Speaker 1: Do we experience gaps in time? Is your consciousness like
Speaker 1: a flame that continually goes out and then gets reignited.
Speaker 1: Why can you see someone else's eyes move but you
Speaker 1: can never see your own eyes move in the mirror?
Speaker 1: The answer is some freaky stuff that's going to shift
Speaker 1: your view of reality. And what does any of this
Speaker 1: have to do with deep sleep or anesthesia or comas
Speaker 1: or amnesia, empires of soft bodied creatures that might have
Speaker 1: come before us, and what you do or don't remember
Speaker 1: about your life. Welcome to Inner Cosmos with me David Eagleman.
Speaker 1: I'm a neuroscientist and author at Stanford and in these
Speaker 1: episodes we sail deeply into our three pound universe to
Speaker 1: understand why and how our lives look the way they do.
Speaker 1: Today's episode is about gaps in time. It's about the
Speaker 1: narrative that we have about what just happened in the world,
Speaker 1: and what happens when chunks of time disappear. When do
Speaker 1: we notice, when do we care? And what does this
Speaker 1: mean at a very deep level in terms of what
Speaker 1: time is for us. I'm going to unpack this mystery
Speaker 1: today by telling the story in six chapters. Gaps in
Speaker 1: Time on the scale of milliseconds, then hours, then weeks, years, millennia,
Speaker 1: and eons. And if this doesn't get you feeling messed
Speaker 1: up about our view of reality, I don't know what. Well,
Speaker 1: So let's start with milliseconds. You are standing in your
Speaker 1: kitchen and looking over at the salt shaker on the table,
Speaker 1: and you think, where's the pepper shaker? And you glance
Speaker 1: over let's say twelve inches to the left of that,
Speaker 1: and there's the pepper shaker. But something strange has just
Speaker 1: happened and you didn't notice it. Your eyes didn't smoothly
Speaker 1: move across the table. Instead between the salt and the pepper,
Speaker 1: your eyes took a ballistic leap. Ballistic just means that
Speaker 1: the movement is launched and can't be changed along the way.
Speaker 1: So there's a sharp movement of your eyes. And these
Speaker 1: jumps are called cecads, and you make three to four
Speaker 1: of these every second while you're looking around the world. Now,
Speaker 1: if you're around anyone else right now, take a careful
Speaker 1: look at their eyes and you will see this. Their
Speaker 1: eyes are jiggling around multiple times a second, fixating on
Speaker 1: one spot, and then a few hundred milliseconds later, jumping
Speaker 1: to the next spot and fixating there. But here's this
Speaker 1: super weird part. Your experience from the inside behind your
Speaker 1: eyes is totally unaware of these secads. You don't notice them.
Speaker 1: You don't feel like the world is jumping around. But
Speaker 1: why not? What does your visual system do while your
Speaker 1: eyes are in motion between the fixations. Why doesn't your
Speaker 1: brain say, oh my god, the world just screamed past.
Speaker 1: Oh no, there it goes again, and so on. Well
Speaker 1: to answer that, I'm going to give you something that
Speaker 1: you can try, and I really want you to do this.
Speaker 1: Take out your cell phone and hit the button to
Speaker 1: record a video. Now, point your camera at something and
Speaker 1: then jerk it over to a nearby position, then jerk
Speaker 1: it to a point at something else, then jerk it again,
Speaker 1: and so on. Now watch the video, and what you'll
Speaker 1: see is that this video is totally nauseating. So here's
Speaker 1: the question. Why isn't it nauseating when your eyes are
Speaker 1: doing exactly what you just did with your cell phone camera.
Speaker 1: The answer is that your vision is not like a camera.
Speaker 1: What you see is your internal model of the world
Speaker 1: out there. Every time you move your eyes, you're just
Speaker 1: gathering more data to add to your internal model of
Speaker 1: the world. So your eyes are jumping around the scene
Speaker 1: like special ops on a secret mission, and they're adding
Speaker 1: little bits of data to your model with each movement.
Speaker 1: And during the periods when your eyes are in motion,
Speaker 1: your visual system essentially shuts down. It says, okay, eyes,
Speaker 1: I want you to take a jump to the next site,
Speaker 1: and while you're in motion, I'm just going to shut
Speaker 1: down information processing until you get there. And that's why
Speaker 1: you don't see the world screaming past. Okay. So that's
Speaker 1: totally amazing, But that's just the beginning of the weirdness
Speaker 1: for today, because the question I want to ask is this.
