actually provides the answer, but I would say that asymmetry is the cause of all the rest of it. And the metaphors, the art, the beauty arises from our not being able to internalize all of that.

David Krakauer (14m 36s): This is an early morning challenge. So, let me expand a little bit. One of the big representational dichotomies and sort of David is alluding to that is the narrative versus the geometric. And sometimes these get called type A theories versus type B theories of time type a time is tense, conjugated, grammatical time. It says as a present, a future in a past, the past exists did exist at best it's a memory, the present is the only thing that's real and the future is potentiality.

That's in distinction to this other time that David might be alluding to, which is Minkowski 40 space time where everything exists, it's a static universe and you just move through the world line and that's your experience of time. And the question then becomes, and we'll get to it later, why you move in a preferred direction. And this, and I wondered, James, you write about it a bit, there was a big debate in 1922 in Paris. It wasn't really a debate, it was really a talk that Einstein gave and Bergson was there and objected to this 4D spacetime block universe.

And the main basis of objection came from this book, 

Creative Evolution

, there's no novel to your Einstein's universe, there's no invention. But do you wanna talk about the debate a bit and where youstand?

James Gleick (15m 53s): Yes. So the debate was, there's a wonderful book about the argument between Bergson and Einstein by Jimena Canales. So I, I should point to that book before I say anything else about it. But this debate in 1922 was a kind of, if it was a turning point, it was a moment where I think looking back we can say that the physicists were taking charge and leaving behind the philosophers, not leaving them behind, burying the philosophers and psychologists who up until that time had been our, let's say, academic specialists on the subject of time.

It wasn't automatic through history that if you wanted to know, if you wanted to talk about time representations of time or the complexity of time, you would talk to a physicist. Newton of course had his view of time which was actually that it flows. Even Newton use resorted to that metaphor in his most famous statement about time that it flows equitably. And Newton himself understood the difference between that mathematical time that he was inventing or defining for the first time and the psychological time that we're all familiar with, all aware of the funny, complicated things that happen that time seems to go faster when you're having fun or is it the other way around? Or when and when you get older the years flash by and when you're young and our seems like a month. Bergson was trying to preserve some of that, was trying to defend time from what he thought was a reductionist, narrower imprisoning view of the physicist of Einstein. Which was, which is what David called the block universe view. In a way, should I resort to HG Wells or should I save that?

David Krakauer (17m 36s): Save HGWells?

James Gleick (17m 37s): I'll save that. I wanna say that this, the idea that we distinguish between the past and the future by saying that we have memories of the past and we only anticipate the future, the present moment is something very special to us. It's the only moment that feels real. That's what Bergson would say. But Einstein would say that's an illusion. The present moment means nothing in physics. His four-dimensional spacetime continuum, his block universe treated time as though were merely another dimension like the other three.

And the whole universe is to be viewed by physicists as existing, now, a word that has no meaning in Einstein's view. And very famously, a few weeks before Einstein died, when he was consoling a grieving friend after someone else's death, he said, we who understand physics, we who believe in physics, he said, believe in physics, not understand, know that the distinction between past and  future is just a stubborn, a stubbornly persistent illusion.

David Krakauer (18m 45s): So on that topic, let's turn to Ted's 

Story of Your Life

. So cuz it touches on this very beautifully I think and I think that, so just again, just to get people keyed into this, so in physics there are two equivalent representations of trajectory through, through time and space. The Newtonian, which you will learn in school or some of you might have, where you write down the coordinates and it's causal. And sorry, could you say that again? Oh, that's Siri. And so and say that again. Okay. Obviously wasn't clear enough.

And then the other representation that comes from Mobius originally the sometimes called the principle least action, the Hamiltonian formalism is an alternative representation of a trajectory. But in this case you have to know exactly where you start and where you end. And so this is something that everyone learns, these are equivalent mathematical frameworks. The latter is much more elegant actually. And Ted turned it into as so as I can see, he took this idea, which is quite esoteric and he turned it into a language that heptapods speak.

And if you remember the beautiful illustrations in the film, seismograms, is that right? It's an action. So I'm just wondering Ted, where that came from, how you immersed yourself in classical mechanics and then came to this idea that the action principle could be the basis of a very touching narrative.

Ted Chiang (20m 3s): So yeah, when I was, when I was in high school, I was reading an explanation of these variational principles physics and yeah, to just to restate what David was saying but up until then, you know, my conception of physics was that you know, you look at an object, what's its position, what's its velocity? Then you know, based on that, where it's gonna be in the future and with its position and its new velocity, then you can, you know, keep going. And with variational principles it works other way. Like you know where the object is right now and you know where it's gonna be at the end.

