What is time?

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1:00Without further ado, this is The Naked Scientist. Hello, welcome to The Naked Scientist podcast, the show that brings you the biggest breakthroughs and talks to the major movers and shakers in the worlds of science, technology and medicine. I'm Chris Smith and today we're talking time. What is time? How do biology and physics keep track of time? And why does our perception of it seem so variable from one minute to the next?

1:34If you think about how often you check the time or look at the clock every day, whether it's on your phone, laptop or watch, the seconds and minutes organise our lives from morning to night. But what actually is time and why does it seem to race by sometimes and drag at others? I vividly remember long car journeys as a child going to see remote grandparents. The journey going seemed to last an eternity, but getting home passed in an instant. Today, we'll find out how time got rooted as a concept, why we experience it differently at different times, like my childhood trips, and how the body actually keeps track of time, as well as the way that physics defines time.

2:17But first, with a brief history of time, including where universal or standard time came from, the importance of Greenwich Mean Time and the origins of Daylight Savings Time. Here's Emily Ackermans, who's curator of time at Royal Museums Greenwich. When we're talking about our timekeeping systems, for centuries they have been based around Earth's daily rotation on its axis and its annual path around the sun. So when we're measuring time in hours, minutes and seconds, we're basically measuring the rotation of the Earth. so one rotation of the Earth, so in 24 hours we spin 360 degrees, and we divide these 24 hours into 60 minutes and 60 seconds.

2:59So every time we're measuring an hour, minute and a second, we're also measuring how much the Earth has rotated. So this is where your location comes in. By measuring this rotation, we know where we are on Earth, because time gives us our position of longitude, so our east or west position, and we also have our latitude, our north-south position, and together these coordinates tell us exactly where we are on Earth, like in the GPS system. And latitude zero is the equator. It's a natural reference point that splits the Earth into a northern and southern hemisphere. But for longitude, we don't have a natural zero reference point.

3:44And so astronomers spent centuries measuring time and mapping the stars and they did this at the Royal Observatory in Greenwich. This data was used by sailors and navigators at sea and they created maps and charts of the globes all based upon this work done at Greenwich. So this meant that the maps that they used had Greenwich as the zero point, zero degrees longitude, because they kept referring back to the data that was produced there. So when people said that they'd gone a certain distance or they were around the world a certain distance they were saying relative to my starting point Greenwich and hence that's why it became zero.

4:19Yes so it's always a reference point to somewhere but it's not fixed so other countries do the same other observatories do the same work so you would have Paris as the zero degrees or Rio de Janeiro for example could be zero degrees on a chart and it's in the late 19th century that people start calling for the standardization of maps and charts with a common zero in Washington at a conference in 1884 that the delegates vote in favour of Greenwich representing zero, zero degrees longitude for all maps and charts for all purposes and thus becoming the prime meridian. Well that's all very well when we're sort of going sailing and we're saying well I know where I am relative to Greenwich but if you think about within our own country we've got west of here the sun is going to rise and set at different times of the day.

5:03So there must be a point before electricity came along and we could actually send a telegraph to say, right, now it's four o 'clock or whenever it was, people must have actually had different time zones and different concepts of what the time was at different points around the country. Basically, the time to the east of the country would have been earlier than to the west. So a good example is Noon occurs at Greenwich about 10 to 11 minutes before it does at Bristol. and yes so in in Great Britain between the east and the west coast of the country it's about 30 minutes the difference but in other countries this difference is much bigger so the United States or Russia or China they have they could have hours of difference between the east and west of the country all that is fine that is not a problem until the railways start connecting people and cities and towns at a much faster pace before that you're traveling on your horse there's only so far and so fast you can push your horse to go so it's not a big deal that there's a slight time difference between these places but it becomes a big deal with this speeding up of travel and communications and people.

6:10Why is that? Why do railways specifically, I mean that would have been the fastest way to get around at the time admittedly, but why is it specifically a headache for the railways? So railways would have to choose which time their timetable is running to. So you gets to the point where you might have a London line running north to Liverpool on London time but then a line running back down on Liverpool time or rugby time. So the railways standardise their time and they also use Greenwich time. It also becomes known as railway time but then you get another problem. So say you're travelling from London to Bristol, you need to get your train, it leaves at 10 o 'clock in London so that's great.

6:52You leave London at 10, you get to Bristol, you hang out for the day and you want to get the 7pm train back, but the train's not there. It's already left. And it wasn't because it was early. It was because you checked the town clock that was showing Bristol time, but the train was using London time. So this was the problem. You've got the railways running to a timetable that doesn't match the time kept by the local towns and cities. And they solved that by saying we're going to have one standard time and we'll call that Greenwich time or universal time? Yes so it's in 1880 I believe that Greenwich time becomes the legal standard time for Britain so it's another three decades after Greenwich starts sharing time via the telegraph networks and so there's a couple of decades of confusion.

