Ep124 "Why don't we notice gaps in time?"

about your life. Welcome to Inner Cosmos with me David Eagleman. I'm a neuroscientist and author at Stanford and in these episodes we sail deeply into our three pound universe to understand why and how our lives look the way they do. Today's episode is about gaps in time. It's about the narrative that we have about what just happened in the world, and what happens when chunks of time disappear. When do we notice, when do we care? And what does this mean at a very deep level in terms of what

time is for us. I'm going to unpack this mystery today by telling the story in six chapters. Gaps in Time on the scale of milliseconds, then hours, then weeks, years, millennia, and eons. And if this doesn't get you feeling messed up about our view of reality, I don't know what. Well, So let's start with milliseconds. You are standing in your kitchen and looking over at the salt shaker on the table,

and you think, where's the pepper shaker? And you glance over let's say twelve inches to the left of that, and there's the pepper shaker. But something strange has just happened and you didn't notice it. Your eyes didn't smoothly move across the table. Instead between the salt and the pepper, your eyes took a ballistic leap. Ballistic just means that the movement is launched and can't be changed along the way.

So there's a sharp movement of your eyes. And these jumps are called cecads, and you make three to four of these every second while you're looking around the world. Now, if you're around anyone else right now, take a careful look at their eyes and you will see this. Their eyes are jiggling around multiple times a second, fixating on one spot, and then a few hundred milliseconds later, jumping to the next spot and fixating there. But here's this

super weird part. Your experience from the inside behind your eyes is totally unaware of these secads. You don't notice them. You don't feel like the world is jumping around. But why not? What does your visual system do while your eyes are in motion between the fixations. Why doesn't your brain say, oh my god, the world just screamed past. Oh no, there it goes again, and so on. Well to answer that, I'm going to give you something that you can try, and I really want you to do this.

Take out your cell phone and hit the button to record a video. Now, point your camera at something and then jerk it over to a nearby position, then jerk it to a point at something else, then jerk it again, and so on. Now watch the video, and what you'll see is that this video is totally nauseating. So here's the question. Why isn't it nauseating when your eyes are doing exactly what you just did with your cell phone camera. The answer is that your vision is not like a camera.

What you see is your internal model of the world out there. Every time you move your eyes, you're just gathering more data to add to your internal model of the world. So your eyes are jumping around the scene like special ops on a secret mission, and they're adding little bits of data to your model with each movement. And during the periods when your eyes are in motion,

your visual system essentially shuts down. It says, okay, eyes, I want you to take a jump to the next site, and while you're in motion, I'm just going to shut down information processing until you get there. And that's why you don't see the world screaming past. Okay. So that's totally amazing, But that's just the beginning of the weirdness for today, because the question I want to ask is this. It takes time for your eyes to move to make

that jump. For a small secada, it takes about thirty milliseconds, and for large ones they can take over one hundred milliseconds a tenth of a second. And as I said, you're doing multiple of these jumps every second. So here's the mystery. What happens to the gaps in time while your eyes are moving. Why don't you notice the small absences of visual input? Okay, So the first thing you might say is, well, I don't know how long thirty milliseconds is maybe that's too short to notice, but it's not.

If I came into your room right now and flicked the lights off and then back on, even for thirty milliseconds, you would detect that, and one hundred milliseconds would be super obvious. So why don't you notice the little gaps while your visual system is on holiday. Well, your brain is doing movie editing and it just gets rid of those little gaps in time. Now, this might all sound a little unbelievable, so I want to give you a

very easy way to demonstrate this to yourself. First, stare up close at your friend's face and ask kim or her to look at your left eye, then your right eye, then your left eye, then your right eye. And what you'll find is that it's very easy to see your friend's eyes move. Their eyes make big jumps from one position to the other, and you can watch that transition. But now what I want you to do is get

up close to a mirror and stare at your own face. Now, look at your own left eye, then your right eye, then your left eye, and what you'll see is bizarre. You can never see your own eyes move. Your experience is that you are fixated on your left eye, and then you are suddenly fixated on your right eye, and then you are suddenly fixated on your left eye again, But you don't see any movement. And the deep, deep thing that I want to address today is that there's

no gap in time. It seems like you're on one eye and then you're immediately on the other. You can't see the gap in time at all. No, how could this possibly be. It's for the same reason that you don't see the world screen past you when you move your eyes. All you see is your internal model. And just like your internal model constructs space for you, it constructs time for you also, and if it doesn't want to include something in there, like the gap in time,

then you simply don't experience it. Now, as our store already proceeds today, we're going to get a deeper understanding of why this is. But for now, let me just say that I've been publishing papers on time perception for my whole career in journals like Science and Nature and so on, because this is such a weird and under explored field. The main thing I want to establish for now is that our sense of time, how much time passed and what happened when is constructed by our brain.

