Time management through the ages

For most of history, there's no concept of time as we understand it today. People get up with the sun... and go to bed when it gets dark. But how do people know when the crops should be planted? When will the rivers flood?

The desire to reliably predict these things leads people to start calculating time. Measuring time begins around 3500 BCE in Mesopotamia. Monuments are built to cast shadows according to the sun’s position. These are shadow clocks. By 1500 BCE, a smaller type of shadow clock, called a sundial, is developed in Egypt.

The Egyptians divide their sundials into 12 hours of daytime and 12 hours of night-time - the origin of the 24 hour day. Over the next 3000 years, timekeepers that use sand, water, liquid mercury and gear systems are developed in China, Greece, and the Islamic world. The first known timekeeper that resembles a modern clock is built in England in 1283. Known as the turret clock, it works using weights and is placed in towers. It rings bells every hour to help monks observe strict prayer times.

In the 1400s, clocks become portable when weights are replaced with a coiled spring. However, the force a spring exerts decreases as it unwinds. This means that spring-driven clocks quickly become inaccurate! The solution is a cone-shaped pulley called a fusee that equalises the uneven pull of the spring. The fusee leads to the development of the pocket watch in 1510.

In 1656, a Dutch scientist named Huygens makes the first clock with a pendulum. Due to gravity, a pendulum always takes the same amount of time to swing each way. It's the first timepiece accurate enough to count minutes and seconds! But wait, where did minutes and seconds come from? Many thousands of years earlier, Sumerian and Babylonian peoples counted in units of 60 for mathematics and astronomy.

We don’t exactly know how this system spread throughout the world, but we do know that, around Huygens’ time, people start counting 60 seconds per minute, and 60 minutes per hour. Technology for telling the time is expensive. Even by the 1800s, most people still rely on the sun for timekeeping. There is no broad agreement about what time it is: each town sets their own local time! This becomes a problem as trains, telegrams, and telephones begin connecting people around the world.

At the 1884 International Meridian Conference in Washington, D.C., 26 countries divide the globe into 24 time zones. They choose Greenwich, England as the line from which all the time zones are measured. The time at this central point is known as Greenwich Mean Time. Not everyone likes this decision! The time zones are organised to suit the interests of mostly Western countries and they threaten local traditions around the world.

Eventually though, all countries move to this standardised time, which becomes Coordinated Universal Time. And almost all adopt the same calendar, at least for government purposes. Today, we rely on standardised time for everything from taking the bus to baking a cake. Thankfully, clocks have become more accurate than ever before. Nearly all modern clocks use electric circuits to regulate their timekeeping.

And the time on your wristwatch or cell phone might rely on signals beamed from satellites! The most accurate clocks operate by measuring the vibrations of atoms as their electrons change energy levels. These atomic clocks are accurate to the nanosecond! We've come a long way from relying on shadows cast by the sun!