International date line

[c00ky83]

What would happen if you could orbit the Earth in a plane in less than 24 hours, and crossed the date line (East to West) twice? Technically you'd gain 2 days, but obviously that's not possible!

[mibn2cweus]

As you went around the earth somewhere in a particular time zone you would revert to the previous/next day depending on the current time and the direction you were traveling.

[smorodina]

What you're forgetting is that when you cross the time zone that is at midday you also change dates. If you were travelling east to west as you cross it you move from, say, the 2nd to the 1st of the month, and when you continue and cross the date you go forward to the 2nd again.

[smorodina]

Of course, I meant midnight!

[c00ky83]

I put it to you this way: You start at midday, then go "backwards" at a rate of one timezone per hour. Thus after every hour of travel, you get to 1:00 and put your watch back to 12:00 - hence it's always midday.

I know you can't time-travel, so where's my flaw?

[mibn2cweus]

Traveling east to west at one time zone per hour would bring you to the "date line" once every 24 hours. Noon on the west side of the date line is always one day (date, 24hrs) later than the east side so here you automatically pay the fiddler.

[boobesque]

on a plane you can travel in 3 dimensions. in time you travel in one. whichever way you go you will still be going forward in time. the time zones are just points where the sun is perpendicular to the certain points of space on the earth. if the time zones were shifted so that in england 11pmt occured while the sun was in the sky, the only difference would be that we would go to bed at 10am. time itself would be unaffected.

[c00ky83]

Schoolboy error: as you go round backwards you GAIN a day...d'oh! Sorry all!

[c00ky83]

I mean LOSE a day! I can't even get my corrections right!

[brachiopod]

It doesn't matter how many times you cross the International Date Line in a 24 hour period, you can't lose or gain more than a day.

Say you are travelling West to east from point A, just East of the IDL, (somewhere like Samoa). You leave point A at just gone midnight (00.01hrs) on Monday, travelling at a speed that takes you around the world four times in 24 hours - that's a time zone every 15 minutes.

After travelling 15 minutes you must put your watch forward 1 hour, since you are now in the next time zone. After an hour travelling, you will have put your watch forward another three times, since you are now in a time zone +4 hours ahead of your start point's time zone.

After six hours travelling, you will be approaching your start point A, having crossed 24 time zones and put your watch forward 24 hours.
Your watch now says it is 06.01 hrs on Tuesday (6 hours real time spent travelling + 24 hours you have advanced your watch due to passing through time zones)
For the people on the ground at point A, however, it is 06:01 hrs on Monday- as it is only six hours since you left, just after midnight on Monday.

You have just crossed the IDL from W to E, so you must put back your watch 24 hours - making it 06:01 hrs on Monday, the same as the people on the ground.

And off you go on another circuit of the World. You will start to see that you must cross another 24 time zones and add 24 hours before you cross the IDL again to have them taken off.

To put it another way;
as you keep rushing round the Earth in order to cross the IDL as many times as you can and try to go back more than one day, in the process, you must also travel through all the World's time zones and must add 24 hours to your watch as you do so.

[c00ky83]

OK, OK, OK, cheers for all the answers but I now realise my mistake and know I'm a dumbass for asking!

[mibn2cweus]

Not any more!