It's not an accurate barometer of what's happening out there. And for today's episode, the issue we're zooming in on is what happens when time disappears. Okay, so during eye movements we lose little gaps, and now we're ready to move to the next chapter of this story of disappearing time. If we can lose fractions of a second and never know it, what happens when we lose hours. There are many hours in your life when you are alive, but

you have no sense of the passage of time. In total, like thirty years worth of hours in a long life are gone. And this is because of sleep. You spend a third of your life asleep. And what's fascinating for today is not simply that you sleep. It's that you don't notice time passing. While you do, you close your eyes, your thoughts begin to drift, and then what feels like an instant later, your alarm is going off. Seven or eight hours are gone. Where exactly did that time go? Well,

here's the trick. The passage of time from the brain's point of view is stitched together from memory. If you happen to have heard the very first episode of this podcast from some years ago. I explained how my students and I dropped volunteers from a one hundred and fifty foot tall tower in free fall and measured their time perception on the way down. And what we covered is that time doesn't actually move in slow motion when you're

in a scary situation. Instead, it's that you lay down more memory when you're scared, and so when your brain says what just happened, what just happened, it has all this detailed footage to draw on, and so it assumes that more time has just passed. In other words, we estimate duration retrospectively, and we do it by looking at how much footage we can pull up. Now, what we're talking about here is the flip side. If there's no footage at all, then your brain concludes that no time passed.

And that's what happens to you in sleep. So when you're awake, your brain uses all the data streaming in, like what happened and who said what and where you were. All these things get used as time landmarks. They're mile markers in the road of experience. But during sleep, especially during slow wave sleep, there's almost no information coming in. The brain becomes decoupled from the external world. Now, interestingly, during rem sleep, the brain reactivates in some ways that

look like waking life. There's intense cortical activity, there's vivid dreaming, and you often have the sense of a passage of time in a dream, sometimes the sense that a long time is passed. But in non rem sleep stages, which is the majority of the night, there's little dreaming. And in the deepest stages of sleep, your neural firing patterns become highly synchronized. Neurons fire and rhythmic bursts followed by silence.

You're not experiencing anything and you're not encoding memories, so the result is no memory, no narrative, and no timestamps. Nothing is written down in the internal log book. So your subjective experience skips from point A falling asleep to point B waking up, and you have no passage in between. Now, equally weird but chemically induced is anesthesia. You'll sometimes hear people describe general anesthesia as a deep sleep, but that's

a little bit misleading because anesthesia doesn't quite simulate sleep. Instead, when you're under an anesthetic agent like propofol, or isofluorane, or ketamine. Your brain is doing something different than just moving into synchronized activity. Instead, it's more of a disconnection. What brain imaging studies show is a breakdown of cortical connectivity, especially between the thalamus and the cortex, and between key regions that are needed for conscious awareness, like the posterior

singular cortex and the prefroneral cortex. So when you're anesthetized, there's no dream, no floating sensation, no tunnel of light, there is nothing. When you wake up, you don't feel like time has passed because you was there to witness it and write anything down. The brain can't register time in the absence of self modeling processes, the default mode network, which normally buzzes along constructing your sense of identity, that

is offline. So when consciousness returns, you emerge from a silent void because you have no memory, you have no sense of the passage of time. Now, one thing that's always struck me is how untroubled we are by this. You go under for surgery, you're counting backward from ten to nine eight, and then you're blinking awake in recovery three hours of past, no questions asked. The continuity of

your self just hops the gap. Now that should feel bizarre, but it doesn't, because, as I said, continuity isn't measured by what happens. It's only measured by what gets remembered. And you didn't miss anything that you can recall, so no time think about how weird that is. Your life can be paused without your awareness. You disappear and the world keeps starting, and when you return you feel whole and intact, like you never left, but you did and

