Time can feel like a subjective experience—different at different points in our lives. It’s also a real, measurable thing. The universe may be too big to fully comprehend, but what we do know could help inform the ways we approach our understanding of ourselves, our purpose, and our time.
Theoretical physicist and black-hole expert Janna Levin explains how the science of time can inspire new thinking and fresh perspectives on a much larger scale.
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The following transcript has been edited for clarity:
Janna Levin: “The one sense in which time is frustratingly different is that I cannot extend equally in each direction. I cannot just turn around and go into the past. And I seem to be always driven forward into the future. I can stand still in space, but I can’t seem to stand still in time.”
Becca Rashid: Welcome to How to Keep Time. I’m Becca Rashid, co-host and producer of the show.
Ian Bogost: And I’m Ian Bogost, co-host and contributing writer at The Atlantic.
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Rashid: One time I took a nap, and I remember I woke up at sunset but it looked like dawn, and I was like, I’m late for work. Like, What have I done? And, uh, that’s why I avoid naps in general. It’s just, I’m so disoriented every time. In one way or the other.
Bogost: Yeah, or like when you travel; you know, I travel overseas, and I’m jetlagged. And the time is all messed up, and I wake up in the middle of the night. And then I can’t go to sleep—or you start falling asleep in the middle of the day because you’re so far away. Like, what time is it even?
Rashid: And you can’t control it. I love how I’m just napping and you’re traveling the world.
Bogost: I have napped like you’ve described too.
Rashid: There are all these ways that I experience these weird lags in my space and time, not just with napping. But sometimes, if I’m really tired, a song sounds slower to me; like the beat feels like it’s delayed in some way. Or if I’m really caffeinated it feels faster. And same thing with time. And maybe I’m just getting older, or it feels like time is moving faster, but—
Bogost: I hate to tell you this, Becca, but I think you may just be getting older. Because, you know, time feels like it moves faster for me year to year. And then sometimes I’ll look at myself in the mirror—you know, after looking at a photo—and I’m like, Okay, that hair didn’t used to be that color quite so much, right?
Rashid: Mm hmm.
Bogost: I feel like much time has passed, you know.
Rashid: Right.
Bogost: Like, there’s a kind of funhouse-mirror effect with time’s passage where you think you look a certain way in time, but it turns out you’re all wonky.
Rashid: Right; it reminds me when I used to go home as a college student and my little brother, who’s six years younger than me, looked like a different person every year I visited. And now, the way I see my parents aging.
Bogost: You’re aging at the same time. Uh, it’s not just them. It’s also you. But you don’t have that sense of it inside your own head. You need some reference from outside of your body to remind you. Oh yeah: time.
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Bogost: Janna, are you a timely person? Do you think of yourself as a timely person?
Janna Levin: I’m very often on time. I really am. But I can also get lost in time. I mean, I think if you’re going to do theoretical physics, and you’re going to hunch over a blank, unlined sheet of paper—which is what I like—with a pencil for 12 hours, that you’ve got to be able to kind of turn off some of the chatter, some of the internal biorhythms, that make you so aware of time passing.
Bogost: So Becca, I spoke with the theoretical physicist Janna Levin to understand what it means to place ourselves in the universe, in particular as it relates to time.
Rashid: Mm hmm.
Levin: I’m Janna Levin, and I’m a professor of physics and astronomy at Barnard College of Columbia University.
Bogost: Levin specializes in black holes, actually.
Rashid: Oh, interesting.
Bogost: Yeah, and black holes are weird because time seems to behave totally differently around them.
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Bogost: So what is it about black holes? What is their role in helping us understand the nature of time?
Levin: The nature of time seems to go more and more out of sync as you get closer and closer to the black hole. So let’s say you’re an astronaut orbiting far from a black hole. And you have this beautiful clock, and it’s telling you what time it is, and your body is exactly in sync with the clock. And movies run at a normal rate and music plays at a normal rate. And your companion—another astronaut—has a perfectly synchronized clock built by the same manufacturer, but they jump into the black hole.
