in this lecture we would answer the question that everyone has when they're
first talking about the mysteries of time namely
why am i always late this is not a question to which i can give a specific
answer it has more to do with your circumstances than with any scientific
principles but what we can do is talk about how
human beings perceive the passage of time
how we in our brains and in our bodies measure
time as it passes we already talked about in earlier lectures the idea of
using a clock to measure time a clock is something
that does the same thing over and over again in a repetitive and
predictable way compared to other clocks the reason why
we human beings feel the passage of time is because our bodies have clocks in
them we have things that happen in a rhythm
over and over again you have your heartbeat
your breathing the pulses in your central nervous system
biological clocks are not very reliable compared to a good mechanical or
electronic clock that's because our bodies are affected
by many things that are outside our control whether we are
tired or exhausted whether we have adrenaline rushing through our system
also our mental state are we focused on something or are we distracted by
the world around us finally the way that we get memories and keep them
affects how we perceive the passage of time so we do feel time passing
in many ways it's pretty accurate but there's always something that
makes us not completely perfect compared to let's say a good
atomic clock to set the stage for this discussion let's just talk about
biological rhythms more generally in any organism there are things that
happen over and over again that's what a rhythm is something that repeats itself
over and over the heartbeat is probably the single
most fundamental rhythm that advanced living organism has we can
compare how these rhythms work in different
kinds of animals and just to keep everything else as
constant as possible we can compare how mammals have
different rhythms inside their bodies one way of thinking about an advanced
organism like a mammal is it's a network you have the brain and
you have all the different things coming out of the brain the
nervous system your circulatory system and so forth
and you can actually make predictions on the basis of network theory
for how the rhythms cascade through your body and then
compare those predictions to data so jeffrey west at
the santa fe institute who studies complexity he was a physicist at first
but he went into complexity studies as that
field came to life and became more exciting
has asked the question about how the networks in different mammals are
affected by their size you find two of the most basic
relationships are that if you're a smaller animal your
networks move faster in particular your heart beats faster
the smaller you are the less weight you have
the faster your heartbeat is on the other hand he found that
smaller animals also live shorter lives the lifespan the typical lifespan
of a tiny little shrew is much shorter than that of a giant elephant or a blue
whale so if you think about this a smaller
animal has faster heartbeats and also doesn't live as long a longer
larger animal has a slower heartbeat and lives longer
you you might wonder do these effects cancel out
and the answer is yes as a very rough rule of thumb
every mammalian species on average has the same number of heartbeats in its
lifespan that number turns out to be one and a
half billion roughly speaking every mammal gets one
and a half billion heartbeats in its life now don't take
this too seriously when i tell this to people
they sometimes worry that this is a strict rule that no matter what you do
it's almost like predicting the future you will live for one and a half billion
heartbeats and they wonder should i exercise more should i exercise less to
get more or less heartbeats that's not how it works it's an average
of course many animals live a little bit shorter a
little bit longer but it's an interesting feature of our biology that
somehow a shrew and an elephant have similar
blueprints just taking reality in different forms
in a really tiny form for the shrew and a bigger one for the elephant
this kind of scaling law goes far beyond organisms it goes all the way down to
the cellular level west and his collaborators were able to
use this kind of scaling relationship to make predictions for the rate at
which individual cells behave in certain ways if they're in an
organism or outside an organism they made predictions
which hadn't yet been tested after they made the prediction they were tested
the idea that a human being is a complex network
of smaller functions talking to each other is a very good fit to how real
animals live of course unlike shrews and
elephants and blue whales we human beings have another
variable which is the culture in which we find ourselves the
environment around us the human environment
in which we're embedded and we all know that different cultures
approach time differently the psychologist robert levine who studies
how human beings interact with time is based in fresno california but he
sometimes spends time in other countries giving lectures and so forth he tells
a wonderful story of his first semester in brazil
when he was going to give a lecture it was scheduled to go from
10 a.m to noon it was a regular class he was teaching
he's walking down the street and he asked someone what time it was and they
said it was 905. he didn't have a watch himself
so he says oh i have plenty of time to get to my lecture at 10 o'clock
about half an hour passes and he asks someone else what time it is and they
say it's 20 minutes after 10. he panics he rushes to the lecture room
and there's almost no students there yet he says
what is going on so he asks the students what time it is one says it's 9 45
they're looking at their watches one says it's 9 55 one says it's 5
minutes past 10. what levine realized was that no
one's clock in brazil reads the same time and nobody
cares the students sort of came in very very
gradually to the 10 a.m class by 11 a.m the room had more
or less filled up but it wasn't that the students were
lazy or didn't want to go to the lecture when noon came along he said that in
