The Infinite Monkey Cage - What’s the time? - Marcus Brigstocke, Leon Lobo, Louise Devoy

Episode Date: November 19, 2025

Robin Ince and Brian Cox wind up at the Royal Observatory in Greenwich – arguably the centre of time – to uncoil the mysteries of what time is and how on Earth (…and on moon) we keep track of it. Taking the time to join them are comedian Marcus Brigstocke, curator of the Royal Observatory Louise Devoy, and Head of the National Timing Centre Leon Lobo.From ancient Egyptian knuckle counting to sun dials, quartz oscillators and atomic clocks, the panel turns back time to discover how we measured and kept it throughout history. Together, they dial into why Greenwich has become such an important place for time and how time is synchronised and sold across the globe. They explore the flaws and future of accurate astronomical and atomic timekeeping, and Marcus blames the ‘leap second’ for his fry-up failures.Producer: Olivia Jani Series Producer: Melanie Brown Executive Producer: Alexandra Feachem A BBC Studios Production

This BBC podcast is supported by ads outside the UK. How does love work exactly? What makes something funny? How does noise affect your health? These are just a sample of the fascinating topics we discuss on my podcast, Something You Should Know. We bring you leading experts on topics important to you, things you can use in your life and that will fascinate you.

We deliver three episodes a week and have a over. a thousand episodes available to listen. So get listening to something you should know wherever you get your podcasts. Hello, I'm Brian Cox. And I am What Remains of Robin Inz. That's the nature of entropy, sadly. This is the infinite monkey cage from the Royal Observatory Greenwich and that is why, of course, the show will be beginning with the Pips. For legal reasons, we can't play the last PIP because apparently it scares the Radio 4 news reader who thinks they've forgotten to do the news and be ready for it.

That last tone activates Gladys Knight. See, I think it might end up just being up. I knew this would happen. The Pips was written by these two sisters in America in the late 1930s, like happy birthday. And if you play the whole pizza, oh my God, the BBC's got to pay 500 pounds

to their estate now. Now, today's monkey cage is about time. Because the show has been recorded at the Greenwich Observatory in its 350th year. In 1675,

King Charles II signed a royal warrant for an observatory to improve navigation at seas and the building was designed by Christopher Wren and Robert Hook. You've never sounded

more like Simon Sharma than you do now, and that worries me because I think you're going to branch out as if you're not on television enough, the fact you're then going to start doing history stuff as well. And as we know, you don't believe in history because you believe in the idea

of the block universe and that all times in many ways happening at once. And so that's going to make a very odd show. Today, Greenwich is still synonymous with navigation and timekeeping and so we will celebrate the observatory's anniversary by exploring time. Why do we need to know the time?

How was the time measured? That's an odd one, is it? Why do we need to know the time? So otherwise we're late. We're going to find out why we need to know the time, the history of timekeeping. Okay. Why do we need to know the time? How has the measurements of time changed and how do we keep time today? To help us explore time, we are joined by a catalogue of collections,

a traverser of time infrastructures and a connoisseur of Kurds, and they are. Hello, I'm Leon Loebel and I've been heading up the National Timing Center program at the National Physical Laboratory. So sort of lead on the strategy and what we need to do in the UK around resilient time. And my favorite timekeeper, actually, is a very personal one a few years ago, was my son, every morning used to wake us up with, where's my breakfast?

And that was particularly amazing for us, not anymore. And thinking back, probably wasn't there, either. But we've got a display back at NPL where we have all the atomic clocks that maintain the UK's time and we've got this display that ticks at the thousandth of a second. And if ever there was a place to set your watch, that was it. It's something to see.