there was no you to notice. So if your conscious self can go entirely offline for seven hours or for the length of a surgery and reappear without damage or awareness of the missing time, that means we should really be thinking about this self not so much like a continuous beam, but more like a flame that gets constantly reignited. So what we've seen so far with psychotic eye movements and sleep and anesthesia is that the movie of your life is full of jump cuts, but your brain, the

great editor, doesn't show you the gaps. It stitches for you a seamless illusion. You were here, now you're here, You've always been even when you weren't. Now, maybe right in the middle of my last sentence, the whole universe froze for five hours. We were all completely frozen, no action, no memories. And then just as suddenly as we froze, the universe started up again. As far as we are concerned,

the sentence flowed smoothly. You got the meaning of it as you continue to drive or walk or drink the coffee. And none of us were the wiser for the universe coming to a sudden stop and then restarting. And now we're ready for chapter three. We've talked about millisecond gaps due to eye movements and hours long gaps due to sleep or anesthesia. Now let's stretch time even further to weeks. What happens when there's no memory laid down for this

kind of period of time. One scenario where this happens is when a person falls into a coma and they wake up after a month of being in a coma, and it feels like no time has passed at all. There are countless stories like this in any hospital war a man gets in a terrible motorcycle accident. He is rushed to the ICU. He's intubated. He's stabilized, but he's in a coma. His brain activity is minimal. There's no communication, no awareness. Weeks pass, and then one day, without warning,

his eyes open. He turns his head, He looks at his mother and says, I'm hungry. To the people around him, this is a miracle. They've been counting the days. They've been pacing the halls, they've been watching the clock. Time has passed agonizingly for them, But for him, it's been nothing. He reports no dreams, no thoughts, no sense that time even moves. One moment, he was riding his motorcycle. The next he was in a hospital bed, maybe a little thinner,

surrounded by unfamiliar machines and unfamiliar faces. It might have been six minutes or six weeks. To him, it's the same. So what's happening here? A lot of what we know about coma comes from EEG readings and fMRI scans, which show severely reduced metabolic activity, especially in the cortex, where higher order processing lives. The reticular activating system in the brain stem, which keeps you aroused, that goes quiet the thalamus,

which is sort of like a central switchboard. It fails to distribute the sensory information and the default mode network, which is that ever chattering backdrop of identity and self awareness that goes dark. So, in effect, the machinery of consciousness powers down, like a city experiencing a blackout. Your lights might flicker a little in one nayemborhood, but the downtown grid where memory and narrative and time perception live,

that downtown grid is silent. When someone wakes from a coma, they have to figure out where they are and what the heck happened. But what's striking is how little distress they show over the lost time itself. They may be confused, but they're not grieving the missing days. Why. It's because you can only feel the passage of time when you have been there to experience it. Duration of time is something that you build neurally, without sensory input, without new memories.

There's no architecture of time. The period where one is in a coma is not perceived as a gap. It's just omitted. So what does this tell us? Consciousness is an evolved interface that gives you the experience of being a unified self moving through time. The interface can crash, and when it does no internal witness remains to keep the clock running. So this phrases deep questions about selfhood. What does it mean to be you? If you can

vanish for months and reappear unchanged. If months of your life can go unregistered, not as memory and therefore not as a duration, then was it part of your life at all? Your life is only what you write down in your neural circuits. And when your consciousness vanishes, so does the passage of time. So we just explored the gaps caused by unconsciousness, sleep and anesthesia and coma. But

now we reach something stranger. When you're fully awake, your eyes are open, your senses are functioning, and time still vanishes. This is in particular let's talk about what's called antaro grade amnesia, which is the inability to make new memories after you get some brain damage. So your short term working memory can remain fine, so you can carry on a conversation, you can make a cup of coffee, but you won't retain any of what just happened fifteen minutes later.

