Deep Dive: The history of timekeeping

Time is invisible, it flows on incessantly, an eternal tide that accompanies our every presence. People have been trying to find a way to capture the phenomenon of time for thousands of years. For long periods, the only way they were able to do this was to use the natural rhythms of nature: the sun, moon and stars provided information about the progress of the day and seasons.

Over the centuries, peopled honed their astronomical knowledge and depicted months and years systematically with the first calendars. Technical apparatus – ranging from sundials, water clocks and hourglasses to precise gears and pendulums – ultimately created a structure of hours and minutes for measuring the day. In more recent times, science and technology have been able to elevate the measurement of time to an unimagined level of precision using the oscillations of atoms and even atomic nuclei.

All these steps in development changed not only our clocks, but also the way we do farming and administration, our rituals, festivals and communication, transport and our working lives. So the story of timekeeping – from the first celestial observations to the nuclear clocks of tomorrow – is also a story about the development of people, the way they live together and social structures.

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1. In time with nature

The first chapter of timekeeping starts off very simply: The day began at sunrise and ended at sunset – the first human beings lived to this natural rhythm. At some point, they started observing the moon: It grew and shrank in a recurring cycle that lasted just under 30 days – from the crescent moon to the full moon and on to the new moon. Some archeologists think that the people who lived in the Paleolithic Age around 38,000 years ago might have documented the phases of the moon by making notches in bones or stones.

The earliest advanced civilizations, such as the Sumerians and Babylonians in southern Mesopotamia (modern-day Iraq), then systematically observed the changes in the sky. In their cuneiform culture, it is around the middle of the third millennium BCE that names of months start appearing for the first time, as LMU researcher Walther Sallaberger writes.

These first calendars were used in particular to determine the dates of sowing and harvesting, which in turn were associated with religious festivals and other rituals. In addition, the Mesopotamians followed the course of the sun and planets and divided the sky into constellations. By introducing a numeral system with 60 as its base, they also created the foundation for modern timekeeping with hours, minutes and seconds.

2. The shadow of time

This development is thought to have occurred as follows: People noticed that the shadow created by a stick – or maybe it was just a tree or branch at first – regularly changes its direction and length as the sun moves round in the sky. This observation led to the development of one of the oldest instruments used for measuring time: the sundial.

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It was probably invented in stages by a number of early advanced civilizations. In Mesopotamia, for example, scholars used the shadow created by sticks for orientation during the course of the day. In ancient Egypt in around 1500 BCE, people created simple sundials: they were elongated stones and sticks whose shadow moved over a scale as the day progressed. Subsequent developments – such as certain orientations of the stick and the dial – made the sundials much more precise.

They were set up in cities, temples and larger courtyards, for example, to enable meetings or gatherings to take place at set times. However, they only worked when the sun was shining – and each city lived according to its own time because the position of the sun is different in each place. Nevertheless, sundials lasted for a surprisingly long time: Even by as late as the 19th century, they were still being used to check and adjust mechanical clocks.

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3. Water, fire and sand

Using uniform processes on Earth makes it possible to detach timekeeping from the sky. In water clocks, water dripped or flowed from a vessel at a constant pace. The oldest documented examples originate from ancient Egypt, Mesopotamia and Persia and date to around 1600 BCE. Candles or oil lamps were also used to measure time: The further they burned down, or the lower the level of the oil, the more time had elapsed. The first reports of this happening come from ancient China.

Hourglasses, on the other hand, allow fine grains of sand to trickle through a narrow opening. The precision required to make these kinds of devices was provided by the art of glassblowing in the Middle Ages; the first documented example of an hourglass made from glass can be found on an Italian fresco painting from the 14th century. Using all these different approaches, people were able to tell the time regardless of the weather or whether there was daylight.

The devices worked at night, inside buildings or when there was cloud cover in the sky. This new ability to measure time anywhere had practical consequences. It became possible to restrict speaking times in court, set times for prayer in monasteries, and structure work around time in workshops or out in fields.

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4. Mechanically precise

In the late 13th century, there was a technical revolution in timekeeping: Europe saw the development of mechanical clocks – the first artificial timekeepers that ticked to a regular rhythm. The principle behind this was that gears, weights and a crucial invention – known as escapement, which converts the stored energy of a suspended weight or a tensioned spring into even pulses – made sure that the clockwork moved in even steps.

The first public mechanical clocks were installed in European cities, usually high up in church towers. The clocks struck every hour, later also every quarter an hour. This meant that time became public and binding: Markets, church services or council meetings began at a fixed time and the hours people worked could be calculated exactly.