Did you ever give your son his breakfast or just every morning? It was the same. Basically pointed him towards the serial down there. He still does it, mind and he's 17. Hello, I'm Louise DeVoy and I'm Senior Curator of the Royal Observatory here at Greenwich and I do research on the history of the site and that includes everything from the buildings to the historic scientific instruments to the stories of the people who lived and worked here. And for me, my favourite timekeeper is actually the park around the observatory because in the spring we just get this explosion of pink cherry blossoms

and then in the autumn it gets that sort of reddy gold hues, really lovely in the more morning. So it's very basic. It doesn't involve any fancy instruments, but it's a really nice, colourful way to start my day. And it's a really profound sort of reminder of the earth's journey around the sun. I'm Marcus Briggs stock. I'm an international cheese judge and comedian as well. But the cheese is the main thing these days. And I think my best, most loved and important timekeeper is also that of a father. I'm a dad to a four-year-old. and if I want to measure one hour, I try to put one of his shoes on.

And that's about an hour. And this is our panel. Leon, Leon, Leon, Leon, I just want to pick up on, because Robin thought that question, why do we need to know the time? Yes. It was kind of a silly question. Somehow there's an obvious answer.

But may I ask? Tell you about why we need the time now, pretty much everything we do in our daily lives, underneath all of it, all our digital infrastructure, relies on time to operate. Whether it's the show being broadcasts when it does, or whether it's how we got here with Satnav, or whether it is we got our tickets for the trains and paying for that, everything that we rely on these days from a digital perspective is underpinned by time for synchronization. typically, but it's everywhere. Louise, historically, when do we start to see any care, let's say, in terms of synchronising time across a country and then across the world? Sure. I mean, Leon raised a really good example with the railways here in the UK.

So in 1847, the railway companies all decided to use Greenwich Mean Time across the whole network because originally the timetables were based on the railway terminus, whether that was in Cardiff, Liverpool, or whatever. So you'd have about a 30-minute variation across the whole country. So trying to get trained from Liverpool to London was just impossible. You'd miss your connection. We'd love a 30-minute barrier now.

I was going to say, I don't want to challenge the proper experts on this, but you may be aware of this already. Southern Rail used an entirely different means of measuring time that is almost entirely arbitrary. So those different, the time, a different railway terminus. Is that just based on the clock at the terminus? Is that based on astronomical observations?

A bit of both. They were still actually using sundials, sun dials and clocks, to sort of regulate local time. And then, yeah, in 1847, they thought, hang on a minute, we need to coordinate. So they chose Greenwich Mean Time, London Time. And then by 1852, the observatory was starting to send out time signals via the telegraph network. so that clocks at Rawi stations could be checked and calibrated and so that really sort of made GMT

just part of everyday life. Ever since you mentioned about the seasons all I've wanted to ask is but how effective are dandelions for telling the exact time? Because I was thinking about that because when you mention the seasons and I know that sounds fast a little bit

but actually that's one of my favourite things during the spring when I was a little bit later on again watching the passing of time by looking at a dandelion so in certain different places again in the nature of the change in seasons, I would go, the dandelions in this area have reached this point of being a flower, at this point they've now become the dandelion clock as such.

Because you were all brought up with that, weren't you, that bit of blowing on that. And I love all of those kind of mythic ideas, and the idea that perhaps that is what Southern Railway are using, this enormous number of dandelions are going, I know some of these kind of modern faddy people are using clocks, some of them even with quartz. But as far as I'm concerned, it does hinder the spread of seeds. Are you, in terms of, are you someone who's, are you interested in time? Marcus, are you someone who kind of likes that sense of time? No.

I found as I've got older, I like it less and less. And I like existing in a space of a bit of uncertainty. Although I'm no longer late for things. I mean, I was for a long time. I think I was late for something when I was about 19. And then I never really made up the time. and then just was consistently late for about sort of 20 years after that and then eventually made up the time.