7:36Did other countries have the same problem presumably they did and did they solve it the same way? Yes so basically you get an observatory or a capital city starts to become like the standard time for that country so you get amsterdam meantime or dublin meantime or paris meantime this is then all used throughout the country in some it's only used for like technological purposes like the railways or the telegraph offices rather it's the legal time it all develops at different paces so would someone from let's call it let's say paris would someone in paris have the time from a clock in paris and then take that time on a pocket watch to some other part of france and say here's the time Paris time this is your official Paris time and then set the clock in that remote location to Paris time is that how they did it?

8:23Yes but what they would do is often they'd know the error of their clock against the standard clock which was mostly an observatory clock and then yeah they would physically have to transfer that time piece to look at it and compare it visually to the clock they were going to adjust to that time. Now if that wasn't complicated enough then another wrinkle comes along which is someone decides now we're going to have daylight saving how did that come along and how did they decide what to do this is based on a man named william willett so he lived in chiselhurst he was a builder and he writes about this in his pamphlet entitled the waste of daylight this is in 1907 and he he writes about he's riding his horse in the early morning and the sun is shining it's a glorious day and everyone's got their curtains closed and the shutters closed because they're all still sleeping and then in the evening when he wants to play his round of golf everyone's still working because they got up late so basically he thinks that people's health will benefit by having that daylight in the evening so by setting the clocks forward an hour you kind of take an hour of daylight from the morning and you stick it to the end of the day in the evening and he thought this would benefit people's health because they'll have more time for outdoor you know sports pursuits or whatever in the evening after work.

9:41He also saw economic benefits because you'd use less artificial lighting in the evenings and thus have a fuel-saving benefit from it. And politicians decided to embrace that. Winston Churchill liked the idea, for example, the astronomer royal hated it. He was like, just get up earlier. But yeah, they debate it in Parliament, which becomes the Daylight Saving Act, but it doesn't get passed. It's not until the First World War when Germany implements it first and they do it purely as a wartime measure. So they want to save those fuel costs of artificial lighting in the evening so that can go to the war effort.

10:17So they implement it first and then Britain follows in 1916 and we have our first daylight saving time. Did people like it? What was the reaction at the time? The debates that raged in Parliament about 120 years ago now are kind of the same today. Some love it, some hate it, some forget all about it until the clocks change each year. and the fact that we're talking about this it keeps on rearing its head doesn't it the debate about whether or not this is something we should do or whether we should just stick to summertime all the time do you think that we will ever row back and unstitch a century of of doing this or do you think people will keep on talking about it but it's so baked in this is the pattern now we had an experiment in 1968 in britain where we stayed on british summertime all year through.

11:07After three years, it was discontinued because it was very difficult to measure if there were really any benefits. And the very northern parts and the very western parts of the country, it was just too dark during the winter mornings. So if you do scrap it, the big question is, is do you keep standard time all year or do you keep summertime all year? And I think from a health perspective, it's generally thought that the standard time is better. but people do seem more inclined to want the summertime. It's an amazing yarn isn't it? Emily Ackerman's there, curator of time at Royal Museums Greenwich.

11:42So now we know what time is, how do we actually perceive it? Put it this way, have you ever noticed how time seems to drag interminably when you're waiting for a train but it flashes by when you're enjoying yourself? Well Ruth Ogden at Liverpool John Moores University studies how our brains construct that perception of time and why it's far less reliable than we might think. When we think about physical clocks, like the ones that you've got on your wall and biological clocks, they're very, very accurate. And they give us the sense that time is a continuous, regular type of variable in our lives.

12:20But the subjective experience of time, what it means to feel time as a human is far, far more variable. And it's based on our emotions. It's based on what we're doing at the time, so who we're with and how we're feeling. We build representation of time in day-to-day life based on our memory, so how many things we've stored. If we've stored lots of things, it feels longer. How much attention we pay to time, so if you watch the clock too much, time drags. If you don't look at it at all, time passes really quickly. And then also how aroused we are, so how much our heart is beating, how excited we are.

12:53These things can make time feel like it's passing more quickly. So time is much more slippy and slidey. It's much more sensitive in our perceptual psychological world than it is in the biological world. There's also sort of multiple ways that we tend to think about time, isn't there? Because there's the keeping track of time. I know the seconds are going by, I know the minutes are going by, and I'm aware of the passage of time. But I've also got a memory of when things happened today or yesterday, this month, this year or across the rest of my life. So how does the brain keep track of where everything is relative to everything else?

13:29What we're talking about there is something called temporal order. Your brain has the ability to know roughly when things happened in time. But one of the key problems that we suffer from as people is that our brain is reasonably good at remembering what's happened recently. So the order of what you did say over the last seven days will probably be quite crystal clear in your mind. When we start to move further backwards across time, so when we maybe think about years or even decades, our brain loses or our memory loses that sort of fine, clear detail about temporal order. And this is when we can start to get confused about the order in which things have happened or the distance between different events.