Levin: What you find is as they get closer and closer to the black hole, the astronaut from far away will literally see the ticks on the clock appear to take longer to be spaced, uh, in a more elongated way—so that it’s as though time is running more slowly for the astronaut who’s falling toward the black hole.
Levin: Now, it’s not just this clock; it’s also the music they’re playing, the movies they’re filming—they all are running slowly compared to the astronaut far away. Now, the one who jumps in thinks their clock is normal; absolutely normal experience.
Levin: They just think the astronaut left on this orbit far from the black hole is running very, very fast, racing through years of their lives. All the movies are fast, the music is fast, and the clocks are all speeding ahead. And they realize that they’ve come out of sync as they get closer and closer to the black hole.
Bogost: So it’s almost like the black hole is a lens for physicists to ask difficult questions about time. You can see it more clearly through the subject of the black hole.
Levin: Yeah, the way the black hole distorts—slows time down as you approach its horizon relative to somebody very far away—it makes the black hole like a magnifying glass, in some sense. So that you can look on higher and higher energies and smaller and smaller time scales, because it’s like this magnifying-glass kind of quality.
Bogost: Okay; the magnifying-glass metaphor is really helpful to me, but Janna, I’m still not sure I understand what time is. Like, I kind of have no idea what time is when I stop and think about it, even though I understand what you’re describing, and I live in time all the time.
So once you use this magnifying glass of the black hole to shed light on the nature of time in the universe, what is the answer? Like, what is time anyway?
Levin: Hmm. I’m not sure anyone can give you a fair answer to that question.
Bogost: Oh, no!
Levin: But we would all love to. I could say, let’s go back and say, “What is space? Let’s start there and see how time is different.” So I can say, “Well, I know I can move, extend my hand to the left, and I can extend my hand to the right in space. I have a kind of intuitive notion of that, and I can also measure space with rulers, and how far away things are.” Now, time can be very similar to space, is what Einstein realized—that there is sort of a four-dimensional space time.
And in some sense, as the person nears the black hole, it’s as though they’re rotating what the astronaut far away called “space” into what they’re calling “time.” It’s as though they’re rotating away in this four-dimensional space time.
But the one sense in which time is frustratingly different is that I cannot extend equally in each direction. I cannot just turn around and go into the past. And I seem to be always driven forward into the future.
Levin: Even if I’m standing still in space, I can’t stop the next moment from passing. I can’t stop my body from aging, and we always go forward in this direction.
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Rashid: You know, some of the happiest memories I have from childhood with my brother was operating under the same schedules, in a way. You know: waking up, going to school together, putting our backpacks on, getting yelled at to put our jackets on, and then sort of rushing out the door. And then, you know, coming home after three; like, eat something, have a snack.
Bogost: Eat something … drink some water!
Rashid: Yeah. [Laughter.] Yes. The thing I forget to do. And, you know, now my brother recently moved to Sweden for grad school. Fancy, fancy!
Bogost: Oh, wow.
Rashid: That feeling that we’re kind of on the same rhythm of each day; we’re kind of operating under the same clock and sort of moving through our days together is completely not there. And you know, I don’t know what time of day he does his work, or I don’t always know where he is in space at any given time.
Bogost: Yeah; I think I see what you mean, Becca. I have two adult kids, and they live in a different city from me, and I’d much rather be closer to them more of the time. And you know, in part that’s just about wanting to be close—like, physically close.
Rashid: Of course.
Bogost: But when I do see them in person, then it also feels different. It feels better, but in a different way because we’re occupying the same time, not just the same space. Even if nothing important is happening, it’s happening to us together.
Rashid: I think that’s exactly what I miss—like, that empty time we would share with each other.
Bogost: So, Becca, there’s space, and there’s time, and time is fundamental to existence, just like space is. But our relationships with space and time as human beings are, like, very different from one another, right?
Rashid: Right, right.
Bogost: Like, you could go visit your brother in Sweden. You could get on a plane and bridge that distance if you wanted to or needed to. Move around in space. If you’re, you know, stuck in your car driving home and like, Oh, if only I can get home, but you will.
You’ll get home eventually, and then you’ll be there. But you can’t really do that in time. You can’t move around in time. You can only go in one direction, and that’s forward.
