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December 18th, 2016, 09:26 PM   #1
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question - Einstein's theory of relativity

In the relativity theory, as I understand it, if a person went on a trip to space in a rocket that travelled close to the speed of light, when they returned to earth they would appear younger in relation to any observers, who in turn would have aged more. But what I don't get, is that you could look at it as though the earth was moving away from the space traveller at the same speed (relative velocities) - so who is really moving away from whom, and why does the space traveller age slower and not the observers in earth ?
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December 18th, 2016, 09:44 PM   #2
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The case of the travelling twins — Einstein Online
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December 19th, 2016, 01:52 PM   #3
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The essential difference is that the space traveler has to stop and turn around. It is not symmetric.
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December 19th, 2016, 03:35 PM   #4
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Also, you need to be careful with the definition of EVENTS that take place. In this specific example (known as the "twin paradox", which results to be not at the end), the two EVENTS are located as:

Event 1- First tick of the clock ON THE SPACE SHIP when it starts the travel from Earth, so you can imagine yourself staring at the clock in your ship and seconds will pass like seconds to you (logically)

Event 2- Last tick of your SPACE SHIP CLOCK, when you have arrived back to Earth. Your total interval of time measured during these two events, known as proper time, is necessarily smaller than the one the others measured from Earth since you travelled.

As someone has written above, the paradox is solved arguing that at some point the space ship needs to come back, which implies an acceleration at some point, and special relativity only works for uniform movements.
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December 19th, 2016, 08:24 PM   #5
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Thank you, Nietzsche for useful information.
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