And based on those you can tell the entire path it's gonna take in between. And I was like that that kind of blew my mind that this was possible. And it turns out that they are actually mathematically equivalent. But yeah, the idea that like, oh you are like if you know, if you can fully specify like the beginning point and the end point that you can determine everything in between, it's like that was just so fascinating to me. And you know, for a longest time I just wanted to talk about it and I had, you know, I had this vague desire like is there a way I can use this to tell a story?

Can I write a science fiction story that illuminates this idea? And you know, it didn't seem possible so, you know, it wasn't really something I was intentionally working on. And then, you know, just purely by chance I was watching a one man show, a solo performance where this man was talking about he was giving a performance about an experience of his wife dying from cancer and both of 'em knew how it was gonna end cuz you know, it was clear what was gonna happen and and it's an incredibly moving piece and, but yeah, while I was watching it, I had this idea that maybe I could use this, I could tell a story about this idea, this physics idea and tie it to this emotional story about you know, like knowing how the story ends.

And so that eventually became 

A Story of Your Life

. And you know, in the course of writing it, I then learned more at linguistics and this idea and linguistics of what they call performative language. Most linguistic utterances are communicative where you are conveying information but there are these utterances which are performative in that you speak in order to actually perform an action. And some like classic examples are like I now pronounce you husband and wife, you're like, you can't actually marry people unless you actually say it.

You have to say it to actually commit the act of marrying people or things like I christened this ship, you know the Santa Maria or something. You can't do it without saying it. You can't do it like just quietly. You have to say it in order to do it. And so that I also thought was like a very interesting idea of this way of acting through language and that seemed like that could also feed into this story I had in mind about an alien species. They see time a different way, they speak language a different way and that you know, all feeds into this story about and in individual's story about loss.

David Krakauer (23m 5s): So, and I asked David a difficult question now, which is, so Ted's 

Story of Your Life 

is classical action, it's not quantum action. And I wonder Ted, if you had to rewrite that story based on the path integral, we're not there. So, so in classical action there's one path and you integrate the lagrangian and as Ted said, you get these equivalent representations of the optimal trajectory in a field like a gravitational field. But in 1933 Dirac said what happens if you do that with quantum mechanics?

And then Feynman famously presented as his framework for this. And the idea there is in the quantum domain you have to sum over an infinite number of weighted probabilistic trajectories, random walks. What happens, David, to Ted's narrative when you do quantum action?

David Wolpert (23m 53s): Quantum mechanics is time symmetric. The underlying basis for the least action principle and for this notion that as far as physics is concerned, what was underlying Einstein and if Newton had been up to the task, what he would've seen as well, all of these equations are time symmetric. They can go forward where they can go backward and you can reformulate quantum mechanics in a completely time symmetric way. It depends ultimately and making sure that you define your system so that it is isolated from the outside world, evolving according to what it's called a unitary evolution and you can go backwards and forwards.

There is no difference. Part of the reason that this is very important, the question you raise part of, there are many reasons why I found Ted's story, which I read. I think, let's see, I wasn't in high school but when I was very young as I read his story, which I guess had his genesis when he was young, is precisely because it indirectly draws attention to this question of why is it that we as opposed to the aliens feel that we know the past and not the future? What science properly speaking should be to get back to your hedonism statement at the very beginning of all this, it really amounts to the four-year-old child who says “why?” and so on so forth. So we're right now talking perhaps a little bit more than metaphor about maybe in the block universe. It all boils down to the fact that we think we have more accurate retrodiction than prediction. But if you really drill into that, if you think about just where the word memory is used, in some situations, like for example the memories that are in this little toy, this little bauble, those are actually completely time symmetric memory in the sense of the ram in your phone.

In that tablet you're looking can actually provide you just as accurate information about the future as it does about the past. If you actually drill down into it by mathematically formalizing it. Other memories like a footprint on a beach do not have that character. You look at that footprint on the beach, you're not gonna come to conclusions about the future, you're gonna come to some conclusions about the past. So, why? What is the basis for those second types of memory which are actually distinct from the first one?

What is it about things like a footprint on the beach or the crater on the moon that allows us to so confidently retrodict that somebody walked on that beach that some meteorite hit that moon in a way that we cannot for the future. And that actually ties in with a whole other body of physics that was, Einstein was involved there too, the guy got around but is mostly associated with other practitioners going back over a century or so, which is statistical physics.

