{"id":72,"date":"2021-12-17T21:14:59","date_gmt":"2021-12-18T02:14:59","guid":{"rendered":"https:\/\/unsung.davidpogue.com\/?p=72"},"modified":"2023-10-27T21:15:13","modified_gmt":"2023-10-28T01:15:13","slug":"leap-seconds-smear-seconds-and-the-slowing-of-the-earth","status":"publish","type":"post","link":"https:\/\/www.unsungscience.com\/index.php\/2021\/12\/17\/leap-seconds-smear-seconds-and-the-slowing-of-the-earth\/","title":{"rendered":"Leap Seconds, Smear Seconds, and the Slowing of the Earth"},"content":{"rendered":"\n<h3 class=\"wp-block-heading\">Season 1 \u2022\u00a0Episode 9<\/h3>\n\n\n\n<p>The earth\u2019s spinning is slowing down. Any clocks pegged to the earth\u2019s rotation are therefore drifting out of alignment with our far more precise atomic clocks\u2014only by a thousandth of a second every 50 years, but that\u2019s still a problem for the computers that run the internet, cellphones, and financial systems.&nbsp;<\/p>\n\n\n\n<p>In 1972, scientists began re-aligning atomic clocks with earth-rotation time by inserting a leap second every December 31, or as needed. It seemed like a good idea at the time\u2014until computers started crashing at Google, Reddit, and major airlines. Google engineers proposed, instead, a leap smear: fractionally lengthening every second on December 31, so that that day contains the same total number of seconds. But really: If computer time drifts so infinitesimally from earth-rotation time, does anybody really care what time it is?&nbsp;<\/p>\n\n\n\n<p>Guests: Theo Gray, scientist and author. Geoff Chester, public affairs officer for the for the Naval Observatory. Peter Hochschild, principal engineer, Google.<\/p>\n\n\n\n<figure class=\"wp-block-audio\"><audio controls src=\"https:\/\/unsung.davidpogue.com\/wp-content\/uploads\/2023\/10\/unsungscience-20211217.mp3\"><\/audio><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Episode transcript<\/h2>\n\n\n\n<h1 class=\"wp-block-heading\"><strong>Leap Seconds Script<\/strong><\/h1>\n\n\n\n<p><em>The earth\u2019s spinning is slowing down. Any clocks pegged to the earth\u2019s rotation are therefore drifting out of alignment with our far more precise atomic clocks\u2014only by a thousandth of a second every 50 years, but that\u2019s still a problem for the computers that run the internet, cell phones, and financial systems.&nbsp;<\/em><\/p>\n\n\n\n<p><em>In 1972, scientists began re-aligning atomic clocks with earth-rotation time by inserting a leap second every December 31, or as needed. It seemed like a good idea at the time\u2014until computers started crashing at Google, Reddit, and major airlines. Google engineers proposed, instead, a leap smear: fractionally lengthening every second on December 31, so that that day contains the same total number of seconds.&nbsp;<\/em><\/p>\n\n\n\n<p><em>But really: If computer time drifts so infinitesimally from earth-rotation time, does anybody really care what time it is? Guests: Theo Gray, scientist and author. Geoff Chester, public affairs officer for the Naval Observatory. Peter Hochschild, principal engineer, Google.&nbsp;<\/em><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Intro<\/strong><\/h2>\n\n\n\n<p>The earth\u2019s rotation is slowing down. Very gradually, but enough that it\u2019s drifting out of sync with our atomic clocks\u2014the ones that run our internet, cell phones, and financial systems.<\/p>\n\n\n\n<p>Theo Since the late 50s, they\u2019ve drifted apart by 37 seconds cumulatively.&nbsp;<\/p>\n\n\n\n<p>David: So how do we\u2014&nbsp;<\/p>\n\n\n\n<p>Theo: Well, so leap, leap seconds is what people do.&nbsp;<\/p>\n\n\n\n<p>Yes, leap seconds. We add one second to each year, as needed. Which is great\u2014unless it crashes your software.<\/p>\n\n\n\n<p>Peter&nbsp;<strong><\/strong>And there were funny reports &nbsp; of some crashes in Google\u2019s servers . And that really caught our attention.<\/p>\n\n\n\n<p>Today on \u201cUnsung Science:\u201d The Earth\u2019s time\u2026computer time\u2026and the battle to manage the difference.&nbsp;&nbsp;<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Story<\/strong><\/h2>\n\n\n\n<p>Season 1, 9: Leap Seconds, Smear Seconds, and the Slowing of the Earth. The perfect topic for the end of the year.<\/p>\n\n\n\n<p>In a way, this episode has been in the works since I was in fourth grade.&nbsp;<\/p>\n\n\n\n<p>[school bell + kids ambi + music]<\/p>\n\n\n\n<p>I will NEVER forget this. A guest came in to talk to our class: Some astronomy professor, hired to try to infuse a little interest in science to elementary schoolers like us.<\/p>\n\n\n\n<p>He was one of these audience-participation dudes. At one point, he was like, \u201cWho knows how many days in a year?\u201d<\/p>\n\n\n\n<p>And I knew that. I was a little smarty pants. I yelled out \u201c365 days!\u201d Because everyone knows that.&nbsp;<\/p>\n\n\n\n<p>But the guy goes, \u201cNope! Guess again!\u201d&nbsp;<\/p>\n\n\n\n<p>What!? That\u2019s not wrong! I was&nbsp;<em>really&nbsp;<\/em>steamed. That\u2019s the kind of kid I was.<\/p>\n\n\n\n<p>So the other kids started shouting their answers. They thought maybe I\u2019d gotten the numbers mixed up. \u201c356!\u201d<\/p>\n\n\n\n<p>And the guys\u2019 like, \u201cNope!