# Q & A: metric time?

Q:
Hello. Do you know if there have ever been any attempts to metricise time? I mean, 100 seconds in a minute, 100 minutes in a hour, a 10-day week etc.
- John (age 36)
Queen’s University Belfast, Northern Ireland
A:

The second is already the unit of time in the "Systeme International" set of units, sometimes called "MKS" -- for meters, kilograms, and seconds. The base-60 stuff for minutes and hours (and the 24-hour stuff) dates way back, perhaps to the Babylonians or even the Sumerians. Seconds are divided up by powers of ten for smaller time measurements, and typically only every third power of ten is used. Examples: one millisecond is 10^-3 seconds, and one microsecond is 10^-6 seconds, one nanosecond is 10^-9 seconds, one picosecond is 10^-12 seconds and one femtosecond is 10^-15 seconds (a unit used most often by laser jocks who make pulses of light which only are a couple of wavelengths long).

For longer times, physicists normally just use seconds and give a big number. A day, a week, and a fortnight are unambiguous, if not particularly metric, time units that are not used in physics very much except for contact with people and their schedules. A month is an ambiguous unit of time -- some are short and others are long and so is not used at all. Even a year is ambiguous -- is it a siderial year, or the funny calendar year which also gets longer on almost every fourth year? We just use seconds to be fully unambiguous in physics calculations.

Since time is useful in arranging our schedules, the number of seconds in a day has to be given a special name. This won't be a power of ten, unfortunately, and the only other option is to redefine what a second is, and it's too late for that.

Tom

(published on 10/22/2007)