In other words, you've got short term memory, but you are not converting it into long term memory. Experience evaporates outside a fifteen minute window. The key player here is a region of the brain called the medial temporal lobe, and inside that the hippocampus and the surrounding cortex. These regions act as a kind of staging ground where new experiences are encoded and then gradually consolidated into long term

memory from interactions with the rest of the cortex. When the hippocampus is damaged, which can happen for a lot of reasons like stroke or trauma, or hypoxia or encephalitis. When the hippocampus is damaged, the encoding of memories gets disrupted. You still got sensory input getting to the brain, Your emotions are still functioning. You still have your motor skills like walking and eating. But the narrative thread of life I was here and then I was there, that part

is severed. So consider this case of Henry Meliason. It's

a pretty well known case. He had epilepsy, and so the surgeons removed a lot of his medial temporal lobe, including the hippocampus on both sides of his brain, and when he woke up from the surgery, it was found that had indeed cured the epilepsy and everything seemed perfectly fine until his clinical team realized that something wasn't quite right, and it became clear that his short term memory was fine and his long term memory was fine, but he

could no longer make the new long term memories. In other words, he could carry on conversationations for ten minutes, but afterward it was as if nothing had ever occurred, no learning, no narrative, no accumulation of time. His consciousness

would reset with each passing moment. So even though the surgery took place in nineteen fifty three when he was twenty seven years old, he lived for fifty five more years after his surgery, and during that time he was stuck in what one of his researchers, Suzanne Corkin, called a permanent present tense. For example, he could remember living with his parents and playing with his cousin's neighbors. His relationship with his mother remained a touchstone even after her death.

He thought she was still alive because his stable memories were from when he lived at home with her in the nineteen forties nineteen fifties. Henry was a teenager during World War Two, and he retained knowledge from that period to him even from the late nineteen forties felt just as near to him in time as they did when

he first underwent the surgery. When asked about his employment, he sometimes mentioned working at a typewriter factory in the nineteen forties, as though that were his current or most recent job. His cultural knowledge was frozen in the early nineteen fifties, so people said that meeting him was like speaking to someone displaced from the Eisenhower era, with none of the intervening decades having registered. So his body aged, but his personal timeline didn't. Events didn't accumulate into a

personal timeline, so decades really did vanish for him. It was as though those years had simply never been lived. Neurosurgeons stopped doing those medial temporal lobe surgeries as soon as they saw what had happened with Henry, But you can still see this condition of antaro g amnesia all the time. For example, it happens in Corsicov's syndrome, which is caused by chronic alcohol abuse leading to thiamine deficiency.

The damage affects a circuit that's critical for laying down memories, and the result is patients who are alert and socially interactive but just like Henry, they live in a kind of temporal groundhog day because they are not laying down long term memory, and so when they say how much time passed since I was last year, there's no memory footage to draw on, and so the answer is no time. Now.

Shift a bit to imagine not just losing the ability to build new memories, but also retrograde amnesia, losing memories that had already been encoded. And this can happen after, for example, a major brain injury. Here the damage tends to affect the areas where memory has previously laid down, like the the temporal in the frontal lobes. Depending on the severity, you can wipe out months or years or

even decades. Now. One of the oldest rules in neurology is called ribos law, and this is that older memories are more stable than newer memories. I wrote about this at length in my book Live Wire. But the bottom line is that older memories get burned more into the

circuitry of the brain with time. So in these medical cases of retrograde amnesia, a person wakes up after head injury and they still know how to speak, how to walk, how to solve a math problem, but they have no memory of their spouse, their job, maybe their own name. Procedural memory, which is how to do things like ead or walk or talk that remains. But autobiographical continuity, the sense of being a single person through time that breaks from the outside. Their life has gone on, but from

the inside, their personal timeline has been redacted. The calendar has skipped, and they have no internal record of the passage. So that brings us back to the central lesson that the experience of duration has everything to do with episodic memory. We crank up a network called the default mode network. This includes a number of regions, but the key is that this network is active during introspection and daydreaming and

imagining the future. It's how we mentally time travel, reliving the past, simulating possible futures, placing ourselves in a temporal context. When episodic memory fails, when nothing gets written down, the internal model of the passage of time collapses. There may be sensory continuity, but there's no narrative continuity. Just like coma patients, the people with amnesia often don't feel distress about the missing time because they don't experience it. Is missing.

