Time Is Way Weirder Than You Think

It’s not an exaggeration to say that “clock time” runs our lives. From the moment our alarms go off in the morning, the clock reigns supreme: our meetings, our appointments, even our social plans are often timed down to the minute. We even measure the quality of our lives with reference to time, often lamenting that time seems to “fly by” when we’re having fun and “drags on” when we’re bored or stagnant. We rarely stop to think about time, but that’s precisely because there are few forces more omnipresent in our lives. “You are the best time machine that has ever been built,” Dean Buonomano writes in his book “Your Brain Is a Time Machine: The Neuroscience and Physics of Time.” Buonomano is a professor of neurobiology and psychology at U. C. L. A. who studies the relationship between time and the human brain. His book tackles the most profound questions about time that affect all of our lives: Why do we feel it so differently at different points in our lives? What do we miss if we live so rigidly bound to the demands of our clocks and appointments? Why during strange periods like pandemic lockdowns do we feel “lost in time”? And what if — as some physicists believe — the future may already exist, with grave implications for our ability to act meaningfully in the present? We discuss what time would be in an empty universe without humans, why humans have not evolved to understand time the way we understand space, how our ability to predict the future differs from animals’, why time during the Covid lockdowns felt so bizarre, why scientists think time “flies” when we’re having fun but slows down when people experience near-death accidents, what humans lost when we invented very precise clocks, why some physicists believe the future is already determined for us and what that would mean for our ethical behavior, why we’re so bad at saving money, what steps we could take to feel as if we’re living longer in time, why it’s so hard — but ultimately possible — to live in the present moment and more. Mentioned:Don’t Sleep, There Are Snakes by Daniel L. Everett Book Recommendations: Noise by Daniel Kahneman, Olivier Sibony and Cass R. Sunstein When We Cease to Understand the World by Benjamin Labatut The Age of A. I. by Henry A. Kissinger, Eric Schmidt and Daniel Huttenlocher Thoughts? Email us at [email protected]. (And if you’re reaching out to recommend a guest, please write “Guest Suggestion” in the subject line.) You can find transcripts (posted midday) and more episodes of “The Ezra Klein Show” at nytimes.com/ezra-klein-podcast, and you can find Ezra on Twitter @ezraklein. Book recommendations from all our guests are listed at https://www.nytimes.com/article/ezra-klein-show-book-recs. “The Ezra Klein Show” is produced by Emefa Agawu, Annie Galvin, Jeff Geld, Rogé Karma and Kristin Lin. Fact-checking by Michelle Harris and Kate Sinclair. Original music by Isaac Jones. Mixing by Jeff Geld and Isaac Jones. Audience strategy by Shannon Busta.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:04Ezra Klein?

  I'm Ezra Klein. This is the Ezra Klein Show.

• 0:22Ezra Klein?

  There is this quote, I think it's from Neil deGrasse Tyson, and I think about it a lot. It says, "The universe is under no obligation to make sense to you." And something I love about that is that it also implies, and I think basically everything we know about physics, particularly quantum physics, gets here, that what we experience is probably quite far from what the universe really is. And nowhere is that truer than time. I mean, nothing is more fundamental to our experience than time. We live in time. We are marked by time. We feel the seconds passing when we're bored. We say that time flies when we're on vacation or in the midst of a great conversation. The one thing we do not have more of is time. Our entire lives are bounded by time.

• 1:06Ezra Klein?

  And you'd think from there that what time is would be pretty clear. But talk to scientists who study time, and they are fundamentally confused about it. What time actually is, particularly outside the human brain, to say nothing of how weird the human brain is in the ways it measures time, is just fascinating. And you get into these really, really weird questions, like, a lot of the math suggests that maybe time is already there. Maybe the future is exactly as real as the present. Does that mean it's predetermined? Does that mean our understanding of causality is entirely wrong? What does any of it mean? My guest today is Dean Bonneman. He's a professor of neurobiology and psychology at UCLA. And his book, Your Brain is a Time Machine, what a great name, it gets at these two

• 1:49Ezra Klein?

  levels of time: the time that we experience and the time that exists as best we understand it, outside of our experience. This is one of those conversations, one of those topics that at times, haha, you might feel like you've taken a handful of mushrooms because it's weird. Ultimate reality, to the extent there is such a thing, is weird. But that's why I love these topics. Reality remains such an unbelievable mystery to us. We see only the tiniest sliver of it. And for me, appreciating that mystery, appreciating how little the world has to accord to my perception of it, how little I will ever know about it, it's a pretty deep spiritual practice. It's fun.

• 2:33Ezra Klein?

  As always, my email, [email protected].

• 2:42Ezra Klein?

  Dean Buonomano, welcome to the show.

• 2:44Speaker 01

  Thank you very much for having me.

