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I was at the Royal Observatory in Greenwich last week. There were several exhibits on the work of the observatory, including a large section on their work dealing with longitude and time.
In the 1700s, people were interested the solving the “Longitude Problem”: how does a sailor determine his longitude? Without a good solution, sailors lacked good position data, which could lead to shipwrecks. It turns out that the Longitude Problem is equivalent to determining local time, and one solution was to build accurate and portable clocks.
These issues of longitude and time are fun to think about, but I noticed that they require making a lot of non-canonical choices. Here, by canonical I mean choices that are natural or motivated; non-canonical choices are
arbitrary and would make just as much sense if chosen any other way.
Consider this: There is a (reasonably) canonical place to set 0 degrees latitude; it is natural to define it as the equator, being halfway between the poles and splitting the globe into equal halves. But as there is no “east pole” or “west pole”, there’s no such natural choice for 0 degrees longitude. We currently use the Greenwich meridian as 0 degrees, but there’s no good reason (besides history and random chance) that Greenwich should be special… in fact, the French used the competing Paris meridian for some time. The way we define longitude on the globe is completely arbitrary, and we could just as well use a Svalbard meridian instead.
The measurement of time is similarly non-canonical. Each civilization in history has come up with their own calendar, with its own quirks. The calendar that we use today is just one of those, and there’s no clear reason that it is naturally better than the others. In the end, the everyday world that feels so natural to us is actually based on an accumulation of historical coincidences.
While we’re discussing non-canonical choices, I’ll quickly list a few more that I noticed recently: