For centuries, humans have developed ever-more increasingly sophisticated ways of measuring time. From the first sundials to the very latest caesium-fountain atomic clocks, scientists and inventors have looked for more accurate ways to measure time. However, for most, time is an abstract concept that is taken for granted, the passing of seconds, minutes and even years is generally not given much thought.
This article discusses many aspects of historical and modern time-keeping, including:
- How humans measure time in relation to movement.
- The fundamental nature of space and time – Einstein’s General Theory of Relativity.
- The accurate measurement of time.
- The concept of world time and international time standards.
The Measurement of Time in Relation to Movement
For centuries, people have accurately measured time by using movement. A year is defined as how long the Earth takes to complete a single orbit of the Sun. A month is defined by how long the Moon takes to complete a single orbit of the Earth. A day is defined as a single rotation of the planet. Each of these definitions involve movement. Even seconds can be described by the movement of a hand around a clock-face. Indeed, many definitions of time involve space, in fact space and time are very closely related.
Einstein’s General Theory of Relativity – Space and Time
As long ago as 1915, Einstein suggested that the concept of time and space are closely intertwined. Although some of his theories are now being called into question, his General Theory of Relativity was ground-breaking at the time. His theories described the universe as being created some 14 billion years ago with a ‘Big Bang’. At the start of time, the whole universe was packed into a tremendously dense, infinitely small, incomprehensibly hot point or ‘singularity’. From this singularity the whole universe exploded into existence, including all the planets, suns and galaxies – in fact all matter contained with the universe. This ‘Big Bang’ marked the start of the universe and the beginning of time, as we know it.
Einstein suggested that the universe will continue to expand at an increasingly slower rate for billions of years, until eventually, it will reach its maximum size. At this maximum, he suggested that the universe will then slowly become more dense and hotter and begin to contract and collapse back in on itself to its original state. However, the latest observations of space by scientists suggest that rather than the universe expanding more slowly, the opposite is in fact true. Galaxies appear to be moving away from each other at an ever-increasing rate. This suggests that over billions of years, the universe will continually cool and expand until, eventually, nothing is left, only atoms floating around the emptiness of space.
The Accurate Measurement of Time
The science of studying time or the measurement of time is called Horology. The term Horology is derived from Greek word for hour. A person interested in the science of time is called a Horologist, this can be anything from a watch or clock maker to scholars of Horology.
Human history is littered with a huge variety of apparatus used to accurately measure time. Ancient peoples used large megalithic stones to mark the beginning or end of seasons. Sundials were the next technological leap, which used a shadow cast by the sun on a series of markings that indicated the current time of day. Water clocks, based on the regulated flow of water into a vessel. Mechanical clocks, regulated by the movement of a pendulum. Modern electronic clocks are regulated by the resonance or vibration of a quartz crystal. All these clocks are still heavily reliant on movement to keep accurate time.
Advances in technology over millennia has led to the development of modern atomic clocks. These devices are based on frequency reference masers and can measure time to an astonishing degree of accuracy. Atomic clocks have wide-ranging applications, from the Global Positioning System (GPS) to maintaining world-wide standards for time.
World Time and International Time Standards
The precise and accurate measurement of time is crucial to the modern way of life. Particularly high technology computer systems and networks, which rely heavily on synchronized time, so much so that world-wide international standards exist to agree and coordinate time. The basis of world time is UTC which stands for Coordinated Universal Time. Local time varies around the world according to a number of longitudinal time-zones. Each time-zone is generally one hour ahead of the previous one, but all are derived from an offset which is applied to UTC time.
The concept of time is difficult to explain, it is an abstract concept that is linked to movement and ultimately the creation of the universe itself. People have strived to create increasingly more accurate time references for millions of years. Currently, at the pinnacle of time-keeping technology are modern atomic clocks which are astonishingly accurate to within a few seconds in a million years. These allow applications such as global positioning to become a reality. Time is so important to the current way of life that there are internationally agreed standards of time-keeping that every country around the world adheres to.