David Krakauer (26m 50s): Yeah, we're gonna get there, we're gonna go to hour of time in a bit. I'm trying to stay a little bit classical, but let me ask this question then you dodge my question David, I just wanna point something out to you. You didn't explain what Ted goes, you know,

David Wolpert (27m 3s): That's what a good interviewer interaction.

David Krakauer (27m 5s): You didn't do it at all. Okay, that's okay. But I did wanna ask this question and I would like to ask Jane, since you did write the biography of Feynman, whether you ever spoke to him on some of these topics, but before I do that, why is it, so you talk about in your book time travel, you do talk about Proust and you talk about Henry James' last book, his 

Edwin Drood

, his unpublished book on time travel, which is a bit like some of Ted's stories actually I think in its intention. But why did time, why is time so given that it's so existentially central, why is it so carefully treated in science fiction and not particularly expansively treated in literary fiction?

Proust is of course a good case, but it's canonical memory, it's not counterfactual. Why do you think that happened? I don't know if either of you have ideas.

James Gleick (27m 53s): I think I would argue with that. I don't think that's quite true. It is true that if we want to draw a line between science fiction and literary fiction and we do that without offending you. No I don't, I don't, I don't actually, I don't believe in that line but we all know what we mean by it and, and it is true that science fiction has talked about time in the last century and a century in a quarter, let's say in a much freer way, in a much crazier, freakish way than at literary fiction has.

But I guess what I would say is that everybody around the time that people started thinking about time travel around the turn of the previous century was thinking about time in more complex and richer ways. And they were doing that for all sorts of cultural reasons to do with railroads and clocks and the development of geology that expanded our sense of real time scales and archeology, which was digging up the past in the most vivid way.

All of these things were making people think about time in more complex ways. And the fact that you think about Proust immediately, he's the right person to think about. And not just because his book is called 

In Search of Lost Time

. He is so explicitly writing about time and inextricably about memory. He is using memory in we don't need to do literary criticism here, but the complexity of his treatment of memory is really something new in literature, which I think brings us back to if it's all right to Ted and David because they both are talking this crucial fact that on the one hand a physicist can think in terms of the Einstein space time continuum in which the present is an illusion and has no particular privileged reality.

But on the other hand, here we are and I say now and we feel now slipping away into the past and we feel intuitively that our memory of the past is something different from our anticipation of the future. I know you're arguing that it's not necessarily qualitatively different or I think you are cuz it's all on the iPhone. What's extraordinary about Ted's story, if I can spoil it some more, is that he takes seriously the possibility that Einstein is right that the universe is determined that the future already exists and asks what if you could have memories of the future that felt just like memories of the past. And for me that's just first it's baffling, then it's annoying because I don't believe in that and then it's incredibly powerful because you really make it so convincing. That is, if you don't believe in a deterministic universe, if you believe in free will, if you believe that we're making choices, I think you can ask what would it feel like to actually have memories of the future and be aware that I don't have free will, that everything I do is, as Ted says in the story, is like an actor reciting lines and could you live that way particularly could you live that way in the face of an oncoming terrible tragedy.

And so actually the question I really want to ask you, but it's possibly unfair is do you actually believe that the world could be like that? You made it so convincing.

Ted Chiang (31m 27s): I guess I, and I think we'll probably talk about this a little more later in the panel, but for now I'll just say, I guess I find Einstein's argument convincing. And so I do believe in a block universe and whether that reflects my lack of sophistication or whatever, but yeah, Einstein convinced me about the block universe. So the implications of that for our, you know, daily life I think are in general not significant I think. But again, we can probably talk about that a little more later.

David Krakauer (31m 53s): Later. I mean let's talk about, so let's to remind everyone who doesn't remember Block universe is the Minkowski 4D space time. So the spatialization of time, and this has been very criticized recently. So this is the idea that you just take time and represent it geometrically. Okay? And one of the consequences of doing that is geometry as a tropic, right? That doesn't matter which way you walk. I can walk over there and I can walk over there, but in time I can't just move around in time. Ted's heptapods can in a certain way, they live at all points in time. But this is this, that's what the block universe is, it's the geometric universe and you need another theory which David is alluding to, which we'll get to, which is Edington's hour of time statistical mechanics to give polarity to your, to the world line.

