Intellectual history of time

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When one speaks about the intellectual history of time, one essentially is stating that changes have occurred in the way we experience and measure time. Our conceived abstract notions of time have presumably developed in accordance with our art, our science, and our social infrastructure. (See also horology.)

Contents

1 Towards time-keeping

2 Isochronous time

3 Further reading

4 See also

Towards time-keeping

The units of time first developed by humans would likely have been days and months (moons). In some parts of the world the cycle of seasons are apparent enough to lead to people speaking about years & seasons (e.g. 4 summers ago, or 4 floods ago). With the invention of agriculture in the 3rd millennium BC, people relied heavily on the cycles of the season for planting and harvesting crops. Most humans came to live in settled societies and the whole community relied upon accurate predictions of the seasonal cycle. This led to the development of calendars. Over time, some people came to recognize patterns of the stars with the seasons. Learning astronomy became an assigned duty for certain people so they could coordinate the lunar and solar calendars by adding days or months to the year.

At about the same time, sundials were developed, likely marked first at noon. Adding marks for sunrise and sunset would lead to those further away from the equator noticing that there was a wide variation with a pattern. More marks were added and eventually numbers so that people began to talk about hours. Ancient traditions did not begin the day at midnight, but rather some at dawn, others at dusk. Many cultures also fixed both day and night at 12 hours (which leads to hours being a different length in different seasons the further you are from the equator). {How 12 came to mark noon, 6 dawn (in the tropics, anyway), and how 1 came to be in the afternoon likely relates to the much later development of dials on mechanical clocks.} In those days, anyway, the idea of "10:14 A.M." or "6:23 P.M." would be meaningless - a sundial isn't that precise, having only one "hand". It took centuries for technology to make measurements precise enough for minutes (and later seconds) to become fixed meaningful units -- longer still for milliseconds, microseconds, nanoseconds, picoseconds, femtoseconds, or attoseconds.

When the water clock was invented, time could also be measured at night - though there was significant variation in flow rate and so not great accuracy nor precision. With the invention of the hourglass (perhaps as early as the 11th Century) hours and units of time smaller than an hour could be measured quite reliably.

The earliest reasonably accurate mechanical clocks are the 13th century tower clocks probably developed for (and perhaps by) monks in Northern Italy. These were adjusted to conform with canonical hours -- which varied with the length of the day.

Isochronous time

With invention of the pendulum clock in 1656 came isochronous time, based on a fixed unit interval. Quickly thereafter the minute hand and then the second hand were added.

But the clocks were still aligned with the noonday sun. It took the steam engine to loosen time reckoning from being completely tied to the position of the sun. Following the invention of the locomotive in 1830, time had to be synchronized across vast distances in order to organize the train schedules. This eventually led to the development of time zones, and, of course, global isochronous time.

Isochronous time was not accepted everywhere right away, because many people's lives were still tied closely to the length of the daytime. With the invention in 1879 of the light bulb, that changed too.

The isochronous clock changed lives. The business day revolved around it, and appointments were no longer "within the hour", but on the hour, and five minutes was late (except for a party). Time technology turned human life into a rigorous schedule.

External BBC article on shortest time ever measured (10^{-16^{seconds) as of 2004.}}