\u201d<\/p>\n\n\n\n<p>\u201c365! 366! 364! A hundred! 52!\u201d<\/p>\n\n\n\n<p>And the guy was like, \u201cNope! No, no, no. Try again!\u201d<\/p>\n\n\n\n<p>Honestly, he let it drag on for way too long.<\/p>\n\n\n\n<p>He finally told us his answer: 365 and a quarter days. Which is why we need a leap year every four years. Those four quarter days add up to what we know as February 29 every four years.&nbsp;<\/p>\n\n\n\n<p>It\u2019s kind of awkward that the earth\u2019s trip around the sun is not evenly divisible by whole days. So we add a leap day to keep our clocks in sync with the earth\u2019s motion.<\/p>\n\n\n\n<p>That explanation was good enough for fourth graders. But it wasn\u2019t quite the whole story.<\/p>\n\n\n\n<p>Theo The man who has one clock always knows what time it is. If you have two clocks, you\u2019re never quite sure. &nbsp; Like, whose clock are you going to believe? And suppose that you do have two clocks, or three clocks, and they\u2019re never going to exactly agree.&nbsp;&nbsp;<\/p>\n\n\n\n<p>This is Theo Gray. I love Theo. We\u2019ve appeared together on a few \u201cNova\u201d specials on PBS, and I collect his big glossy hardbound photo books of elements, and molecules, and machines. By profession, he\u2019s a\u2014what is he?&nbsp;<\/p>\n\n\n\n<p>Theo&nbsp;<strong><\/strong>I don\u2019t really have a career, as such, I don\u2019t think. &nbsp; I mean, I did work as a software engineer for 23 years, cofounding and developing Mathematica, Wolfram Research, Wolfram Language, etc., but I haven\u2019t done that for a while and I think probably you call me an author at this point, because I just make a living writing books, and people pay me to do that. And that\u2019s fun.&nbsp;<\/p>\n\n\n\n<p>In his book \u201cHow things Work,\u201d he\u2019s got this huge section on the history of clocks.&nbsp;<\/p>\n\n\n\n<p>Theo I mean, obviously the simplest, the crudest, the most universal clock, is a sundial, or otherwise known as a stick in the ground. &nbsp; It\u2019s a nice clock, but it has some disadvantages. It \u2013it only works when the sun is shining. So, you know, clouds, rain, whatever, nighttime. This is the problem. &nbsp; I think what\u2019s really the most remarkable about sundials is that up until 1955, they were the most accurate clocks in the world.&nbsp; And, you know, you might say, what are you talking about? That\u2019s ridiculous. &nbsp;<\/p>\n\n\n\n<p>But it\u2019s true. Until the 1800\u2019s, the famous clock in Greenwich, England, the official world standard of time, was based on the sun\u2019s position in the sky. At some point they switched to observation of&nbsp;<em>stars\u2019&nbsp;<\/em>position in the sky, because they\u2019re sharper and therefore easier to see.&nbsp;&nbsp;<\/p>\n\n\n\n<p>Theo And yeah, but it was all based on the rotation of the Earth. In other words, a glorified sundial.&nbsp;<\/p>\n\n\n\n<p>There was actually a clock, which is still there to this day, outside the main gate at the Greenwich Observatory.&nbsp; And then there\u2019s a giant red ball on a tower and the top of the observatory, which drops at noon precisely. And you can see that ball from central London. So all the bankers could, you know, see that clock, that that ball drop. And that was how the time was communicated.&nbsp;<\/p>\n\n\n\n<p>Until 1955. Then the cesium atomic clock was invented.&nbsp;<\/p>\n\n\n\n<p>Ah, yes\u2014the atomic clock.&nbsp;<\/p>\n\n\n\n<p>Theo Get yourself some cesium atoms, put them in a controlled environment, low temperature, beam in a certain microwave frequency &nbsp; and then count the cycles. You count the correct number of cycles of that, that cesium atomic resonance frequency. That\u2019s a second.&nbsp;<\/p>\n\n\n\n<p>Anybody can do it anywhere in the world. And you don\u2019t have to have\u2014you don\u2019t have to go to Paris. &nbsp; You just read the definition, build the machine and you\u2019ve got the thing. And systematically\u2014&nbsp; time was replaced. The Earth was replaced with cesium atomic clocks.&nbsp;<\/p>\n\n\n\n<p>Now, atomic clocks are going to be the star of this show, so I should probably take a moment to tell you where&nbsp;<em>yours&nbsp;<\/em>are. The ones that tell your phone, your computer, and your internet what time it is.<\/p>\n\n\n\n<p>Well, they\u2019re in Maryland, at the US Naval Observatory.&nbsp;<\/p>\n\n\n\n<p>[music]<\/p>\n\n\n\n<p>If you\u2019ve ever heard of the Naval Observatory, you probably think of it as the home of the U.S. Vice President\u2014and yes, that\u2019s where he or she always lives. But if you\u2019ve ever benefited from the internet, cell phones, airplanes, GPS, the financial system, or the military, you might care much more about the Naval Observatory\u2019s second function: As the home of the United States master clock.&nbsp;<\/p>\n\n\n\n<p>We go now to the library of the US Naval Observatory\u2014an astonishing rotunda lined with 90,000 books about navigation, astronomy, and time.<\/p>\n\n\n\n<p>CHESTER: If it looks like I\u2019m in a closet, it\u2019s because I am in a closet. This is room W, which is where we keep the journal archives for our library. But it\u2019s quiet.&nbsp;&nbsp;<\/p>\n\n\n\n<p>POGUE If you had six inches of books to put under it on that table, it would be then closer to your mouth and sound a lot better.