The Grand Story of Time

Right now, somewhere

At this moment it is already tomorrow on a coral atoll in the middle of the Pacific, and still yesterday on an empty island a short flight away. Above you, the clocks on GPS satellites run fast because of Einstein, and your phone quietly corrects for it. In a laboratory in Colorado, a clock raised one foot off a table ticks measurably faster than its twin below.

Time is the most ordinary thing in your life, and it may be the strangest. This is the story of how people learned to measure it, divide it, argue about it, bend it, and feel it.

Part I: Inventing the second

From shadows to dripping water

For most of human history, time came from the sky. The sun crossed overhead, shadows shrank and stretched, and every town kept its own noon. Sundials told the hour on a clear day; water clocks, which measured time by water flowing steadily from one vessel to another, worked at night and under clouds (more in sundials, water clocks and hourglasses).

Water clocks reached their peak in China. In 1092 the Song dynasty statesman Su Song completed a tower in the capital, Kaifeng, about 40 feet tall, that was a clock, an observatory and a model of the heavens at once. A great water wheel with 36 scoops advanced one notch at a time, held back by a kind of escapement, and turned a bronze armillary sphere while little figures rang bells and beat drums to announce the hours. When Jurchen armies captured Kaifeng in 1127, the tower was dismantled and carried north. It never ran again.

The swinging weight

Europe's mechanical clocks appeared around 1300, driven by falling weights and regulated by the verge escapement (who invented the mechanical clock?). They were marvels, and they were bad at their job, drifting by a quarter of an hour a day. On Christmas Day 1656, the Dutch scientist Christiaan Huygens built the first pendulum clock. Its error fell to something like 15 seconds a day, about sixty times better, and the pendulum remained the world's most precise timekeeper until the 1930s.

The crystal on your wrist

Nearly every quartz watch and clock runs on a tiny tuning fork of quartz crystal that vibrates 32,768 times a second. The number is chosen with care: it is 2 to the 15th power, so a chip can halve it fifteen times to get exactly one pulse per second, and it sits just above the range of human hearing. That is why your watch never hums (how a quartz watch works).

The atom takes over

In 1967 the world stopped defining the second by the Earth's spin and started defining it by the atom. One second is officially 9,192,631,770 cycles of the radiation from a cesium-133 atom (how a second is defined). The old definition, a fraction of the average day, was retired because the Earth turns unevenly, speeding up and slowing down by tiny amounts. That decision set up a half-century tug of war between two kinds of time.

Part II: Atom time vs. Earth time

The leap second, and its end

Starting in 1972, whenever atomic time and the Earth's rotation drifted close to 0.9 seconds apart, timekeepers added a leap second to UTC: a 61-second minute, inserted 27 times so far. Computers hate surprise seconds. Companies handled them differently, and more than once the extra second knocked websites and systems offline.

Then the Earth did something unexpected: it sped up. July 5, 2024 was the shortest day ever measured, about 1.66 milliseconds shorter than 24 hours. That raised the prospect of the first negative leap second, a second removed from the clock, something no software had ever had to handle.

So the world's timekeepers changed the rules. On October 15, 2026, the General Conference on Weights and Measures, meeting at Versailles, voted to stop adding leap seconds from May 20, 2027. Atomic time and Earth time will be allowed to drift apart by as much as an hour, which should take at least several centuries. After 2027, the official clock will no longer chase the sun one second at a time.

Part III: The map of time

The Earth turns 15 degrees every hour, so in theory the planet divides into 24 tidy slices. In practice, time zones were drawn by railways, trade, war and national pride, and the result is one of the strangest maps people have ever made.

The day of two noons

Before 1883, American towns set their clocks by the sun, and the railroads juggled dozens of local times. On November 18, 1883, the railroads switched to four standard zones at noon. Cities east of their new zone's center line had to turn their clocks back, so they heard noon twice: "the Day of Two Noons." Chicago's clocks went back about nine and a half minutes. The zones didn't become federal law until 1918 (how time zones began, who invented time zones).

Strange places on the clock

• China: one clock for a continent. China stretches across about five geographic time zones but uses only Beijing Time, UTC+8. In far-western Xinjiang, many people keep an unofficial local time two hours behind, while trains and official business run on Beijing time.
• The biggest jump at a land border. Crossing from Afghanistan (UTC+4:30) into China (UTC+8) moves the clock three and a half hours, the largest time change at any land border. It happens high in the Pamir mountains at the Wakhjir Pass, where there is no official crossing.
• The country with the most time zones is France. Thanks to territories around the globe, from French Polynesia to Wallis and Futuna, France spans 12 time zones, more than Russia or the United States.
• Half and quarter hours. India runs on UTC+5:30 and Nepal on UTC+5:45. New Zealand's Chatham Islands go further, celebrating the new year at UTC+13:45, just 15 minutes after the first of Kiribati.

More of these oddities: the world's strangest time zones.

The date line, where calendars bend

Somewhere in the Pacific, the calendar has to change. The International Date Line zigzags around islands so that countries can keep the same day as their neighbors and trading partners.

