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This question already has an answer here:

Let there be two children Allen and George .

now Alan boards a train and the train moves at a speed comparable to light. now because George is on the station for George being at rest Allen is moving and its lock is moving slowly so time passes slower for Allen and faster for George. for George after sometime when he will be very old then Allen will be of lesser age.

now but Allen in his own frame in train sees George moving in the opposite direction.so for him George is moving and so the clock of George must be moving slowly hence for Allen George time is running slower than his.

after sometime when he will be old enough then George will be of lesser age as he was standing on the platform but moving for Allen so my question is if George if Georges on the platform and sees that Allen old and, when Allen is in the train thinking he is at rest and observe George he will see George younger

then wont it be a contradiction that both will see each other relatively younger when both meet each other?

Also if there is a third person who is also a twin to George and Allen who is moving in another train but it is lower than alan's train and so he must see George at a different age than Allen right then please tell how will the third person and Allen willbdisagree or agree about George age?

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marked as duplicate by Aaron Stevens, WillO, safesphere, PM 2Ring, John Rennie special-relativity Jun 12 at 8:11

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ Yes, that's the twin paradox. Have you looked at some of the existing twin paradox questions? $\endgroup$ – PM 2Ring Jun 12 at 4:44
  • $\begingroup$ @PM2Ring doesn't the twin paradox involve the two people somehow meeting up later? This just seems to be confusion on the symmetry time dilation in each frame. $\endgroup$ – Aaron Stevens Jun 12 at 4:51
  • $\begingroup$ @Aaron Fair point, although the OP does have Alan & George seeing each other after some time, so I assume they are meeting up, somehow. $\endgroup$ – PM 2Ring Jun 12 at 4:54
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    $\begingroup$ @Tanmay If you need more information than what's given in the answers of the linked question, please ask a new question, clearly explaining what you need further help with. $\endgroup$ – PM 2Ring Jun 12 at 8:20
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    $\begingroup$ It is hard to read because there are many typos, run on sentences, unclear explanations, etc. $\endgroup$ – Aaron Stevens Jun 12 at 16:12
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It is true they will both observe the other twin's clock as running slower than their own. But to meet again, the twin on the train moving close to light speed, will have to decelerate, stop, and accelerate back to return. acceleration and deceleration slow time like gravity does. So while Alan is decelerating and accelerating, George will see Alan's clock slow much more, and Alan will see George's clock speed up enough so that when he returns to the station they will both see that George is older than Alan.

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    $\begingroup$ This answer is incorrect. For example, Allen can travel for 1 day or for 1 year. In either case the amount and time period of his acceleration while turning around would be the same. The same acceleration cannot account for the time difference accumulated over one day and over one year. This is not a correct resolution of the twin paradox. $\endgroup$ – safesphere Jun 12 at 8:42
  • $\begingroup$ this is correct, I did not say whether George is one day older or one year older, just that they would both agree $\endgroup$ – Adrian Howard Jun 12 at 8:54
  • $\begingroup$ They would not agree based on the logic in your answer. Also, please use the proper @ address while replying. $\endgroup$ – safesphere Jun 12 at 8:57
  • $\begingroup$ if you disagree with Einstein and Lorentz there is nothing more I can say $\endgroup$ – Adrian Howard Jun 14 at 0:33
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    $\begingroup$ I did not see Lorentz or Einstein commenting here, but in all seriousness, you should not be offended by comments posted to help you improve your understanding. I did not downvote your answer, but someone did, because it is not ncorrect. You should search this site for the twin paradox to see that it is resolved by the change of the reference frame, but not by acceleration. And also, once again, please learn to use the proper @ address. Otherwise people don't know that you have replied. $\endgroup$ – safesphere Jun 14 at 8:42

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