But I don't know, David, do you want to, I want you to introduce an alternative and I dunno how much you know about. So it's the Girdle metric. So when Einstein at the end of his life was becoming very misanthropic and annoyed that he hadn't achieved a grand unified theory, the only person you'd ever spend any time with that he enjoyed was Kurt Girdle. And they'd walked back and forth in Princeton and girdle had solved the Einstein field equation and one of the solution that Girdle came up with very famous cuz it gives something called closed time like curves. So the possibility of time travel.

And I'm just wondering is that something David, you know, anything about or thought

David Wolpert (33m 9s): About? Yeah to my courses in gr. So actually Girdle was not the first he was, there were others who had come up with solution to Einstein's equations which allowed for close timeline curves. They did not recognize it as such. And the Girdle universe, Einstein's equations are do you want me to talk a little bit about what a little bit, okay, so Einstein's equation, people I assume are glancingly familiar at least with Newton's equations, F equals M and so on.

You write down derivatives if you are so brave as to take your senior lyric calculus and then that provides you a machinery that you can, let's say, okay, if I know the starting conditions or if I know the ending conditions or so on of a system, I can then solve first exact state everywhere else across the entire space or whatever my differential equations consider. What's called sometimes you'll read what's called Einstein's equations, they are an extension in a certain sense of Newton's equations that are the basis of general relativity.

They unlike Newton's equations, they are expletives have deleted, I believe you had a nice quixotic beep in your presentation concerning expletives being deleted. They are an experts have deleted to solve, they are very difficult to solve to this day. That's a major problem with people doing things like black hole physics, what's called the information paradox, which is still a very active field of research. Girdle found a particular solution, that solution to Einstein's equation.

So this possibility for how the universe could, according to the laws of the universe have been constituent was an infinite universe that actually has a uniform density of gruel of gas everywhere to prevent that universe from actually collapsing under gravitational attraction. It's rotating in a nice cool general relativistic way. It actually, every single point in the universe sees it is rotating about itself.

So every point is actually the same. These are valid solutions and they have in them this rather strange property of what's called a closed timelike curve. That means that there's actually an infinite number of spots you can go to where if you just accelerate your rocket in the correct way, you're never going faster than the speed of light or anything like that, you will eventually go and everything will just keep changing in front of you until you start seeing this weird guy sitting on a stage with three other weird, I noticed we're all guys on the same stage and you'll come in and see this person from their past.

So rather than just traveling around and going down over to farmer's market, you'll go traveling around and where you end up with is exactly where you started. And of course this has become a trope indirectly in many science fiction films and so on and so forth. I think like the Matrix movies had this kind of stuff built into a lot of them and so on and so forth. The question then is what are the implications of that? And as I say, there are more realistic models of universes that were constructed before Girdle and actually after Girdle as well.

There's what are called tipler cylinders and a whole bunch of things. There are actually other ways to construct these closed timelike curves. Girdle had some weird ideas about what time is that are essentially elaboration of cottian distinctions between what's called synthetic and analytic. And it's hard to really make sense of them. But from a certain perspective, the consensus in the physics community now I would say consensus, at least a large fraction of the people who are working in cosmology is that the possibility of closed time like curves really if you, they are loath to phrase it this way, but what that amounts to is the fait accomplicase closed.

That free will is just a delusion grow up you young, immature humans, there ain't no such thing. Free will in fact is itself a variation of this metaphor, of this perception that time is moving forward. If you don't view time as unfolding in this way, notion of free will loses all strength, it loses all traction. This is actually inherent in the block universe, arguably close time like curves make the case done. Or else you get these silly things like the grandfather paradox or the grandmother paradox or what have you, that you go back into the past, you destroy your parents so therefore you could not have existed.

And oh, paradox, if you don't have this notion of free will instead all of reality into all the future and all of the past and all of different points in space is all just a solution to the equation, then you just got a solution. It's sitting there, it's a static object. There's no sense in which you could go along a world line and make a decision with some freedom to undo what was there in the past. No, it's all going to be consistent.

David Krakauer (38m 22s): Okay, so let me just quickly ask quick here about, since we started a bit late and then we'll just open it up HG Wells cause I know you wanna talk about HG Wells and then also the 

Merchant in the Alchemist Gate 

because these are two wonderful time travel narrative. So the 

Time Machine

, which I don't particularly love, you seem to love it. And then your particular treatment of time travel.

James Gleick (38m 44s): All right, I wanted to also respond to all of

David Krakauer (38m 46s): That. Do it, yeah, we'll do that first and then we'll then do a little response.

