What are days for? Days are where we live. They come, they wake us, time and time over.Where can we live but days? – Philip Larkin
In the West, the majority of us rule our lives by standardized clocks and calendars. They provide objective units – like minutes, days, months and years – to track the passing of an assumed material time. But scientists still can’t prove that this form of time actually exists. Despite the sheer range of our timekeepers, countable metric time is nothing more than a social creation. But how, exactly, did we get here?
Inventing the day
Metric time is something successive societies have invented to organize, coordinate and self-regulate. It initially took cues from the environment – using repeated natural cycles to try and measure time:
“Time reckoning is built up through dividing elements that are evident in the universe – the day, the year, the month…are identifiable cycles. Particular moments can be recognised and repeatedly identified as the start of a particular unit. – Dr Paul Glennie
The day was probably the first recorded human interval of time, alongside seasons and the appearance of events in the natural world – like moon cycles, constellations and tides.
But environmental cues are notoriously unreliable. Tide height and consistency change across the moon’s monthly orbit; the appearance of daylight changes dramatically across seasons; the Earth’s irregular rotation is actually slowing down. So, the 24-hour time we have since used to divide days is borne out of social convenience for a regular, repeating unit, rather than based on a physical constant.
Calendars as cultural products
Unlike days and months, weeks are completely artificial divisions of time – they aren’t based on celestial movement within the universe. The sheer number of different lengths of week throughout history is a telling indicator of how arbitrary they are: in ancient Rome and pre-Christian Celtic society, a week lasted for 8 days; in ancient China and Egypt, it lasted for 10; and in Javanese, Korean and 10th century Icelandic calendars, it lasted just 5.
Annual calendars are informed by the Earth’s rotation, but they suffer from serious cultural intrusions. For one, the world’s calendars use different religious events to denote the start of each year. They can express socio-political designs and value systems – as former President Niyazov of Turkmenistan demonstrated when he renamed April after his mother.
Creating clock time
Hours, minutes, seconds – it’s in the drive to track more granular time that we see the social construction of metric time most clearly. To truly conquer time, we had to organize it better than nature could.
And here we got really creative. We embedded marbles in burning candles – and tied knots in burning rope – to mark off regular, equal increments of time. We created hourglasses and waterclocks, using the level within a bowl to meter out hours. And, when we got frustrated by the inconsistencies of these flow-based timekeepers, we started playing around with falling weights to create measured oscillations.
The desire to create a constant motion within timepieces then led to vibration, with coiled irons springs gradually replacing drive weights. But you couldn’t measure things as delicate as the speed of light with pendulums or coiled springs. So scientists then turned to frequency – first using electricity for its steady flow of charge, and later quartz to harness the vibrations it produced under pressure.
When these inventions fell short of the quest for “fine” time, scientists started to measure the natural resonant frequency of atoms. Atomic time still serves as the ultimate standard for timekeeping throughout the world, informing every wristwatch, computer, radio telescope and mobile clock and disseminated through the satellites of the global positioning system (GPS).
Measuring the abstract
By imposing closed, repeating units, clocks and calendars have made the abstract concept of time measurable. Given their sophistication and centuries-old heritage, it’s easy to believe that time is a physically real thing. But in reality, there is no proven physical truth to what we are counting; we have just created useful systems for observing and talking about change.
Yet all of us – even the most fundamental physicists – count the days and contemplate the years. We happily live a double life, where time is both individually experienced and objectively true for everyone. And in being so pervasive and so useful, metric time may just be the greatest tool humans have ever invented.