SPEAKER_01: Amazing, fascinating stories of inventions, ideas and innovations. Yes, this is the podcast about the things that have helped to shape our lives. Podcasts from the BBC World Service are supported by advertising.
SPEAKER_02: 50 Things That Made the Modern Economy with Tim Harford
SPEAKER_00: In 1845, a curious feature was added to the clock on St John's Church in Exeter, western England. Another minute hand, running 40 minutes faster than the original. This was, as true to what humans Exeter Flying Post explained, a matter of great public convenience, for it enabled the clock to exhibit, as well as the correct time at Exeter, the railway time.
SPEAKER_00: The human sense of time has always been defined by planetary motion. We talked of days and years long before we knew that the Earth rotates on its axis and orbits the sun. From the waxing and waning of the moon we got the idea of a month. The sun's passage across the sky gives us phrases like mid-day or high noon. Exactly when the sun reaches its highest point depends of course on where you're looking from. If you happen to be in Exeter, you'll see it about 40 minutes after someone in London. Naturally, as clocks became commonplace, people set them by their own celestial observations. That was fine if you needed to coordinate only with other locals. If we both live in Exeter and say we'll meet at 7 o'clock, it hardly matters that in London, 200 miles away, they think it's 7.14. But as soon as a train connects Exeter and London, stopping at multiple other towns, all with their own idea of what the time is, we face a logistical nightmare. Early British train timetables valiantly informed travellers that London time is about four minutes earlier than Reading time, seven and a half minutes before Sirencester, and so on. But many, understandably, got hopelessly confused. More seriously, so did drivers and signalling staff, which raised the risk of collisions. So the railways adopted railway time, and they based it on Greenwich Mean Time, set by the famous observatory in the London borough of Greenwich. Some municipal authorities quickly grasped the usefulness of standardising time across the country, and adjusted their own clocks accordingly. Others resented this high-handed metropolitan imposition, and clung to the idea that their time was, as the Flying Post put it with charming parochialism, the correct time. For years, the Dean of Exeter stubbornly refused to adjust the clock on the city's cathedral. In fact, there's no such thing as the correct time. Like the value of money, it's a convention that derives its usefulness from the widespread acceptance of others. But there is such a thing as accurate timekeeping. That dates from 1656, and a Dutchman named Christiane Huygens. There were clocks before Huygens, of course. Water clocks appear in civilisations from ancient Egypt to medieval Persia. Others kept time from marks on candles. But even the most accurate devices might wander by 15 minutes a day. This didn't matter much if you were a monk wanting to know when to pray, unless God's a stickler for punctuality. But there was one increasingly important area of life where the inability to keep accurate time was of huge economic significance. Navigation. By observing the angle of the sun, it was clear that sailors could figure out their latitude, where they were from north to south. But their longitude, where they were from east to west, had to be guessed. Wrong guesses could and frequently did lead to ships hitting land hundreds of miles away from where navigators thought they were, sometimes literally hitting land. And sinking. How could accurate timekeeping help? Remember why Exeter's clocks differed from London's 200 miles away? High noon happened 14 minutes later. If you knew when it was midday at Greenwich Observatory, or any other reference point, you could observe the sun, calculate the time difference, and work out the distance. Huygens' pendulum clock was 60 times more accurate than any previous device. But even 15 seconds a day soon mounts up on long, seafaring voyages, and pendulums don't swing neatly on the deck of a lurching ship. Rulers of maritime nations were acutely aware of the longitude problem. The King of Spain was offering a prize for solving it nearly a century before Huygens' work. Famously, it was a subsequent prize offered by the British government that led to a sufficiently accurate device being painstakingly refined in the 1700s by an Englishman named John Harrison. It lost only a couple of seconds a day. Since the Dean of Exeter's intransigence, the whole world has agreed on the correct time. Coordinated Universal Time, or UTC, as mediated by various global time zones. Usually, these zones maintain the convention of midday being vaguely near the sun's highest point. But not always. Since Chairman Mao abolished China's five time zones and put everyone on Beijing time, residents of westerly Tibet and Xinjiang have heard their clocks strike 12 not long after sunrise. Meanwhile since Huygens and Harrison, clocks have become much more accurate still. UTC is based on atomic clocks, which measure oscillations in the energy levels of electrons. They're accurate to within a second every hundred million years. Does such accuracy have a point? We don't plan our morning commutes to the millisecond. In truth, an accurate wristwatch has always been more about prestige than practicality. For over a century, before the hourly beeps of early radio broadcasts, members of the Belleville family made a living in London by collecting the time from Greenwich every morning and selling it around the city for a modest fee. But there are places where milliseconds now matter. One is the stock market. Fortunes can be won by exploiting an arbitrage opportunity an instant before your competitors. Some financiers recently calculated it was worth spending $300 million on drilling through mountains between Chicago and New York to lay fiber optic cables in a slightly straighter line. That sped up communication between the two CITES exchanges by three milliseconds. The accurate keeping of universally accepted time also underpins computing and communications networks. But perhaps the most significant impact of the atomic clock, as it was first with ships and then with trains, has been on travel. Nobody now needs to navigate by the angle of the sun. We have GPS. The most basic of smartphones can locate you by picking up signals from a network of satellites. Because we know where each of those satellites should be in the sky at any given moment, triangulating their signals can tell you where you are on Earth. It's a technology that has revolutionized everything from sailing to aviation, surveying to hiking. But it works only if those satellites agree on the time.
SPEAKER_00: GPS satellites typically house four atomic clocks made from cesium or rubidium. Huygens and Harrison could only have dreamed of their precision, but it's still enough to misidentify your position by a couple of meters, a fuzziness amplified by interference as signals pass through the Earth's ionosphere. That's why self-driving cars need sensors as well as GPS. On the highway, a couple of meters is the difference between lane discipline and a head-on collision. Meanwhile, clocks continue to advance. Scientists have recently developed one based on an element called ytterbium that won't have lost more than a hundredth of a second by the time the sun dies and swallows up the Earth in about five billion years. How might this extra accuracy transform the economy between now and then? Only time will tell.
SPEAKER_02: Some splendid details about the coming of railway time come from Stuart Hilton's book, What the Railways Did for Us. For a full list of our sources, please see bbcworldservice.com slash 50 things.
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