• 2:46Ezra Klein?

  So let's imagine there are no human beings, there are no animals, the universe is just cold and dead. What is time in that universe?

• 2:56Speaker 01

  Well, that's a tricky question. We define time in a number of ways. So time is actually the most common noun in the English language. And one of the reasons that's the case is because it means different things depending on what we are referring to. So in your scenario, time would still be change. So things are dynamic, even in the cold universe, particularly if it's in the initial part of the universe, things will be dynamic and changing and expanding. So time exists in the sense that the universe is undergoing a change. Now practically, it's, there's a couple of ways to sort of try to define time. One is simply clock time. And clock time is a bit circular, right?

• 3:39Speaker 01

  Because time is what clocks tell, so the definition is a bit circular. But in a way, that's mostly what we mean by the passage of time. And all the clock is, is a device that changes in a predictable manner. So even particles that disintegrate with specific temporal properties are, in a sense, clocks. So there's clocks all around. The universe is a clock, in a manner of speaking. But other aspects of time are subjective. Subjective time. So this, you said, in a universe without animals and humans, so we wouldn't have that subjective time, what you and I are aware of, of the flow of time that's passing.

• 4:19Speaker 01

  And then we also have this idea of what we could call a natural time or the time of physics in which the question is, is if time is a dimension, much like space, in which time is sort of already laid out and the past exists in much the same way as the present exists and in much the same way as the future exists, they would all coexist, if you will. And that's, that's an ongoing debate in philosophy and physics.

• 4:46Ezra Klein?

  I want to come back to that physics level of time. But first, I want to get at the human level of time. So let's now think about the world that we do inhabit, where we exist and animals exist and time exists. You write in the book, "The human brain did not evolve to understand or to experience a true nature of time." Tell me what you mean by that.

• 5:06Speaker 01

  So all animals exist in time, of course, and they have to anticipate and interact with other beings and other, their conspecifics and predators and prey. But humans are unique in our ability to represent time and to have a conceptualization of time, of long temporal periods, to make cause and effect relationships between now and one year from now. So while humans have the ability to conceptualize time, that's sort of what gives us the ability to have this discussion of what is the nature of time?

• 5:51Speaker 01

  What's the difference between past, present, and future? So this ability that humans have to conceptualize time, I think, is, is what makes Homo sapiens sapiens. It's what makes us wise. But at the same time, we're not very good at it. We know what we mean by time, but it's something we're still struggling to understand. There's the famous quote by Saint Augustine, which is translated various ways. But the gist of it is, "If you don't ask me what time is, I know what it is. If you ask me what it is, I do not know." So we struggle to define time. And so that's what I mean, that the brain didn't evolve to understand not only time, the nature of time, but a lot of things, including the fundamental nature of the universe.

• 6:36Speaker 01

  And it remains to be seen if the human brain can understand the human brain. So the brain is a very limited information processing system. And I think an awareness of that, both in science and in society and our day to day lives, is actually rather important.

• 6:53Ezra Klein?

  So we did evolve to survive, to reproduce. So what kind of relationship to time did we evolve with? What do we use time for?

• 7:05Speaker 01

  So all animals have the ability to anticipate what's about to happen and make cause and effect relationships that if they hear a sound, that sound might reflect a predator prey hidden in the bushes. So we, like all other mammals, we inherited that ability. Because in many ways, that ability to predict the future is one of the brain's main jobs, right? The brain's main tasks in many ways is to use the past to anticipate the future. And that's something everybody's doing. Right now, you're unconsciously attempting to predict the future. And if I were to pause my speech there, sorry to make you nervous, you would notice that

• 7:49Speaker 01

  pause because you were predicting I was about to say something. I created a temporal prediction error. So all animals have this ability to anticipate and predict time and be aware of time on the short scale. And the degree to which animals predicted what's about to happen translated very effectively into the evolutionary currency of survival and reproduction. But humans came along and did something radically different. They were able to not just try to predict the future, but create it. So think about something like agriculture. For most of evolution, animals sought food.

• 8:30Speaker 01

  And survival required figuring out where food sources would be. And humans came up with idea of creating food, in essence, planting a seed and reaping the fruits of that action sometime in the future. And that ability to conceptualize cause and effect across months or years is something that really evades the cognitive capacity of most animals. It's not that complex, right? The idea of agriculture. But because the brain of most animals is not particularly good at linking cause and effect across large periods of time, agriculture wasn't invented by other animals.

• 9:15Speaker 01

  So this ability to create the future, this ability to engage in what we call mental time travel is really, in many ways, the defining cognitive signature of our species. You think of something like tool use, which we often relate to being a unique to human beings. But in many ways, the key cognitive breakthrough with tool use is not simply carving a tool out of obsidian stone, but having the conceptualization to say, I'm going to use this at some point in the future. I'm going to create this. I'm going to store it because it will come in handy.

