Crossing a time zone does not conjure up a time warp, so how can it be Friday in one place, and Shabbat in another? It just doesn't seem possible.
closed as not constructive by Isaac Moses♦ May 11 '12 at 21:19
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Shabbat starts no later than sunset (Shulchan Aruch, Orach Chayim 293:2).
Sunset is a subjective phenomenon describing the apparent descent of the Sun below the horizon. It happens because the Earth is round and rotates about its own axis much more quickly than it revolves around the Sun, so observers on its surface observe, once per rotation, their part of the Earth rotating away from the Sun to the point that the rest of the Earth blocks them from seeing the Sun. That point is sunset.
Because the timing of this phenomenon depends on the observer's location on the Earth, so does the timing of the latest time to start Shabbat. This timing varies continuously with the observer's location on Earth, meaning that two people who are almost in the same place will observe almost the same time for sunset and would therefore be subject to almost the same limit for starting Shabbat, so there's no discontinuous "time warp" except at the Halachic International Date Line (wherever that is).
It's because the world is Round!
After I posted this correct anwer, the OP decided to change his question