Use your imagination and try to picture this: clocks haven’t been invented yet. What did people in ancient times think about time?
They probably lived simple lives in tune with the sunrise and slept when it was dark. If it was cloudy or raining, they may have stayed in bed longer or taken naps during the day.
Defining time isn’t easy. Does time have a single meaning, or can it represent various things that exist separately from clocks?
Historically, time was viewed as the sun moving across the sky, followed by nighttime. The daily pattern of light and darkness manifests as our sleep-wake rhythm. Is this daily cycle our experience of time?
The earliest way to see time was from a sundial, which showed the dial’s shadow move across the surface on a sunny day. As humanity progressed, we sought ways to measure time more accurately.
A Brief History of Time Accuracy
Timekeeping took a major step forward in 1283, when the first weight-driven mechanical clock was invented in England. It was accurate to about 15 minutes per day.
Time was based on Earth’s rotation of 12 hours of daylight and 12 hours of darkness. Each hour has 60 minutes, and each minute has 60 seconds.
The calendar became an important indicator of the passage of time, which allows us to write about historical events. The 1,600-year-old Julian calendar had drifted 10 days out of sync with the solar year because a year isn’t exactly 365 days long.
The modern calendar, known as the Gregorian calendar, was introduced by Pope Gregory XIII in October 1582. It was designed to correct inaccuracies by using a leap-year formula to track the days more accurately.
In 1657, the pendulum clock was the first accurate clock, losing only one minute per day. It was based on the motion of a swinging arm. Heavy weights hung from chains that turned the gears in the mechanism to move the minute and hour hands around the clock’s face.
The first clocks were placed in a church steeple, and a bell would ring each hour, the number of times matching the hour. If you wanted to know the time of day, you had to listen and count the number of rings.
The digital age began with the invention of quartz technology in 1927, but it wasn’t put into practical use until Seiko introduced the first quartz wristwatch on Christmas Day, 1969. A tiny battery vibrates a quartz crystal, and the mechanism counts the vibrations until they total one second, equivalent to a pendulum clock. Digital watches are accurate and still in use.
The next generation of timekeeping was based on atomic oscillations. In 1955, the first precise cesium-133 atomic clock was built, providing superior accuracy over quartz clocks.
Thus, in 1967, the atomic second was officially defined as the time it takes for a cesium atom to oscillate 9,192,631,770 times. Such a clock is accurate to the second for several million years.
A second was previously defined as a fraction, 1/86,400 of a mean solar day, but the astronomical definition was abandoned because Earth’s rotation is not perfectly constant.
Also, the duration of a year isn’t exact, so every four years, an extra day is added to account for Earth’s orbit. Moreover, many countries use daylight saving time to lengthen the hours of daylight.
Our timekeeping methods are adjusted to suit our needs. When we adjust clocks, are we changing the clock or time itself? Can we describe time without using clocks?
A Description of Time
Time seems to have two parts. The first part comes from seeing trees bending in the wind, birds flying, and the sun moving across the sky. The second part is what we feel with our senses.
While we sleep, we hear our heartbeat, feel the air enter our nose, and sense our chest rise and fall. When we combine these feelings with the visible movement, we believe that everything is moving…
Clocks count the oscillation of atoms, and they let us measure the movement and speed of all things. Is time a physical thing, like the movement we witness, or a concept based on clocks?
We observe that time has many aspects that affect our lives, but it’s not easy to define. Is time a measurement or a force that moves things?
Our definition of time came from Earth’s rotation, and now it comes from atoms. Does time exist in everything? The Sun keeps shining, the Earth keeps spinning, but what exactly is time?
We began by imagining a world without clocks, watching the sun move across the sky. We created clocks from moving gears and pendulums, and now from the energy in atoms. In every era, we fine-tuned the movement of things into clocks with greater accuracy.
We live on a spinning planet with our beating hearts and vibrating atoms. However, there’s one final question… What are clocks really measuring?