• 9:54Speaker 01

  That's the cognitive breakthrough that at some point we achieved.

• 10:02Ezra Klein?

  Tell me about the relationship between our sense of time and our memory.

• 10:08Speaker 01

  Time and memory indeed are tightly coupled in a number of ways. So when we talk about our perception of time, there's two distinct frameworks that we should be aware of. One is prospective timing. So one is as you're living in the moment and time might seem to be going quickly or slowly. This came up a lot during COVID. It was widely felt that during lockdown periods, time was going by slowly.

• 10:40Speaker 01

  So that's what we call prospective timing. Now, interestingly, when you're looking back at what happened, sometimes you have this paradoxical effect in which we call retrospective timing. And maybe during the COVID period, or the acute part of the COVID period during the lockdown, looking back, it seemed to have flown by, it seemed had gone by very quickly. And that's because it's linked with memory. And so our retrospective judgments of time are really, in many ways, sort of guestimates based on how many items we have in memory. So this goes back to William James, Henry James's brother, who made the observation

• 11:23Speaker 01

  well over a century ago, that moments of time filled with new experiences seem to go by quickly in passing, but seem to have lasted very long in retrospect, because you had a lot of new memories being formed. So you can imagine, in the extreme case, somebody with very severe amnesia. So there's actually a couple of famous cases, one gentleman called Clive Waring, who has no ability to form new, no new memories about his own experiences, no new autobiographical memories.

• 12:04Speaker 01

  And he's essentially locked into an eternal present. He has a diary in which he writes down, 11 o'clock, I just woke up, and then 12 o'clock, I just woke up, and 2 o'clock, I just woke up. So if you don't have the ability to form new memories, you really are locked in the eternal present. You don't have any real conscious access to your recent history. So one can only imagine how disorienting that is.

• 12:32Ezra Klein?

  This gets to something that you brought up at the beginning about this difference between subjective time and perhaps other kinds of time.

• 12:42Ezra Klein?

  This idea that the way we experience time actually shifts depending on what we're experiencing in it. You mentioned a minute ago that the less it happens, the quicker things seem to go by. And that's what I'd always heard too. And I feel like in some points in my life I've felt. But I was struck by some research in your book, or some experiments, I guess, more to the point, where people would volunteer, for one reason or another, to be functionally in a cave or a dark room for quite a long time. And then, months or a year later, they would come out. And they would think much less time had passed than actually had. And given our view that time seems to speed up when nothing is happening, the fact that

• 13:27Ezra Klein?

  for them it slowed down is really interesting to me. Why do you think that is?

• 13:30Speaker 01

  Yeah, that's a great point as well. So it is absolutely the case that when we're measuring passage of time, our subjective experience, if you're in a fun movie, or you're enjoying yourself with your friends, we report subjectively that time seems to be going by quickly. So that's as if the external clock is going by more quickly. And when we're bored, the opposite happens. It seems to be then, external clock is going by more slowly. And there's a couple of famous cases. And one of the first was Michel Siegfried, a Frenchman who spent maybe six months in a cave. We infer that they would be quite bored, and thus that as time is going by, they would report it to be going

• 14:14Speaker 01

  very slowly. The reason, I think, has a different factor in play there. And that's the circadian clock. So the circadian clock, of course, is what keeps track of our daily rhythms in terms of when we're hungry, when we go to sleep, and when we get up. The circadian clock seems to actually, in those cases, have slowed down.

• 14:37Speaker 01

  And so his circadian rhythm has gone over our standard of approximately 24 hours. And he gets the impression that he's the fewer days have gone by when he's in the cave. So this has happened time and time again in those studies in which they're in for, say, six months. Six months later, somebody comes knocking on the cave door and says, time to go out. And they're saying, whoa, already? It's I thought it was only four months. We believe that's in part because the circadian clock has expanded their period. So they're oscillating their sleep cycle is probably significantly over 24 hours.

• 15:17Speaker 01

  And it's important to realize in these cases that unlike the clocks on our wrist, which are amazing technological achievements and that they can tell time on the scale of microseconds, seconds, minutes, hours, days, years, et cetera. We have clocks in our brain that can also tell time across those time scales, but they're fundamentally different clocks. The circadian clock doesn't have a second hand. And the mechanisms in your brain responsible for, say, timing the duration of a traffic light don't have an hour hand. So the notion that subjective time is sometimes distorted as during, under the influence

• 15:57Speaker 01

  of psychoactive drugs or during periods of isolation during the COVID pandemic, or simply moments of boredom or excitement.

• 16:07Ezra Klein?

  When I'm writing or really engaged in reading or having a really remarkable conversation, and I have that sense you just mentioned of this passage of time falling away. What's happening in me when that occurs?