14:13So this can lead to telescoping. Sometimes you can feel like a distant event was very, very very far in the past rather than at its actual point in time or it can refer to reverse telescoping which is the opposite where a recent event feels much further in the past than it actually was. When you say that we also store lots of information because we make a lot of memories of something and that gives us the impression that time's slowed down that would be an example of that would be if I think I'm about to have a car crash and I experience the crash in slow motion because it's very arousing, it's very exciting in some respects, and so my brain stores a lot of information.

14:52But at the same time, if I'm having a really exciting time, I go to a party, I'm interviewing you. Fascinating conversation. The time whips by, you know, 10 minutes goes by. I don't even notice the time. Surely I should be making loads of memories because I'm excited, I'm learning new things from you, and that should make the interview seem to go on forever. But it doesn't seem to work like that. It seems to almost contradict itself. Yes, definitely. one of the key things that can determine how we experience time is how important time is and what I would call temporal certainty or temporal uncertainty.

15:23So when we're in a degree of high temporal uncertainty, so maybe you're waiting for a train and your train is delayed and you don't know when it's going to get here. So time is super important to you. You're watching the clock all of the time. And when we pay too much attention to time or more attention to time than normal, it gives us a sensation of time dragging. This also happens when we're a little bit understimulated. So time can drag when we don't quite have enough going on in our lives or enough in our minds to keep us from paying too much attention to time. I would like to think that when you're in conversation with me and we're having these riveting chats, your attention is fully taken by the conversation we're having.

16:04We have to remember our brain is a limited resource. It can only pay attention to so much at any given time. So whilst we're chatting, we're fully engaged, our brain is constantly being occupied, and there just isn't the capacity to think about time. And that makes it feel like it's flying by in an instant. And the older I seem to get, the faster it goes. Everyone says this. I remember it took me forever to get to age 10. I remember longing to be 10. It just took forever to get there. And ever since, it's been faster and faster and faster. Now, why is that? Why do I feel that the days just go racing by?

16:37You and I started this conversation before we pressed record and we both remarked that uncannily it's the beginning of April already and we're both a bit shocked about that. Why is this happening to us? This is one of my favourite things to talk about with time because as you say it's something everybody talks about. Everyone feels like time passes more quickly as they get older but when we look into the scientific research behind this we haven't really been able to capture the extent of this experience in questionnaire research so we often ask people you know like how quickly does time feel like it's passing now in comparison with when you were 10 or 20.

17:10And then we try and predict this experience based on a range of cognitive factors like memory function or age. And what we seem to see is that age plays a very small role in our perception of time. And that got me thinking that what we're doing here is that we're asking the wrong questions. So everybody says that time passes more quickly as they got older. Maybe we need to talk to them about why they feel like this. So some recent research that I've conducted asked people just to tell us about how time felt when they were passing as a child and how time felt when it was passing as an adult. And what we found with this work is that part of the reason time passes very quickly when you're older is that you just don't have any of it.

17:49Like we live in these incredibly time pressured environments and these time pressured environments make us feel like time is slipping away before our eyes because there is no time to catch up and do all the things that you want to do. Childhood in comparison is an abundance of time. It's periods where you have all these opportunities to do all the things that you want. But as you just said before, there's also periods of waiting in childhood. And we know that waiting makes time pass very slowly. So you're waiting for Christmas, you're waiting for your birthday, you're waiting to get your driving licence.

18:22And this obsession with time that waiting can create can add to the sense that time is passing more slowly in childhood. And the absence of free time in adulthood makes it feel like it's passing very quickly. But of course, there's also the fact that mathematically speaking, a year when you are 10 is only a tenth of your life. A year when you're 70 is a 70th of your life. So there's that relativity in the years as well. Again, much like the subjective experience of time that we talked about at the start of the programme, the fact that time changes as we age is probably also a multifaceted concept made up of many, many different drivers rather than just the one.

18:58There's a lovely line in the novel Catch-22 where the lead character muses that he likes spending time with a certain individual because that person is really boring. And so in their company, time goes really slowly and that makes your leave or time off feel like it's lasted a whole lot longer. That was Ruth Ogden on The Perception of Time at Liverpool John Moores University. Have you ever been stuck on a weight loss plateau, trying everything and anything you can to lose that extra weight and reach peak health? We've all been there, but Noom's unlocked the secret to reaching the mountaintop, going micro.

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20:28Music in the programme is sponsored by Epidemic Sound, perfect music for audio and video productions. This is the Naked Scientist podcast with me, Chris Smith, a programme where time never drags. And indeed, today we are exploring the science of time and how we perceive it. Coming up, how physics measures time and also the future of timekeeping going forward. But first, we're going to explore how biology keeps time. There's a clock that ticks inside every single one of us. In fact, there's not just one clock. There are trillions of clocks because every single one of our cells effectively knows what time it is.