&nbsp;<\/p>\n\n\n\n<p>Geoff So let\u2019s see, OK: \u201cMonthly Notices of the Royal Astronomical Society.\u201d That ought to do it.&nbsp;<\/p>\n\n\n\n<p>Pogue That\u2019ll make it sound&nbsp;<em>really<\/em>&nbsp;good.&nbsp;<\/p>\n\n\n\n<p>Thus began my Zoom interview with Geoffrey Chester, the public affairs officer for the Naval Observatory. The official keepers of time and location.&nbsp;<\/p>\n\n\n\n<p>Geoff We are a Navy command. All told, we have about 150 on staff and so it\u2019s mostly civilian. &nbsp; When we get a new superintendent,&nbsp; the first thing I tell them is you may not necessarily want to go to sea with this crew, but I can guarantee you that we will never get lost and we always know what time it is.&nbsp;<\/p>\n\n\n\n<p>David Why is it the Navy\u2019s job to set the standards for time and space?&nbsp;<\/p>\n\n\n\n<p>Geoff All the countries that had big navies had observatories so they can calibrate chronometers and create almanacs, so that they knew where the heck they were going.&nbsp;<\/p>\n\n\n\n<p>And so we are actually kind of the new kids on the block, because we started in 1830, when most of these other institutions started back in the 1700s. But we are the only one that is still associated with the Navy of its host country.&nbsp;<\/p>\n\n\n\n<p>See, dear listener? Four minutes in, and you\u2019ve already learned something fascinating. I&nbsp;<em>know&nbsp;<\/em>you didn\u2019t know that.<\/p>\n\n\n\n<p>Geoff Here at the Naval Observatory, we are responsible for\u2014for determining and disseminating a long term, precise time scale. So we operate about one hundred clocks here. &nbsp; What we do essentially is, we take a weighted mean of our 100 or so atomic clocks. &nbsp; We have computers that do this about every two minutes.&nbsp;&nbsp;<\/p>\n\n\n\n<p>We have the ability to keep a time scale here that on some level can be measured down to the femtosecond level. A femtosecond is ten to the minus 15, or 1 1000th of a trillionth of a second. &nbsp; We actually built those clocks that keep it that precise. We actually built those in-house, because we could not find a commercial supplier that could do it for us at a price we can afford.&nbsp;<\/p>\n\n\n\n<p>David I\u2019ve had the privilege of visiting the Naval Observatory. I\u2019ve been in the room that has all those clocks. Can you describe it for the folks at home?&nbsp;<\/p>\n\n\n\n<p>Geoff Most of the clocks are kept in a building that was specially built. &nbsp; The temperature does not vary by more than one tenth of a degree centigrade throughout the year, and the humidity stays within three percent of a nominal mean. &nbsp; So you go into that building in the dead of winter or in the heat of a Washington summer, and the temperature and humidity are the same. It\u2019s a great place to hang out.&nbsp;&nbsp;<\/p>\n\n\n\n<p>But in that room, we have racks of equipment.&nbsp; These are beige boxes that look like they kind of look like a stereo amplifier. Except they have a little display that ticks off the time.&nbsp;&nbsp;<\/p>\n\n\n\n<p>OK. So remember how everything changed with the invention of the cesium atomic clock in 1955? Not long thereafter, the world officially adopted the atomic clock as its master timekeeping machine. The rotation of the earth was retired.&nbsp;<\/p>\n\n\n\n<p>GEOFF: In 1967, the definition of the second was changed. It was no longer one 86,400th part of a mean solar day. It was from thence forward until the present, the interval of 9,192,631,770 hyperfine transmissions of a neutral cesium 133 atom in its ground state. When I started working here, I thought a second was one Mississippi, so\u2026&nbsp;<\/p>\n\n\n\n<p>That\u2019s my favorite joke of the podcast year.&nbsp;<\/p>\n\n\n\n<p>[music]<\/p>\n\n\n\n<p>But now we go from comedy to tragedy, or at least something that\u2019s existentially depressing.<\/p>\n\n\n\n<p>See, in one regard, the atomic clock\u2019s astonishing precision is actually a problem, because it exposed the flaws of our old, earth-based system. What it revealed is\u2014ready for existential depression?\u2014that the earth\u2019s spin is slowing down. Here\u2019s Theo Gray.<\/p>\n\n\n\n<p>Theo: It\u2019s so bad that, like, we\u2019re now I think it\u2019s 37 seconds off from the, the late 1950s, when we first started to be able to measure more accurately.<\/p>\n\n\n\n<p>David Oh, I used to worry about the sun exploding\u2014now I have to worry about the world stopping spinning?&nbsp;<\/p>\n\n\n\n<p>Theo You know, that is actually a very good question, that somebody should do the math\u2014like which is going to happen first? Like I say, we always worry about the sun\u2019s going to burn us all up in five billion years. But if the earth stops turning before then, we\u2019d be in a lot more trouble, or different trouble anyway.&nbsp;&nbsp;<\/p>\n\n\n\n<p>David I guess at some point I\u2019m relieved that this is the one way that we are not responsible for destroying the way things are supposed to be.&nbsp;<\/p>\n\n\n\n<p>Theo Yeah, well, I mean \u2014 global warming, because it would make the earth on average warmer, is going to drive more moisture into the atmosphere and is therefore going to slow the earth down a little bit more.