The brain doesn't alert you to what it failed to store. If no memory was written, the time doesn't register as empty. It just is non existent. Again, this is just like your deep sleep at night. You don't lay down memories and the time just poof disappears. In this sense, we're all like Henry. Eight hours just passed, but we splice the film together, just like Henry between his twenty seventh birthday and sixty seventh birthday. Okay, so we've talked about

missing milliseconds and hours and even years. But there's another kind of time distortion, one that doesn't happen in your direct experience, but instead inside your imagination. And that happens when we try to think about centuries or about millennia, about things way older than our own lives or our parents' lives or the oldest thing we've ever touched personally, were really bad at long time. So ask a group of sixth graders what happened one hundred years ago, and they'll

say the olden days or maybe before the Internet. But one hundred years ago was nineteen twenty five, when the Model t Ford was rolling off assembly lines and the Great War was over, and quantum mechanics was controversial. Asked them about five hundred years ago, and you might as well be describing mythology. The timeline collapses into a soup of olden stuff, where Genghis Khan and Cleopatra and Abraham

Lincoln all might live at the same time. Now, as you grow older, you get better at understanding time, in part because you have more practice at it. You get to know what longer and longer periods feel like. In other words, the ability to judge historical time requires a cognitive map of scale, and that map has to be built. Children's brains are still developing ways of representing duration and

sequence and castality over large time scales. What it has to do with is the gradual accumulation of memory across years. In other words, you get better at representing long time scals because you've lived more time. To a six year old, one year is a sixth of their entire life, it's massive. But to a sixty year old, one year is a blip. It's a small ripple in the pool of memory. So our internal yardstick for time stretches. As we age, we

got a better sense of proportion. We begin to feel what a century might mean not because we remember it directly, but because we've had enough decades to simulate it with some emotional weight. But go further back, like ten thousand years or one hundred thousand, and your mental simulation is not particularly good. You've got evolutionary time, in geological time, and cosmological time. These scales are too vast to inhabit intuitively. You can say the invention of writing is six thousand

years old, but does that number feel real? Can you feel the difference between six thousand and sixty thousand? For example, there's an internet meme that asks did Cleopatra live closer in time to the building of the Great Pyramid at Giza or to the lunar landing. Now you'll remember that Cleopatra was the Greek queen of Egypt from fifty one to thirty BC. So what comes as a great surprise to a lot of people was that she was actually

closer in time to the moon landing. Why because she was born about two thousand, five hundred years after the Great Pyramid at Giza was built, and only about two thousand years before the first lunar landing, So she was five hundred years closer to moon landings. And iPhones and chat GPT than to the Great Pyramid. It's surprising, right, And what it demonstrates is that none of us have

particularly good intuitions about deep time. Now, if you are an evolutionary biologist or a geologist or an astrophysicist, you can learn how to do temporal sequencing, like that event happened a billion years before that other event, But you may as well be memorizing the order of exits on the highway in the sense that you're not feeling or simulating a billion year. You're mostly just memorizing that road sign.

So what seems clear is that as soon as we start talking really long timescales, our brains just weren't built for that. Really, think about this, what's the longest period of time that you can realistically simulate emotionally? You can sort of feel what a day feels like, probably a week, a month, and you may even have enough experience in the world that you can really feel the weight of

a year or maybe even a decade. But can you really simulate what it would be like to spend a century of time hanging out and doom scrolling and cooking meals and taking your dog for a walk for a thousand years. Just try to imagine ten thousand years since the invention of agriculture. Try to feel ten thousand years. Your brain might conjure up some images like cave paintings and mammoths and spears, but can you actually understand the sheer stretch of a time period like that. Presumably not,

We're just not wired for it. Our temporal reasoning evolved in the service of short term prediction, hunting and gathering, planning social exchanges, maybe tracking seasons, but that's it. The oldest parts of the brain work in rhythms of hours and days, or sometimes weeks. This is why we struggle to grasp timelines like civilizational collapse, or for younger people,

even something like retirement planning. Our cognitive system compresses distant time the way it compresses vision, blurring the edges to focus on what's close. Just like we have a phobia in the eye, a center of sharp focus, we have what you can think of as a temporal phobia, which sharpens the present and blurs the deep past and distant future. The truth is it's sort of a biological miracle that

we can contemplate large time scales at all. We can look at a fossil and say this was alive three hundred million years ago, and feel even the faintest flicker of what that means. It's surprising that our brains can even attempt to model epics that no organism ever lived to see. We've talked about missing time, milliseconds loss to eye movements, hours lost to sleep, years vanished to amnesia,

