How far in the past do you live? Why are live television shows not actually live? What does any of this have to do with nuclear bombs, car accidents, plane crashes, volcanos, or the last episode of the Sopranos? Join Eagleman in a mind-bending dive into the neuroscience of time and what it could mean for your last moment.
How far in the past do you live? Why are live television shows not actually live? And what does any of this have to do with nuclear bombs or car accidents where the Boeing airlines crash in Ethiopia or volcanoes or the last episode of The Sopranos. Welcome to Inner Cosmos with me David Eagleman. I'm a neuroscientist and an author at Stanford University, and I've always been obsessed with how we perceive time. In this episode, I'm going to dive into an issue about time perception that's always intrigued me, which is how long do we have to wait before we have a conscious perception of something that just happened in the world. And that leads to a very wild question, will you perceive the event that kills you? So imagine that you're walking down the sidewalk and you're enjoying the sunshine, and you're sipping your coffee from a paper cup and watching two dogs wrestling around and having fun in the distance, and suddenly, from a crane perched ten stories in the air, a piano falls and lands right on top of you. The question we want to dive into today is will you be aware of that final moment, or while you feel you're happily watching the dogs and sipping the coffee, will the footage just end? Now this is not an idle question. It's one that allows us to dig deep into what happens in the brain, and it's one that sometimes gets wrestled with in courts of law. So let's start this story in twenty seventeen when the United States it proved a new generation of the Boeing seven thirty seven airplane. This was called the Boeing seven thirty seven Max, and it was a great evolution for this leading airliner company, and it immediately produced hundreds of orders that came pouring in from around the world. So everything looked great. But then in October of twenty eighteen, a seven thirty seven Max took off from Jakarta on its way to Indonesia, and thirteen minutes after takeoff, it crashed into the Java Sea and it killed all one hundred and eighty nine people on board. So that immediately triggered investigations into whether something about this new airplane design had anything to do with the crash, and those investigations uncovered a serious issue. It turns out that some previous seven thirty seven Max flights had had serious problems. There hadn't been a crash, but nonetheless the passengers had been traumatized. And the problems had to do with the failure of a sensor that detects the angle of attack, which is just the angle between the wing and the wind, and that mattered because it affects the amount of lift that the airplane gets. So, without going into details, it surfaced that there was this inherent design flaw in the seven thirty seven Maxes that made these planes really hard to control in some circumstances and really dangerous. So the Federal Aviation Administration and Boeing moved quickly to give out warnings and training advisories to all the operators of the seven thirty seven Max series to avoid this kind of problem. But before these got implemented, something awful happened. In March of twenty nineteen, Ethiopian Airlines Flight three h two crashed because of this exact same problem, and that crash instantly killed all one hundred and fifty seven people on board, and that led to an immediate grounding of all seven thirty seven Max airplanes around the planet. Now there are hundreds of angles to the enormous legal case around the crash of the Ethiopian Airlines flight, including negligence and collusion. But I'm going to zoom in on a part of the lawsuit that's currently in the courts, and that part of the legal argument comes down to millions of dollars and the final half second, and that's where neuroscience unexpectedly intersects with aviation. In the aftermath of the crash, Boeing executives met with the victims' families and they pledged a one hundred million dollar fund for the families, separate from any lawsuit. And then Boeing settled for two and a half billion with the Justice Department, and they agreed to pay five hundred million more to the victim's beneficiaries. Then they also paid other fines for alleged misleading statements and so on. But Boeing's attorneys argued that they shouldn't have to pay out any money for pain and suffering. Now, let's be clear on what the legal argument is here. In legal terms, while the plane was tilting and heading towards the ground, the nausea and terrible fear falls into a legal category of mental anguish. But that's a different category of damages than pain and suffering, which is what happens between a physical injury and the time of death. Now this is grim stuff, but it's the kind of analysis that comes up in courtrooms all the time. Imagine that there's a factory and there's a poorly braced machine and it falls on a worker, and that person ends up pinned for hours and bleeding out, and they're conscious the whole time of what is happening to them, and they pass away. Now, that would fall under the legal category of pain and suffering. That category of damages starts at the moment of physical injury and runs until the time of death. But Boeing's attorneys argued that while there certainly was mental anguish during the six minute roller coaster ride, there was no pain in suffering that could be argued in this case. Why because the planes impact with the ground caused instantaneous death. What Boeing said