&nbsp;<\/p>\n\n\n\n<p>David Oh, great.&nbsp;<\/p>\n\n\n\n<p>Theo So just, you know, if you want to go that way and you want to feel guilty about it, I\u2019ll give you a way to feel bad about it.&nbsp;<\/p>\n\n\n\n<p>David Oh, man. Well, how much has it slowed down already, measurably?&nbsp;<\/p>\n\n\n\n<p>Theo I think the figure is one second per 500 years.&nbsp; The days used to be significantly shorter.&nbsp;<\/p>\n\n\n\n<p>David The days have not always been 24 hours long?!&nbsp;&nbsp;&nbsp;<\/p>\n\n\n\n<p>Theo&nbsp;<strong><\/strong>Yeah, no, I mean, I think in the dinosaur era, they were, what, maybe 20 hours?&nbsp;&nbsp;<\/p>\n\n\n\n<p>You think there\u2019s not enough time in a day in&nbsp;<em>your&nbsp;<\/em>life? How\u2019d you like to have been one of the workers who built the Egyptian pyramids?&nbsp;<\/p>\n\n\n\n<p>Theo<strong>&nbsp;<\/strong><strong><\/strong>I counted, they had nine seconds less per day to work on the pyramids.&nbsp;<\/p>\n\n\n\n<p>I need to insert an audio footnote here so I don\u2019t get scientist hate mail. To be absolutely clear, the earth\u2019s spin isn\u2019t&nbsp;<em>just&nbsp;<\/em>slowing down.<\/p>\n\n\n\n<p>Theo&nbsp;<strong><\/strong>The Earth\u2019s rotation is not steady. Like, it wobbles a little bit from day to day, and it systematically speeds up and slows down throughout the seasons.&nbsp; You know, when the earth is warmer, more of the water kind of migrates up to higher up in the atmosphere. And when it\u2019s colder, the water, rain falls down, and it\u2019s lower. So, you know, the classic example of the figure skater who, you know, spins faster when they pull their arms in, when the earth pulls its water in closer, it spins faster. And when the water goes out, higher up into the atmosphere, the earth goes slower.&nbsp;<\/p>\n\n\n\n<p>But the&nbsp;<em>overall&nbsp;<\/em>result of all of this wobbling\u2014the long-term trend\u2014is a slowing.<\/p>\n\n\n\n<p>Theo It\u2019s slowing down systematically because of things like tidal friction. So, you know,&nbsp; the water on the earth, the ocean being pulled by the moon, it sloshes around\u2014that\u2019s, you know, that\u2019s friction.&nbsp;<\/p>\n\n\n\n<p>David&nbsp;<strong><\/strong>This is all well-known to physicists and scientists, the fact that the Earth not only does not rotate steadily, but is slowing down?&nbsp;<\/p>\n\n\n\n<p>Theo Oh, absolutely. Yeah. You might think, well, who cares\u2014&nbsp; one second a year, really. But if you\u2019re trying to run, for example, a GPS satellite network or even a financial system, this is a big deal.&nbsp; So there\u2019s one rule of thumb, a very convenient fact, that the speed of light is one nanosecond per foot.&nbsp;<\/p>\n\n\n\n<p>So, you know, your car would be halfway to the moon if GPS were off by a second.&nbsp;<\/p>\n\n\n\n<p>David Hate when that happens.&nbsp;<\/p>\n\n\n\n<p>Theo Let\u2019s say you\u2019ve got a billion dollar interbank loan at some interest rate, right? And, you know, you\u2019re charging interest by the microsecond or something on this billion-dollar loan. You know, it actually makes a difference.&nbsp;&nbsp;<\/p>\n\n\n\n<p>David So here\u2019s \u2013here\u2019s what\u2019s deep down bugging me. We\u2019ve got these cesium atomic clocks that are not susceptible to slowing down and the variability of the earth\u2019s rotation. And then we\u2019ve got the earth, which is. Aren\u2019t they eventually going to drift apart?<\/p>\n\n\n\n<p>Theo Well, they do, yes.&nbsp; since the late 50s, they\u2019ve drifted apart by 37 seconds cumulatively.&nbsp;<\/p>\n\n\n\n<p>David So how do we\u2014&nbsp;<\/p>\n\n\n\n<p>Theo Well, so leap, leap seconds is what people do.&nbsp;<\/p>\n\n\n\n<p>That\u2019s right. There are leap seconds. You\u2019ve lived through at least several of them. There is, of course, a global committee in charge of leap seconds\u2014and it has a fantastic name: the International Earth Rotation Service. (OK, in 2003, they bulked up the name. Now it\u2019s the International Earth Rotation and Reference Systems Service, but that\u2019s not nearly as excellent.)<\/p>\n\n\n\n<p>Once every few years, as needed, IERS scientists schedule one extra second, tacked on to June 30 or December 31, to bring the atomic clocks back into alignment with the earth\u2019s spinnature. In recent years, we\u2019ve enjoyed the luxury of that extra one second in 2005, 2008, 2012, 2015, and 2016.&nbsp;<\/p>\n\n\n\n<p>David So as it is right now, if I were watching my phone on, on the day when a leap second is scheduled, would I see one of the hours go 57, 58, 59, 60, then the next minute begins?&nbsp;<\/p>\n\n\n\n<p>Theo Yes, you see a hard jump. It\u2019s the same second repeats twice.&nbsp;<\/p>\n\n\n\n<p>David Right.&nbsp;<\/p>\n\n\n\n<p>Theo And, you know, I mean, most people don\u2019t notice that, right? Like you\u2019d have to watch pretty close. It\u2019d be exciting. It\u2019s like watching your odometer, you know, turn over. So it\u2019s not like this is a big issue for most people most of the time.