Speaker 1: It takes time for your eyes to move to make
Speaker 1: that jump. For a small secada, it takes about thirty milliseconds,
Speaker 1: and for large ones they can take over one hundred
Speaker 1: milliseconds a tenth of a second. And as I said,
Speaker 1: you're doing multiple of these jumps every second. So here's
Speaker 1: the mystery. What happens to the gaps in time while
Speaker 1: your eyes are moving. Why don't you notice the small
Speaker 1: absences of visual input? Okay, So the first thing you
Speaker 1: might say is, well, I don't know how long thirty
Speaker 1: milliseconds is maybe that's too short to notice, but it's not.
Speaker 1: If I came into your room right now and flicked
Speaker 1: the lights off and then back on, even for thirty milliseconds,
Speaker 1: you would detect that, and one hundred milliseconds would be
Speaker 1: super obvious. So why don't you notice the little gaps
Speaker 1: while your visual system is on holiday. Well, your brain
Speaker 1: is doing movie editing and it just gets rid of
Speaker 1: those little gaps in time. Now, this might all sound
Speaker 1: a little unbelievable, so I want to give you a
Speaker 1: very easy way to demonstrate this to yourself. First, stare
Speaker 1: up close at your friend's face and ask kim or
Speaker 1: her to look at your left eye, then your right eye,
Speaker 1: then your left eye, then your right eye. And what
Speaker 1: you'll find is that it's very easy to see your
Speaker 1: friend's eyes move. Their eyes make big jumps from one
Speaker 1: position to the other, and you can watch that transition.
Speaker 1: But now what I want you to do is get
Speaker 1: up close to a mirror and stare at your own face. Now,
Speaker 1: look at your own left eye, then your right eye,
Speaker 1: then your left eye, and what you'll see is bizarre.
Speaker 1: You can never see your own eyes move. Your experience
Speaker 1: is that you are fixated on your left eye, and
Speaker 1: then you are suddenly fixated on your right eye, and
Speaker 1: then you are suddenly fixated on your left eye again,
Speaker 1: But you don't see any movement. And the deep, deep
Speaker 1: thing that I want to address today is that there's
Speaker 1: no gap in time. It seems like you're on one
Speaker 1: eye and then you're immediately on the other. You can't
Speaker 1: see the gap in time at all. No, how could
Speaker 1: this possibly be. It's for the same reason that you
Speaker 1: don't see the world screen past you when you move
Speaker 1: your eyes. All you see is your internal model. And
Speaker 1: just like your internal model constructs space for you, it
Speaker 1: constructs time for you also, and if it doesn't want
Speaker 1: to include something in there, like the gap in time,
Speaker 1: then you simply don't experience it. Now, as our store
Speaker 1: already proceeds today, we're going to get a deeper understanding
Speaker 1: of why this is. But for now, let me just
Speaker 1: say that I've been publishing papers on time perception for
Speaker 1: my whole career in journals like Science and Nature and
Speaker 1: so on, because this is such a weird and under
Speaker 1: explored field. The main thing I want to establish for
Speaker 1: now is that our sense of time, how much time
Speaker 1: passed and what happened when is constructed by our brain.
Speaker 1: It's not an accurate barometer of what's happening out there.
Speaker 1: And for today's episode, the issue we're zooming in on
Speaker 1: is what happens when time disappears. Okay, so during eye
Speaker 1: movements we lose little gaps, and now we're ready to
Speaker 1: move to the next chapter of this story of disappearing time.
Speaker 1: If we can lose fractions of a second and never
Speaker 1: know it, what happens when we lose hours. There are
Speaker 1: many hours in your life when you are alive, but
Speaker 1: you have no sense of the passage of time. In total,
Speaker 1: like thirty years worth of hours in a long life
Speaker 1: are gone. And this is because of sleep. You spend
Speaker 1: a third of your life asleep. And what's fascinating for
Speaker 1: today is not simply that you sleep. It's that you
Speaker 1: don't notice time passing. While you do, you close your eyes,
Speaker 1: your thoughts begin to drift, and then what feels like
Speaker 1: an instant later, your alarm is going off. Seven or
Speaker 1: eight hours are gone. Where exactly did that time go? Well,
Speaker 1: here's the trick. The passage of time from the brain's
Speaker 1: point of view is stitched together from memory. If you
Speaker 1: happen to have heard the very first episode of this
Speaker 1: podcast from some years ago. I explained how my students
Speaker 1: and I dropped volunteers from a one hundred and fifty
Speaker 1: foot tall tower in free fall and measured their time
Speaker 1: perception on the way down. And what we covered is
Speaker 1: that time doesn't actually move in slow motion when you're
Speaker 1: in a scary situation. Instead, it's that you lay down
Speaker 1: more memory when you're scared, and so when your brain
Speaker 1: says what just happened, what just happened, it has all
Speaker 1: this detailed footage to draw on, and so it assumes
Speaker 1: that more time has just passed. In other words, we
Speaker 1: estimate duration retrospectively, and we do it by looking at
Speaker 1: how much footage we can pull up. Now, what we're
Speaker 1: talking about here is the flip side. If there's no
Speaker 1: footage at all, then your brain concludes that no time passed.