is that the victims died painlessly because the airplane crashed into the ground so fast that their brains didn't have time to process pain signals. In other words, there was no time between injury and death. Just to be clear, Boeing's attorneys aren't arguing that the families can't recover massive damages in the lawsuit. They're just talking about this specific category of pain and suffering, and this isn't an unusual argument in wrongful death cases like plane crashes and car accidents, to argue in a courtroom about what someone's experience would have been like in their final moments, and therefore whether they experienced any pain and suffering. It comes down to the issue of whether the passengers were aware that the plane hit the ground, and this boils down to a question that can only be addressed by neuroscience. Time is one of the most important elements in our lives, but how we perceive time is one of the least understood. So I've devoted a large part of my career to try to figure out our experience of time, and the lesson that surfaces is that our perceptual experience is the result of lots of computation in the brain and it doesn't necessarily map on to what reality actually is. Now. In a different episode, I talked about time seeming to run in slow motion. Many people have had this impression when they're in a life threatening situation that an event seemed to last longer than normal. And in that episode, I told the story about when I was eight years old and fell off of the roof of a house inner construction and time seemed to run in slow motion, and how that eventually led to me becoming a neuroscientist because I grew so fascinated with this almost totally unexplored area. In this episode, I'm going to take you on a totally different path through time perception, and we're going to see some mind bending surprises along the way. Now, to tackle something as big and mysterious as time, it helps begin with something very simple, and many years ago I stumbled on a simple visual illusion that ended up opening big doors for my understanding of time. And that illusion was first noticed in the nineteen twenties. It's called the flash lag illusion. And here's how it goes. Imagine you're looking out your window and you see a bicyclist zipping along the road in front of your house, going from the left side to the right side, and as they're going by, a bright light flashes very briefly on their helmet. Flash. That's all I need you to picture. Bike moves along light flashes on their helmet. So what hits your eye is the bike and the flash in the same location, but what you consciously perceive is something different. The way it looks to you is that the bike was some distance ahead of the flash. It doesn't look like they're in the same spot. Now, this flash lag illusion is very easy to demonstrate and to quantify, and you can see demos of this at Eagleman dot com Slash podcast. But the question is why does this happen? So what had been proposed in the literature is that maybe what's happening is your visual system watches the bicyclist, but it doesn't see the bike where it is right now, but instead your brain is guessing where the bike will be in the next moment. Your brain is making a prediction, and that's what you see is this predicted position a little bit ahead. But your brain doesn't have that luxury with the flash because it didn't know that was about to happen, and so it can't make any predictions there. And so the bike looks farther ahead to the right in this case, and the flash appears exactly where it happened. Now, I had some reasons to doubt that framework. So I set up a very simple experiment which I presented to test participants. Imagine on the screen you're watching the bike moving to the right, and I have a flash appear for just one frame, and it's perfectly lined up with the bike. Now, that's what gives you the flashlight illusion. But now I'm going to do one of three things at random after the flash is over. Either the bike keeps going, or the bike instantly stops, or the bike reverses direction. The key thing to note here is that everything up to and including the flash is identical, and all I'm doing is changing what happens in the future of the flash. So if prediction is happening, if your brain is just guessing ahead where the moving bike is, then of course we'll expect to see the same thing every time, which is that the bike should be ahead of the flash to the right, because it shouldn't matter what happens after the flash is already gone. But here's what actually happens. If the bike keeps going, it looks like it's ahead of the flash on the right, as expected. But if the bike stops instantly in the frame after the flash, it looks like the flash was on the helmet, there's no more illusion. And if the bike reverses its direction immediately after the flash, then it looks like the flash is off the helmet. In the other direction, the bike is off to the left now instead of to the right. Now. Why is that's such a weird result. It's so weird because I'm asking you what you see at the moment of the flash, and your answer depends on what happens in the future of the flash. And remember, these conditions are randomly interleaved, so you can't know what's actually going to happen on any given trial. So there's only two possibilities here. Either my test subjects were clairvoyantly seeing into the future, which I don't think is happening, or the perception that we attribute to some moment in time actually depends on what happens next. In other words, what we think happen in some moment depends on what happens after that moment. Now, this is a wild finding because