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Acordding to Einstein's Relativity, while Space-man lives for 1 day(just a number for example , not an exact number calculated from the corresponding relative speed), Earth-man can live for 1000 years (just an example number too). But from the view of Space-man, while Space-man lives for 1 day, Earth-man lives for 1 second. So while Space-man lives for 1 day, then how long does Earth-man live ? 1000 years or 1 second? Or 1000 years = 1 second actully ?!

Thank you in advance!!

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    $\begingroup$ As long as the two never meet again, that question has no answer. Only if they meet again, their age can be meaningfully compared. $\endgroup$ – celtschk Apr 27 '14 at 8:48
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    $\begingroup$ The "Twin Paradox" is not a paradox at all. You have to decide which person has experienced acceleration - usually spaceman. The one who experience acceleration is the one whose clock runs slower in the space-man Earth-man frame (they have to start at the same place or it is meaningless). The acceleration is easy to measure, so they know which one has the slower clock all the time. $\endgroup$ – C. Towne Springer Apr 27 '14 at 8:50
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    $\begingroup$ @C.TowneSpringer: From Wikipedia: "A paradox is a statement that apparently contradicts itself and yet might be true." The twin paradox fits that description quite nicely. More exactly, the twin paradox is a veridical paradox, a claim that actually is true, despite the apparent contradiction. $\endgroup$ – celtschk Apr 27 '14 at 9:06
  • $\begingroup$ @celtschk The Twin Paradox usually has "One twin takes off in a rocket...". At that point, no contradiction and no might be, and no paradox. The statement made by the OP is more of a of a para-problem and I assumed a lot was left out in order to make sense of it. $\endgroup$ – C. Towne Springer Apr 27 '14 at 13:59
  • $\begingroup$ @C.TowneSpringer: Of course no true contradiction (otherwise it would not be a veridical paradox). But an apparent contradiction (because at first view the situation looks symmetric, until you think about it). If there were no apparent contradiction, it would not be asked so often. $\endgroup$ – celtschk Apr 27 '14 at 14:03
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If you consider this situation strictly in Special Relativity terms, i.e. as long as you stay in the classical SR situation and consider both reference frames inertial, there is no (falsifiable) answer to you question. Therefore, if there are no accelerations involved (and no acceleration appears in the Lorenz transform showing time dilatation), you can always claim that the other body is time dilated. Any proof showing otherwise should actually be interpreted as falsifying the very Special Relativity Theory as it currently stands.

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    $\begingroup$ No, I don't think so. Maybe you'd like to consider my answer. $\endgroup$ – Lincoln Apr 28 '14 at 2:53
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This question makes my head spin for hours. And I think the point is the reference frame of Earth-man is not running in a high speed referring to a photon-reference-frame. So for a definite distance(let say, L) of a photon-clock, if the speed of a reference frame is bigger, the time takes less. So in the situation of Earth-man, the time takes more because the speed of his reference frame is smaller.

I don't think this is a paradox now too. It's a mistake make by the poor quality of the physics text book.

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    $\begingroup$ As long as both observer remain inertia the situation is completely symmetric. The apparent paradox can be resolved when the observers meet again by computing the proper time of both paths. $\endgroup$ – dmckee --- ex-moderator kitten Apr 28 '14 at 3:23
  • $\begingroup$ Oh, my fault, the key is : from the Earth-man's view, he lives for 1000 years; from the Space-man's view, Earth-man lives for 1 second !!! @dmckee $\endgroup$ – Lincoln Apr 28 '14 at 9:24

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