centuries gone because we can't understand deep time. We've seen how the brain edits the story and patches the gaps. But what if entire chapters of Earth's history are missing, not from your memory, but from the planet's memory. Here's what I mean. It seems clear enough that we humans are the first intelligent civilization. We're the only creatures to build cities, to form empires, to write literature about ourselves. But we've only been here for the last last blink

of evolutionary time. We invented agriculture only ten thousand years ago, in something like a big urban center with laws and organization. It's all unbelievably new. But the Earth is four point five billion years old, and complex life has been around for hundreds of millions of years. So here's a speculation that Some thinkers have chewed on what if we are

not the first? What if something like a civilization had arisen, say six hundred million years ago, way before Homo sapiens, like a full civilization with philosophies and literature and politics and music and wars, And maybe the civilization lasted for twenty million years, and we would have no idea it had ever been here. Now, how could that possibly be? Wouldn't we find fossil evidence of them? Well, under certain circumstances, we might, But let's say they were soft bodied organisms,

we would almost certainly never know. Soft tissues decay quickly. Fossilization is very rare, and if things aren't buried in the right sediment, they can vanish without a trace. So our fossil record as it stands is a shattered mosaic. It's a few lucky remnants scattered across eons of erosion. So think about the Ediacaran period, about six hundred million years ago. That's before trilobytes, before shells, before vertebrates. We have impressions in sandstone of strange, soft bodied life forms,

organisms with no clear ancestors or descendants. Their biology is strange, Their symmetry is unfamiliar. Could some of them have evolved intelligence? Could they have had cognition, maybe not quite like ours, but in some way parallel. Could they have built societies

and languages and structure that we can't even imagine. If they did, and if they were made of soft flesh, glatinous matter, fragile compounds, and they built their civilizations with adobe homes, the odds are that none of the appropriate evidence would exist anymore for us to find. No bones, no ruins, just a story that played out hundreds of millions of years before us and was completely erased. So we assume we're the first ones to tell a story.

But maybe we're just the ones holding the pen at the moment, totally unaware of how many other pens were lifted and scratched across time and then lost. Here's the link to what I've been talking about. The Earth has no central memory or backup drive. If there are no records that survive, no fossils, no scars on the crust that lasted this long, then that time is gone and it's therefore forgotten and unrecoverable. Just like you falling into

a deep sleep or having amnesia. It's another gap in time. We like to believe that history is cumulative, that it adds up in layers like strata in a canyon wall. But as we saw in the neuroscience of the first four chapters of today's podcast, history can be fragile and erasable. Any story from milliseconds to eons can pass, and if there's no record, then there's no memory. What we've seen today is that time is a narrative medium, and narratives can fail, They can go unrecorded, they can be lost.

We began with milliseconds lost to eye movements called secods, where the brain quietly deletes motion, blur and pastes your world back together as if nothing ever vanished. We moved to hours lost to sleep, where consciousness dissolves and time drops out unnoticed. We looked into anesthesia, where the self disappears completely, no memory, no mind, no time, and then returns like a light flicked back on. We stretched to

weeks and months and years. Time scale is lost not to unconsciousness, but to amnesia, where the person continues but the story does not, a life lived but not remembered because the timeline never makes it to the page. Then we pushed it further to centuries and millennia, where even our best efforts at understanding falter, where time becomes too

vast to meaningfully simulate it anymore. And finally, we looked back into deep time, hundreds of millions of years, where entire histories may have unfolded before us, only to be erased by geology, by the quiet forgetting of a planet with no memory. The wild part is that in all these cases, we move forward, stitching together a story from fragments,

believing it to be complete. But it's important to remember that we are the inheritors of a story that is largely erased, and if you ask me, it's a story that we do not fully understand, a story whose missing pages occasionally outnumber the ones that we have. And yet we keep telling our stories because that's all we've got. So across all these scales milliseconds to eons, we see a common thread. If events are not remembered, they might

as well not have happened. Our sense of time is simply what gets recorded by anything from neurons to fossils. When the record fails, the time disappears. So we assemble our narrative from scraps moments we notice, memories, we hold, traces, we dig from the earth, and what we call reality is just the part that we managed to write down. Go to eagleman dot com slash podcast more information and

to find further reading. Join the weekly discussions on my substack, and check out and subscribe to Inner Cosmos on YouTube for videos of each episode and to leave comments until next time. I'm David Eagleman, and this is Inner Cosmos.