This is something I’ve always wondered about. Say I’ve got an airplane that’s capable of crossing the international date line multiple times in a day–maybe a Concorde that I’m flying up above the arctic circle. Say that I’ve also got a very sophisticated clock that can display the time and date that someone directly below me on the ground would have. What happens as I fly east? What about as I fly west?
If there are complications from being that far north, ignore that part and assume that I’ve got a Double-Secret Concorde and I’m flying further south.
Are you trying to do time-travel or what? It doesn’t matter where you are on the globe, be it by the North Pole or not, or how fast you go. For the two options you mentioned:
Going West you gain hours (it gets earlier), but you lose a day when you cross the International Date Line.
Going East you lose hours, but you gain a day when you cross the IDL.
Either way it’s a wash, except that you’ve lost jet fuel.
Heck, why go that far? Just travel to the North Pole and run around it in a tight circle.
What happens? as you “go around” the world you gain a day every time you go around. But then you cross that International date line and you lose it… which brings you back to reality. Or you run around the world in the opposite direction and you lose a day. Or you would, except you gain it on crossing the date line. Keeps you from travelling into the past.
Of course, you can’t really travel into the past or the future by running in a tight little circle – not even Superman can, and I don’t give a damn about the movie. That Date Line is a bookkeeping matter that brings us back to reality – you’re stuck here in the present with the rest of us.
It was a cute little device when Verne used it (and he took it from Poe’s “Three Sundayd in a week”, and Poe took it from some other obscure writer), but nowadays Phileas Fogg would’ve realized the truth of the matter long before he got back to England.
At the risk of veering into Cafe Society territory, he would have realized it even at the time the story was set! The United States is on the eastern side of the line, and Verne had Fogg cross the entire breadth of the United States, consulting railroad timetables every step of the way, without realizing his calendar was a day off. This has always bugged me; glad to finally get it off my chest.
Astronauts do this all the time. Basically, the clocks simply use the setting from the launch point. (Note, that on a computer, the operator has to tell the device what time zone to use.)
Now, as to clocks being affected by global circumnavigation, try looking up more information of the Hafele-Keating Experiment.
If you could suddenly accelerate beyond the speed of light, you could pass yourself either in the future or the past, depending on which direction you were traveling.
There are two date lines you will cross on almost every “orbit”. One is the usual aforementioned International Date Line the other is the moving “local midnight” line.
Flying west you lose a day crossing the IDL and gain a day when crossing the local midnight line. So, it will generally balance out on most fast orbits. But the local midnight line is moving and (depending on your relative speed) on an occasional orbit you will cross the IDL consecutively without having crossed the local midnight line. I.e., you have lost a day. The reason: you just spent a day travelling! Clearly you will lose exactly one day for each day travelling. If you “orbit” the Earth 20 times in 24 hours, you will have 19 orbits where you cross both the IDL and the local midnight line and one orbit when you cross only the IDL.
When going east, it’s the opposite. Crossing the IDL gains a day, crossing local midnight loses a day. If you do 20 orbits in a day, 19 orbits will cross both lines once and one orbit cross the IDL once and local midnight twice. So you still lose exactly a day during a day’s travel.