california when the end of the lecture was scheduled you would know
every single student would be rustling in their chair looking at the clock
ready to go in brazil none of the students moved who
cares it was 12 o'clock at the end of the lecture they
were still interested they had questions they kept discussing it became 12 30
eventually he had to escape the point is that
different cultures approach time differently levine also spent time in
japan and he says of course compared to what you would do in california the
japanese found that his natural time keeping was
incredibly lax and kept telling him to hurry up in brazil they kept telling him
to calm down it's not these anecdotes that are really
important what's important is data can we actually do a scientific
experiment to justify these stories about how different
cultures perceive time and the answer is yes a bunch of
different studies have been done to basically try to measure the pace of
life in different cities different cultures
different environments for example you can take how long it goes if you
walk up to a post office and you want to order some stamps
psychologists have sent people to order stamps in different post offices in
different cities throughout the world and found consistent differences in how
long it takes to get those stamps to get to you
there's also a study where you can just measure how fast people are
walking you sit there in the cafe you walk watch people walk by
you measure how fast they're moving and once again you find
systematic differences in different cultures and in different cities
for example you will not be surprised to learn that in
higher population areas people walk faster
people literally will walk faster down the streets of new york city
than they will down the streets of a small town in massachusetts
it's not because everyone else is walking faster it's just because that's
what the environment does to you another obvious effect is technology and
industrialization psychologist richard weissman has
compared the pace of life in cities over time so he does this walking
experiment he sees how fast people are walking down the
street but rather than comparing one city to
another one he compares one city 20 years ago to the same city
today what he found was that over the last 20 years the pace of life has
increased by 10 percent that doesn't sound like a lot 10
but it's only in 20 years how quickly will it go over the next
century wiseman also found that the effects are different from place to
place singapore was up 30 percent guangzhou
a city in china was up 20 the areas of the world that are developing and
industrializing and gaining high technology the most quickly
also see their pace of life increasing the most quickly
nevertheless your stereotypical guesses aren't always right it turns out that
new york city is far and away not the fastest walking
city in the world in fact it's behind cities like
dublin and madrid and copenhagen there are many
complex features that go into how quickly life is lived in different
environments technology and density are very
important but we are very far away from having a complete theory of how this
works another place where we're very far away
from having a complete theory is how individual people perceive the passage
of time there's one lesson that we have
certainly learned which is that the human brain is not a computer
program we think about the human brain as very
similar to computers because the human brain clearly
computes in some sense we can mimic some things the brain do
in a computer program but the way the brain came together
is very different than the way you would write a computer program the brain
developed over literally billions of years of evolution of life here on earth
by an incremental change through random possibilities being tested and seeing
what works a computer program on the other hand is
usually written from the start you have a task in mind and you're going
to design it from the top down in the most efficient way you can
therefore in a computer program if you want to store
data for example well you have a array that you can put the data in and that's
that in the brain any task that you might
want to do is probably shared among many different
pieces because that's what was useful at the time
in particular when it comes to keeping time to measuring duration
there are different parts of the brain that kick in
it's a highly distributed feature it's not like a simple clock that you have in
your computer there's some chip that has a rate that you can buy a
faster and faster chip the brain has many many pieces each one
of which contributes to our understanding of time
as one experiment to demonstrate this that is very vivid
neurologists did an experiment with rats and we should keep in mind is that
neurologists neuroscientists hate rats they're constantly torturing
these poor little rats so the rats have a brain much like we do
they're mammals you know as far as all of life is concerned rats
are pretty close biologically to human beings
they have a complex brain they have a cerebral cortex which we
we have also it's the gray matter in our brain the cerebral cortex
is the outside part of our brain it's where we do our higher
information processing the life of consciousness
is happening within our cerebral cortex there's also
other organs inside the cerebral cortex which are more primitive
we think of them as giving us subconscious brain functions
so you can actually take a rat and remove its cerebral cortex
remove sort of the advanced parts of its brain
but the rat will still be alive it won't be able to do
mazes and other things that we teach rats to do but
what the neurologists neuroscientists have found is that rats can still
tell time even with their cerebral cortex removed
they give them a little task like pushing on a lever
if they push on the lever once every 40 seconds they get a food reward
the rats without a cerebral cortex can measure the time interval of 40 seconds
that means that whatever we're doing when we're measuring duration and time
it's not a matter of our conscious brain there are unconscious things going on
and there's more than one thing going on another experiment with mice