The day that never happened. At the end of December 29, 2011, Samoa jumped straight to December 31, erasing Friday, December 30, to line up with Australia and New Zealand. It was Samoa's second jump: in 1892 it had moved the other way to please American traders, and lived July 4 twice. Because neighboring American Samoa stayed put, you can now celebrate the same birthday on two different days with a short flight between them.

New Year takes 26 hours. In 1995 Kiribati bent the date line around its eastern islands, creating UTC+14, the farthest-forward time on Earth. Its Line Islands greet each new year first, about 26 hours before the uninhabited US islands at UTC−12. For more than a day each year, it is next year somewhere and last year somewhere else.

Daylight saving time, a wartime idea

Germany was the first country to put its clocks forward, on April 30, 1916, during World War I, to save coal. A Canadian town, Port Arthur in Ontario, had tried it in 1908, but Germany's move spread the idea across Europe within weeks (daylight saving time).

The body notices. A Michigan study of hospital data found heart attacks rose about 24% on the Monday after clocks sprang forward, and fell about 21% on the Tuesday after they went back. Over the whole week, though, the total didn't change: the clock change seems to move heart attacks around rather than cause more of them.

Part IV: Einstein's elastic clock

Time does not pass at the same rate everywhere. Speed slows it down. Gravity slows it down. And we measure both effects every day (does time really slow down?).

Your head ages faster than your feet

In 2010, scientists at NIST in Boulder, Colorado, compared two ultra-precise aluminum-ion clocks, then raised one by just 33 centimeters, about a foot. The higher clock ran measurably faster, exactly as general relativity predicts. The difference is about 90 billionths of a second over a 79-year lifetime: tiny, but real. Someone living in a penthouse ages a little faster than the doorman.

GPS runs on relativity

Every GPS satellite carries an atomic clock, and every one is affected by both of Einstein's theories at once:

• Speed (special relativity): the satellites move fast, which slows their clocks by about 7 microseconds a day.
• Weaker gravity (general relativity): they are 20,000 km up, where gravity is weaker, which speeds their clocks up by about 45 microseconds a day.
• Net result: GPS clocks would run about 38 microseconds a day fast.

That sounds like nothing, but GPS works by timing signals that travel at the speed of light. Left uncorrected, positions would drift by roughly 10 kilometers a day. So engineers set the satellite clocks before launch to tick at 10.22999999543 MHz instead of 10.23 MHz, and in orbit they tick at exactly the right rate. Every time a map app finds you, it is confirming Einstein.

Part V: Time inside the mind

The holiday paradox

Why does a great vacation fly by while you're on it, yet feel long when you look back? The psychologist and broadcaster Claudia Hammond calls this the holiday paradox. We judge time two ways: while it's happening, and afterward. Looking back, the brain measures a stretch of time by how many new memories it made. A fortnight of routine leaves very few; a single day somewhere new can leave dozens. So the trip feels short while it happens and long in memory.

It also helps explain why years seem to speed up as we age: fewer firsts, more repetition. Hammond's suggestion is simple: change things up. A new route to work, a new place for lunch, and life feels a little longer.

A people who face the past

Most languages put the future ahead of us and the past behind. The Aymara of the Andes do the opposite. In Aymara, the word for "front," nayra, also refers to the past, and qhipa, "back" or "behind," is used for the future. Older speakers gesture forward when they talk about long ago and back over their shoulder for tomorrow. The logic is beautiful: the past has been seen, so it lies before your eyes; the future is unseen, so it's behind you.

Part VI: How you know what time it is

Today you don't need a sundial, a pendulum or an atomic clock in your basement. National laboratories keep atomic time; it flows through satellites, radio signals and internet time servers; and your phone and computer set themselves from it many times a day.

This site checks your device against that system every time you open a clock, and tells you how far off you are, usually by a few hundredths of a second (how we get the time, exact time now). Four thousand years after the first water clocks, knowing the exact time anywhere on Earth takes less than a blink.

The takeaway

Time has a precise definition, 9,192,631,770 vibrations of a cesium atom, and a deeply human side. Nations draw its borders. Railroads moved its noon. Island governments erased days to help their economies. Gravity bends it by the foot, satellites correct for it every day, and our memories stretch or shrink it depending on how we live. And from May 20, 2027, the world's official clock stops chasing the sun one second at a time.

The clock on your wall is a human agreement. The time you actually live is up to you.

Remarkable numbers

Sources

• Euronews: global timekeeping rules change, leap second scrapped from 2027 (Oct 16, 2026)
• Nippon.com / Jiji Press: leap second effectively scrapped (Oct 16, 2026)
• NIST: pair of aluminum atomic clocks reveal Einstein's relativity at a personal scale (2010)
• Library of Congress, In Custodia Legis: a brief history of standardized time zones in the US
• Sandhu et al., daylight saving time and acute myocardial infarction, Open Heart (2014)
• Núñez and Sweetser, Aymara and the reverse direction of time, Cognitive Science (2006)
• Why July 9 is likely among the shortest days on record (record: July 5, 2024)

Checked October 2026. Spotted a mistake? Tell us.