James Gleick (38m 49s): All right, so do I love the 

Time Machine

. Has anybody, actually everybody thinks they've read the 

Time Machine

, so I won't ask you if you've read it. Have, has anybody read the 

Time Machine 

recently? One hand, two hands. It's not easy to read. I was actually a little shocked, a little depressed when I went back to it. One of the things that makes it not a particularly I think artfully constructed story is that the way it begins is with a bunch of people sitting around talking and they're actually, I should say a bunch of people sitting around listening cuz the guy who's doing all the talking is the guy who HG Wells calls only the time traveler.

He has no name. And what he does at the outset of this story to lay the groundwork for it is explain to them that everything they have always known about geometry is wrong. They've thought there are just three dimensions that this object, I can't hold it up and talk into it at the same time it has height, width, and length. But he also says, if you think about it, it has a fourth dimension, it has duration because if it didn't have duration it wouldn't exist and so on.

He goes on to lay out what we now recognize as the block universe picture that Einstein created 10 years later. Nobody's gonna claim that Einstein got it from HG Wells. But I think we can at least admit that there was something in the air that was leading people to think, I guess some people would say the smoke was clearing and our illusions were fading away and we were seeing the universe as it really is. But you can also say that people were starting to find this an interesting and convenient way to think about the universe.

David Krakauer (40m 30s): 1895, 1895

James Gleick (40m 32s): Or so, this is where it started. We can call it the Einstein Minkovski Block Universe, but it's really HG Wellses, right?

David Wolpert (40m 40s): Actually I would say it goes earlier than that's Boltzmann and Loschmidtand things like that. In any case.

David Krakauer (40m 46s): How about you talk about your story or most explicit time travel story as being inspired by a talk by Kip Thorne.

Ted Chiang (40m 53s): Actually before I get there I'd like to rebut.

Ted Chiang (40m 56s): I know that you've said that you know HG Wells, you know, invented the idea of time travel and that you've said that it's odd that before HG Wells no one ever wondered about, you know, the possibility of, you know, going back and you know, fixing a mistake that they had in their past.

James Gleick (41m 11s): No, not quite. That's putting my claim a little more strongly than I think I made it. But go ahead. I know there are lots of counterexamples of things that time tap travelers things before Wells.

Ted Chiang (41m 23s): But, so I guess this is all leading up to 


. Yes, but so I think that time travel stories are actually a modern version of a very old kind of story and that is prophecy stories and you know, we don't usually think of them as being the same, but they actually, you know, I think in a lot of ways they are, because I think any physicists will say that, you know, sending matter back in time is the same thing as sending information back in time. It's, you know, it's pretty much the same issue. And so prophecy stories, they are stories about information moving backward in time. It's just that the perspective is different. They're told from the point of view of the person receiving the information from the future.

So, and real prophecy stories, they're really old, they go back thousands of years. So you know, I think of them as, you know, this sort of antecedent of time travel stories that are almost as old as storytelling. But the thing is that all prophecy stories of old that I'm aware of, someone gets a prophecy of something that'll happen in their future. They take steps to avert it and then they what the steps they've taken merely bring about the prophecy they cause it to come true. So prophecy stories all have this, you know, these classic prophecy stories, they all have this commonality where getting knowledge from the future does not help you avoid that future.

And so I think that you'll as a step along the evolution to time travel stories, if you don't believe that you can change your future, it's certainly not gonna occur to you that you could change your past. I think the big turning point comes actually in like around 1830 when Dickens publishes a 

Christmas Carol 

because in a 

Christmas Carol 

Ebenezer Scrooge, he gets a prophecy. He has shown his death and he doesn't like what he sees. You go cuz he's unmourned, you know, no one has a good thing to say about him. And he says to the spirit, you know, the spirit of Christmas yet to come.

He says, what you've shown me are these shadows of what will be, or shadows of what may be. And so like he's basically asking, do I have free will? Can I do anything about this? And when he wakes up, he changes his life. He sets about to make sure that what he has seen does not come to pass and it's, it is implied that he is successful. And so I believe that this is the first time in literature where someone, a character received a prophecy about the future and was able to avert the future that they saw. So they got information from the future and they used it to prevent that future from coming to pass.