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Bogost: Okay; I want to ask you more about this. And I was thinking about it as I tried to prepare for our conversation. So, I have three kids. And two of them are grown up, and one of them is a lot younger. And before my youngest was born, I didn’t think about her at all, because she didn’t exist. But now, the idea that she once didn’t exist is kind of impossible for me to imagine. And there’s a name for this, right? It’s called the Arrow of Time. So what does that idea mean: the Arrow of Time?
Levin: Just in response to what you just described so beautifully—we all feel this asymmetry. Intuitively, we have a great deal of anxiety about the idea that we might not exist in the future. But we’re completely okay with the idea that we did not exist prior to some point in the past. That asymmetry is just built into us. We’re not distressed to believe that there was a point before which your daughter didn’t exist.
Bogost: Yeah.
Levin: This is just because we all fundamentally feel the asymmetry. We intuit it was just part of our everyday experience. Now, we don’t actually know that it’s that firm. It is conceivable; many people have played with this within the context of Einstein’s theory of relativity, that you could find a path where you did go backward in time.
And, there are all kinds of solutions that we know exist mathematically, but we think that reality will forbid these mathematical solutions from ever becoming actualized in the universe. But we don’t know for sure that the asymmetry absolutely cannot be violated.
Bogost: So does that contribute to our, like, cultural obsession with time and the way that it flows forward? I’m thinking here of time loops and their popularity in science fiction. You know, Tenet or Doctor Strange or the time-dilation effects in a film like Interstellar or even alternate timelines; these examples in novels and film of playing with time. What do you make of those as a physicist? Is this, like, our cultural attempt to wrestle with the Arrow of Time?
Levin: Yeah; I think it’s a really good way to challenge your belief system. One of the things we have to do in theoretical physics is get over our intuitions that are based on a very limited experience of being a certain size, evolving under the sun and having certain eyes as a result of that, and living a certain duration and moving relatively slowly. So we don’t really notice relativity as an experience.
So it’s beautiful, actually, to do these thought experiments and really challenge your biases and try to break them. And see—maybe we could go backward in time. Maybe I shouldn’t presume that just because it’s never happened to me that it couldn’t happen.
And that there wouldn’t be a physical, mathematically realizable way to do that. And so we play those games all the time.
Bogost: I wonder in your job—which is to think about cosmic things—how does that impact your daily life? Like, when you’re, you know, commuting or going to the grocery store, what is your knowledge or understanding of the nature of the universe? How does it contribute to your day-to-day life?
Levin: Well, there’s a lot of scientists who will say that whether or not they’re comfortable using the word spiritual, that thinking about these things gives them a profound sense of meaning and a connectedness to something much vaster than their ordinary lives.
And I often, especially—you know, we’re at a time of great pain and strife and trouble in the world. And I often will meditate on this bird’s eye, even beyond the bird’s eye, to really imagine the Earth under this star, and the star that’s been burning for billions of years. And then panning away from the star and imagining this entire solar system, all of us, silly little people warring together, orbiting together around a supermassive black hole 26,000 light-years away. And that is where we are. That is how we got here. And so, do I think about that if I get cut off on my bike on my way over to the studio to talk to you?
I don’t; you know, I’m shaking my fist in the air, and I’m frustrated. But I do believe that in a deep sense, it really has altered my sense of who we are.
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Rashid: Ian, you know how people make, like, a five-year plan or like a 10-year plan? I’ve never ever been that kind of planner, because that’s just not how my experience of life or time has ever been.
But I realize that people can have this impulse to control their time. Because you’re one person in the universe with very little control, and all you can do is sort of map out, you know, maybe your weeks, maybe your years, in a way that feels like it’s under your control. And hopefully at the end of the day feels like you’ve made the most of whatever chunk you’re given.
Bogost: Yeah. And you know, as Janna’s explaining, that feeling comes from the fact that we can go forward and backward and sideways in space, but we can’t do the same thing in time.
Rashid: Right.