• 16:23Speaker 01

  These are conscious experiences. So this is a fundamental mystery in neuroscience is what is consciousness? So the feeling of the passage of time is one of the many flavors of conscious experiences. So it's very hard to address what defines the feeling of time passing slowly or quickly without understanding consciousness, which we don't know yet. But I think one of the things that's happening there is a large part of your neural circuitry, if you will, is devoted to whatever task is at hand. And you're not doing this parallel processing and phasing in and out of different modes

• 17:07Speaker 01

  of thinking, going back and forth, well, should I be doing this? And you're not daydreaming and so forth. So I think it's just a cognitive state in which you can imagine chess players or athletes being in during critical moments, or anybody who's engaged in writing, as you said, or programming, that they're very engaged in a task. And most of us find that fairly rewarding. And so it's as if the brain makes that rewarding, although it's very challenging and difficult, presumably because it's also, in many ways, adaptive to be focused on certain types of tasks.

• 17:50Speaker 01

  But these are deep questions we just really don't know the answer to in terms of what causes these distortions, because the distortions are distortions of subjective experiences. And we don't really know what causes subjective experiences to begin with.

• 18:06Ezra Klein?

  You write about some research that has been done on people who have survived life-threatening accidents. What tends to happen to people's sense of time during a car crash or a skiing accident?

• 18:19Speaker 01

  So there's, as you may or may not know, I guess I should hope that you don't know, many people have this rapport of time dramatically slowing down, often reported as their life flying before their eyes. And I think this has been debated as what's possibly happening in the brain. And there's a couple of different views of this. One idea is that your brain is really functioning at a very high speed. It's sort of like boosting the clock speed of your computer called overclocking. That's probably not what's happening to a large degree because the brain can't be overclocking. Clocks in any significant way, it can't be sped up.

• 19:04Speaker 01

  Neurons can only fire at specific rates most of the time. Another view is that it's sort of an illusion in the sense that it's just that you remember everything that happened very well after the fact, after you're recounting what's happening. And that's sort of a idea that it's sort of like a flash memory of what happened during your accident. But more generally, I think this speaks to the general challenge of understanding our subjective experience of time to begin with. So it's not surprising that time gets distorted because it's a subjective experience and all subjective experiences get distorted. So when people are reporting these experiences,

• 19:49Speaker 01

  they often report space being distorted as well. I recount my personal anecdote in that situation when I was hit by a car and my car was spinning around. I recall thinking to myself at the time, wow, time really does slow down when you're about to die. And so that to me led credence to the theory that it's not a trick of memory. It's really that your brain is processing information at a different level. So I think it's a bit more akin to an hallucination and perhaps to the influence of psychoactive drugs or equivalent to the influence of psychoactive drugs creating temporal spatial hallucinations.

• 21:02Ezra Klein?

  When were clocks invented? And how, to the best as we understand it, have they changed our experience of time?

• 21:09Speaker 01

  So the evolution of human culture and civilization has really tracked the creation of more and more sophisticated clocks, going back from sundials to hourglasses to water clocks, to mechanical clocks, pendulum clocks, quartz crystals, and today atomic clocks. So, human civilization has been accompanied by this endless quest to measure time with more and more and more accuracy. And this quest has been absurdly successful in that today we measure time with more accuracy than we measure anything else, including distance or mass.

• 21:54Speaker 01

  Indeed, today, we define space using time. A meter is defined by how far light travels in one second. So, for reasons that aren't always immediately clear, we have had an obsession with measuring time, and it has had profound impacts on society and culture. You know, some people have argued that during the Industrial Revolution, that was driven by the invention of the steam engine. But other people have argued that, well, it was really the availability of clocks, of cheap clocks, that were widely available to the population and the people who worked in factories that allowed for the Industrial Revolution,

• 22:39Speaker 01

  because in the factories you needed to synchronize human behavior. You need to synchronize work hours in which everybody had to show up at the same time to do the production lines that were being created at the time. So, there's no doubt that we have become more and more synchronized. Clocks have allowed us to synchronize our behaviors, like meeting you today at a specific time. That 500 years ago, that those type of things would not be possible with the accuracy that we have today. Indeed, it's been argued that even Einstein's theory of

• 23:19Speaker 01

  Special relativity was in part related to the need to synchronize train schedules, to synchronize clocks that were being used locally and in other areas, in different cities and different states in order to synchronize train schedules. So clocks have a profound effect on our technology, from computer technology to GPS technology. So I think it is one of the most successful or one of the most impactful technologies on human civilization.

• 23:54Ezra Klein?

  Is there anything to lament in the dominance and omnipresence of clocks? We know a fair amount about societies before clocks. We know of certain tribes even now that don't much use them or, you know, in recent history haven't used them. What is lost by being a member of modernity with the constant tick of the clock behind you? What, how would my experience of the world be different? What would be enriched by its absence?