was able to show that mice with their whole brains intact
could keep track of at least three different rhythms
these mice had three different paddles that they would push to get food
and to get the food one paddle needed to be pushed once every 10 seconds
once had to be pushed once every 3 30 seconds
and once had to be pushed once every 90 seconds the mice were able to separately
keep track of the time intervals necessary to get
the rhythms right in all three paddles simultaneously and you
might think well 30 seconds is 3 times 10 and 90 seconds
is 3 times 30 so you just press this one three times and this one
once etc but you could actually turn on and off
the rhythms you could displace the rhythm so that the 10 second one was out
of phase with the 30 second one in the 90 second one
the mice could still keep track so inside our brains is more than one
time keeping device in fact you can sort of roughly divide it up into different
kinds of time keeping as you are listening to
this lecture right now there is a part of your brain that is
keeping track of what time of day it is this is your circadian rhythm
that tells you when you wake up when you go to sleep
there's another part of your brain that is keeping track of how much time has
passed since the lecture started or since you
started listening to it and there are yet other parts of your
brain that are more or less like alarm clocks they keep
the amount of time before some relevant future event if you want to
go to dinner or go to bed or something is going to happen
how much time do you have before that happens your brain is keeping track of
that now this is a complex set of operations
we don't have a grand unified theory of everything this is why
brain science and biology is much more complex than physics is
but neuroscientists have been able to isolate at least three different
kinds of time perception three different ways
in which we increase or decrease the rate at which time seems to pass
for us the three ways are number one pulses
sort of the basic way that you would keep track of time in a
clock or with a pendulum going back and forth there are pulses in our brains and
we simply count them another thing that affects the passage
of time is our sensory input and focus what are we paying attention
to and finally and sort of most intriguingly
the way in which we accumulate memories affects our notion of how much time has
passed the more memories we accumulate the more time we attribute to what
happened so let's consider these three aspects in order
when we say counting pulses it makes you think that there
is a little part of your brain that is almost like a pendulum
going back and forth and that is not true or at least we don't know of any
single part of the brain that acts exactly like a clock like the chip in
your computer rather there are multiple levels of
pulses the different neurons in your brain do work via pulses
it's not that the neuron is constantly sending signals
it's that there's a signal or there's not a signal so neurons turn on and off
there's multiple levels of pulses due to all the neurons in our brain
and together they help us perceive the passage of time
again you will not be surprised to learn that we can affect
how quickly those pulses go for example we can affect them through drugs
stimulants make our pulses beat faster if you drink caffeine
the pulses in your brain that keep track of time go a little bit faster
depressants will slow them down if you have alcohol or other depressants even
something like marijuana the pulses decrease in their rate and it
takes us longer to accumulate a certain perceived amount of
time now whenever we talk about this kind of
phenomenon we have to be very very careful because people say well
you drink caffeine and time speeds up but in fact as we talked about way back
when in the early lectures time is always moving at one second per
second when you want to say that time speeds up
what you mean is that one clock has sped up compared to some other
clock when you drink caffeine your clock
speeds up but what that means is that when you compare it to the world
the world has slowed down so your clock has sped up
compared to the outside world we have to be sure to get that
right when we're talking about effects on our internal clocks
these effects from stimulants or depressants we think
are effects on the neurotransmitter that send signals from our neurons
to other cells in our brain neurotransmitters like dopamine and
other chemicals are what the neurons send and they do it
in the form of pulses caffeine or alcohol or other drugs can
make it easier or harder for these neurotransmitters to
be sent that speeds up or slows down our internal
clocks but that's usually not what makes you
late if you want to know why you're always late it might not have
anything to do with caffeine or booze or anything like that
it's probably due to the second aspect which is the sensory input and focus
when you are focused on a task when you have you know a really hot first date
or when you're in a really engrossing project for work or at home that you're
really in love with you don't pay as much attention to the
outside world and in some sense which psychologists still don't understand you
also don't pay as much attention to your internal clocks
so your effective internal timekeeping device
slows down the outside world speeds up if you're having a really interesting
date or conversation with someone you think that a half an hour has passed
but in fact it's been like two hours your focus on one task makes it harder
for you to tell time usually if you're late it's because
you've been focusing on something else contrary wise if you're bored if you're
on a plane ride and there's nothing going on
if you have a tedious aspect to your job your attention is constantly flitting
around you are not focused on any one thing and
the opposite effect happens your internal clock seems to go faster
the outside world slows down it seems to take forever to
get that plane ride across the country simply because you're bored and your
attention keeps wandering the final aspect is the rate at which we
form new memories so this is a fascinating thing
that neuroscientists are just beginning to understand
