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# Relativity/About time dilation in relativistic motion

Question
My question is about time dilation in relativity.

Suppose there are two person, A and B. Originally they are in the same reference frame (on the earth).B then accelerate away from the earth and moving in a constant velocity relative to the earth(Person A). According to relativity, as both of them are having constant relative motion, there will be a time dilation between the two frames. When A is looking at the clock of B, he will find her clock running slow, the same happen when B is looking at A's clock.

However, it is supposed if Person B return to the earth (experiencing acceleration) after travelling for a period of time, B's clock will run slower than that of A.

Then what is going to happen if i observe A's clock from B's reference frame since the start of the journey until end? I will observe a slower clock and finally a faster clock at A? How does this change happen? And when will it happen?

Simon, the problem you are trying to solve is called the Twin Paradox and it is discussed in every textbook.  Fortunately for you, it is also discussed in many posts on the web.  So instead of my writing you a book about the Twin Paradox, search Google for that title and you will find lots of information.

Then if you want to discuss it with me, just submit another question. But it will help if you first take advantage of the excellent discussions that you can find on the web.

Relativity

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#### Uncle Ben

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I can answer questions regarding Einstein's Theory of Relativity, particularly in Special Relativity. I will not answer homework questions or mathematical problems that require special symbols.

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I have taught physics at the college level, undergraduate and graduate, for many years including Special Relativity. I have taught at Johns Hopkins, Case-Western, and MIT. I have also served as a staff member of the Commission on College Physics, which was supported by the National Science Foundation to recommend improvements in the curriculum of college physics departments in the US. I am also the author of a textbook titled Vector Calculus, which was used at MIT in the teaching of electromagnetic theory and relativity. My research interests were mainly in solid state physics, especially the properties of metals at low temperatures. I am listed in the publication known as American Men of Science.

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