• 24:21Speaker 01

  I think there's always things that are lost when we rely on certain technologies. And with the advent of the sundial, there's this famous poem by a philosopher lamenting that the sundial took away his free will and was telling him when it was time to have dinner instead of being guided by his own eternal clock. And so one can only imagine what he would have thought of today's precision in terms of our 10-minute meetings timed to the second or the initiation of events on TV that are timed to the second. But in many ways, you know, it's not the clocks that are imposing that.

• 25:05Speaker 01

  It's our use of the clocks. So we can, you know, this is true in a lot of technologies, right? It's not. The technology itself that might be constraining our behavior in ways that aren't always helpful. So not having free time, so having just ability to not have anything on our schedules and have an open period of think is something that is invaluable for how our brains work. Our brains need time, empty time, to consolidate memories, to rehearse what we've already learned. And when we have continuous exposure to things in terms of,

• 25:50Speaker 01

  I don't know, social media, streaming, TV, and so forth, I think that takes away a bit of our really ability to absorb information and reflect upon that information. But again, that's not so much the fault of the technology. That's the fault of how we use the technology. But I'm very curious, Ezra. I mean, so what's your feeling about that? How do you feel that clocks constrain or enhance our life as individuals and as a society?

• 26:26Ezra Klein?

  I think this is a little bit like asking a fish what it's like to not live in water. I mean, I'm so clocked in my life. I've had periods, though, you know, a vacation here or there, or a camping trip, or the ingestion of some kind of substance that really warped or detached me from clock time. One effect of that in each time has been a sharper focus on the present. I think clocks and particularly scheduling and so on that they encourage keeps you constantly living, particularly in the future and with a constant eye on what's coming and where you are and how much time has passed and what did you do this morning?

• 27:09Ezra Klein?

  And then I think that there is a false precision to how long a day or a life is that actually strikes me as a quite profound question. I mean, there's so much emphasis in question of life extension and can human beings ever become immortal? Or, you know, what if we could add 50 years or 20 years? And I think a lot of these questions of particularly subjective time. At least gently pose the question of what if our lives could feel longer? And what if we are doing things that in certain ways make them feel shorter? And I certainly have the experience that a highly scheduled life makes my life seem

• 27:48Ezra Klein?

  to fly by in a way that open time creates a spaciousness in the flow of time that feels a little bit more satisfying. I don't know what to do about that because I got to get things done and my kids got to get places and I got deadlines, but it's not lost on me. And actually, it's something that I think about quite a lot, that I seem to live a life that is speeding up my own passage through time in a way that doesn't always feel good as I'm watching it or feeling it slip through my fingers.

• 28:20Speaker 01

  Yeah, I think that's a good way to put it. And it is certainly in terms of sort of trying to imagine what if you were a fish, what it is to be outside of the water. And this notion on the present and we're encouraged to live in the present and focus on the present. And that's really solid advice in that I think it helps our enjoyment and not only enjoyment, but ability to process and reflect upon what's happening. But it's a double edged sword in the sense that we want to have as much time as possible. But if you're only living in the present, you will actually have less of a future because

• 29:05Speaker 01

  survival requires planning and preparing for the future. If you were a native of the Amazon forest and you might not have to think about the future as much if food is always available. But if you're an Eskimo and you're not thinking about the future in terms of what to prepare and save for the winter, you know, you're not going to have much of a future. So there's this balance between preparing for the future and living in the present. But many cases, Living in the present can include thinking about the future. And that's often how I try to think about it is that what we mean is not necessarily living in the present, but focusing on whatever it is we're doing, even if that is a future-oriented

• 29:49Speaker 01

  behavior. And as we've discussed, this future-oriented behavior is something very unique to humans. Other animals don't seem to have this capacity to engage in mental time travel. But just because we humans are capable of it, doesn't mean we're very good at it. Indeed, I think that many of the most significant problems we have as individuals and as members of society reflect our lack of long-term thinking and preparation for the long-term future at the level of individuals that's clear in the context of saving for retirement, or exercising, or taking care of one's health.

• 30:34Speaker 01

  And at the society level, of course, this comes up in the context of climate change, that our ability to take actions in the present that might require short-term sacrifices for large payoffs or large advantages in the long-term future are very difficult for our species to take.

• 30:57Ezra Klein?

  I want to segue here into a very different view of time that you mentioned at the beginning of the conversation, and I said we'd come back to. So tell me about presentism and eternalism as theories of time, and why eternalism has come to be more widely accepted.

• 31:10Speaker 01

  It is counterintuitive. It is surprising because on our day-to-day life, there's nothing sort of as salient as the fact that the present is fundamentally different from the past and the future. The past no longer exists. We can't manipulate it. And the future, hopefully, we can by our actions that take place in the present. And so that is what we would call presentism. This idea that the past no longer exists, the present is where we exist, and the future does exist.