Speaker 1: And that's what happens to you in sleep. So when
Speaker 1: you're awake, your brain uses all the data streaming in,
Speaker 1: like what happened and who said what and where you were.
Speaker 1: All these things get used as time landmarks. They're mile
Speaker 1: markers in the road of experience. But during sleep, especially
Speaker 1: during slow wave sleep, there's almost no information coming in.
Speaker 1: The brain becomes decoupled from the external world. Now, interestingly,
Speaker 1: during rem sleep, the brain reactivates in some ways that
Speaker 1: look like waking life. There's intense cortical activity, there's vivid dreaming,
Speaker 1: and you often have the sense of a passage of
Speaker 1: time in a dream, sometimes the sense that a long
Speaker 1: time is passed. But in non rem sleep stages, which
Speaker 1: is the majority of the night, there's little dreaming. And
Speaker 1: in the deepest stages of sleep, your neural firing patterns
Speaker 1: become highly synchronized. Neurons fire and rhythmic bursts followed by silence.
Speaker 1: You're not experiencing anything and you're not encoding memories, so
Speaker 1: the result is no memory, no narrative, and no timestamps.
Speaker 1: Nothing is written down in the internal log book. So
Speaker 1: your subjective experience skips from point A falling asleep to
Speaker 1: point B waking up, and you have no passage in between. Now,
Speaker 1: equally weird but chemically induced is anesthesia. You'll sometimes hear
Speaker 1: people describe general anesthesia as a deep sleep, but that's
Speaker 1: a little bit misleading because anesthesia doesn't quite simulate sleep. Instead,
Speaker 1: when you're under an anesthetic agent like propofol, or isofluorane,
Speaker 1: or ketamine. Your brain is doing something different than just
Speaker 1: moving into synchronized activity. Instead, it's more of a disconnection.
Speaker 1: What brain imaging studies show is a breakdown of cortical connectivity,
Speaker 1: especially between the thalamus and the cortex, and between key
Speaker 1: regions that are needed for conscious awareness, like the posterior
Speaker 1: singular cortex and the prefroneral cortex. So when you're anesthetized,
Speaker 1: there's no dream, no floating sensation, no tunnel of light,
Speaker 1: there is nothing. When you wake up, you don't feel
Speaker 1: like time has passed because you was there to witness
Speaker 1: it and write anything down. The brain can't register time
Speaker 1: in the absence of self modeling processes, the default mode network,
Speaker 1: which normally buzzes along constructing your sense of identity, that
Speaker 1: is offline. So when consciousness returns, you emerge from a
Speaker 1: silent void because you have no memory, you have no
Speaker 1: sense of the passage of time. Now, one thing that's
Speaker 1: always struck me is how untroubled we are by this.
Speaker 1: You go under for surgery, you're counting backward from ten
Speaker 1: to nine eight, and then you're blinking awake in recovery
Speaker 1: three hours of past, no questions asked. The continuity of
Speaker 1: your self just hops the gap. Now that should feel bizarre,
Speaker 1: but it doesn't, because, as I said, continuity isn't measured
Speaker 1: by what happens. It's only measured by what gets remembered.
Speaker 1: And you didn't miss anything that you can recall, so
Speaker 1: no time think about how weird that is. Your life
Speaker 1: can be paused without your awareness. You disappear and the
Speaker 1: world keeps starting, and when you return you feel whole
Speaker 1: and intact, like you never left, but you did and
Speaker 1: there was no you to notice. So if your conscious
Speaker 1: self can go entirely offline for seven hours or for
Speaker 1: the length of a surgery and reappear without damage or
Speaker 1: awareness of the missing time, that means we should really
Speaker 1: be thinking about this self not so much like a
Speaker 1: continuous beam, but more like a flame that gets constantly reignited.
Speaker 1: So what we've seen so far with psychotic eye movements
Speaker 1: and sleep and anesthesia is that the movie of your
Speaker 1: life is full of jump cuts, but your brain, the
Speaker 1: great editor, doesn't show you the gaps. It stitches for
Speaker 1: you a seamless illusion. You were here, now you're here,
Speaker 1: You've always been even when you weren't. Now, maybe right
Speaker 1: in the middle of my last sentence, the whole universe
Speaker 1: froze for five hours. We were all completely frozen, no action,
Speaker 1: no memories. And then just as suddenly as we froze,
Speaker 1: the universe started up again. As far as we are concerned,
Speaker 1: the sentence flowed smoothly. You got the meaning of it
Speaker 1: as you continue to drive or walk or drink the coffee.
