A question of time
Frank Bailey, of Hamilton, asked:
Why can’t it be the same time all over the world? Where the hands of the clock are when we get up in the morning is irrelevant — there is no reason why we cannot start the day when the clock shows, say, 3pm. It is ludicrous that when leaving Auckland for LA you arrive there earlier than you left. More importantly, why not a 10hour day — no am’s or pm’s? All other measurements are decimalised these days.
Adam Dunford, a physicist in charge of time at the Measurement Standards Laboratory of New Zealand, responded:
For most of history, time varied all over the world because ‘‘time’’ came from where things were in the sky. If the sun was directly overhead it was midday. When train and telegraph networks spread in the late 1800s, they needed time to be the same across large areas, as you suggest, to work safely and effectively. This led to time zones, where time was fixed relative to some universal time. The first country to use a time zone was New Zealand, in 1868!
Originally, ‘‘universal time’’ came from the earth spinning, but since 1967 ‘‘the second’’ has been based on properties of caesium atoms. From this atomic time we get Coordinated Universal Time, or, in French, Temps Universel Coordonne´. As a compromise, we call this UTC.
UTC is the same everywhere, as you suggest, and is used in things such as computing and aviation to avoid confusion. In fact, because atomic time is so regular, we need ‘‘leap seconds’’ to keep UTC close to solar time!
But despite having UTC we mostly still use time zones, which make local midday close to the middle of the day. One reason may be that we all have an internal ‘‘body clock’’ which needs to be regularly reset by the lightdark cycle of day and night. Jet lag and some people’s response to the time changes of Daylight Saving are examples of ‘‘body time’’ and solar time being out of step. Another benefit of a local time based on time zones is that times used in books and movies don’t depend on the story’s location!
‘‘Tenhour’’ days have been tried. For example in ancient China and during the French Revolution, but we’ve stuck with a system based around 60 and 12 which dates back thousands of years. Twelve and 60 are easy to work with because they divide evenly by more numbers than anything smaller than themselves. That’s probably why the ancient Egyptians and Babylonians used them and maybe why we still do.
‘‘Time’’, in some ways, is what we decide best suits our needs and it’s changed as our needs change. Who knows, maybe one day we’ll have a single worldwide time with ‘‘10hour’’ days. Right now, though, for arriving somewhere later than you left, UTC is the best we have and although it has 24 hours instead of 10, at least there’s no am or pm!
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