21:06And this circadian rhythm ultimately governs our sleep patterns, hormone levels, metabolism, appetite and mood. But unlike Greenwich Mean Time, it doesn't follow schedules or timetables. The body clock ticks genetically, with one gene turning off another and feeding back to turn off others. And it's set by the sun, other external signals, and it's shared across all our tissues. Eva Winnebeck works on biological clocks at the University of Surrey. We notice that there's lots of things in our body that are actually out of our control, but that are controlled by this internal biological clock or real clock system.

21:47Every cell of us has a time keeper that tells us where in the 24 hours we are. So like this internal representation of day and night. So if I took a skin cell, I could ask it what time it is. One of my skin cells ought to know what time of day it is. Absolutely, it better do. And you can actually take skin cells or recently hair follicles. You rip out hair from your head and then people can actually read off your internal time. How would I ask a skin cell what time it actually is, though? How do we read the time in my notional skin cell? Well, unfortunately, your skin cell doesn't have an obvious hand or hands that we can read off.

22:31But it has lots of molecules in it that change over time. And if we look at how much of each molecule is in there or in relation to another, then we can tell what time of day it is for your skin cell. And does it keep that time itself and occasionally update it? Or does it rely on an external signal to then tell it what to do with those molecules so it knows the time? Well, it's a mix of everything how the skin cell knows what time it is. It does have its own clock system. So if it doesn't receive signals, it will just keep on ticking. But luckily, it does sync with the other skin cells and with other tissues in the body.

23:14And there's one really big signal that we get through the so-called suprachiasmatic nuclei in the brain. They're so-called the master clock, but that's a bit of an oversimplification. But if you want, it's sort of the top clock in your body that sends around a signal to other tissues. so they are as best in sync as they can be. So the skin cell has a clock ticking and it can keep time. It can share that time with other adjacent skin cells, but it can also update that time via signals that arrive externally, including from the brain. Perfectly put, exactly that. And what actually is it doing in order to share that signal then with other skin cells?

23:59How might one skin cell tell the adjacent neighbour so they can compare notes and keep to time? That depends really on the cell type and how they communicate. It's oftentimes hormones, but it can also be neural connections. Or another signal that's really great across the body is, for example, your body temperature. So that changes over the course of a day, not just because you move or you sleep, but also there's a daily regulation from your circadian clock changing that temperature over the course of the day. That is also a synchronising signal across the body. And do all of the clocks line up?

24:38Do you have different time zones in your body, I guess, like the planet? Or do we all live in one time zone? All our organs are in sync with each other in health? Well, the different time zones within a body is really a matter of current research, we're trying to understand what it means if you have a different time zone between your liver and your lung and your brain, if that is sometimes beneficial in certain situations or not. We call it different phase relationships where the physics of clocks and oscillation comes in. So it may be in certain situations advantageous that your liver is slightly timed differently.

25:16But generally, we think about it as one system that sends signal back and forth. So it's optimally aligned between the different tissues. In health everything should line up but sometimes they don't and it might even be possible to manipulate them so they don't and that might under certain circumstances be advantageous. Well that's what we think depending on what we do to the clocks. For example if you go through jet lag we know they desynchronise quite heavily which actually causes many of the symptoms that you feel really awful because nothing fits together but with shift work sometimes there's a theory that maybe it's advantageous if it's not all in exactly the same alignment as during your normal day shift for example do they all catch up at roughly the same rate so if we do travel and get jet lagged or like you say you do a night shift and you throw your metabolism off kilter does one bit of your body say your liver catch up sooner or does everything roughly realign at the same sort of time?

26:20The problem is exactly that they do resynchronise at different speeds. For example, your sleep-wake behaviour, which is often really determined by circadian rhythms to a large extent, might catch up much more quickly because you have some control over it to a certain extent, but then your metabolism might be a lot slower. And that's actually where we think lots of those adverse events during jet lag, how you feel miserable actually comes about that it doesn't fit together as well anymore because it resynchronises at different speeds. I'm just minded of research that's emerged in the last couple of decades where, for instance, cancer treatments have been found to work better at some times of day than others because stem cells appear at certain times of the day more than others and they turn out to be the ones that might be driving a tumour.

27:11So are we actively pursuing that? Are doctors and circadian biologists looking at how we can use the body clock in order to optimise treatments for diseases like cancer now? Absolutely. That is one of the main research topics in chronobiology. Can we use the time of day information in the body to actually reduce the side effect of drugs and make them more potent so the effects that we do want to happen? can we emphasize them? And cancer treatment is one of the prime examples where this has been tried. And especially immunotherapy against cancer seems to often in many instances also depend on the time you've received that first drug.