Speaker 1: And none of us were the wiser for the universe
Speaker 1: coming to a sudden stop and then restarting. And now
Speaker 1: we're ready for chapter three. We've talked about millisecond gaps
Speaker 1: due to eye movements and hours long gaps due to
Speaker 1: sleep or anesthesia. Now let's stretch time even further to weeks.
Speaker 1: What happens when there's no memory laid down for this
Speaker 1: kind of period of time. One scenario where this happens
Speaker 1: is when a person falls into a coma and they
Speaker 1: wake up after a month of being in a coma,
Speaker 1: and it feels like no time has passed at all.
Speaker 1: There are countless stories like this in any hospital war
Speaker 1: a man gets in a terrible motorcycle accident. He is
Speaker 1: rushed to the ICU. He's intubated. He's stabilized, but he's
Speaker 1: in a coma. His brain activity is minimal. There's no communication,
Speaker 1: no awareness. Weeks pass, and then one day, without warning,
Speaker 1: his eyes open. He turns his head, He looks at
Speaker 1: his mother and says, I'm hungry. To the people around him,
Speaker 1: this is a miracle. They've been counting the days. They've
Speaker 1: been pacing the halls, they've been watching the clock. Time
Speaker 1: has passed agonizingly for them, But for him, it's been nothing.
Speaker 1: He reports no dreams, no thoughts, no sense that time
Speaker 1: even moves. One moment, he was riding his motorcycle. The
Speaker 1: next he was in a hospital bed, maybe a little thinner,
Speaker 1: surrounded by unfamiliar machines and unfamiliar faces. It might have
Speaker 1: been six minutes or six weeks. To him, it's the same.
Speaker 1: So what's happening here? A lot of what we know
Speaker 1: about coma comes from EEG readings and fMRI scans, which
Speaker 1: show severely reduced metabolic activity, especially in the cortex, where
Speaker 1: higher order processing lives. The reticular activating system in the
Speaker 1: brain stem, which keeps you aroused, that goes quiet the thalamus,
Speaker 1: which is sort of like a central switchboard. It fails
Speaker 1: to distribute the sensory information and the default mode network,
Speaker 1: which is that ever chattering backdrop of identity and self
Speaker 1: awareness that goes dark. So, in effect, the machinery of
Speaker 1: consciousness powers down, like a city experiencing a blackout. Your
Speaker 1: lights might flicker a little in one nayemborhood, but the
Speaker 1: downtown grid where memory and narrative and time perception live,
Speaker 1: that downtown grid is silent. When someone wakes from a coma,
Speaker 1: they have to figure out where they are and what
Speaker 1: the heck happened. But what's striking is how little distress
Speaker 1: they show over the lost time itself. They may be confused,
Speaker 1: but they're not grieving the missing days. Why. It's because
Speaker 1: you can only feel the passage of time when you
Speaker 1: have been there to experience it. Duration of time is
Speaker 1: something that you build neurally, without sensory input, without new memories.
Speaker 1: There's no architecture of time. The period where one is
Speaker 1: in a coma is not perceived as a gap. It's
Speaker 1: just omitted. So what does this tell us? Consciousness is
Speaker 1: an evolved interface that gives you the experience of being
Speaker 1: a unified self moving through time. The interface can crash,
Speaker 1: and when it does no internal witness remains to keep
Speaker 1: the clock running. So this phrases deep questions about selfhood.
Speaker 1: What does it mean to be you? If you can
Speaker 1: vanish for months and reappear unchanged. If months of your
Speaker 1: life can go unregistered, not as memory and therefore not
Speaker 1: as a duration, then was it part of your life
Speaker 1: at all? Your life is only what you write down
Speaker 1: in your neural circuits. And when your consciousness vanishes, so
Speaker 1: does the passage of time. So we just explored the
Speaker 1: gaps caused by unconsciousness, sleep and anesthesia and coma. But
Speaker 1: now we reach something stranger. When you're fully awake, your
Speaker 1: eyes are open, your senses are functioning, and time still vanishes.
Speaker 1: This is in particular let's talk about what's called antaro
Speaker 1: grade amnesia, which is the inability to make new memories
Speaker 1: after you get some brain damage. So your short term
Speaker 1: working memory can remain fine, so you can carry on
Speaker 1: a conversation, you can make a cup of coffee, but
Speaker 1: you won't retain any of what just happened fifteen minutes later.
Speaker 1: In other words, you've got short term memory, but you
Speaker 1: are not converting it into long term memory. Experience evaporates
Speaker 1: outside a fifteen minute window. The key player here is
Speaker 1: a region of the brain called the medial temporal lobe,
Speaker 1: and inside that the hippocampus and the surrounding cortex. These
Speaker 1: regions act as a kind of staging ground where new
Speaker 1: experiences are encoded and then gradually consolidated into long term
Speaker 1: memory from interactions with the rest of the cortex. When
Speaker 1: the hippocampus is damaged, which can happen for a lot
Speaker 1: of reasons like stroke or trauma, or hypoxia or encephalitis.
