June 19, 2023 • 32 mins
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.
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Speaker 1 (00:05):
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
(00:26):
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
(00:49):
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,
(01:09):
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
(01:30):
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
(01:51):
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,
(02:13):
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
(02:35):
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,
(02:56):
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
(03:16):
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
(03:37):
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
(03:59):
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
(04:20):
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
(04:43):
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,
(05:03):
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
(05:23):
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
(05:45):
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,
(06:09):
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
(06:30):
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
(06:52):
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
(07:13):
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
(07:35):
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
(07:56):
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
(08:20):
bending surprises along the way. Now, to tackle something as
big and mysterious as time, it helps begin with something
(08:44):
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
(09:06):
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
(09:30):
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
(09:51):
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
(10:11):
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.
(10:35):
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
(11:00):
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
(11:21):
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,
(11:41):
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
(12:03):
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
(12:27):
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
(12:49):
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
(13:09):
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
(13:32):
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.
(13:54):
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
(14:16):
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
(14:38):
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
(14:59):
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
(15:23):
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
(15:43):
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,
(16:06):
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,
(16:27):
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
(16:48):
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
(17:09):
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
(17:29):
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.
(17:50):
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,
(18:13):
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,
(18:33):
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
(18:56):
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,
(19:17):
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
(19:39):
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
(20:01):
this whole process completes itself, the event itself in the
world is already long gone. Now the more I study this,
(20:24):
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
(20:44):
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.
(21:05):
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
(21:26):
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
(21:50):
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
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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,
(22:34):
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,
(22:55):
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
(23:18):
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
(23:43):
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.
(24:03):
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
(24:26):
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
(24:47):
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
(25:10):
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
(25:30):
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
(25:55):
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
(26:17):
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
(26:41):
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
(27:01):
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,
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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
(27:47):
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.
(28:10):
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
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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
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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
(29:17):
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
(29:39):
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
(30:01):
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
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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
(30:46):
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
(31:09):
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
(31:30):
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
(31:50):
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
(32:12):
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
(32:35):
new episodes every week until next time. I'm David Eagleman,
signing out from the Inner
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
(00:26):
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
(00:49):
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,
(01:09):
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
(01:30):
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
(01:51):
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,
(02:13):
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
(02:35):
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,
(02:56):
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
(03:16):
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
(03:37):
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
(03:59):
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
(04:20):
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
(04:43):
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,
(05:03):
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
(05:23):
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
(05:45):
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,
(06:09):
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
(06:30):
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
(06:52):
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
(07:13):
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
(07:35):
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
(07:56):
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
(08:20):
bending surprises along the way. Now, to tackle something as
big and mysterious as time, it helps begin with something
(08:44):
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
(09:06):
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
(09:30):
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
(09:51):
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
(10:11):
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.
(10:35):
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
(11:00):
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
(11:21):
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,
(11:41):
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
(12:03):
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
(12:27):
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
(12:49):
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
(13:09):
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
(13:32):
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.
(13:54):
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
(14:16):
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
(14:38):
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
(14:59):
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
(15:23):
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
(15:43):
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,
(16:06):
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,
(16:27):
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
(16:48):
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
(17:09):
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
(17:29):
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.
(17:50):
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,
(18:13):
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,
(18:33):
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
(18:56):
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,
(19:17):
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
(19:39):
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
(20:01):
this whole process completes itself, the event itself in the
world is already long gone. Now the more I study this,
(20:24):
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
(20:44):
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.
(21:05):
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
(21:26):
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
(21:50):
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
(22:14):
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,
(22:34):
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,
(22:55):
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
(23:18):
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
(23:43):
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.
(24:03):
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
(24:26):
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
(24:47):
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
(25:10):
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
(25:30):
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
(25:55):
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
(26:17):
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
(26:41):
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
(27:01):
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,
(27:25):
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
(27:47):
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.
(28:10):
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
(28:30):
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
(28:54):
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
(29:17):
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
(29:39):
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
(30:01):
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
(30:21):
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
(30:46):
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
(31:09):
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
(31:30):
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
(31:50):
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
(32:12):
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
(32:35):
new episodes every week until next time. I'm David Eagleman,
signing out from the Inner
Host
David Eagleman
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