• 31:42Speaker 01

  Doesn't exist yet, but the counter view called eternalism, and that's similarly also called the block universe. There, the view is that in many ways here is to space as now is to time. In other words, it's arbitrary. The now is arbitrary. There's another now for some other version of me in the past or the future. And here, the idea is that past, present, and future all are equally real or coexist. And if you could see me, I would be doing air quotes, because the word exist is a bit tricky in this context. But the idea is that the temporal structure of the universe has already been laid out, or is already there, in a manner

• 32:26Speaker 01

  of speaking, and that the past, present, and future are equally real.

• 32:31Ezra Klein?

  So you just described there eternalism. It's very unintuitive. But you say it's a more dominant view among the people who spend their lives studying the fundamental laws of the world. So why? Why do they believe that? How can it be possible in a world where, depending on what I do next, the future changes, at least it seems to, that somewhere the future is already laid out?

• 32:54Speaker 01

  It's a bit dangerous to say it's the dominant view. I would say it is probably the most accepted view in philosophy and physics, but certain people would probably take issue with that statement. But the reason that view is favored, there's a couple of reasons. One is that the laws of physics, the equations that are used in physics, don't have any you are here in time. They don't have any special role for the present moment. So you can run the equations of physics forwards, backwards, starting in the future, starting in the past. The laws of physics don't tell us anything that, hey, the now is special in any way. Okay, no, that's not perhaps

• 33:34Speaker 01

  the best argument, because the laws of physics don't also tell us that the present is not special. So that's one reason. The other reason relates certainly to Einstein's theory of relativity. So Einstein's special theory to relativity established very compellingly.

• 33:53Speaker 01

  And without a shadow of doubt that there's no absolute present. So it doesn't really make sense if I tell you it's 11 o'clock where I am to ask what somebody is doing on another planet in a distant galaxy at 11 o'clock. There's no, because time is relative, or the absolute present is certainly relative. And it turns out that one of the best ways to make sense of this, or at least intuitively, is to sort of assume that time is spatialized. So sometimes people think of a four dimensional block in which the past, present, and future

• 34:33Speaker 01

  are all equally real, or in a sense, already present in the universe. And relatedly, in Einstein's so-called General Theory of Relativity, the equations that he discovered or invented allow for time travel. And they don't, I won't say they predict time travel, but they allow time travel. Why I'm bringing that up is probably the best way, the most intuitive way to think of the difference between presentism and eternalism, is that under presentism, time travel, as we see in the movies, true time travel, where you can go forward and backwards, is absolutely impossible.

• 35:17Speaker 01

  It's off the table because there's nowhere to go. I can't go back to visit my grandparents because they no longer exist. So under presentism, time travel is off the table. Under eternalism, time travel is on the table, and that's why it's so, sometimes so predominant in science fiction, and it's actually hard to get away from, I think, nowadays. So the fact that some of the equations of general relativity allow for the possibility of time travel, I think, has been one motivation for embracing the eternalist view amongst some physicists and philosophers.

• 35:55Ezra Klein?

  I think that brings up an interesting tension between at least one of the the main views of what time is and and the way we experience time, because for everything we've talked about here, on the one hand, there's the human experience of time, connected to memory, connected to clocks, where we are taking information from the past, applying it in the present in ways intended, and as you say, imperfectly so, but in ways intended to change the future. And then there's this idea that, you know, comes out of special relativity and and other theories and physics experiments and equations, that, well, maybe the future, the present

• 36:36Ezra Klein?

  and the past are all laid out, maybe they exist somewhere. And so this sense that we are changing the future through what we do in the present based on what we've learned in the past is in some, at least linguistic tension with this idea the future is already out there, that the future exists in some fundamental way. How do you think about that?

• 36:59Speaker 01

  Well, in this debate and this tension between presentism and eternalism, I clearly fall in the camp of presentism. So to me, it doesn't alter our intuitive view of that, yes, we can alter the future. And I think that's a fundamental aspect of animal evolution in the sense that the brain evolved to survive in a world governed by the laws of physics.

• 37:38Speaker 01

  And part of that, as a result of that evolution, we have this feeling of the passage of time. And we have the feeling that the past is fundamentally different from the present, which is fundamentally different from the future. And I don't think we would have evolved that. Subjective experience if it didn't reflect some aspect of reality. Remember, our subjective experiences aren't simply for our viewing pleasure. They enhance our chances of survival. So, pain enhances our chances of survival. Love presumably enhances our chances of survival, as do feelings, subjective feelings of the passage of time, or color, and so forth.