Speaker 1: When the hippocampus is damaged, the encoding of memories gets disrupted.
Speaker 1: You still got sensory input getting to the brain, Your
Speaker 1: emotions are still functioning. You still have your motor skills
Speaker 1: like walking and eating. But the narrative thread of life
Speaker 1: I was here and then I was there, that part
Speaker 1: is severed. So consider this case of Henry Meliason. It's
Speaker 1: a pretty well known case. He had epilepsy, and so
Speaker 1: the surgeons removed a lot of his medial temporal lobe,
Speaker 1: including the hippocampus on both sides of his brain, and
Speaker 1: when he woke up from the surgery, it was found
Speaker 1: that had indeed cured the epilepsy and everything seemed perfectly
Speaker 1: fine until his clinical team realized that something wasn't quite right,
Speaker 1: and it became clear that his short term memory was
Speaker 1: fine and his long term memory was fine, but he
Speaker 1: could no longer make the new long term memories. In
Speaker 1: other words, he could carry on conversationations for ten minutes,
Speaker 1: but afterward it was as if nothing had ever occurred,
Speaker 1: no learning, no narrative, no accumulation of time. His consciousness
Speaker 1: would reset with each passing moment. So even though the
Speaker 1: surgery took place in nineteen fifty three when he was
Speaker 1: twenty seven years old, he lived for fifty five more
Speaker 1: years after his surgery, and during that time he was
Speaker 1: stuck in what one of his researchers, Suzanne Corkin, called
Speaker 1: a permanent present tense. For example, he could remember living
Speaker 1: with his parents and playing with his cousin's neighbors. His
Speaker 1: relationship with his mother remained a touchstone even after her death.
Speaker 1: He thought she was still alive because his stable memories
Speaker 1: were from when he lived at home with her in
Speaker 1: the nineteen forties nineteen fifties. Henry was a teenager during
Speaker 1: World War Two, and he retained knowledge from that period
Speaker 1: to him even from the late nineteen forties felt just
Speaker 1: as near to him in time as they did when
Speaker 1: he first underwent the surgery. When asked about his employment,
Speaker 1: he sometimes mentioned working at a typewriter factory in the
Speaker 1: nineteen forties, as though that were his current or most
Speaker 1: recent job. His cultural knowledge was frozen in the early
Speaker 1: nineteen fifties, so people said that meeting him was like
Speaker 1: speaking to someone displaced from the Eisenhower era, with none
Speaker 1: of the intervening decades having registered. So his body aged,
Speaker 1: but his personal timeline didn't. Events didn't accumulate into a
Speaker 1: personal timeline, so decades really did vanish for him. It
Speaker 1: was as though those years had simply never been lived.
Speaker 1: Neurosurgeons stopped doing those medial temporal lobe surgeries as soon
Speaker 1: as they saw what had happened with Henry, But you
Speaker 1: can still see this condition of antaro g amnesia all
Speaker 1: the time. For example, it happens in Corsicov's syndrome, which
Speaker 1: is caused by chronic alcohol abuse leading to thiamine deficiency.
Speaker 1: The damage affects a circuit that's critical for laying down memories,
Speaker 1: and the result is patients who are alert and socially
Speaker 1: interactive but just like Henry, they live in a kind
Speaker 1: of temporal groundhog day because they are not laying down
Speaker 1: long term memory, and so when they say how much
Speaker 1: time passed since I was last year, there's no memory
Speaker 1: footage to draw on, and so the answer is no time. Now.
Speaker 1: Shift a bit to imagine not just losing the ability
Speaker 1: to build new memories, but also retrograde amnesia, losing memories
Speaker 1: that had already been encoded. And this can happen after,
Speaker 1: for example, a major brain injury. Here the damage tends
Speaker 1: to affect the areas where memory has previously laid down,
Speaker 1: like the the temporal in the frontal lobes. Depending on
Speaker 1: the severity, you can wipe out months or years or
Speaker 1: even decades. Now. One of the oldest rules in neurology
Speaker 1: is called ribos law, and this is that older memories
Speaker 1: are more stable than newer memories. I wrote about this
Speaker 1: at length in my book Live Wire. But the bottom
Speaker 1: line is that older memories get burned more into the
Speaker 1: circuitry of the brain with time. So in these medical
Speaker 1: cases of retrograde amnesia, a person wakes up after head
Speaker 1: injury and they still know how to speak, how to walk,
Speaker 1: how to solve a math problem, but they have no
Speaker 1: memory of their spouse, their job, maybe their own name.