&nbsp;&nbsp;<\/p>\n\n\n\n<p>[music]<\/p>\n\n\n\n<p>But it&nbsp;<em>is&nbsp;<\/em>a big issue for scientists and other technical people. Like, if you\u2019re a surveyor or an astronomer, your work is still connected very much to the earth and its movements, so you probably rely on the original earth-based time scale. But if you\u2019re an internet or banking or space company, you need absolute precision\u2014you use the atomic clock.&nbsp;<\/p>\n\n\n\n<p>So I asked Geoff Chester how we manage two different timekeeping systems.&nbsp;<\/p>\n\n\n\n<p>David So it sounds like if the earth spinning is variable and slowing overall, it sounds like these atomic clocks are more precise than the planet spinning. Eventually, aren\u2019t they going to drift out of sync with each other?&nbsp;<\/p>\n\n\n\n<p>Geoff So this was something that was recognized early on after they defined the second in terms of the atomic frequency standard. And so they hammered out this idea, which they essentially codified in 1972, that there would be two concurrent timescales.&nbsp;<\/p>\n\n\n\n<p>So there is what is called International Atomic Time, or the Temps Atomique Internazionale, because the International Bureau of Weights and Measures is headquartered in France. So TAI is the time that\u2019s kept by atomic clocks.&nbsp;<\/p>\n\n\n\n<p>And then there is what is called Coordinated Universal Time.&nbsp;<\/p>\n\n\n\n<p>Coordinated Universal Time is based on the earth\u2019s rotation. That\u2019s the time we adjust with leap seconds. And they call it UTC, because, once again, that\u2019s the acronym for its French name.&nbsp;<\/p>\n\n\n\n<p>Geoff:&nbsp;<em>(continues)&nbsp;<\/em>So these two concurrent time scales, one essentially based on atomic time and the other based on Earth rotation time, have a cumulative error of roughly one and a half milliseconds, that compounds on a day-to-day basis. So after about 500 days, you have a difference of one second between the two time scales.&nbsp;<\/p>\n\n\n\n<p>And\u2026when that happens, &nbsp; \u2014there is a provision in the 1972 definition that essentially allows us to stop atomic time for one second to let the earth catch up. And that\u2019s what\u2019s known as a leap second.&nbsp;<\/p>\n\n\n\n<p>Aha! Very cool! So let me see if we\u2019ve got this straight. Because the earth is slowing down, there aren\u2019t exactly 24 hours in a day anymore. But that means that we wind up with two time scales: the one based on atomic clocks, and the one based on the earth\u2019s rotation. And we introduce a leap second as necessary to keep them synced up.<\/p>\n\n\n\n<p>[Begin fake conclusion music]<\/p>\n\n\n\n<p>YAY! We did it! We saw a problem, and we fixed it with science! Let\u2019s celebrate the ingenuity of the leap second. Everyone come to my house for a party next time we have a leap second! It\u2019ll be a really short party, but, you know. Nerdy and fun.<\/p>\n\n\n\n<p>And that concludes this episode of\u2014&nbsp;<\/p>\n\n\n\n<p><em>Geoff should interrupt me (and the music) \u2013&nbsp;<\/em>[needle slowdown fx]<\/p>\n\n\n\n<p>Geoff: So today, leap seconds are a real problem.&nbsp;<\/p>\n\n\n\n<p>Wait, what? That\u2019s not the end of the story?<\/p>\n\n\n\n<p>Geoff: The thing is, we can\u2019t predict with any real precision more than about six months in advance whether or not a leap second is necessary at a particular time. So when it is determined that a leap second will need to be inserted, &nbsp; we can give the world about six months\u2019 notice saying, \u201chey, you know, here\u2019s a leap second coming up, get your networks ready,\u201d whatever. But every year, typically about 10 percent of the world\u2019s networks fail, and sometimes they can be very spectacular. I think it was 2012. I believe it was Qantas Airlines that botched the leap second in their enterprise, and they lost a day of revenue because their system was kaput.&nbsp;<\/p>\n\n\n\n<p>It&nbsp;<em>was&nbsp;<\/em>2012, and it wasn\u2019t just Qantas. The 2012 leap second also took down Reddit, Gawker, LinkedIn, FourSquare, Mozilla, and Yelp that year. But&nbsp;<em>every<\/em>&nbsp;time there\u2019s a leap second, somebody suffers. In 2008, it was Oracle\u2019s computers and Sun\u2019s computers. In 2015, it was Twitter and Android. In 2016, it was Cloudflare, the website security company.&nbsp;<\/p>\n\n\n\n<p>Well dang! If leap seconds aren\u2019t the ultimate solution, how else are we supposed to fix the discrepancy between earth time and atomic time?<\/p>\n\n\n\n<p>Peter We thought about various possible approaches to the problem, and the leap smear seemed to be by far the most practical and reasonable.&nbsp;<\/p>\n\n\n\n<p>Yes, this Google engineer just said \u201cleap smear.\u201d After the break: The future of time discrepancies, as rethought by Google.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><strong>BREAK<\/strong><\/h1>\n\n\n\n<p>Book Ad&nbsp;<\/p>\n\n\n\n<p>[music]<\/p>\n\n\n\n<p>Welcome back. Before the break, you\u2019d absorbed some heady science: Like the fact that the earth\u2019s gradual rotational slowing has thrown off our timekeeping, and now atomic clocks and earth-based clocks gradually drift out of sync.<\/p>\n\n\n\n<p>And we learned that the international masters of time thought they\u2019d solved the problem by adding one leap second as needed to keep the two time systems in sync.