How We Perceive Time | Sean Carroll

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 [Music] so [Music]

Channel: Wondrium

Views: 108,020

Keywords: great courses, great courses plus, teaching company, free online learning, free online courses, online learning, online education, time perception, time dilation problems, time perception distortion, sean carroll

Id: N-uX2pexJqk

Length: 31min 33sec (1893 seconds)

Published: Sat May 08 2021