But no, I find more and more I like it when I don't quite know the time or also where I am. You mean you're reaching your Ken Dodgers in terms of the... He doesn't realise it's three in the morning. When can we leave the Weymouth Pavilion? Well, yeah, no, I mean, as a comic, I've always loved that Steve Martin line. He said, comedy's all about Thai...

timing. There's something a bit magical about the timing of when you see something on stage, not just comedy, anything, that it's kind of perfect. The same in music, right? When the time signature changes, you don't feel often, don't feel thrown by it. You feel elated by it. Leon, so we talked about the time being synchronized to Greenwich in 1847. Yes. So what does that mean exactly? So how is Greenwich keeping the time? So Greenwich is the home of time in the UK, the historical home of time. There are few changes that occurred over at the last century, effectively, where the advent of pendulums and then you're looking at quarts coming on the scene

and being able to start to regulate time much, much better. One of the things that also changed was some of the work that took place, at our end in Teddington in fact at the National Physical Laboratory where there's a scientist called Louis Essin who built this system that demonstrated for the first time that an atom was actually a better regulator than the earth itself which led on to atomic timekeeping and the basis how we measure time now but the whole piece around how we relate to time GMT is still used quite heavily but the global time standard

as such is UTC now it's coordinated universal time is what it's called So historically Could you just run through what we mean by How do you keep time on the earth Before you have a mechanical clock And then before you have an atomic clock

And how do you synchronize all that together So the Greenwich Meridian is key to that So when the sun is at its peak, you've got noon. And essentially, it was decided that 86,400 seconds was a day. I love that, Marcus, it was decided that. Yeah, rather than it started getting light again. No, the division, though, right? You're talking about the division.

Okay. So why that number? So it's one rotation, 24 hours, divided by 60 minutes, divided by 60 seconds. This gives you your fraction of one second as a part of the Earth's rotation. And that's really your sort of fundamental unit for centuries. The 24 hours stems from the Egyptians. They had 12 hours of light and 12 hours of darkness. And that made really good sense from the latitude of Egypt

because the daylight only varies between 10 to 14 hours across the year. But also 12 is their favorite number. Because if you've got your four fingers, you've got your three joints, you can count to 12. You've got your own sort of portable abacus. You can carry around with you. So that's why 12 are so important within their culture and numerical system.

And we've kind of inherited that legacy. We were talking about this very briefly before, but in the end of the 1700s, 1793, I think it was, following one of their revolutions, France decided to change it to decimal time. And it was chaos immediately. trying to divide the day up into tens literally nothing worked

and no French person knew where they were or what the time was and they've stuck with that lesson but my favourite just on France very briefly my favourite clock is in Saint-Roupe in France there's a wonderful clock tower there

if you're ever lucky enough to go and the clock tower in Santa Fe has clocks on three sides of the four of the of the lock tower. And the reason it doesn't have a fourth one is that faces San Maxime across the bay. And they said, if they want to clog, they can get their own. It's so beautifully French. It's like, no, get your own clock.

You raised the question about the definition of the second. So as you defined it there, as the Egyptians would have defined it, it's just a fraction of the length of the day, which is related to how many knuckles and I didn't know of that on fingers you have. So how has that changed? How do we define the second now? So the second is now defined by the cesium atom,

and it's defined by a particular transition, an electronic transition in the cesium atom. A good clock within an atom is one where you have electrons in their shells, but you need a very, very specific energy to transition an electron from one shell to the other. Now, in the case of cesium, that hyperfine electronic transition essentially allows us to put in this very specific energy and then count the cycles to essentially determine what duration is one second,

which is 9.2 gigacles of the cesium frequency. and that's the basis of how we measure the second now. So Essen, when he first demonstrated that, his clock, which is in the Science Museum, it's a beautiful thing. It's not a mechanical device in the same way as Harrison's clocks here, but it's as beautiful, was stable at the second over 300 years. So we'd lose or gain a second over 300 years.