• 38:23Speaker 01

  So, my view is that this is a case in which we have to trust our intuitive, subjective experience that time is passing, and that does tell us something about the nature of the universe. Now, you're absolutely correct, in the sense that, under eternalism, the question of free will is seriously put in jeopardy, in that we wouldn't really have free will, because things have already happened. So, I think at a level of your philosophical experience of what's happening, that is, can be perceived as a blow. I don't know if it should be either way, but I think philosophically, those have very

• 39:07Speaker 01

  profound and distinct implications for topics of free will. But as I said, as a presentist, I strongly feel that we are, in effect, have the ability to make decisions in the present that shape future outcomes.

• 39:51Ezra Klein?

  You write about this fascinating study that was done on a tribe of people called the Badaha, people in the Amazon. Tell me about that study, and what was unusual or interesting about the results.

• 40:04Speaker 01

  Yeah, so this is mostly work by a linguist and anthropologist called Daniel Everett. And he has a great book, by the way, called Don't Sleep, There Are Snakes. And his report, and I think we have to always interpret these reports with some caution, because these cross-cultural studies are, in first place, very, very difficult to do, and, second place, even more difficult to confirm or replicate. So I think these interpretations might be a bit controversial. But he argues that in this tribe, the Pidahai, that they're very present-oriented, that they don't think that much about the long-term future.

• 40:47Speaker 01

  And the implication, perhaps, being that in that tribe, maybe they didn't need to, because the circumstances of that local environment for survival didn't require much long-term planning or long-term thinking. So it is interesting if, under those circumstances, you know, are they more satisfied or happier, living in the present? I think that that's a reasonable debate. But as we were just discussing, yeah, for most of us, long-term thinking is a necessary prerequisite for long-term survival.

• 41:28Speaker 01

  It is something that humans have to engage in for our long-term well-being, but something, probably, that we don't do enough.

• 41:39Ezra Klein?

  So then I want to ask about our relationship to the future. Because we know something about how we can change the way we mentally recollect the past. We know some things and have some practices about how to be more in the present, and people chase flow and meditation and so on. You had touched on the way we have trouble treating even our own future as as real as we would tell you we believe it is, right? Trouble saving, trouble exercising, trouble preventing things we know we don't want to happen from happening, or making things we do want to have happen, happen. Is there anything in our evolving understanding of the way the brain anticipates or thinks

• 42:23Ezra Klein?

  about the future that can help give us a healthier relationship to our own individual or collective futures?

• 42:30Speaker 01

  Yes. So... This idea of thinking about the future, delaying gratification, long-term planning, is something that is, as we've said, unique to humans. But we're not very good at it, and that's not very surprising, right? Because think about human evolution 100,000 years ago, when the average lifespan was maybe 30 years. The concept of saving for retirement was nonsensical because the idea of saving or planning for the future, if the future was so unpredictable that you might either die of disease or of hunger, or of predation,

• 43:14Speaker 01

  or of tribal warfare in the next six months, it really didn't make much sense to think long-term. This is why we have a present bias. So the present bias is this notion that if I'm offered $100 today or $120 tomorrow, we have this bias to accept the present, the sure thing that's immediate, even though it's a lower value. So it's not surprising at all that we have this implicit bias for the present and for short-term decisions, and it's hard to delay gratification, if you will. Now, what we can do about that, of course, is, like many cognitive skills, this comes with practice.

• 43:56Speaker 01

  And part of growing up and part of the educational system is helping people learn to delay gratification and think long-term. Even studying for a test is something that engages long-term thinking because you're studying today for something that will happen tomorrow. And the earlier you study for the test, in a way, you're thinking in a longer temporal scale. And this goes back to the famous marshmallow tests with children and their ability to delay gratification in terms of waiting 15 minutes to eat their marshmallow and then get two, as opposed to eating just one immediately. And the ability of children to delay that gratification

• 44:40Speaker 01

  correlated weakly, sometimes I think a bit. Too much is made of those data with future academic success, for example. So practice is key. And people have shown that exercises in terms of when you're faced with a decision, well, should I spend this money now? Or should I put it in a savings account for retirement? Few studies have suggested that sort of visualizing the future, just engaging in exercises of, you know, being old, what I will be able to do with that funds, if I'll be healthy and so forth, help people engage more future oriented behavior, future oriented actions in the present.

• 45:23Speaker 01

  But again, on this longer time scale of generations and centuries, evolutionarily there, you can see it's even a bit harder. But again, I think it's a question of practice and discipline, much like learning math is or learning programming is. But these are difficult questions and I don't think we fully know the answers to them, Ezra.

• 45:48Ezra Klein?

  I want to talk about what all this knowledge about living in time might say about how one should live in time. So to go back to something I was touching on earlier, if you wanted life to feel longer, how should you live?