Bogost: And when it comes down to it, that’s sort of just the fundamental puzzle and problem with time. That is, as you know, like normal-sized objects, beings in the universe, we cannot go backward. And so that feeling is also weird, you know. But with black holes—those are interesting to physicists because they’re exceptions, or at least potentially exceptions, to the normal rules of physics.
And so, therefore, they offer these kinds of lenses through which scientists can look at time and understand it better. You know, that’s great for theoretical physicists, but not so great for the rest of us. Like: I don’t have a black hole nearby, Becca, that I can sort of ask questions about time.
Rashid: Thankfully, yes.
Bogost: But I wonder, like, are there other lenses that ordinary people can use to make sense of time?
Rashid: Right. I feel like we humans need a few ways to understand ourselves better. And even though it’s not directly related to physics, Ian, this theory called the social clock—which Bernice Neugarten, a social psychologist, came up with in the 1960s—can help explain that feeling of pressure that we can feel: that we should be hitting certain social markers at different stages of our life, at different ages specifically.
Bogost: Okay.
Rashid: Obviously the big things—marriage, having children—but I was thinking about how those are norms dictated by society, right? But let’s say you’re someone who was raised with two cultures. Then the social clock can have sort of different terms, depending on which society or cultural norms you’re trying to fit into. So.
Bogost: It’s like keeping track of different time zones; you have to keep track of different social clocks.
Rashid: Exactly; exactly.
Bogost: If you think about the social clock not as a set of hard-and-fast rules or even cultural rules, but as something more like that lens—like the way that Janna thinks about black holes, like she’s going to look at time through the lens of the black hole—you can look at your own personal time through the lens of a particular social clock.
Bogost: And that could be an American one, or it could be a different one. And there’s less pressure, perhaps.
Rashid: But it can start to make the social clock feel as chaotic as time itself. From like one line moving chronologically through all these different life changes and events into this sort of wave of unpredictability. But maybe that leaves more room for the unexpected, and for serendipity too.
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Bogost: So Janna, how much time do we have? Like, is time infinite?
Levin: It’s a really difficult question. I don’t know if space is infinite, either. We know it has a finite past. We can’t think of time as outside of the universe anymore. We can only think of time as a quality of the universe. Or it could be that the universe just expands and, uh, expands and expands, until essentially each particle is so far away from every other that there’s really no meaning to the passage of time anymore. How would you even know time has passed? To know time has passed, I have to experience some change.
Levin: It could be a change just in my thoughts. It could be an accumulation of heartbeats. Or it could be a tick on a clock. But all of those things require more than a single particle floating alone in the universe. And, in fact, if I were to show you this as a movie—if I were to show you a movie of a single particle—you would have no idea if the movie was running fast or slow, if it was true to time, whatever that could possibly mean. You would not have any scientific way of measuring the passage of time.
Bogost: Janna, you mentioned change. Is that all time really is? Just change?
Levin: We do, yes, measure time through change. If I were to—classic example—take this glass of water I have here and smash it to the floor and film this for you, you would absolutely believe the movie had run forward in time. Because you know that individual pieces of glass everywhere and water splashed everywhere: That’s the logical way things unfold. They don’t—if I were to show you the movie running backward—reassemble into a seamless glass with water inside it, naturally. That’s not something we see.
Levin: What we do see is: We see change in the direction of greater disorder. We do not see change in the direction of increased order. And so that’s also part of the Arrow of Time conversation.
If I were to show you movies, you’re always going to be able to guess that one’s running forward in time if you see things going toward greater disorder, like smashing apart. More disordered. And you’re always going to know they’re running backward if you see things perfectly reassembling.
Bogost: Huh.
Levin: So we do seem to measure the passage of time as tightly correlated with the increase in disorder.
Bogost: Janna, this is making me feel a little more at peace with the chaos in my own life, I think. But it reminds me of the fact that, you know, time feels different at different times. Like, a long flight can feel really slow—but then the vacation that you’re flying to goes by really quickly. Is there a physical reason why time feels different, or is that a psychological thing?
Levin: I think one of the explanations could be this one of disorder—and a lot of people will cite this—that when there is a lot of change relative to your overall experience psychologically, you will consider that to be time moving more quickly.