Speaker 1: Procedural memory, which is how to do things like ead
Speaker 1: or walk or talk that remains. But autobiographical continuity, the
Speaker 1: sense of being a single person through time that breaks
Speaker 1: from the outside. Their life has gone on, but from
Speaker 1: the inside, their personal timeline has been redacted. The calendar
Speaker 1: has skipped, and they have no internal record of the passage.
Speaker 1: So that brings us back to the central lesson that
Speaker 1: the experience of duration has everything to do with episodic memory.
Speaker 1: We crank up a network called the default mode network.
Speaker 1: This includes a number of regions, but the key is
Speaker 1: that this network is active during introspection and daydreaming and
Speaker 1: imagining the future. It's how we mentally time travel, reliving
Speaker 1: the past, simulating possible futures, placing ourselves in a temporal context.
Speaker 1: When episodic memory fails, when nothing gets written down, the
Speaker 1: internal model of the passage of time collapses. There may
Speaker 1: be sensory continuity, but there's no narrative continuity. Just like
Speaker 1: coma patients, the people with amnesia often don't feel distress
Speaker 1: about the missing time because they don't experience it. Is missing.
Speaker 1: The brain doesn't alert you to what it failed to store.
Speaker 1: If no memory was written, the time doesn't register as empty.
Speaker 1: It just is non existent. Again, this is just like
Speaker 1: your deep sleep at night. You don't lay down memories
Speaker 1: and the time just poof disappears. In this sense, we're
Speaker 1: all like Henry. Eight hours just passed, but we splice
Speaker 1: the film together, just like Henry between his twenty seventh
Speaker 1: birthday and sixty seventh birthday. Okay, so we've talked about
Speaker 1: missing milliseconds and hours and even years. But there's another
Speaker 1: kind of time distortion, one that doesn't happen in your
Speaker 1: direct experience, but instead inside your imagination. And that happens
Speaker 1: when we try to think about centuries or about millennia,
Speaker 1: about things way older than our own lives or our parents'
Speaker 1: lives or the oldest thing we've ever touched personally, were
Speaker 1: really bad at long time. So ask a group of
Speaker 1: sixth graders what happened one hundred years ago, and they'll
Speaker 1: say the olden days or maybe before the Internet. But
Speaker 1: one hundred years ago was nineteen twenty five, when the
Speaker 1: Model t Ford was rolling off assembly lines and the
Speaker 1: Great War was over, and quantum mechanics was controversial. Asked
Speaker 1: them about five hundred years ago, and you might as
Speaker 1: well be describing mythology. The timeline collapses into a soup
Speaker 1: of olden stuff, where Genghis Khan and Cleopatra and Abraham
Speaker 1: Lincoln all might live at the same time. Now, as
Speaker 1: you grow older, you get better at understanding time, in
Speaker 1: part because you have more practice at it. You get
Speaker 1: to know what longer and longer periods feel like. In
Speaker 1: other words, the ability to judge historical time requires a
Speaker 1: cognitive map of scale, and that map has to be built.
Speaker 1: Children's brains are still developing ways of representing duration and
Speaker 1: sequence and castality over large time scales. What it has
Speaker 1: to do with is the gradual accumulation of memory across years.
Speaker 1: In other words, you get better at representing long time
Speaker 1: scals because you've lived more time. To a six year old,
Speaker 1: one year is a sixth of their entire life, it's massive.
Speaker 1: But to a sixty year old, one year is a blip.
Speaker 1: It's a small ripple in the pool of memory. So
Speaker 1: our internal yardstick for time stretches. As we age, we
Speaker 1: got a better sense of proportion. We begin to feel
Speaker 1: what a century might mean not because we remember it directly,
Speaker 1: but because we've had enough decades to simulate it with
Speaker 1: some emotional weight. But go further back, like ten thousand
Speaker 1: years or one hundred thousand, and your mental simulation is
Speaker 1: not particularly good. You've got evolutionary time, in geological time,
Speaker 1: and cosmological time. These scales are too vast to inhabit intuitively.