• 46:02Speaker 01

  So going back to this idea of retrospective timing, being related to memory and the amount of information we have stored in memory. The standard sort of view there is that the more novel experiences, the more this goes to sort of the self-help genre of novel experiences, new learning experiences help us have a life filled with memories and certainly give us the impression that it may have been a period well-lived or that we have taken advantage of or put into good use.

• 46:44Speaker 01

  So this is intuitive, I think, that we want to use our time for productive ventures, whatever each of us. Finds or defines as a productive venture, which is clearly variable and a highly personal choice. So I think these are just consequences of the fact that time passes inexorably and we are flowing through it, depending on your perspective. And these are just life choices, like all choices we make in our life, how we want to, what we want to do with our time, who we are as individuals, in many ways is defined by what we do with our time.

• 47:26Speaker 01

  And the common piece of advice there is yes, if you want to have the subjective experience of having a long period of accomplishments or of in your memories, that the more diverse those experiences are, the more likely you are to store those events in memory and retrospectively feel that that was a long temporal period that has elapsed.

• 47:54Ezra Klein?

  What about our relationship with the present? I mean, there are deep religious and spiritual traditions that take our constant tendency to mentally time travel. It's a quite profound problem. Many kinds of mystical and chemical and meditative experiences are about creating a deep relationship to this moment. What is, in your view, what does it mean to be more present focused? I mean, what are we actually saying is happening in a human mind when we're saying somebody is is more in the present? And is that something to strive for? What is the relationship we should have with the present?

• 48:32Speaker 01

  Yeah, I mean, these are profound questions that I wouldn't pretend to know the answer to. But in terms of what it means to be in the present, strangely enough, in many ways, that often means to be very unaware of the passage of time. So even in sort of these theories or hypotheses or models of how the brain tells time, that one of the ideas is, is that the more we're using our cognitive apparatus, our cognitive circuits to engage in a specific activity.

• 49:08Speaker 01

  That's independent of the passage of time. The more you're involved in reading a book or playing chess or trying to figure out the best move or developing a novel idea, the less you are aware of the passage of time. So in many ways, living in the present or being focused in the present means being unaware of the passage of time. And the more we're aware of the passage of time, you become a bit more cognizant of whether time's going by quickly or slowly. Now, what that means for our day-to-day goals, as we've touched upon, I think it is important to,

• 49:51Speaker 01

  and it's an important goal, to be involved in whatever tasks we're involved in at the time, even if that task is thinking about the nature of time or thinking about the future or preparing for the future.

• 50:06Ezra Klein?

  I think that is a good spot of ambiguity to end on. So always a final question. What are three books you would recommend to the audience?

• 50:13Speaker 01

  The first is called Noise: A Flaw in Human Judgment. It's by Kahneman, Simbonya, and Sunstein. Kahneman is, of course, famous for his studies on irrational and biased decision-making in the context of framing, for example, that humans might be more apt or likely to choose a surgery that's framed as having an 80% survival rate as opposed to one that has a 20% mortality rate, those, of course, being the same thing. In this book, he's focusing more on noise and variability of human decisions. So for example, given identical cases, a judge might make different rulings,

• 50:56Speaker 01

  perhaps influenced by whether his or her local sports team won or lost that weekend. The second book is a bit hard to describe. It's sort of a fictionalized biography of real scientists. It's "When We Cease to Understand the World" by Benjamin Labatut. It's independent short stories, and some are fairly dark, so it might not be for everyone. But the main story of the title is a dialogue between the founders of quantum mechanics, Niels Bohr and Werner Heisenberg, and they're coming to realization and grappling with the idea that at the quantum level, the universe is stochastic and unpredictable and highly

• 51:40Speaker 01

  counterintuitive and beyond our really ability to understand what's happening. And that's when we cease to understand the world. This offers an important lesson in quantum mechanics, is a good reminder of the limitations of the human brain and that it didn't evolve to understand or to grasp many of the things we're asking of it today. And this may be the case in neuroscience. It remains to be seen if the human brain can understand the human brain. The third is "The Age of AI and Our Human Future." It's written by a sort of surprising trio of authors: Henry Kissinger, Eric Schmidt,

• 52:23Speaker 01

  the ex-CEO of Google, and an academic at N隆. It's not technical, but I think it's a good review and does a good job at conveying the promise, the societal promise and dangers of AI. Personally, one of the things I find interesting going forward in the context of AI is what our reaction to AI will tell us about ourselves. Dean Buonomano, thank you very much. Thank you, Ezra. It was a pleasure.

• 53:03Ezra Klein?

  The Azur Khan Show is produced by Amafa Agawu, Annie Galvin, Jeff Geld, Raja Karma, and Kristin Lin. Fact checking by Michelle Harris and Kate Sinclair. Original music by Isaac Jones, mixing by Jeff Geld and Isaac Jones, and audience strategy by Shannon Busta.