When the spring drive was invented in the early 15th century, clocks ultimately became much smaller and portable. Time made its way from church towers into houses and people’s trouser pockets. Minutes could be measured precisely for the first time – and punctuality developed into a virtue, even an expectation within society.

5. Precise pendulums

When the Dutch scholar Christiaan Huygens built and patented his first reliable pendulum clock in 1657, timekeeping became significantly more accurate: The regular oscillation of the pendulum reduced the deviation in time to just a few seconds per day.

A short time after this, he developed a balance spring for the balance wheel of pocket watches, which significantly improved the standard of watches that people could wear on their wrists. The balance wheel is the centerpiece of mechanical watches; it acts as a mechanical regulator that combines with the escapement to release and stop the gear train in increments. The exact time became much more important for science and navigation. At sea, for example, it was used to determine the degree of longitude.

In the middle of the 18th century, the English watchmaker John Harrison succeeded in constructing a mechanical watch that was also able to cope with the waves and the harsh, changing conditions encountered on the open seas. The marine chronometer that he developed made seafaring much safer, and global trade flourished as a result. At the same time, astronomers and physicists used these precise clocks and watches to study natural phenomena with an unprecedented level of accuracy.

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6. Oscillating crystal

The 20th century saw electricity enter the world of timekeeping. From then on, electromagnets drove the pendulums and provided a much more even rhythm. However, it was a physical effect that elevated timekeeping to a new level: When a quartz crystal is electrically excited, it oscillates at an extremely stable frequency. In 1927, researchers from Bell Laboratories in the USA used this principle to develop the first quartz watch, which only went wrong for a few seconds each month.

From the 1970s, quartz wristwatches started to be mass-produced, making precise timekeeping affordable for millions of people. At the same time, they formed the basis for our modern infrastructure: timetables, telephone networks, radio broadcasting, trading on the stock exchange and later digital communication – all of this is based on a very precise timestamp, which is synchronized via radio and digital networks so that whole societies can operate at the same rhythm.

7. In time with the atoms

As physicists began to delve deeper and deeper into the innermost processes of matter in the 20th century, they had an idea: Why not use even more fundamental physical variables as the basis for measuring time? One example is the extremely stable frequencies of energy transitions in atoms.

The first working, accurate atomic clock was created in 1955 and was based on cesium. These timekeepers will only deviate by a second after several hundred million years. More modern optical versions in which the atoms of elements like strontium or ytterbium are excited with lasers actually boast an even greater level of accuracy.

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This level of precision has long become established as part of our daily lives: navigation systems like GPS only work because satellites and receivers synchronize their time precisely down to the nearest billionth of a second. The Internet, power grids and financial markets also require exact timestamps. In high-frequency trading, for example, a difference of a millionth or a billionth of a second can determine whether a trade produces a profit or a loss. At the same time, researchers are using atomic clocks to investigate fundamental questions in physics – including miniscule effects of gravity or the theory of relativity.

8. Fundamental time

Physicists are now already working on the next generation of timekeepers: nuclear clocks. Whereas atomic clocks are based on energy transitions of electrons in the atomic shell, nuclear clocks utilize energy transitions in the atomic nucleus. They are much less sensitive to external interference. The first experimental prototypes, based on the isotope thorium-229, have been under development for several years.

Researchers from LMU are also involved in this work: they have managed, for example, to measure the lifetime of the excited state of the thorium-229 nucleus for the first time – a crucial step in the process of constructing a corresponding clock. More sophisticated versions could be one to two orders of magnitude more precise than the best optical atomic clocks. This would take timekeeping to a fundamental frontier of physics.

This level of accuracy is set to open up new possibilities: tests of gravity and the theory of relativity, the search for variations in natural constants or even evidence of dark matter. At the same time, extremely stable time standards could emerge, making global navigation, communication and energy systems much more robust. The history of timekeeping would reach its final chapter – at least for the time being – with the construction of a fully functioning nuclear clock.

More Research and Innovation:

• Humankind’s first calendars – when the day began with the evening: The cuneiform expert Walther Sallaberger is researching how a common understanding of time 5,000 years ago created a sense of community and enabled city-states to function. Read now!
• Deep Dive – Into the fiery heart of Earth: Magma normally seethes far down in the depths - but under the Krafla volcano in Iceland it gets surprisingly close to us. Read now!
• Against the clock: Sleep, hunger, alertness – the body’s natural processes are regulated throughout the day by our internal clock. But what happens when the body’s clock gets out of sync? Read now!
  

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