<\/p>\n\n\n\n<p>And&nbsp;<em>then<\/em>&nbsp;we learned that the leap-second solution is actually a problem. Once again, here\u2019s Geoff Chester, of the U.S. Naval Observatory.<\/p>\n\n\n\n<p>GEOFF: As large scale computer networks began to spring up, ultimately leading to the Internet and things like that, leap seconds became kind of a colossal pain. Because if you are a system manager and you do not incorporate the leap second across your entire enterprise, at the same instant in time, your network will fail. And if your network fails, you don\u2019t make any money and if your company doesn\u2019t make any money, the odds are you\u2019re going to get fired.<\/p>\n\n\n\n<p>Now I\u2019d like to introduce you to a man who will not be getting fired any time soon. He\u2019s too important.<\/p>\n\n\n\n<p>Peter I\u2019ve spent a number of years working on making Google\u2019s computers synchronized.&nbsp; It\u2019s not a great cocktail party conversation, but it\u2019s surprisingly pretty popular.&nbsp;<\/p>\n\n\n\n<p>Pogue Oh, you wait \u2018till this episode drops. They\u2019ll be stopping you on the streets.&nbsp;<\/p>\n\n\n\n<p>Peter Okay.&nbsp;<\/p>\n\n\n\n<p>Peter Hochschild is a principal engineer at Google. He is basically Google\u2019s director of time. His job entails keeping all of Google\u2019s servers perfectly synchronized\u2014and Google has a&nbsp;<em>lot&nbsp;<\/em>of servers. Google search, and Gmail, and YouTube, and Android, and Chrome, Google Docs, Google Maps, and on and on.<\/p>\n\n\n\n<p>Peter If everything in the world was done by one computer, that wouldn\u2019t be so difficult. That computer would know the order that things happened in. But that isn\u2019t how the world works. Everything is \u2014 all jobs, more or less, are divided among multiple computers, and now they, they have to agree with each other about the order of events, or else chaos will ensue.&nbsp;<\/p>\n\n\n\n<p>Pogue We wouldn\u2019t want that.&nbsp;<\/p>\n\n\n\n<p>Peter You wouldn\u2019t want that.&nbsp;<\/p>\n\n\n\n<p>Peter first heard about leap seconds one day in 2008.&nbsp;<\/p>\n\n\n\n<p>Peter Somebody wandered into our office and said, \u201cHey, you people know about leap seconds, don\u2019t you?\u201d And I said, \u201cNo, I\u2019ve never heard of a leap second.\u201d I had never heard of a leap second.&nbsp;<\/p>\n\n\n\n<p>Right away, he thought that they sounded like trouble.<\/p>\n\n\n\n<p>The way computers keep time and handle leap seconds, it turns out,is the computer clock jumps back one second at the leap second.&nbsp;<\/p>\n\n\n\n<p>That made us very uneasy, because \u2014 I don\u2019t know, the one thing you know about time is that it goes forwards. And here\u2019s a case where time seems to go backwards.&nbsp;<\/p>\n\n\n\n<p>Yeah\u2014trying to teach your computer network to run in reverse for one second sounds like a recipe for crashes.&nbsp;<\/p>\n\n\n\n<p>Now, Google was a relatively small company in 2008\u2014small enough that Peter and his team could easily get access to its computer logs. At the time, the most recent leap second had arrived in 2005. Out of curiosity, he checked the records.&nbsp;<\/p>\n\n\n\n<p>Peter And there were funny reports written from the very last day of 2005 of some crashes in Google\u2019s servers, some fairly widespread crashes that were not fully understood. And that really caught our attention, we thought, \u201cOh, that\u2019s interesting.\u201d The computer programs \u2014 first of all, they are assuming that time just goes forwards, because everybody assumes that. And they also made some assumptions about the rate at which time advances, and those are perfectly good assumptions at every instant, except around a leap second.&nbsp;<\/p>\n\n\n\n<p>And that set us to work, because we realized for two reasons we had to deal with leap seconds. One was to make the internet more reliable, because things would break if we handled leap seconds the old way they were handled. And because we wanted in the future much better synchronization across the computers, and the sudden step back in time would wreck that.&nbsp;<\/p>\n\n\n\n<p>But if the leap second wasn\u2019t the perfect solution to the difference between the earth and the atomic clocks, what was? Google\u2019s time team came up with a different idea, which those clever dogs decided to call\u2014the leap smear.&nbsp;<\/p>\n\n\n\n<p>Peter What we would have the computers do is very slowly smear out that one second \u2014&nbsp;leap second \u2014 rather than do it all of a sudden. And by doing it slowly, they would all be in very close alignment. And there would be no sudden discrepancy that would break the coordination of the multiple computers.&nbsp; The basic idea is don\u2019t do it suddenly, spread it out over time.&nbsp;<\/p>\n\n\n\n<p>Pogue And as a handy bonus, time doesn\u2019t go backwards.&nbsp;<\/p>\n\n\n\n<p>Peter Correct.&nbsp; And that\u2019s a huge, that\u2019s a huge thing, because &nbsp; that\u2019s, first of all, hard to think about. And secondly, it\u2019s really hard to test and it only happens every few years. And it\u2019s, it\u2019s not so much fun.&nbsp;<\/p>\n\n\n\n<p>Pogue So you still do the leap smear on the day when a leap second is prescribed?