and the devices that we use now to tell us what duration in time is second are accurate and stable at a second over 158 million years give or take a second and then there's a whole next generation of clocks that are coming as well which are even more stable

and by the end of this decade or in the next few years after that the international measurement community or metrology community are going to be now looking at how we redefine the second by a different set of atoms. That makes me think then, though, going back to old clock mechanisms. You know, I was thinking about before we have, you know, Greenwich Mean Time, when people might have had fob watches or whatever it was,

and this idea of how to watchmakers, when they're making those watches, I presume not every second was the same length in a watch. Yeah, the observatory was very much involved with this. So you have these portable, accurate sea clocks called Conombal. that mariners were using to work out their longitude by providing a reference time and the makers will be making them and you assess each instrument according to its rate so how much it speeds up or slows down every day but obviously you need to compare it against something so the chronometer makers in clarkinwell in north london used to come over to the

observatory and check the time here and then go back and try and check their instruments but obviously that was really tedious so the astronomer royal then set up a time time board that could drop at precisely 1pm every day in 1833 so that both mariners on the Thames could check the time and check to see if their chronometers were too fast or too slow but also chronometer makers and then later on in 1852 we installed the gate clock I don't know if you've seen the big dial with the 24 hours so now people could see GMT for themselves without hassling the Astronomer Royal we mentioned in the introduction actually this this observatory is about navigation so it could

Could you explain why it is that you need accurate time in order to navigate? For navigation, it's all about the Earth's rotation. So you're out at sea, you're looking at the stars, you know your local time, and you want to compare it with something else to work out how far the Earth has rotated and essentially how far away you are. Now there's one technique that involves using the Moon, but for that you need really good star charts. You're trying to plot the position of the Moon against the background stars. So that's one option.

The other idea is to take this clock with you, this reference time, that essentially tells you what time it is back home. So you can compare that to your local time to a reference time and then work out the difference. So navigation and timekeeping are completely wrapped up together. And that was really fundamental to the observatory's work. So your local time is coming from just midday, essentially. Yeah. So you'd measure noon from the highest point of the sun.

And then you'd perhaps keep track of that during the day, either with a sandglass or a watch, and then when you do your observations at night, then you can see how much time has passed. So it loses a second, your atomic clock, you were talking about, every 168 million years? 158. Oh, it's not as good as I thought, actually.

It sounds a bit shabby. I'd work harder. First of all, that's very much the clock of an optimist, isn't it, in terms of the longevity of us. But what are the changing needs within our culture and within our economies that just says we need this so exact. So our telecom networks as an example

requires synchronization and in order for those to operate and be able to send out data between your devices at that sort of rate for you to make video calls, the synchronization requirement is very, very stringent.

You're looking at the microsecond level. So a lot of the metrology institutes, the measurement institute, around the world that contribute to UTC formulation, the global timescale, is really about being able to have the systems and the devices that are many orders of magnitude better than what use cases require in order to be able to commercialize and put those in place. That's just one example, of course.

Face synchronization of the energy grid relies on time. Trading systems in the finance sector, They are trading at tens of thousands of trades per second, which absolutely need to be synchronised and be able to be correlated with each other. Everything is only going to get faster and more volume of data and more distributed and all of that needs to be underpinned by time.

You mentioned UTC several times. So we're here in Greenwich. Everyone will know about Greenwich meantime. And now UTC. Yes. So what's the difference? UTC essentially is the global time standard that is used for civilian time around the world. What it is essentially is all these atomic clocks globally.

There are about 500 and about 85 national labs around the globe that contribute data to create something called free atomic time. But free atomic time essentially is like a weighted average of all this data. and you could consider it to be sort of stretchable. Now, we lock down what duration in time is a second by getting data from the cesium fountains that we have, which are what we call primary frequency standards. So essentially they provide us with the realization of the second,

so what duration in time is a second, and to lock down that stretchy time scale to create something that's what's called international atomic time then. And UTC essentially ensures that both atomic timekeeping and the mean solar day stay true to each other as such, and not diverge. And that introduces something that many people haven't heard of. You've all heard of leap years. There's something called the leap second.

