DANGER ZONES

The return of global travel sparks an examination of international time zones. You might know about GMT and UTC, but it might surprise you to learn that the matter is far from settled

- JOSH SIMS

In the world of physics, there are only two sorts of time, the relativistic sort that makes up one part of the fourth dimension, as described by Einstein, and the arow of time that moves in the direction of entropy. In the world of technology, commerce, health, culture and politics there are multiple times - and, it seems, often a complete lack of logic to underpin them. While anyone who has had to catch a plane, or make an international phone call, knows how tricky time zones can be- and for all that they just seem part of the fabric of global living - next year marks what is only their 140th anniversary. The idea of time zones is young. It is also in flux.

"The whole issue of time zones is simple in essence but a complex problem in reality," as Emily Akkermans puts it. She is the fantastically-titled Curator of Time at the Greenwich Royal Observatory in London ("I haven't managed to bend time to my will yet," she jokes). "We meddle with time zones around the world and make changes all the time. Whether those reasons are good ones depends on what side of the fence you're sitting."

Greenwich is where, for reasons of its history in pioneering navigation at sea, there is a literal line in the ground that, since 1884, has demarcated point zero for global time zones. This remains a fact even if improved measurements of our planetary globe afforded by satellites has meant that, since the mid-1980s, the line has actually moved about 100m eastwards.

Necessary Exposition