Four thousand years ago, ancient Egyptians and Sumerians started to develop calendars, sundials, and temporal hours to help organize trade and agriculture.
Since then, timekeeping technology has become ever more precise. Let’s look at a few of the most important milestones that led to our modern era of accuracy.
Calendars and Hours — Circa 2100 BCE
Humankind’s earliest attempts to catalog the passage of time date back to some of the earliest civilizations, when the Sumerian, Egyptian, and Babylonian cultures first started using calendars to choose when to plant and harvest.
Arguably, the age of more precise timekeeping began when the Egyptians added a major innovation to their calendar: a system that divided each interval of daylight into twelve equal parts, or temporal hours. These units were later adopted by the Romans, who then spread the idea throughout their empire.
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Stone Sundial — Circa 1200 BCE
To measure these temporal hours, the Egyptians relied on sunlight. The first Egyptian stone sundials date back to around 1200 BCE and consist of plates with a gnomon—an element designed to cast a shadow—to project shade on carved marks that indicate time.
Tell time with the starsBut it’s possible that sundials originated even further back in history, as some artifacts that may be gnomons have been recovered in Egypt and China that date back to around 3500 BCE.
Sundials were probably the first widely-used timekeeping devices.
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For hours of darkness, the Egyptians developed a water clock. One of the first examples we know of is a basin with a small drain at the bottom which allowed the liquid to seep out evenly, exposing marks that indicate the nocturnal hours.
First Mechanical Clock — 1283 CE
Timekeeping took a major step forward in 1283, when the first weight-driven mechanical clock was set in motion in England. Much of the motivation behind this development came from Catholic monks who wanted a more precise way to set their prayer times, and an increasingly large merchant class that was demanding consistent timekeeping to make trade easier.
Since many of these early mechanical timekeepers were installed in European churches to signal the ringing of the bells, the name for this technology was drawn from the Latin word for bell: clocca .
Mechanical clocks often became the ornate center points of medieval cities, like this 13th-century clock tower in Freiburg im Breisgau, Germany.
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First Pendulum Clock — 1656 CE
But the early mechanical clocks were too inaccurate for astronomers, who wanted to track the movement of stars more precisely. In 1656, Dutch scientist Christiaan Huygens added a pendulum to the existing mechanical clock systems, and achieved a 100-fold improvement in accuracy over older clocks. With this new technology, Huygens reduced the typical gain or loss of 15 minutes a day to a variation of only about a minute a week.
Huygens added another major improvement a few years later: the spiral balance spring, which controls the oscillation of a balance wheel in portable timepieces, leading to the evolution of pocket watches.
Time Zones — 1884 CE
The benefits of standardized time for local trade became clear. International commerce, however, still struggled with differences in local timekeeping until the late 19th century. To remedy this situation, the US government established four time zones in 1883. The next year, the International Meridian Conference declared Greenwich Mean Time to be the world’s time standard, which later provided the basis for Coordinated Universal Time (UTC) and today’s international time zone system.
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First Atomic Clock — 1955 CE
The leap into modern hyper-accurate timekeeping arguably started with the development of regulators in the late 18th century, which improved accuracy in contemporary clocks to a tenth of a second a day.
But the more dramatic breakthrough was the invention of cesium-beam atomic clocks in the US in the early 1950’s, which enabled scientists to calculate the standard frequency for Coordinated Universal Time with an accuracy rate of less than one nanosecond a day.
More than hours, minutes, and seconds: Modern technology measures all kinds of intervals, like heartbeats, with a remarkable degree of accuracy.
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And the future looks even more precise. The latest innovations, like optical lattice clocks, are outperforming even atomic clocks like the hydrogen maser. Some of these new timers are expected to become mind-bogglingly accurate, losing only one second every 30 billion years.
Deep Time: understanding eonsFirst Apple Watch Fitness Tracker — 2014 CE
Limiting your wristwatch to information about the time of day seems almost quaint these days. Fitness watches equipped with integrated sensors can measure your heart rate, fitness, sleep patterns, water intake, and more, creating data that can be uploaded and shared to improve your health. But these ubiquitous pieces of technology also raise questions about the privacy of personal data in the digital age.