it shows right away that the brain is not using prediction guessing ahead. Instead, it's something more like filling in behind. The key is that after the flash, your brain continues to collect up in information and it retrospectively says what it thinks it saw. Nothing is moving backwards in time. The correct way to think about this is to think about two timelines. There's time in the real world and there's time in your head. This is physical time and subjective time. And the timeline in your head is simply shifted later. It's a delayed version of what is happening in the real world. And this is because it takes time for signals to move around in the brain and get processed. So by the time the information from the flash gets fully through the machinery, new information about the movement of the bike has been streaming in. So by the time you become consciously aware of the flash, your brain has incorporated some information that happened after the flash. So I published this in the journal Science, and I called this phenomenon postdiction as opposed to prediction, and it actually became the most highly cited paper of my career so far because what it surfaces, in a very simple way, is a fundamental feature of our perception, which is that we live in the past. The brain collects information and that flows around and eventually comes to a conclusion and gives you a story of what happened in the world out there, and then we think, oh, that's what's happening right now. So when I say we're living in the past, I mean that by the time we think the moment now has occurred, it's already happened. Remember that signals in the brain move very slowly. In the cerebral cortex, which is the wrinkly outer covering of the brain, most signals are traveling around at one meter per second, which is three hundred million times slower than signals in fiber optic cables. So your brain has a challenge, which is that it's true trying to understand what's going on in the outside world. But it's big and it's made of billions of cells, and so its only good solution is to wait until all the signals have been collected up and compiled. It gathers the signals from the various senses, and once all that information has arrived, your brain develops a conscious narrative about what just happened. And the consequence is that your conscious mind lives behind reality. When I clap my hands together and we think the moment now is occurring, we're wrong. It already happens. Some time ago. Our brains had to collect the information from the visual system, the auditory system process that, stitch it all together and serve up a story, and then you say, oh, I just heard a clap. The consequence is that your perception of the world is something like the airing of a live television show like Saturday Night Live, which is not actually live, but it's aired with a delay in case someone cusses or falls down, or there's a wardrobe mishap, and so it goes with your consciousness. It is delayed by a small window while your brain puts together its story. What you perceive is a delayed version of reality. For all you know, this podcast is already over. Okay, not that far in the past, but how far in the past are we well in the flash lag effect, I was able to show that we were about a tenth of a second behind what was happening out there, one hundred milliseconds. But that was measured from experiments I did in the visual system. And for a unified perception of the world with all its sights and sounds and textures, you need to wait for all the information to stream in from all of the senses. And that means that if your brain wants to wait to collect up all the information before putting together a story of what happened, it needs to wait for the slowest information, which is from your toes. That information has to climb all the way up the nerves and your legs and then up the entire spinal cord all the way to your brain. And although the nerves that carry touch information are fast compared to some other kinds of nerves, they're super slow compared to say, the speed of signals in your computer, and so the whole thing takes more than one hundred milliseconds. And what I realized was that if your brain wants a unified perception of what just happened in the world, rather than different pieces streaming at different times, it has no choice but to wait for all that information to arrive. And one way to demonstrate this is if I touch your nose and your toe at the same time, you will feel that as simultaneous. It's not like you feel the signal from your nose and then you feel it later from your toe, even though the signal from your nose gets to your brain much more quickly. So the question is does your brain capture the information from the nose and then say, Okay, cool, I've got that, but I'm not going to perceive anything yet because something else might be coming up the pipeline. Yes, I think that's actually what happens. And because the brain has to wait for this slow information to arrive, this leads to the bizarre but testable prediction that tall people live further in the past than short people. So I mentioned my prediction once on a live interview on NPR, and then I drove back to my lab and I opened my email, and I saw that I had received dozens of emails from people who said, I'm short, and I really appreciate what you said. But let's get back to this question of how far behind reality does your consciousness lag. In the nineteen seventies, a neuroscientist named Benjamin Libbitt did some studies with people who were undergoing neuros, and those studies suggested that we lag as much as five hundred milliseconds half a second. I'm not