(I have to make some assumptions about your understanding of relativity.) The big breakthrough that Einstein made in general relativity was the 'relative' bit

(I have to make some assumptions about your understanding of relativity.) The big breakthrough that Einstein made in general relativity was the 'relative' bit. There is no absolute thing of 'time', no universal tick of a clock. There is the time as experience by the traveller and the time as experienced by the brother. So there is no discontinuity that has to be merged when they meet. It seems to me your question makes an implicit assumption that there is a universal tick that is thrown out of whack when the brothers meet. But there isn't, so the question is invalid. I wonder if perhaps you regard space as one thing and time as a separate thing. It might help to throw that out and regard it as a four-dimensional object called spacetime. For the merry-go-round, I'm not sure why you say one voice sounds low and the other high. They won't. Einstein's big thought experiment was to realise that the speed of light is constant no matter the speed of the observer. As an aside, it is an unfortunate historical artifact that we call c the speed of light. It isn't. C is the "speed" of any massless particle in spacetime; it is unitless and equals 1. Photons are massless so they travel at c. http://www.reddit.com/r/askscience/comments/g6zbd/if_we_depart_earth_at_the_speed_of_light_and/ http://www.reddit.com/r/askscience/comments/g6zbd/if_we_depa... http://www.reddit.com/r/askscience/comments/fu5io/help_me_understand_time/ http://www.reddit.com/r/askscience/comments/fu5io/help_me_un...