Levin: If you’re a child and you’re having an experience, your overall body of experience is so small that actually, psychologically, your perception of time is kind of slower. And as you get older, that same experience you might share with a child, seems to you that time is passing faster—because your overall body of experience is larger relative to the amount of change you’re perceiving.
Bogost: Do you find yourself using your knowledge of the physics of change in your day-to-day life? Like, does it make you feel better during a busy week that, oh, there’s just a lot of change happening right now?
Levin: It can, but it can also remind me not to have such fractured attention.
Bogost: Huh.
Levin: Because I think it can feel like life just flies by. And more considered attention, I do think, elongates—at least for me—that experience of a stillness, or being in the moment, or a slower passage of life.
Levin: But I have to say I’m an incredibly busy person. I have a real problem with that. [Laughter.] I don’t wanna pretend like I’m the Buddha here. And I do find I’m always thinking about the future, which is, you know, the proverbial saying not to do. Be in the moment.
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Bogost: Becca, sorry to get morbid here for a second.
Rashid: Oh!
Bogost: But like, the idea of living in the moment—it makes me think about the moment when all your moments end, you know.
Rashid: Oh no.
Bogost: And if you read about the things that people say on their deathbeds at the end of their lives, a lot of those sentiments have to do with regret. With things that those people are happy that they did, or things they wish they’d done.
A few years ago in a story for The Atlantic, the writer Michael Erard explained how the dying often use these metaphors of travel to talk about their impending deaths: like, just trying to make sense of what’s happening to them.
Rashid: Wow.
Bogost: Yeah. Oh, the sentiment, like, “If I could just find the map, I’d know where to go next.” And the way I understand that sentiment, is that, like, even at the end of life—when you know there’s no more moments left, and there’s no choice but to face the forward flow of time into oblivion—people still haven’t fully come to terms with it. They’re still yearning to go back, to make changes. Or take comfort in the fact that they can’t go back and make changes, but they recognize that pull or that tension, you know?
Rashid: I mean, my own sort of fascination with the social-clock stuff, I think, came from a similar yearning to go back and turn back the clock and make the changes to my life that would, you know, put me in line with what I should have done.
And that is the scary time thing; right, Ian? We’re all coping with it in different ways. Realizing that no action—no sort of doing anything can turn back the clock. No mental tricks can bring that time back.
Rashid: How is it that we have to approach time with this forward-looking sort of optimistic approach, when almost everything else we do involves going back, to some capacity? Editing an email before we send it; revising, like, a text. You know, we can kind of do everything forward and backward to elicit a different result.
Bogost: People think they’ve gotten used to the undo key, right? There’s a sense that you should be able to undo anything. Like, we can redo it. I can Control-Z my life.
Rashid: Totally. You know, I think about the time I must have lost with my parents when I was a teenager, just, you know, dreaming about the day I’d move out. [Laughter.] Time is just this sort of train I feel like I’m on, that’s moving along, you know, without my consent. And I just have to be okay with that.
Bogost: That’s what Janna is saying. You’re on the train, Becca. It’s like the constant tragedy of time—that you from 10 years ago will never return. Neither will you from yesterday.
Bogost: But it’s also, like, the great comfort of time. Time allows change to happen. It allows you to change.
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Levin: I very much feel part of a vast ecosystem going back to the Big Bang. I really remember learning that. And I remember being floored at the idea that there are atoms in my body that are primordial. And of course, many people say we’re made of stardust. And some of that primordial material went through stars and had to be cast back out in the universe. And are in my body, right now—from a star.
Bogost: Uh huh.
Levin: And I know that that’s something lots of people know now and talk about. But there are times where, yes, I can suspend the feeling of that being just an intellectual fact and actually, uh, feel a real sense of comfort that there will be a future where we will all be part of that larger ecosystem again.
Bogost: Okay, well, speaking of being part of that larger ecosystem: I mean, it’s almost like a euphemism for a difficult topic that we nevertheless have to talk about. Which is that, you know, if time is change, that part of the change that we experience as human beings is death. Like, we’re gonna die someday.