&nbsp;<\/p>\n\n\n\n<p>Peter Correct. &nbsp; The smear is centered on the actual leap second, and it extends to the previous and following noon.&nbsp;<\/p>\n\n\n\n<p>Pogue Is, is there more than one Leap Smear Proposal, or is Google the sole holder of this idea?&nbsp;<\/p>\n\n\n\n<p>Peter We published it pretty widely, because we thought, \u201cLook, this is a great way to make the whole internet more reliable.\u201d It\u2019s not a competitive thing. It\u2019s just good for everybody. And so &nbsp; several companies use the same smear, and I believe there are organizations that use somewhat different smears.&nbsp;&nbsp;<\/p>\n\n\n\n<p>Actually, even Google did several. The first one that we did in \u2014 at the end of 2008, when we were scared, because we\u2019d never done it before, we actually made a more complicated one that sort of started \u2014started slow, sped up even more, and then slowed back down again. And then we measured very carefully what happened during that first leap smear, and we realized, \u201cOK, this worked great, we can simplify it and we\u2019ll just do a straight-line correction.\u201d<\/p>\n\n\n\n<p>Pogue Okay, great. So at this point, how long is a second on leap smear day?&nbsp;<\/p>\n\n\n\n<p>Peter You\u2019ll love the way we describe it. A second is 11 parts per million slower during the leap smear.&nbsp;<\/p>\n\n\n\n<p>Pogue Is it the same as saying 11 millionths of a second ?&nbsp;<\/p>\n\n\n\n<p>Peter Yes. Yes.&nbsp; Sorry, I was just being a nerd. I apologize.&nbsp;<\/p>\n\n\n\n<p>Pogue So on Leap Second Day, the leap smear adds one, 60 x 60 x 24th of a day to every second of the day?<\/p>\n\n\n\n<p>Peter Yes. Perfect.&nbsp;<\/p>\n\n\n\n<p>Pogue Okay, thank you. I\u2019m not going to embarrass myself.<\/p>\n\n\n\n<p>Believe it or not, leap seconds and smear seconds aren\u2019t the only solutions people are kicking around. Maybe we don\u2019t need the TAI and UTC clocks to be&nbsp;<em>exactly&nbsp;<\/em>in sync, down to the second. Some scientists maintain that adding a leap second every few years is overkill; maybe we can wait a couple hundred years to accumulate those seconds into a single leap&nbsp;<em>minute.&nbsp;<\/em>Here\u2019s Peter from Google again:<\/p>\n\n\n\n<p>Peter There have been interesting proposals, and they\u2019re clever, in a way, of saying, \u201cWell, instead of correcting by one second every so often, why don\u2019t we make at least a pro forma leap minute that would happen once every few centuries? And that would at least kick the problem way down in the future.\u201d And there might be an argument, a sensible argument for that \u2014 as science develops, there may be further corrections to the way humans keep time. And so it\u2019s perhaps not a crazy proposal.&nbsp;<\/p>\n\n\n\n<p>Now, none of these time-adjustment solutions is universally beloved. Every one of them involves compromise and causes problems for somebody.<\/p>\n\n\n\n<p>So maybe this is the time to mention what might be the most radical solution of all. This might freak you out, so I hope you\u2019re sitting down. Preferably reclining. Ready?&nbsp;<\/p>\n\n\n\n<p>Maybe it doesn\u2019t matter if the earth clock and the atomic clocks drift apart.&nbsp;<\/p>\n\n\n\n<p>I mean, what,&nbsp;<em>really,&nbsp;<\/em>is the issue? What if they do get of sync? What\u2019s the worst that could happen?<\/p>\n\n\n\n<p>[music]<\/p>\n\n\n\n<p>Sure, we\u2019re used to certain times of day matching up with certain numbers on our watches. If you\u2019re used to seeing the sun directly overhead at 12 noon, maybe you\u2019re disturbed by the notion of a future where the sun is actually low to the horizon at 12 noon.<\/p>\n\n\n\n<p>But first of all, that noticeable a difference will take thousands of years to come about. And second, keep in mind that we&nbsp;<em>deliberately&nbsp;<\/em>set our clocks off that familiar pattern by a&nbsp;<em>whole hour&nbsp;<\/em>every year!<em>&nbsp;<\/em>It\u2019s called Daylight Savings Time. If we value the \u201c12 noon sun overhead\u201d thing so much, why on earth do we go out of our way to mess it up by a whole hour?&nbsp;<\/p>\n\n\n\n<p>This radical notion has occurred to the international time-keeping bodies, too. Here\u2019s Google\u2019s Peter Hochschild.<\/p>\n\n\n\n<p>Peter Every decade or so, there\u2019s a fairly serious discussion in one of the international standards bodies. Should we keep leap seconds or should we stop doing them?&nbsp;&nbsp;<\/p>\n\n\n\n<p>And sure enough: the ITU, the United Nation\u2019s International Telecommunication Union, periodically polls its members on whether or not to abolish the leap second. They go around this huge auditorium and let each country\u2019s representative make its case.<\/p>\n\n\n\n<p><em>UN audio<\/em><\/p>\n\n\n\n<p>US: The use of leap seconds introduces discontinuities into what would be otherwise continuous time stream.&nbsp;<\/p>\n\n\n\n<p>UK: In the view of the UK, leap seconds have already been inserted without causing difficulty.<\/p>\n\n\n\n<p>Canada: Canada does not see any compelling reason to change its definition.<\/p>\n\n\n\n<p>Chair: I believe that the appropriate course of action is that we return this draft revision for further work.<\/p>\n\n\n\n<p>US: Thank you, Mr. Chairman.