Precise timekeeping is of the utmost importance in science and technology and has been since the beginning of recorded time. Yet no one really knows what time is. If you look up the word “time” in a good dictionary, you will see one of the longest entries, with dozens of definitions.
In 400 AD, St. Augustine said, “What, then, is time? If no one asks me, I know; if I wish to explain to him who asks, I know not.” Time is what a clock measures. The first clocks were natural phenomena like the sun rising and setting and the motions of the stars in the heavens. Sundials were developed, and then water clocks and sand-filled hourglasses. Later, pendulum clocks became the ultimate in precision. Physicists needed accurate clocks to measure natural phenomena, and accurate timekeeping was crucial to navigation. In the eighteenth century, we understood light as one example of an electromagnetic wave with very short wavelengths and high frequency. Frequency is the inverse of time or how often something happens in a given time interval. Thus, measuring time and frequency was crucial to the most cutting-edge physics.
In the twentieth century, Einstein’s theory of relativity defined time as part of a four-dimensional space-time. Furthermore, time was relative; measured time was different for observers moving at different speeds. Communicating with our satellites depends on taking relativistic time into account, and our GPS systems would only work correctly by doing so. To meet the timekeeping needs of modern technology, the most accurate clocks are atomic clocks and crystal oscillators. Atomic clocks, which depend on the frequencies of energy transitions in atoms, are the most precise measuring device for long periods. Crystal oscillators are most accurate for times less than 1 second, which is also crucial. The best clocks today, like in satellites, include an atomic clock and a crystal oscillator working together.
Quantum physics took the mysteries of time to a whole other level. Is time continuous or discrete? Is there a minimum size of time duration, a quantum of time? Is time fundamental, or is it an emergent phenomenon, or is it an illusion?
Many scientists now think that time is not fundamental but that it emerges out of nothingness. Of course, nothingness itself is being redefined. Thoroughly empty space is now believed to be a quantum foam, with virtual particles popping into and out of existence randomly and continuously. When these virtual particles interact, they become entangled, and the information is recorded as a sort of Akashic* record that is created and begins to manifest as what we call space.
Time, in this view of things, is the record of the sequence, the order in which events between particles occur. Remember that the particles themselves are just blips in the waves in the quantum field. And that’s about as far as I can go for now because even a crystal professor doesn’t understand quantum physics.
But the precise measurement of time and frequency are at the cutting edge of how quantum physicists attempt to further our understanding of things at the smallest scales and, surprisingly, also at the largest scales. Advances in precise timekeeping help cosmologists investigate the Big Bang and the history and structure of the entire universe.
More practically, almost all our modern electronic technologies depend on precise timing. Because atomic clocks are expensive, large, and power-hungry, crystal oscillators are the workhorses in electronic devices, from your kitchen appliances, radios, TVs, computers, watches, cell phones, satellites, and fiber optic high-speed data communications.
* Akasha is a Sanskrit word and means “Primary Substance,” from which all things are formed.