you might have as an example this idea that if you're in a high stress
situation time seems to slow down by which we mean
your clock speeds up the rest of the world seems to slow down
this was uh noticed by a neuroscientist named david eagleman long before he was
a working neuroscientist when he was a child he once fell out of
a tree and it was long enough that it was not so long that he was really
hurt long enough that he was very scared as he was falling out of the tree and he
remembered as he grew up and became a working
neuroscientist that the world seemed to slow down if you've
ever been in an accident or a very very stressful
sudden situation everything around you seems to move more slowly
so eagleman wanted to know is it really true that in these high stress
situations your internal clock beats faster therefore making the rest
of the world seem to slow down the problem with this question as a
working scientist is that to answer it you need to scare people and that's not
really good procedure when it comes to human subjects
but what eagleman did was to figure out a way to scare people in a way that
wasn't really dangerous he threw them off of a tall building but
he threw them off of a tall building onto
a trampoline so it was actually perfectly safe
and while they were falling off the building the theory was they would get
scared there'd be adrenaline going through them even though they knew there
was a trampoline down there they they weren't surprised by the trampoline
and he had them actually do little recognition tests he gave them little
pieces of equipment that would flash numbers on a screen
and it flashed them either fast or slow if they were so fast
they would be flat flashing so fast that you couldn't recognize the numbers if
they were going slow then you had the time to see what the
numbers were and what eagleman did was to compare
how good you were at recognizing the numbers when your adrenaline was running
and you were falling out of the building versus when you were just sitting at a
desk calmly the answer is there was no difference
despite the fact that there was adrenaline going and your pulses were
racing you were not any better at recognizing the quick flashing numbers
than you would have been sitting calmly at your desk so therefore in that sense
the speeding up clock inside didn't help you
perceive the outside world nevertheless if you talked to the subjects
afterward they said that the outside world slowed down they had a perception
that time had slowed down for them in recollection
after the effect so there's a theory about what is going on
the question the theory is and it's just a theory it's not something that we can
test very accurately that the more memories you accumulate
the more time seems to have passed when you're in
a high stressed scary situation your brain does its best to record
absolutely everything that has happened it's scared it's looking around
it's accumulating a huge amount of data even though it's not perceiving things
any more quickly than it would otherwise when you think about that event
afterward you have more memories you have more data to leave through
and therefore it seems to us like more time
has passed this hypothesis is gets a little bit of support from a
related fact which again everyone knows even if you haven't been
in a scary situation you know that time seems to pass more
quickly as we age when you're older the summer seems to
rush by when you were a kid the summer seemed to
last forever this is not just an anecdote this is not just
an idea that people have this is something that you can test
the theory that eagleman has and other people have
is simply that when you're young in the summertime you're going to the beach and
whatever it's all new to you everything around you is a
new experience when you're older you've been there
before it's a little bit more blase so it seems to pass more quickly for you
compared to what it did when you were a child and this is something that again
we can try to test the way that neuroscientists have tried
to test it is to give 20 year olds a test where they're simply told
starting now tell me after three minutes had passed
and then they give the same test to 60 year olds and the answer is that 20
year olds are pretty good at measuring about how long three
minutes are so they have no clocks around them they're just sitting there
quietly in an empty room they say three minutes have passed and on average
the actual amount of time that is passed is about three minutes and three seconds
very very accurate but you do exactly the same test to 60
year old people and when they say three minutes have
passed the actual elapsed time is more like
three minutes and 20 or 40 seconds so 20 year olds are better at estimating
time than 60 year olds for an older person it takes longer for
the same amount of subjective time to pass the theory is that that's
because they don't create as many new memories
but the fact is that it does take longer there's even a hypothesis that tries to
make it quantitative that says the amount of time we
experience grows logarithmically with our age it would be very hard to
put exact data about that but it makes sense to us think back to
that boring plane ride if you're on a boring plane ride it seems to last
forever but if you recall it after the fact it
seems to go by very quickly you might remember that you were bored
but you don't have some elaborate memory of every single event because none of
the events were interesting you're you were not focusing so your
subjective time at the time seemed to last forever
but you were also not making new memories so your subjective time
after the fact seems to make the trip actually quite short
another aspect that is very interesting when it comes to how human beings
perceive time is a simple statement that we live
in the past so forgetting about measuring time using
our internal clocks what about when we actually just
perceive the moment now we all think whether we're presentists
or eternalists that there is a moment called now we are perceiving it we're
looking around we're getting data sense data from outside of ourselves
and we experience what we call the present moment