So I think that is, you know, a literary indicator of a shift away from, you know, this popular belief that we had, that we were bound by fate and toward a belief that like we can actually make decisions that make a difference. We can actually control our destiny, we can change our life, we can be, you can be a better person. And so once you start thinking that way, then it is possible to think about time travel because then you start thinking about like, I can change what will happen. And you know, and the odd thing is, you know, HG Wells' story never touches on this at all cuz the time traveler, at one point he meets this woman and she dies in a fire and like it never occurs to him you do have a time machine, you could go back and maybe rescue her from being, you know, killed in a fire, never occurs to him. And like when he goes back to Victorian England, he's seen the future and it's terrible. Like doesn't seem to occur to him. Like maybe you could do something to prevent that, that future from coming to pass. But, but yeah, I think like gradually, you know, we start moving into a way of thinking where it's like, you know, I can change things. I have agency, I can make decisions that will have a difference. And that's where you get the bulk of modern time travel stories. So the thing with, so to get to

Merchant Alchemist Gate

, if you think about contemporary time travel stories, if you divide them into, you know, stories where it is not possible to change history and stories where it is possible to change history and usually the stories where it's not possible to change history, those are downbeat stories.

There's tragedies, you know, it's like, you know, we traveled their time, we tried to do this thing and we failed. Whereas stories where you can change history, they're seen as victories, there's like, we traveled through time, we made a change, things are better. And so there's this real sort of, you know, sad ending, happy ending dichotomy that correlates to the ability to change in the inability or ability to change the past. And so what I was interested in is, can I tell a story where it is not possible to change the past? Can I tell a time travel story where it's not possible to change the past but it's not a tragedy, it's not a downbeat ending.

The fact that you cannot change the past, that is something that I was, you know, what does a story like that look like? And you know, in a sense I think that is, you know, we are starting to see that as a type the assertive, a subcategory of time travel stories. If you've watched the Netflix series, 

Russian Doll 

season two of 

Russian Doll 

is actually this the same message that you know about time travel, but you can't actually change things. And I think, you know, this type of time travel story, it has what it, in some ways it carries the same message as, as a lot of therapy does, which is that you cannot change what happened to you, but maybe you can change the effect of what happened to you on you right now.

Yeah, that's, and I think is something that therapists always try to tell people, yeah you can't change what happened to you but maybe you can change the effect it has on you. And so that I think is the message of, you know, the sort of news category of time travel story. 

David Krakauer (46m 28s): Thank you. I know we have to, I know we're bit late, I know I'm being looked at over there and we are opening this up a bit. I'm not quite sure how we've reset timer. But I do think this makes a really interesting point about one of the things that Ted brings to bear in all, and if you've not read the stories you should is this very interesting on the one hand exploration of the union of existential narrative and the structure of scientific theory. I think it's way beyond HG Wells actually in terms of what he's actually done in combining human sensibility and analytical sensibility.

But with that point, I would like to open it up to question got any of them then we'll spread it around the panel. There's a question back there.

Question #1 (47m 9s): I'd like to ask the panelists, I am not a mathematician, I have background in physics, so this is not a concept I understand, but with regard to the block universe, I've read just in the popular press about the idea of in intuitionist mathematics, which refutes the idea of the objective existence of infinite precision numbers, which is what you require for an absolutist block universe. My naive understanding is that this was an idea put forth by radical splinter sector of mathematicians who lost a fight with David Hilbert in the early 20th century.

I would love to hear the panel's thoughts on whether there's anything to this idea.

David Wolpert (47m 43s): Should I take it, take the investment? I feel the the early ones, oh they're going talk all about my 

Connecticut King Arthur's Court 

very explicitly time travel and true,

James Gleick (47m 54s): Yeah, two years before HG Wells. Yeah, explicitly time travel except, do you remember what the technology of time travel is in the story?

James Gleick (48m 3s): Sleeping, he gets banged on the head. Yeah, he gets into a fight and gets whacked on the head. I don't wanna say that. No,

James Gleick (48m 8s): Oh okay. Cause I do response. I have so much to say about the Connecticut. Alright, now go ahead. I have nothing to say intuition

David Wolpert (48m 15s): There, which is that there's a very crucial role played by prediction, predicting gonna be lunar eclipse, which of course is a really big deal if you go back to Babylon and so on and so forth. And Ted was raising some very interesting points. Some of them have to do with information. Information is formally at its foundation all about probabilities. Prediction is all about probabilities. And actually a very good example of the difference between memory retrodiction and prediction is that there are some things, there are some memories we have of the future that aren't quite accurate, things like eclipses the sunrise and so on and so forth. But they have a different nature and it's very challenging ongoing work actually in foundations of physics to elucidate this of what is it that's the difference about those kinds of predictions from the other kinds of transfers of information from one moment to a time retrodictions, which we recall memory. So back over there, sorry, I had to get that in, had to get that in license of somebody who's got the mic. So I believe you're referring to Brouwer, intuitionist mathematics and then Nicholas Gisin in particular, some of his recent hypothesizing so and so forth.