And in order to keep those two time scales within point nine, of a second of each other, because the earth is wobbling and slowing down and now it's actually speeding up. We introduce a second into the day and that unfortunately can't play havoc with digital systems that are trading or operating so quickly. Which day did it come in this year because... It didn't. It didn't happen this year. Oh, okay. What happened? Well, I was cooking an egg and it was over-cooked. And I just wondered if that was you. I like a soft yolk But I was going to ask you that

It's complicated Did you have any idea That time Of God, I think we're asking him about his eggs It is complicated It's four minutes It's naturally always right, is it? We're only halfway through

This explanation of what It's how we keep time It's way more complicated Than I expected And of course I feel disturbed If we haven't disturbed you We have failed

Yes. How does love work exactly? What makes something funny? How does noise affect your health? These are just a sample of the fascinating topics we discuss on my podcast, Something You Should Know. We bring you leading experts on topics important to you, things you can use in your life and that will fascinate you. We deliver three episodes a week and have over a thousand episodes available to listen. So get listening to Something You Should Know, wherever you get your podcasts.

Louise, Leon described today we have this global infrastructure to set the time, so therefore an agreement, a global agreement on how to set the time. So we talked about the agreement across the UK in the 1840s. How do we see the development of the international standardisation of time? This really comes about because of travel and trade. So in the mid-1800s, you've got new technologies, railways, steamships, telegraph networks, and so that the world is effectively shrinking, becoming very sort of globalised. And at the time, there were about 11 or 12 different prime meridians, zero degrees in use,

all set up by various national observatories. And it just became so confusing. So a conference was organised for 1884, and people came together, various delegates from different countries. and after about a month's worth of discussions, they decided upon choosing Greenwich as the prime meridian zero degrees longitudes simply because the majority of shipping companies were already using British charts and maps

that were based on Greenwich. So it was a very pragmatic decision with hopefully the minimal disruption. Now, as we're looking at this change, this kind of advance, we start to think about the distances that we might be travelling, whether we do travel to Mars,

whether we become a more kind of extraterrestrial species. How does that change as well in terms of how we examine time and how we measure time? Gosh, I think it's going to be a real challenge. Say, for example, if we start to explore the moon more, are we going to have lunar time? We could try and use UTC, but it's going to be tricky because there's going to be a time delay. We want to try and coordinate with what's happening on Earth, but we also need to be true to sort of lunar time itself, because it's slightly different.

So, yeah, I think we're probably almost going to have to have different times for different planets. It'll be interesting to see how it pans out. So it'll be like Chico time as well, I think. It's another system that's been used previously. Hammer time, of course, in the early 90s, which I know was something that, you know, you kept to hammer time for a good few years in the 90s, didn't you? That's how I got up in the morning. It's how I knew it was time to go to bed.

And it meant you never got out of your pajamas because they just looked so similar. Leon, given the importance of this infrastructure, so we've talked about the importance of synchronisation across the economy, it's clearly vital to everything that we do today. How robust is that system? Where is it who owns it? Should Marcus worry? Don't worry about it too much.

Oh, the tone of that was very worrying, wasn't it? So managing the time as a timescale is pretty, much useless to anyone unless you can disseminate it. And that's been the case forever. Belville is a hero of mine who came to the observatory every day, synchronized a pocket watch and sold the time to the traders in London. That's such a, again, sold the time. That is such a beautiful. We sell the time these days as well. Yeah. Yes. That carries on. We've not stopped sort of innovating on that front. So we've got radio signals that are broadcast across the UK. We've got time over the internet. And we've got a very dedicated service for the traders and the stock

exchanges where they need very, very precise time. Most people would say, well, it's probably my phone. That's probably the most accurate thing. So where is that getting its time? So there are several methods. So computer systems typically get their time over. the internet. So as soon as you log in or turn on a computer, it'll sync its time to what's called a network time protocol server. But on your phone, you probably get your time from your telecom provider, who probably gets its time, almost definitely gets their time, from the global navigation satellite systems like GPS and Galileo, which the constellation gets its time from a UTC lab.

