Concepts of Time:

Ancient Greece

Over the centuries, philosophers and scientists have developed various ideas about time. One of the earliest views came from the ancient Greek philosopher Aristotle (384-322 BC), who described time as “a number of movement in respect of the before and after.” In simple terms, Aristotle saw time as a way to measure change, which depends on motion or some form of transformation. He believed that time was infinite, continuous, and that the universe had always existed and would always continue to exist. Interestingly, he also questioned the very existence of time, suggesting that it might be made up of two types of non-existence. His theories about time were just the beginning of many, with later thinkers like Sir Isaac Newton and Gottfried Leibniz offering different perspectives.

Newton & Leibniz

Isaac Newton and Gottfried Leibniz had fundamentally different ideas about time. In his Philosophiæ Naturalis Principia Mathematica, Newton proposed that time exists independently of everything else, flowing uniformly and constantly regardless of external factors. He called this absolute time or “duration,” which could only be understood mathematically. On the other hand, the time we experience, called relative time, is tied to the motion of objects like the sun and moon.

Leibniz, however, disagreed with Newton. He argued that time only exists when objects interact with each other. For Leibniz, time was a concept humans use to compare and order events, much like space and numbers. According to his relational time theory, time itself couldn’t be measured on its own. It was simply a way for us to perceive and organize the events in our lives.

The debate between Newton and Leibniz became famous in what’s called the bucket argument. Imagine a bucket filled with water hanging from a rope. When the bucket is spun, the water’s surface becomes concave. Even after the bucket stops, the water remains concave for a while. Newton argued that the water’s concave shape was due to its movement relative to a third entity, absolute space. Leibniz, however, believed the shape of the water was based on the relations between the bucket and the water itself. This disagreement over absolute space dominated scientific thinking for nearly 200 years.

Einstein

Fast forward to the 20th century, and Albert Einstein brought a new perspective to time with his theory of relativity. Unlike Newton, who believed that time flowed the same for everyone, Einstein proposed that time is relative and connected to space in a unified concept called spacetime. Einstein showed that the speed of light is constant for all observers, no matter their motion, and that this constancy changes how time and space are measured.

In simple terms, Einstein’s theory says that as an object moves faster through space, time moves slower for it. Conversely, if an object moves slower, time speeds up. This has to happen to keep the speed of light constant. Einstein also addressed Newton’s bucket argument with his theory of general relativity. In this theory, an object in free fall follows a geodesic—a straight line in curved spacetime. So, the water in the bucket doesn’t rotate relative to some distant stars; it rotates relative to the geodesic of spacetime.

Despite the breakthroughs in physics, time is still a mystery in many ways, and who knows—future discoveries could change our understanding once again. Time travel, anyone?

How We Measure Time

Today, we measure time using two main tools: the clock and the calendar. Both systems are based on the sexagesimal numeral system, which has its roots in ancient Sumer (around the 3rd millennium BC) and was later adopted by the Babylonians. This system is based on the number 60, which is divisible by many smaller numbers, making it a convenient choice for dividing time. For example, one hour is made up of 60 minutes, and each minute contains 60 seconds.

The Development of the Second, Minute, and 24-Hour Day

The Egyptians were likely the first civilization to divide the day into smaller segments, thanks to their use of sundials. They divided the daylight into 12 parts and created a similar system for the night using stars. Later, around 147-127 BC, the Greek astronomer Hipparchus proposed a system that divided both day and night into 12 hours each, based on the equinoxes. This led to the 24-hour day that we use today.

Hipparchus also helped develop the idea of longitude and latitude, dividing the earth into 360 degrees. Each degree was then subdivided into 60 parts, creating minutes and seconds.

Early Timekeeping Devices

Early timekeeping devices varied greatly across cultures and regions, often designed to regulate work or religious practices. Some of the earliest devices included oil lamps and candle clocks, which tracked the passage of time based on the consumption of oil or wax. Water clocks, or clepsydra, were one of the most accurate ancient timekeepers. These devices measured time by controlling the flow of water in and out of a container.

The first mechanical pendulum clock was created by Christiaan Huygens in 1656. His clock was the first to be regulated by a natural period of oscillation. This invention dramatically improved accuracy, allowing clocks to lose less than 10 seconds a day. Today, we use atomic clocks, which are based on the vibrations of cesium atoms. These clocks are the most precise timekeepers we have, and they define the second as the SI unit of time.

Despite the many advances in our understanding and measurement of time, there’s still much we don’t know. Who knows—maybe future breakthroughs will redefine time as we know it!