<\/p>\n\n\n\n<p>They went through this debate in 2005\u2026in 2008\u2026in 2012\u2026and in 2015. And every single time, the members of this august body made the same decision, which is \u2014not to decide. To kick the decision down the road. The vote is scheduled to come up again in 2023, at which point it will probably be postponed again.<\/p>\n\n\n\n<p>In the meantime, our species will continue to use leap seconds, leap smears, and maybe other approaches to keeping the earth\u2019s clock and our computer clocks in sync. It\u2019s a challenge that will only get harder as our atomic clocks get better. Here\u2019s Geoff Chester from the Naval Observatory.<\/p>\n\n\n\n<p>Geoff Our most recent clocks are what we call rubidium fountain clocks. &nbsp; These things are really cool. These are clocks which are designed &nbsp; to incorporate five Nobel prizes in physics.<\/p>\n\n\n\n<p>&nbsp;We can provide a time scale that\u2019s precise down to about one hundred picoseconds. That\u2019s one hundred-trillionth of a second. But I can guarantee you that &nbsp; somebody is going to find a need for a more precise time scale. &nbsp; And that\u2019s why we are now building these prototype optical frequency standards.&nbsp;<\/p>\n\n\n\n<p>[music starts fading in]<\/p>\n\n\n\n<p>In a cesium atomic clock, we use microwaves to bombard cesium atoms. But in the optical clock he\u2019s talking about, we\u2019ll shoot light at atoms\u2014laser beams\u2014for an astonishing leap in precision.&nbsp;<\/p>\n\n\n\n<p>Geoff:&nbsp; Optical frequencies are five orders of magnitude higher than microwave frequencies.&nbsp;&nbsp;<\/p>\n\n\n\n<p>(continued) So I would say that in 10 years, we are going to have optical frequency standards, we are going to redefine the second. &nbsp; And that means I will have to memorize a number with five more digits in it. So I think I\u2019m going to retire before that happens because, my brain just won\u2019t absorb that anymore.&nbsp;<\/p>\n\n\n\n<p>[THEME MUSIC]<\/p>\n\n\n\n<p>CREDITS<\/p>\n<div class=\"powerpress_player\" id=\"powerpress_player_4032\"><audio class=\"wp-audio-shortcode\" id=\"audio-72-1\" preload=\"none\" style=\"width: 100%;\" controls=\"controls\"><source type=\"audio\/mpeg\" src=\"https:\/\/unsung.davidpogue.com\/wp-content\/uploads\/2023\/10\/unsungscience-20211217.mp3?_=1\" \/><a href=\"https:\/\/unsung.davidpogue.com\/wp-content\/uploads\/2023\/10\/unsungscience-20211217.mp3\">https:\/\/unsung.davidpogue.com\/wp-content\/uploads\/2023\/10\/unsungscience-20211217.mp3<\/a><\/audio><\/div><p class=\"powerpress_links powerpress_links_mp3\" style=\"margin-bottom: 1px !important;\">Podcast: <a href=\"https:\/\/unsung.davidpogue.com\/wp-content\/uploads\/2023\/10\/unsungscience-20211217.mp3\" class=\"powerpress_link_pinw\" target=\"_blank\" title=\"Play in new window\" onclick=\"return powerpress_pinw('https:\/\/www.unsungscience.com\/?powerpress_pinw=72-podcast');\" rel=\"nofollow\">Play in new window<\/a> | <a href=\"https:\/\/unsung.davidpogue.com\/wp-content\/uploads\/2023\/10\/unsungscience-20211217.mp3\" class=\"powerpress_link_d\" title=\"Download\" rel=\"nofollow\" download=\"unsungscience-20211217.mp3\">Download<\/a><\/p>","protected":false},"excerpt":{"rendered":"<p>The earth\u2019s spinning is slowing down. Any clocks pegged to the earth\u2019s rotation are therefore drifting out of alignment with our far more precise atomic clocks\u2014only by a thousandth of a second every 50 years, but that\u2019s still a problem for the computers that run the internet, cellphones, and financial systems.<span class=\"excerpt-more-link\"><a class=\"more-link\" href=\"https:\/\/www.unsungscience.com\/index.php\/2021\/12\/17\/leap-seconds-smear-seconds-and-the-slowing-of-the-earth\/\">More <svg class=\"svg-icon\" width=\"24\" height=\"24\" aria-hidden=\"true\" role=\"img\" focusable=\"false\" viewBox=\"0 0 24 24\" fill=\"none\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path fill-rule=\"evenodd\" clip-rule=\"evenodd\" d=\"M6.96954 10.2804L11.9999 15.3107L17.0302 10.2804L15.9695 9.21973L11.9999 13.1894L8.0302 9.21973L6.96954 10.2804Z\" fill=\"currentColor\"\/><\/svg><\/a><\/span><\/p>\n<div class=\"excerpt-audio-block\">\n<figure class=\"wp-block-audio\"><audio controls src=\"https:\/\/unsung.davidpogue.com\/wp-content\/uploads\/2023\/10\/unsungscience-20211217.mp3\"><\/audio><\/figure>\n<\/div>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-72","post","type-post","status-publish","format-standard","hentry","category-uncategorized","entry"],"_links":{"self":[{"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/posts\/72","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/comments?post=72"}],"version-history":[{"count":1,"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/posts\/72\/revisions"}],"predecessor-version":[{"id":74,"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/posts\/72\/revisions\/74"}],"wp:attachment":[{"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/media?parent=72"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/categories?post=72"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.unsungscience.com\/index.php\/wp-json\/wp\/v2\/tags?post=72"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}