So this actually touches on different projects of mine. But in mathematics and the foundations of mathematics are actually very many different types of logic. Philosophers of mathematics work on these things a lot. People here think that they know what logical versus illogical is, but there's actually nothing close to receive consensus about this. What is being referred to over there started primarily with Brouwer. I believe a brilliant mathematician is called intuitionist mathematics. Among other things, you don't assume the law of the excluded middle.

You allow both A and not A, you allow it to be both the case that David Krakauer is on this stage and he's not on the stage. So it is not a view of the what yours allowable in terms of logic that I subscribe to by many, but it is subscribed to by some. And Nicholas Gisin is I believe he's primarily a high energy theorist Italian I think who has recently hypothesized sort of building on intuition that maybe actually when you look at the successive digits of a real number that you're measuring and experimental in an experimental situation that each new digit is not so to speak preordained and you are just learning it.

But it is constructed sarcastically on the fly. That work has not been elaborated and drilled down really behind high level conceptualizing in terms of what its implications might be of if you just reversed because he's not anywhere that I've seen at least hypothesize that there might be time asymmetries in the foundations of physics. So all of this will be just as true going backwards as forwards.

But so it is a very interesting question that there are these notions that reality is constructed as we go forward, which are mathematically allowed so to speak if you just adopt a, the appropriate flavors of logic. But nobody yet has actually certainly experimentally established that there's any sense in which they apply to us. It's like a Girdle universe in that it's allowed, but it's very clear that we do not live in a Girdle universe.

I don't know if that's actually answering your question or not. 

David Krakauer (51m 51s): Okay, thank you. David was not easy question some, do we have another question? I see one up front and then maybe, oh, Austin has the mic.

Question #2 (51m 58s): Have the microphone?

David Krakauer (51m 59s): You have the mic.

Question #2 (52m 1s): So I have a question about the block universe. So we had like a fleeting mansion of the criticism, right, that lacks novelty, but subjective novelty is definitely not a criticism because it is just a description, subjective description of a transition in this block universe I would imagine, right? But saying that the universe lacks novelty as a criticism against model is just, I don't want it to be this way. So I was wondering other, any legitimate criticisms, right? 

David Krakauer (52m 29s): Just say quickly. I think that, and again let's have opinions on this, I think all the, I think it's something irrefutable and it would be because it's arbitrary dimensionality, it's the usual solution to the problem of novelty, which is just opening up another dimension. So it's cheat. I think Bergson was just more interested in the psychological fact that people make discoveries. So another way of saying this is that physics time is inadequate to explain the psychological time. And for that you need the second law. And everything that we do at SFI complexity, it's new concepts of time that go way beyond physical concepts of time, but they sit on physical concepts.

So it's a just a different, I think it's a different world actually, not a physical.

James Gleick (53m 9s): Yeah, I think that's right. And I think you must be disappointed that we've gotten to this point in the discussion and the word entropy has not even.

James Gleick (53m 16s): I could have appeared. You're relieved. My answer to the question is that I don't refute the block universe. How could I, how would I dare I complete, I accept that this is one of the most powerful, if not the most powerful conceptions that physics has given us in the past century. But it's not an explanation for everything. It applies in its domain. I think you're allowed to believe that the block universe model, the Einsteinian space time continuum is a fantastic model of physics that that allows scientists to make very accurate predictions about a broad range of phenomena, but not about everything.

It rules out, as David to my left said, any notion of free will. You can't accept that as a complete description of reality and also believe that free will has any meaning. But beyond that, I would say it rules out practically every direction of research that is done at the Santa Fe Institute. 

James Gleick (54m 18s): No, it's not relevant. Yeah, that is, if you're, if you want to subtract time from your worldview, if you wanna say that there is no meaningful difference between the past and the future, if you wanna say that the concept of the present and the concept of chain is just an illusion, then what most scientists do has no particular use.

David Krakauer (54m 39s): Yeah. Let me just open up, sorry, I don't know. I just wanna make sure that we get a question in over here. There's a, can we have a mic just right there? Thank you. Sorry.