So in the case of GPS, it's the U.S. Naval Observatory in Washington, D.C. And GPS, particularly, and now more so Galileo and some of the other constellations, is the easiest way to get precise time because it's global. But with that also, we've got to ensure that we have access to many different methods, because if you rely on just one, you can be vulnerable. when you lose it. Louise, sorry, I have a question.

What sort of excuses to people give at your office when they're late? So as a measurement institute, we can tell you that it's not that we're never late at any meeting, we can tell you exactly how late we are. Louise, we've heard about this technology,

the atomic clocks, this remarkable technology, before the atomic clock. So the clocks that you have here at Greenwich, Could you run through how accurate they became and the different technologies that were used? For us, it's really all about pendulum clocks. So when the observatory was founded in 1675, we had some state-of-the-art pendulum clocks installed by Thomas Tompion, the best maker in London at the time.

And these were very accurate. They had very long pendulums, about four metres long. And these only needed to be wound up once a year. And the Flamsteed, the first Astronomer Royal, used these pendulum clocks to prove that the Earth rotates at a constant rate. And this was really important for those crucial longitude calculations. Fast forward then to the 1920s, and we actually have now even better pendulum clocks that show that the Earth's rotation is not quite as constant as previously thought. These are pendulum clocks where the pendulum is now suspended within a vacuum tank. so you're minimising any aerod disturbance and that really sort of ushers in a new age of accuracy

and proves that the earth is slightly varying, it's wobbling, it's slowing down. So, yeah, 250 years, those pendulum clocks were absolute king. So the earth was the most accurate clock until about the 1920s? Pretty much, yes, yeah. And then in the 1920s, we then start to use sort of the legacy of the First World War where people are really interested in radio technology. And so people start applying electric currents to quartz crystals and find that they vibrate at this very, very consistent rate.

And that really leads to the development of quartz clock technology. And then in the aftermath of the Second World War, we find that physicists have now got a lot of experience of work with microwaves because they've been working on radar. And then that leads to the evolution of the atomic clock. So we really sort of benefited from those military technologies. Louise, I wanted to go back. You're talking about that high accuracy today.

Who is it who you said was coming with the clock to synchronise here at Greenwich and then go into the city, delivering the time to the city of London? Could you tell that story? Yeah, I think that's a really good point because also we talk about accuracy and the importance of trade. But it's also about human choices as well and trusting in your provider of time. So this relates to John Henry Belleville, who was an assistant working here at the Observatory in the 1830s. and he realised that chronometer makers needed accurate time for checking their instruments. The better their instruments performed, the more money they got from the Admiralty. So it really was time equals money.

So he started a side hustle where he would take a chronometer set to accurate GMT around the city, selling it to about 200 subscribers. When he died in 1856, his widow Maria took on the business. And then later on in the 1890s, his daughter, Ruth carried on the business right up until the 1940s of the Blitz. Now, this might sound a bit daft. Why is you selling time, this person physically carrying time across London when you've got telegraph networks, you've got radio signals from the 1920s?

But it was all about trust. They were very reliable. They came every Monday morning. It was accurate GMT. There were no technical issues if the wires got broken or eaten by rats or affected by snow. It was this very trusted sort of family service. And that's why people used it, even though technologically there were other ways of doing it. Were they setting that time from the ball here that dropped at exactly 1 o'clock?