going to go into the details of his experiment here, but I've linked the research on the podcast website. So Libbett's claim was that we are half a second in the past, and it's worth noting that it might be impossible for us to measure the moment of onset of conscious experience, so the exact time delay is very hard to know for sure, but for now, let's call it about half a second in the past. And this happens because the brain needs to collect all the signals from the eyes and the ears and the skin, and those need to travel along their respective nerves and enter the brain in the place that they come in in the primary sensory cortex for each sense, and then move to the secondary sensory cortex and tertiary, and the signals splash out into multimodal areas, and everything needs to get stitched together into a story of what just happened. And by the time this whole process completes itself, the event itself in the world is already long gone. Now the more I study this, the more I realized that this strange fact has an interesting and unappreciated consequence. You probably won't perceive the event that kills you, at least if that event happens suddenly. So let's return to this scenario of you walking down the street and joining your coffee and suddenly the piano falls on you. That would be so terrible, right, But what we've just seen is that it takes time for signals to come together to form a conscious story. So that means that if your brain gets damaged before the signals come together, then it says though the footage suddenly ends. And this would be true not only for our pianos, but for any unexpected event like a bullet or a bomb explosion. The damage to the brain would happen much faster than the time it takes to process the signals and come to a conscious conclusion. Now, I've been studying this in my lab for many years, and so I was really amazed when I saw the great author Cormick McCarthy point to this in his post apocalyptic novel The Road. So at one point in the novel, the main character levels his pistol on a bad guy who was trying to attack him, and the bad guy says, quote, you won't shoot My companions will hear the shot, And our hero says, yes, they will, but you won't. And the bad guy says, how do you figure that? And our hero says, because the bullet travels faster than the sound, it'll be in your brain before you can hear it. To hear it, you'll need a frontal lobe and things with names like colliculus and temporal gyrus, and you won't have them anymore. They'll just be soup. In other words, what McCarthy was pointing out is the same issue, which is that you need your brain to perceive. No brain, no perception. Now, one of the most popular shows in television history was The Sopranos, and if you didn't see it, it was an intimate story of a mafia family in New Jersey, and it was told over eight years. It had tens of millions of dedicated fans, and so when the finale to the whole show finally arrived, everyone was tuned in to see how the show would end. The series centers on Tony Soprano, this mafia head in New Jersey, and the thing about Tony Soprano is that he's always struggling to balance his fan family life and his role as a mob boss. So he has panic attacks and we get to see him in therapy sessions with his psychiatrist throughout the series, and if you've never seen it, you can imagine there are life threatening complications all the time with other mobsters inside his family and outside, and specifically with the New York City based Lupertazzi family, which had been working to take down the Soprano family by decapitating them, in other words, by taking out their leadership some of Tony's family and collaborators. They were gunned down, one was put in a coma, and shots were taken to Tony. But now in the final episode, things seem to have calmed down. Tony seems to be in control of his New Jersey empire, and yet as the episode is coming to an end, something seems just slightly off. Tony is sitting in a diner eating onion rings and listening to Don't Stop Believing by Journey on the jukebox. The camera passes by people here and there. It's hard to tell if anyone seems out of place, like when the camera follows one seemingly random man who goes into the bathroom behind where Tony is sitting, and we see Tony's daughter park across the street, and she runs across the street to join him, and we hear the bell on the door, which is presumably her entrance, and he looks up from his food, and then the video and audio cut to blackness and silence, So fans went into an uproar. What just happened to the show? Was there a broadcasting hiccup? Was this a technical problem with their television? But it wasn't. The show ends that way because we are in Tony's point of view, and suddenly there simply is no more point of view. The fragile circuits necessary for Tony's brain to construct a story have been wrecked by a bullet, and the damage happens before they've been able to stitch together a story about that last half second of his life. Now, this scene of Tony's death connected back to an earlier snippet of dialogue from two seasons earlier, in which Bobby Bachlieri says to Tony, quote, you probably don't even hear it when it happens. Right, because of the slow propagation of signals in the nervous system and the slow stitching together of consciousness, you might never even be aware that a gun fired, or that a bomb exploded, or that a truck just crashed through the wall, or a jet engine fell on your head. One moment you're present and thinking, and the next moment, your machinery for thought is gone. The broadcast of consciousness just cuts way to appreciate the sluggishness