Speaker 1: You can say the invention of writing is six thousand
Speaker 1: years old, but does that number feel real? Can you
Speaker 1: feel the difference between six thousand and sixty thousand? For example,
Speaker 1: there's an internet meme that asks did Cleopatra live closer
Speaker 1: in time to the building of the Great Pyramid at
Speaker 1: Giza or to the lunar landing. Now you'll remember that
Speaker 1: Cleopatra was the Greek queen of Egypt from fifty one
Speaker 1: to thirty BC. So what comes as a great surprise
Speaker 1: to a lot of people was that she was actually
Speaker 1: closer in time to the moon landing. Why because she
Speaker 1: was born about two thousand, five hundred years after the
Speaker 1: Great Pyramid at Giza was built, and only about two
Speaker 1: thousand years before the first lunar landing, So she was
Speaker 1: five hundred years closer to moon landings. And iPhones and
Speaker 1: chat GPT than to the Great Pyramid. It's surprising, right,
Speaker 1: And what it demonstrates is that none of us have
Speaker 1: particularly good intuitions about deep time. Now, if you are
Speaker 1: an evolutionary biologist or a geologist or an astrophysicist, you
Speaker 1: can learn how to do temporal sequencing, like that event
Speaker 1: happened a billion years before that other event, But you
Speaker 1: may as well be memorizing the order of exits on
Speaker 1: the highway in the sense that you're not feeling or
Speaker 1: simulating a billion year. You're mostly just memorizing that road sign.
Speaker 1: So what seems clear is that as soon as we
Speaker 1: start talking really long timescales, our brains just weren't built
Speaker 1: for that. Really, think about this, what's the longest period
Speaker 1: of time that you can realistically simulate emotionally? You can
Speaker 1: sort of feel what a day feels like, probably a week,
Speaker 1: a month, and you may even have enough experience in
Speaker 1: the world that you can really feel the weight of
Speaker 1: a year or maybe even a decade. But can you
Speaker 1: really simulate what it would be like to spend a
Speaker 1: century of time hanging out and doom scrolling and cooking
Speaker 1: meals and taking your dog for a walk for a
Speaker 1: thousand years. Just try to imagine ten thousand years since
Speaker 1: the invention of agriculture. Try to feel ten thousand years.
Speaker 1: Your brain might conjure up some images like cave paintings
Speaker 1: and mammoths and spears, but can you actually understand the
Speaker 1: sheer stretch of a time period like that. Presumably not,
Speaker 1: We're just not wired for it. Our temporal reasoning evolved
Speaker 1: in the service of short term prediction, hunting and gathering,
Speaker 1: planning social exchanges, maybe tracking seasons, but that's it. The
Speaker 1: oldest parts of the brain work in rhythms of hours
Speaker 1: and days, or sometimes weeks. This is why we struggle
Speaker 1: to grasp timelines like civilizational collapse, or for younger people,
Speaker 1: even something like retirement planning. Our cognitive system compresses distant
Speaker 1: time the way it compresses vision, blurring the edges to
Speaker 1: focus on what's close. Just like we have a phobia
Speaker 1: in the eye, a center of sharp focus, we have
Speaker 1: what you can think of as a temporal phobia, which
Speaker 1: sharpens the present and blurs the deep past and distant future.
Speaker 1: The truth is it's sort of a biological miracle that
Speaker 1: we can contemplate large time scales at all. We can
Speaker 1: look at a fossil and say this was alive three
Speaker 1: hundred million years ago, and feel even the faintest flicker
Speaker 1: of what that means. It's surprising that our brains can
Speaker 1: even attempt to model epics that no organism ever lived
Speaker 1: to see. We've talked about missing time, milliseconds loss to
Speaker 1: eye movements, hours lost to sleep, years vanished to amnesia,
Speaker 1: centuries gone because we can't understand deep time. We've seen
Speaker 1: how the brain edits the story and patches the gaps.
Speaker 1: But what if entire chapters of Earth's history are missing,
Speaker 1: not from your memory, but from the planet's memory. Here's
Speaker 1: what I mean. It seems clear enough that we humans
Speaker 1: are the first intelligent civilization. We're the only creatures to
Speaker 1: build cities, to form empires, to write literature about ourselves.
Speaker 1: But we've only been here for the last last blink
Speaker 1: of evolutionary time. We invented agriculture only ten thousand years ago,
Speaker 1: in something like a big urban center with laws and organization.
Speaker 1: It's all unbelievably new. But the Earth is four point
Speaker 1: five billion years old, and complex life has been around
Speaker 1: for hundreds of millions of years. So here's a speculation
Speaker 1: that Some thinkers have chewed on what if we are
Speaker 1: not the first? What if something like a civilization had arisen,
Speaker 1: say six hundred million years ago, way before Homo sapiens,
Speaker 1: like a full civilization with philosophies and literature and politics
Speaker 1: and music and wars, And maybe the civilization lasted for
Speaker 1: twenty million years, and we would have no idea it
Speaker 1: had ever been here. Now, how could that possibly be?
Speaker 1: Wouldn't we find fossil evidence of them? Well, under certain circumstances,
Speaker 1: we might, But let's say they were soft bodied organisms,
Speaker 1: we would almost certainly never know. Soft tissues decay quickly.