Ted Chiang (54m 46s): Yeah, so I'm thinking about, there's a version of time travel where there is just one you and you go and inhabit yourself in another time. And then there's a version where you get doubled up and you can, you know, be both on the stage and then watching yourself on the stage. And I'm curious if there's any distinction between them mathematically.

Ted Chiang (55m 4s): So I think the you'll, those are just two narrative, you know, tropes. I think the physics, you know, the only one that has any kind of physical justification would be the one where you're doubled up. The idea that if you travel back in time and then you'll wind up in your same body. That I think exists purely as a, a narrative convention. And it has, I think it's a kind of a result of the fact that I think most time travel stories are actually about free will. And so in order to better tell a story about free will it is easier to send your time traveler back into their same body so that they can, you know, actually, you know, exert their will. But yeah, it's I think just a narrative trope. There's no basis for us in physics.

David Krakauer (55m 48s): The next question, or wait one more question, but this question has to be about entropy because you can't talk about time from our point of view. James wrote a book called The Information. Ted has a beautiful story on the heat death of the universe, exhalation. All of David's work is based in some sense on the air of time. This question has to be entropy. Andres, this has to be entropy.

Ted Chiang (56m 10s): So you talked about the close time like curves, and we know from second law, thermodynamics of entropy breaks the symmetry of time. Isn't this a paradox? If I'm in a, okay, so maybe I'm completely misunderstanding, but it seems like a paradox to me. If I get started at a point and I follow trajectory and then come back to the same position and the time and then my entropy is higher now, but it shouldn't be the same?

David Wolpert (56m 34s): Should I feel this way? Yeah. By the way, just to elaborate a point before, I wouldn't say that the block universe is actually the foundation for what the SFI does. It's not that it's actually irrelevant, it's the starting point. It is incomplete almost in the sense of like Girdles’, incompleteness, serums in that it does not have anything to do with the psychology, with innovation, with all that we focus on, which is certainly true and real, and going back to the foundations of the SFI, it's like the SFI does not somehow refute the laws of quantum mechanics in physics.

It's just saying there's a whole bunch of stuff. Everything and more is different and we need to investigate all that as well. So the block universe is real and true and is not at some sense at odds. It's actually the starting point. To get to Andres's question there was, for example, it's now not so popular, but there was a kind of a universe, a cosmology that is a solution to Einstein's equation where it's periodic that you have a, yeah, the big bang in the past. And by the way, here's a mind bender for people out there. The fact that time seems to you to be going forward, that we seem to have memories that we can look backwards but not forwards with the same accuracy.

That ultimately the current consensus is that's a residue, that's a proof within your conceptions as you wake up in the morning. That there was a big bang 13 billion years ago, which the universe had minimal entropy. So if you want to have your brain get blown up every time you wake up in the morning, that's a good thought to have in there. But so anyway, under the periodic universe, there was a big bang in our past. And there's also a big crunch in the future, and this is actually still, some people talk about this actually, Sean Carroll, who's SFI is he Miller or External?

Fractal? Fractal. Fractal. He has had some ruminations concerning that you run into a same kind of so the idea here is that the universe started at the society. We essence started a white hole, so to speak, 13 billion years ago. And we are now just exploding outwards, but that eventually we get as far as we can. And then we just go through, in essence, a time reversed version of things to hit a big crunch, some number of billions of years into the future. There's an obvious question about what happens right in the middle. If as I just globally threw out there, the reason that we think that time feels like it's going forward to us the second law, the thermodynamic era of time, is due to this big bang in our relatively recent past. Presumably over in the big crunch side of things, time will seem according to the second law, in all the senses in which we have been discussing today, to be going in the opposite direction. So what the blankety blank happens in the middle, and this actually gets to other issues which I will shut up and not get into, which is how you can actually have the time asymmetric second law in a time symmetric universe in a certain sense, that is the essence of the SFI’s mission.

Just instantiated in all these other systems and how you actually derive the second law and so on, is a very subtle, deep, super cool issue, not leave it at that.

David Krakauer (59m 46s): So thank you very much, panelists. Thank you very much. And I So how's this now working given the schedule's been completely messed up by us?

Michael Garfield (59m 55s): Thank you for listening. Complexity is produced by the Santa Fe Institute, a nonprofit hub for complex system science located in the high desert of New Mexico. For more information, including transcripts, research links, and educational resources, or to support our science and communication efforts, visit