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I just started to learned modern physic for a two weeks, and the i got some problem to understand about the resolution of twin paradox

I have attached two pages of picture above that makes me confused, in the part of jane's point of view (last paragraph) why does jane receive signal every 3 years for (20+25) years? And receive signal every 1/3 year for 5 year??

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  • $\begingroup$ There are many questions here already about the twin paradox. $\endgroup$ – PM 2Ring Feb 21 at 11:01
  • $\begingroup$ Why? Because relativity. It would help if you described what you think Jane sees, then we can proceed from there. Note: the book's statement, "time dilation doesn't apply Dicks observation of [Jane]" is incorrect, in fact, that is the paradox. On each leg, Dicks sees Jane's clock running slowly, as does she his--yet he comes home younger. $\endgroup$ – JEB Feb 21 at 16:35
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She receives a signal every 3 years during his 25 year trip to the star when he is moving away from her (explained here by the Doppler shift). After 25 years, he arrived at the star and sends out his last signal on the outward trip. Because he is 20 light years away, it takes 20 years for all the signals up to the last one to reach earth. Therefore she receives signals every 3 years for 25+20 years.

By the time she starts recieving the signals from his trip back to earth, he has been moving towards earth for 20 years already (the time it took for the light from the furthest point to travel to earth), so he is only 5 years away. During these 5 years she receives 3 signals per year, again due to the Doppler shift.

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