Speaker 1: Fossilization is very rare, and if things aren't buried in
Speaker 1: the right sediment, they can vanish without a trace. So
Speaker 1: our fossil record as it stands is a shattered mosaic.
Speaker 1: It's a few lucky remnants scattered across eons of erosion.
Speaker 1: So think about the Ediacaran period, about six hundred million
Speaker 1: years ago. That's before trilobytes, before shells, before vertebrates. We
Speaker 1: have impressions in sandstone of strange, soft bodied life forms,
Speaker 1: organisms with no clear ancestors or descendants. Their biology is strange,
Speaker 1: Their symmetry is unfamiliar. Could some of them have evolved intelligence?
Speaker 1: Could they have had cognition, maybe not quite like ours,
Speaker 1: but in some way parallel. Could they have built societies
Speaker 1: and languages and structure that we can't even imagine. If
Speaker 1: they did, and if they were made of soft flesh,
Speaker 1: glatinous matter, fragile compounds, and they built their civilizations with
Speaker 1: adobe homes, the odds are that none of the appropriate
Speaker 1: evidence would exist anymore for us to find. No bones,
Speaker 1: no ruins, just a story that played out hundreds of
Speaker 1: millions of years before us and was completely erased. So
Speaker 1: we assume we're the first ones to tell a story.
Speaker 1: But maybe we're just the ones holding the pen at
Speaker 1: the moment, totally unaware of how many other pens were
Speaker 1: lifted and scratched across time and then lost. Here's the
Speaker 1: link to what I've been talking about. The Earth has
Speaker 1: no central memory or backup drive. If there are no
Speaker 1: records that survive, no fossils, no scars on the crust
Speaker 1: that lasted this long, then that time is gone and
Speaker 1: it's therefore forgotten and unrecoverable. Just like you falling into
Speaker 1: a deep sleep or having amnesia. It's another gap in time.
Speaker 1: We like to believe that history is cumulative, that it
Speaker 1: adds up in layers like strata in a canyon wall.
Speaker 1: But as we saw in the neuroscience of the first
Speaker 1: four chapters of today's podcast, history can be fragile and erasable.
Speaker 1: Any story from milliseconds to eons can pass, and if
Speaker 1: there's no record, then there's no memory. What we've seen
Speaker 1: today is that time is a narrative medium, and narratives
Speaker 1: can fail, They can go unrecorded, they can be lost.
Speaker 1: We began with milliseconds lost to eye movements called secods,
Speaker 1: where the brain quietly deletes motion, blur and pastes your
Speaker 1: world back together as if nothing ever vanished. We moved
Speaker 1: to hours lost to sleep, where consciousness dissolves and time
Speaker 1: drops out unnoticed. We looked into anesthesia, where the self
Speaker 1: disappears completely, no memory, no mind, no time, and then
Speaker 1: returns like a light flicked back on. We stretched to
Speaker 1: weeks and months and years. Time scale is lost not
Speaker 1: to unconsciousness, but to amnesia, where the person continues but
Speaker 1: the story does not, a life lived but not remembered
Speaker 1: because the timeline never makes it to the page. Then
Speaker 1: we pushed it further to centuries and millennia, where even
Speaker 1: our best efforts at understanding falter, where time becomes too
Speaker 1: vast to meaningfully simulate it anymore. And finally, we looked
Speaker 1: back into deep time, hundreds of millions of years, where
Speaker 1: entire histories may have unfolded before us, only to be
Speaker 1: erased by geology, by the quiet forgetting of a planet
Speaker 1: with no memory. The wild part is that in all
Speaker 1: these cases, we move forward, stitching together a story from fragments,
Speaker 1: believing it to be complete. But it's important to remember
Speaker 1: that we are the inheritors of a story that is
Speaker 1: largely erased, and if you ask me, it's a story
Speaker 1: that we do not fully understand, a story whose missing
Speaker 1: pages occasionally outnumber the ones that we have. And yet
Speaker 1: we keep telling our stories because that's all we've got.
Speaker 1: So across all these scales milliseconds to eons, we see
Speaker 1: a common thread. If events are not remembered, they might
Speaker 1: as well not have happened. Our sense of time is
Speaker 1: simply what gets recorded by anything from neurons to fossils.
Speaker 1: When the record fails, the time disappears. So we assemble
Speaker 1: our narrative from scraps moments we notice, memories, we hold, traces,
Speaker 1: we dig from the earth, and what we call reality
Speaker 1: is just the part that we managed to write down.
Speaker 1: Go to eagleman dot com slash podcast more information and
Speaker 1: to find further reading. Join the weekly discussions on my substack,
Speaker 1: and check out and subscribe to Inner Cosmos on YouTube
Speaker 1: for videos of each episode and to leave comments until
Speaker 1: next time. I'm David Eagleman, and this is Inner Cosmos.