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Hypothetically, suppose someone came to you and stated that they have been living in Australia for a while and since it's timezone is ahead by x number of hours, during that time they've been living in the future.

Obviously it's ridiculous, but how would you reason with them that they're wrong?

My reasoning would be that time zones are a human artifact, created due to the rotation of the Earth to ensure that certain points in the day, such as noon happen when the sun is in a certain position in the sky, are the same at all points on Earth (by this I mean that midday is always when the sun is straight overhead, wherever you are on Earth). As such, it cannot have any effect on the physical passage of time.

Importantly, the notion of "present" is the same no matter where you are located on Earth - time passes at the same rate at all points on Earth. An event, such as a flash of lightning, at one point on Earth, occurs "at the same time" for observers located at any point on Earth, it is simply that they have labelled the particular instant in time with different coordinate values (one shifted with respect to the other). The point being that what happens in the present for one observer on Earth, happens in the present for all observers on Earth (it doesn't happen in the past for some, the present for others, and the future for another).

Would this be a reasonable argument?

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    $\begingroup$ "An event, such as a flash of lightning, at one point on Earth, occurs "at the same time" for observers located at any point on Earth," Must. Not. Mention. Relativistic. Effects. $\endgroup$ – dmckee --- ex-moderator kitten Oct 20 '16 at 19:36
  • $\begingroup$ @dmckee I was neglecting relativistic effects since in most everyday cases they will be negligible - certainly the rate at which time passes will not change for humans at different points on Earth. In any case, is the argument I gave acceptable, or would there be a better way to put it? $\endgroup$ – Feyn_example Oct 20 '16 at 19:47
  • $\begingroup$ I figure I'm always living in the future, since it keeps arriving whether I like it or not. I am a real time traveler (finding relevant XKCD left up to the reader). $\endgroup$ – Jon Custer Oct 20 '16 at 19:47
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    $\begingroup$ Also, when the temperature on one side of the Canadian border is zero degrees, the temperature on the other side is 32 degrees, so the United States is a much warmer country. $\endgroup$ – WillO Oct 20 '16 at 22:34
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    $\begingroup$ Move your watch forward a couple of hours and tell them you are now in the future? $\endgroup$ – fqq Oct 20 '16 at 23:05
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A visual demonstration. Shine a torch at a globe and explain that it is daytime in Australia and night time in Europe/America simultaneously.

Then show him two watches that are set to different times. Ask him to hold one while you hold the other, standing on the other side of the room shine the torch on him. Ask him if he believes he is in the future since his watch is set to a different time to yours and he is standing in the light.

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A simple explanation would be that a person in Australia and on the other side of the globe can communicate practically instantly by phone or ham radio. With a person living in the future you could not do this. This shows that both have the same present and different times only because of different time counting conventions.

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  • $\begingroup$ Would what I wrote in my original post be an acceptable argument? The arbitrary assignment of time zones is a human artifact and has no effect on the physical passage of time. As such an event that happens in the present (i.e. at a given instant in time) for someone at one point on Earth, will happen in the present (at the same instant in time) for all other people on Earth, regardless of where they're located on Earth. $\endgroup$ – Feyn_example Oct 20 '16 at 20:38
  • $\begingroup$ ... In the framework of Newtonian mechanics (which is a good enough approximation for this discussion), the notion of simultaneity (i.e. the collection of all events occurring at a given instant in time) is absolute, and as such, the present is the same for all points on the Earth. $\endgroup$ – Feyn_example Oct 20 '16 at 20:48
  • $\begingroup$ @Feyn_example - You are right! $\endgroup$ – freecharly Oct 20 '16 at 23:40

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