of your perception is to compare it to the speed of the machinery that we're surrounded with. I recently read this great article on the anatomy of a car crash, which was in the Australian magazine Drive, and the article describes what happens when a car is hit in the driver's door by another car traveling at fifty kilometers per hour. At zero milliseconds is when the other car first touches the driver's door. At one millisecond, the car's door pressure sensor detects a pressure wave. From here, over the next few milliseconds, different sensors pick up on the crash vibrations. So I'll skip ahead to five milliseconds, when the car's crash computer starts searching for what's going on, trying to work out the severity of the crash. By six point five milliseconds, the door pressure sensor is registering peak pressures, which causes by seven milliseconds the crash computer to con firm that the crash is serious and send the next steps into action. At eight milliseconds, the computer sends a signal to the side airbag, and by eight point five milliseconds the airbag fires off. By fifteen milliseconds, it bursts through the foam and begins to fill. By seventeen milliseconds, it covers the driver's chest and pushes the shoulder away from the impact zone, and then by a few milliseconds later, it's pushing the chest away. All the while the physical structure of the car is crumpling in such a way as to transfer the energy away from the driver. By twenty seven milliseconds, a mechanism in the seat moves the driver's pelvis away from the impact zone, and the air bag starts its controlled deflation. Over the next tens of milliseconds, the driver and airbag move together as the structure of the car deforms, and by fifty milliseconds, the crash computer unlocks the car's doors. By seventy milliseconds, the driver moves back towards the middle of the car, and the air bag continues to deflate. At this point, seventy milliseconds in, the engineers classify the crash as complete. Now here's the zinger. After about another four hundred milliseconds, the driver becomes aware that there was a collision. From the machinery's point of view, the entire show is over before consciousness even flickers onto the screen. If you ever talk to someone who's been in a car accident, you'll already know that no one ever sees the airbag deploy They have the experience of driving, and suddenly there's a deflating air bag and a strange smell of nitrates, But the actual deployment of the bag happens way too fast for a person to be conscious of it. It strikes me that this sudden disappearance of consciousness with no bad feelings or fear probably happens with victims of pyroclastic flow from volcanoes. This is a one thousand degree wall of hot rock and gas that travels faster than one hundred miles per hour, meaning that if you're in your house and you don't know that this pyroclastic flow is coming, you're going to be consumed before your neural signals ever come together to form the conclusion that something is amiss and just came crashing through your wall. In this case, the speed of the danger outstrips the speed of the neural signals, and it's the same with a nuclear blast if that comes without warning. Nuclear blasts have a series of events. There's a flash of light and a pulsive thermal energy heat, and a pulse of nuclear radiation, and these all happen at the speed of light. So if you see a bomb descending and you realize you're going to be quite close to the point blank detonation, there's actually no reason to panic, because, just like the drivers who never witnessed the airbag's deploy you won't witness the bomb burst. Our evolution took place over millions of years in which this delay of a few hundred milliseconds was plenty fast to react to humans or horses or hippopotamia coming to attack you. This window might not have been fast enough for a pouncing lion, but our existence here allows us to conclude that the signals were fast enough that our species was not selected out. But we didn't evolve in a world with racing metal cars and bullets and nuclear bombs. Under these conditions, the speed of the events outstrips the leisurely neural signals. So if you've been having a tough day, take this all as a piece of good news, which is that your consciousness is so slow that you might completely miss out on the final thing that brings your story to a close. Like Tony Soprano, the song will be playing on the jukebox, and then it's not, and the horror that everyone else sees is simply not experienced by you. This tardiness of consciousness is why I have no fear of dying by something sudden, a piano falling on me, or an explosion or an unseen hit man. And this is why Boeing's council argued the unpopular but presumably correct position that the moment of impact at hundreds of miles per hour was too fast for any conscious awareness that an impact had ever occurred, and therefore, while Boeing's attorneys paid damages for all other aspects of the tragedy, they argued against that one. Perhaps there's no reason to fear dying from a piano falling on your head, because, as your consciousness won't yet have caught up, you'll simply be there enjoying a nice cup of coffee on a beautiful day, noticing the nice clouds in the sky, birds chirping, thinking about something you need to remember to put on your to do list, and then the footage will suddenly end. To find out more and to share your thoughts, head to eagleman dot com, slash podcasts, and you can also watch full episodes of Inner Cosmos on YouTube at inner Cosmospod. Subscribe to see new episodes every week until next time. I'm David Eagleman, signing out from the Inner