it turns out of course and if you thought about it a little bit it would
make sense that what we call the present moment
isn't the present moment that's because it takes time number one
for the information to get to us and number two for our brain to process
that information the most obvious example of this is if you see
lightning very very far away you see it and we all know that if lightning is far
away it takes time for the sound to get to us you can even count how many
seconds it takes and figure out how far away the
lightning storm is that's because sound moves more slowly than light
but it's not just the external world that matters it's the internal world
that matters as well so for example you can do this at home i
won't demonstrate but you can touch your nose and you can
also touch your toes do it at the same time put your finger
to your nose and to your toes and what you will notice is that you
feel the touch simultaneously if you perform the touch
simultaneously you will feel the touch simultaneously
that seems very natural to us but it shouldn't be natural because the amount
of time it takes the nerve signal to travel from our nose to our
brain is much less the amount of time it takes
the nerve signal to travel from our feet to our brain now the nerves are moving
pretty quickly but we as our our brains are very very
good at measuring tiny differences in time
more than good enough to be able to measure the difference between the
signal coming from our feet and the single coming from
our face nevertheless we don't perceive that
difference we perceive the simultaneous touches as simultaneous
events why is that it's because our brain
knows that our feet are further away and takes that into consideration
it turns out that what we consider to be the correct moment
right now is actually about 80 milliseconds
in the past the way that you can get that number one simple way to do it is
to watch a person dribbling a basketball as they're dribbling the basketball you
both see it and hear it just like the lightning bolt
and your brain corrects for the fact that it takes the sound longer to get
to you so as the person dribbling the basketball moves away
you see and you hear the sound at the same time in your brain
until they get so far away that it takes more than 80 milliseconds for the sound
to get to you at that point suddenly there's a
mismatch between the sound that gets to you
and the sight that's because you get the vision of it and you put together that
in the conscious now before the sound can get to you so we
live about 80 milliseconds in the past and
really the primary lesson to learn from this
is that consciousness is kind of a messy thing it's very difficult
to understand what's going on in the brain because it's a very elaborate
mechanism this is why physics is the right thing
right field of study to go into if you have a short attention span
speaking of which people have different attitudes toward
time and this has nothing to do with culture this is just within any one
culture individual human beings approach time
differently it turns out the psychologists have
shown that our orientation toward time is a crucial component
of how we live the rest of our lives there's a great experiment that
illustrates this called the stanford marshmallow experiment it was first done
by walter mitchell a professor at stanford in 1972 and it's
a simple setup you offer a child a marshmallow you you
fool the child first every psychology experiment involves fooling the subject
into thinking that it's an experiment about something else
so you make the kid do something and then as a reward you say
here is a marshmallow for being a good test subject but then you say i have
another marshmallow you first check that the kid likes marshmallows
i can give you a second marshmallow if i need to go out of the room for a few
minutes if you wait and you don't eat that first
marshmallow i will give you a second one when i come back
so roughly speaking when you do this experiment on three or four year old
kids only about a half or a third of them can
actually wait for you to come back the kids eat the
marshmallow some of them others are very very patient they use
elaborate strategies of self-deception looking around trying their best not to
look at the marshmallow the claim of modern psychologists is that the
difference between eating the first marshmallow
immediately and waiting to get two marshmallows
later shows you something about your orientation toward time
there are people who really in some sense dwell
in the past what they care about most what they're talking about all the time
are what happened in the past what happened they were growing up
high school college whatever there are other people who live in the present
they want something right now they want that marshmallow there it is and they're
going to eat it there are other people who are future
oriented they know that there is some benefit coming to them in the future
they will sacrifice the marshmallow right in front of them to get that
marshmallow in the future they're future oriented
this is not a matter of being rational or irrational
economists will tell you it makes perfect sense to
discount something that is a reward that you won't get until the future
if someone offers you ten dollars now or eleven 11
10 years from now you should just take the 10
now because our brain says how do we know that they'll be around 10 years
from now to give us the 11 that is a perfectly rational thing to do
nevertheless the ability to take the future just as seriously as we take the
present turns out to be a good predictor through
how we approach many things in our lives the
psychologist philip zimbardo also at stanford
has done a follow-up study on mitchell's marshmallow
study he studied now the kids who were three and four years old they're now in
high school and in college what he found was that children who
waited who got the second marshmallow by being good
scored higher on their sats had better behaviors in school
and more scholastic achievement it turns out that our attitude as human beings
toward time is a crucial component in making us
who we are
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