Is that how they sort of started? They've come to the gate. Then they'd hand over their portable chronometer to be checked by one of the assistants. Stay for a cup of tea, have a chat, and then pick it up, put it in your bag, and then start heading off. Was there any indication? Because the ball here, the big red bull, dropped at exactly 1 o'clock. right and so ships and everybody were like that's it it's one o'clock was there some warning like it's going to go or did you they just have to wait and go oh we've been here for hours i think i don't know

literally nothing's happening it's stuck it's stuck yeah it's so about 1255 it goes about halfway up to give you a warning so there's some movement yeah then it goes the top at 1258 and then it drops at precisely 1 p.m and then you'll notice as it comes down it just sort of hovered very slightly, and that's because we've got pistons to stop it from smashing through the roof. We've been talking about time without actually then thinking about also, you've mentioned a little bit about the difference in time

say in Penzance compared to in London etc. But what about actually forming the kind of the time zones as they exist where we do have these very specific lines which say you're now in this time zone if you've got America, you've got the specific time zones there. How are those worked out? It's back to that conference

in 1884 where they designated the Meridian at Greenwich has zero degrees longitude, they also discussed the idea of having a universal day starting at Greenwich at midnight. And so that's a way of thinking about time. And so over the decade since then, we've created this sort of system of about 32 different time zones. Now, in theory, you'd chop the earth up a bit like an orange with different segments. You'd have, say, 24 different segments. But we're human. We like to make things complicated. So different countries have opted to be in different time zones and so that's why it's not quite as clear cut as the segments i don't know if

it's china somewhere with an enormous landmass and they basically just don't they haven't observed the time zones i can't remember which nation it is yeah it's china it is china so to enhance coordination they have the same time zone across the whole sort of area of the country it's all set to sort of Beijing time geographically you could have say multiple time zones because it'd extends so far in longitude. But in terms of coordination and government, it just makes more sense if everyone's on the same time zone. Why do we bother now correcting this UTC with these tremendously accurate clocks and all these international agreements? Why do we bother correcting it back to the Earth's orbit? As you spoke about leap seconds and indeed leap years, leap centuries

and so on. Why not just say atomic time is what we need now? We don't care. The Earth's as clock is an artifact? There are still applications in astronomy, I'd say, is the predominant driver, really, to maintain, be able to maintain that and provide that information. But from a leap second perspective, that conversation is actually happening at the moment because the introduction of leap seconds is indeterministic. So there's an organisation called the International Earth Rotation and Reference System Service. Snappy.

It actually takes so long to say that by the time you've done it, you have to introduce a leap second. But what they do is essentially they monitor what the earth is doing in terms of wobbling, slowing down, speeding up. And then based on the divergence of the two timescales, determine whether we need to introduce a new leap second or potentially take one away if the earth is speeding up, which it is at the moment. So the conversation amongst the international metrology community is about because it's indeterministic and causes havoc with digital systems is what do we do, you know, should we make it a leap minute or larger and kick the problem down the road to our great-grandchildren. I just do a leap minute now and then leave it for 200 years. Exactly. So those discussions are happening at the moment.

But it's a big problem because there's a very specific process to introduce it. So it's always introduced only either at the end of June or the end of December, the last second of that day. But unfortunately, lots of firms around the world do their own thing. So as an example, Google smears the leap second across every second of that day. And is that literally at 2359? There's two 2359s? No, it goes from 59 and normally it go to 0.

Yeah. But it goes from 59 to 60 to 0. Oh. So, Marcus, now we've got to smeared leap seconds. How's your existential anxiety at the end of today's show? I'm terribly worried. None of the listeners know that his watch is one of the, of those ones with Mickey Mouse's fingers on it.

I mean, it's ridiculous. Well, that's, Brian. We've run out of time. Don't say we've run out of time, that's all I need. Time has ended. The last question, though, isn't it almost, the idea that we care about keeping UCC

in synchronisation with the variable rate of spin of the earth seems to me almost like a almost, emotional thing. Does it really matter at that level? Because as you said, you could just kick it down. You say, okay, we'll do a leap minute and forget about it until 23. It's a dangerous way to end this show by saying

but does any of it matter? No, bye-bye. Louise, the important thing there is even if it goes to, say, a leap minute or beyond, it's about continuously being able to measure and be able to provide what that difference is.