Bogost: Or even before that, you know: My kids will grow up and leave the house, and they won’t be around anymore. Do physicists have something to say about that? About how humankind can grapple with our minor role in the universe? And you’re kind of touching on that with your own personal experience.
Bogost: But is there something in physics that gives us clues about how to live—without, you know, checking out or without falling into existential despair?
Levin: That’s a very difficult question, but I have already left behind a part of myself that will never exist again. There will never be 7-year-old me again.
Bogost: Uh huh.
Levin: There might be some deep sense in which that does exist: 7-year-old me. It’s just not one of the movie frames I can make my way back to.
There are all these deaths along the way. I have children, and they’ll never be babies again. I will never hold my little babies. And I think that when we kind of see it that way, and we begin to ask, “What does it mean to be me?”
I left so much of that behind. Am I still the same person? I mean, these are philosophical questions. I think you’re wondering: What does a physicist have to say about that?
I think it’s really going to sound quite difficult, but the physicist is likely to go as far as to say, there really is no self. You are a collection of quantum particles and interactions, and they change. And we see this all the time. I certainly could take a chemical that would completely change my chemistry and completely change my personality. In what sense am I still me?
Levin: I could have an injury to my brain, and the tissue is reoriented and reconfigured. In what sense is that still me? And in what sense was it ever me? We are just a collection of particles. And one day we will go back into the galaxy.
Bogost: So what, then, is the purpose or value of your and my time on Earth, in that context?
Levin: Well, this is back to taking that astronomical view of the Earth and why people are so stirred by things like, uh, the International Space Station taking a photograph of the Earth rising, “Earthrise.” I believe it helps us to understand that so much that we take so seriously is completely devoid of any meaning.
Levin: And most of all: This kind of notion of our differences, I think, has been kind of historically catastrophic. To think of all of us in this way can be transcendent, and it can be quite unifying. And I think it’s okay to still say, I really love the color green, even if I believe it’s only in my mind. I can live with that. I can sit with that.
Bogost: Janna, I have one last question for you. In a sentence, how do you define time?
Levin: [Laughter.] One last question that people have been wringing their hands over for centuries to come and will for centuries to come. [Laughter.] I, if forced, would say, “To the best of my present understanding, time is a measure of change.” And I’m very unsatisfied with that answer. I almost should be more rebellious and say, “I can’t do that, and I don’t want to do that.” Because if I were to do that, I’d be saying something so tricky.
Levin: So, for instance, it would be very easy for me to argue with that statement and say, “Well now, what do you mean, change?” Change happens over time. We’re caught in a little loop. I could say something like, “Time is a dimension.” But it’s a dimension that has an arrow, where you’re forced to always move in a particular direction.
Levin: So it’s a dimension just like north, south, east, west. Up and down. Spatial dimension. But it has this weird restriction that I can only move in one direction in that dimension. Why does it have the Arrow of Time? Well, that is a hotly debated topic that will continue to go on.
Levin: But some scientists, some cosmologists, feel a lot more comfortable now saying things like, “Oh, that’s just because in the early universe things were in a very ordered state. And so the only place it can go is to become more and more disordered.” And so time passes. [Laughter.]
If the universe began in a maximally disordered state, just a blender of everything was maximally randomized, that there would be no passage of time. There also wouldn’t be galaxies or people, or radio shows, or thoughts. So some people feel very confident that it’s a cosmological question. The question is, “Why did the universe begin in such an ordered state?” And that’s the big mystery.
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Rashid: That’s all for this episode of How to Keep Time. This episode was hosted by Ian Bogost and me, Becca Rashid. I also produce the show. Our editors are Claudine Ebeid and Jocelyn Frank. Fact-check by Ena Alvarado. Our engineer is Rob Smierciak. Rob also composed some of our music. The executive producer of audio is Claudine Ebeid, and the managing editor of audio is Andrea Valdez.
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Bogost: Becca, I was going to tell you a joke about time travel, but you didn’t like it.
Rashid: What? I didn’t… I don’t?
Bogost: [Laughter.]
Rashid: [Laughter.] I don’t get the joke… Oh, I get it, I get it, I get it!