a brief history of time

Lost time is never found again.

Benjamin Franklin, Poor Richard’s Almanac.

It is impossible to say when humans first became aware of the concept of time, but the remorseless cycle of day and night must have provided an early clue, especially because it links intimately to the natural rhythm of sleep and waking. At the same time, they couldn’t have failed to notice the waxing and waning of the moon over a longer period. Observation of the seasons would have come later, as Homo sapiens spread into more northerly latitudes. For these early times, the day, month and year that these phenomena represent would have been adequate to communicate any time-related message, and it is unlikely that anyone would have considered how the three are related, let alone what caused them.

However, we do know that by the time of the first city-states, the development of arithmetic combined with crude astronomical observations to make it possible to estimate the length of the month or year in terms of days. The extreme example of this development is probably the Maya of Central America, who were obsessed with recording the passage of time, their central dilemma being that they had two calendars, and the two were never in step.

Meanwhile, a new and entirely arbitrary unit, the week, which has as its sole basis the creation myths of the Middle East, was making its first appearance. It has the distinction of being the only unit of time, other than the day, that imposes a cycle of behaviour on people. Religion was also the driving force behind the impulse to subdivide the day into smaller units (peasants toiling in the fields to support the city’s astronomer priests would have had no need for such fine distinctions).

Bronze Age civilizations of the Fertile Crescent used sundials to perform the task of subdivision, which means that the smallest unit measurable with any degree of accuracy would have been several minutes long by modern reckoning. The same can be said for the various mechanized water clocks built by the Greeks, Romans and Chinese, among others. It is only with the invention of mechanical clocks in Europe that the smallest measurable unit eventually shrinks to a minute. But this didn’t happen straight away: the earliest clocks were not sufficiently accurate, and minute hands didn’t appear until 1670, by which time pendulum clocks with an accuracy of 10 seconds per day were being built.

John Harrison’s marine chronometer of 1761 improved that figure to one-fifth of a second per day, making it necessary to add yet another unit at the lower end of the measurement scale. The second, once defined as 1/86,400 of a day, has since become the only unit to have been given a rigorous scientific definition, relating to the oscillation period of the cæsium atoms used in atomic clocks. However, back in the eighteenth century, when the second first appeared, there was still scope for individuality in the recording of time: every town and village that had a town hall or church clock kept its own time, but the railways changed all that. Not only did they flag up the need for a standardized time; they were also responsible for the concept of a timetable, which has been a constant bugbear for humanity ever since.

How tactless, therefore, of Albert Einstein to prove mathematically that time is relative after all. There is no celestial clock that always has the correct time. There is no such thing as the correct time. Two observers travelling at different speeds will be unable to synchronize their watches, because any communication between them will be constrained by the speed of light.

I wonder who first noticed that time went only one way. I don’t think that, even now, that thought occurs to many people. Time is a dimension of our lives in the same way that the three spatial dimensions of length, width and height are, and we take them all for granted. However, by the mid-nineteenth century, science had explained the arrow of time with the second law of thermodynamics, which can best be illustrated as follows:

Humpty Dumpty sat on a wall.
Humpty Dumpty had a great fall.
All the king’s horses and all the king’s men,
Couldn’t put Humpty Dumpty together again.

In other words, time progresses from a state of relative order to a state of relative disorder. There is no going back. You can put things back together again after a fashion, but it won’t be quite the same. You’ll be able to see the joins (even if you have to use a microscope).

One of the characteristics of science is that just when everyone else is comfortable with a new explanation, along comes another cabal of scientists to discover some phenomenon or other that cannot be explained by the existing rules. In this case, twentieth-century particle physicists were the culprits, discovering a particle that went backwards in time. They refer to it as a virtual particle. In optics, a virtual image is one that doesn’t exist, so I’m assuming that this particle is also one that doesn’t exist. So how was it detected? This seems to me a paradox worthy of any aspiring ancient Greek philosopher.

Meanwhile, back in the real world, there is much anecdotal evidence that time is relative after all. Ask anyone of my age and they will tell you that the years seem to pass faster and faster as you get older. What is less well known is that there is a rational explanation for this observation. For a 19-year-old, the coming year will represent 5 percent of their life to date. However, in my case, the coming year, if I survive it, will represent just over 1.5 percent of my life to date. In other words, the perceived rate at which the years pass by is more than three times as fast for me as it would be for a 19-year-old. But it does seem a very long time since I was 19.