That's the important thing. Yeah, I think it's still important to connect with the rotation of the earth and still using sort of the Greenwich as a reference point at a start and finish is still very useful. You would say that. Still using Greno, as long as Greenwich. But I think, yeah, it's still connected. So the international reference meridian that we use for satellite navigation is still pretty much parallel to the historic prime meridian defined by the Aerie Transit Circle here at Greenwich. And I think just from a human level, we still want to keep in sync with daylight, with our daily activities within a solar day.

So it's still having atomic time, but sort of shifting it so that it could start and begin at any moment, it just seems quite strange. And does anyone here at Greenwich, when the clocks change, you know, when it goes forward, does anyone know how to change the one in my car? Because I just count it back an hour for six months. Yeah, well, I'm still struggling with the microwave, so yeah. Right, fine, fine, good. This is a science show

In terms of practical things That may change your day to day living That will not happen In terms of existential anxiety That will fill your days This will occur Massive, that's the way it works philosophically It's big

There are several other things afoot as well Oh, there we go Marcus, are you ready for this? So I mentioned previously that there's a huge amount of effort being conducted at the moment around redefining the seconds. So shifting from what currently is based on the seism atom, we can measure that second over 158 million years if you want to call it that, if it was

a clock. But there's a big shift now to redefining the second by an optical transition. So moving from the microwave at the gigahertz to the optical at the hundreds of terrahertz, which gives you five orders of magnitude, better precision that you can break down the second, and inherent additional enhanced stability and the like. So that is happening at the moment. And those clocks are already demonstrating stability at the 18th decimal place, effectively, or a second loss or gained over the lifetime of the universe. So it's a significant shift that's coming. They are now sensitive to gravity

potential. So if you raise one of those clocks by a centimeter, you can measure that because the frequency changes because it's sensitive to gravity being slightly different. And so from a navigation perspective, eventually,

we'll be using clocks to map the geoid, create gravity maps, and potentially have navigation systems based on that. I like the fact that our episode about time has gone really over time. So we have run out of time now. We asked our audience question as well and that question was, what is the slowest you have ever felt time move? Marcus, what have you got there? From Paul Foster outside in the queue waiting to come in here. Brian, what have you got?

Well, this is a very accurate and perceptive answer. Okay, so it's rude about me, I presume. No, no. At the event horizon of a black hole. It's absolutely true. So when Bied from the outside time stops on the event horizon of the black hole. Which is the same effect that we're talking about essentially but rather more extreme in moving the clock up and down in a gravitational field and seeing that time passes at a different rate

because of the distortion of space time I shut up. Yeah, if you haven't had enough at essential anxiety of the distortion of space time for you as well. Running to the loo in a D-REME the sheets will only get wetter. So mine was a very educational and sensible answer. Which they're not meant to be, Brian.

They're meant to be facile. Come on. What have you got there, Marcus? You got another one there? Yes, this is from Alex. The 15 years it took my girlfriend to agree to go on a date with me. I mean, if nothing else, the persistence of Alex, is either to be admired or, no, we'll just... I have to interject.

I was so carried away by the precision and insight of the answer that I missed the joke. that I missed the joke there is a joke here because it's at the event horizon of the black hole named M25 which is even because I skipped that

because I thought no you mean M87 which is the one we've got a photograph of or the one it's Sagittarius but no it's the motorway in it that right

well let's leave you so thank you very much to our panel Dr Leon Lobo Dr Louise Tovoy and Marcus Brickstock Next week we'll be discussing eels. Goodbye.

So that's what we're going to be talking about next week. Eels, eels, eels and more eels. So thanks very much for listening. Bye-bye. Greetings, malevolent monkey cage. and devilish do-gooders. Welcome back to the home of the oxymoron. Evil genius!

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