From: utzoo!decvax!cca!JGA@MIT-MC@sri-unix Newsgroups: net.physics Title: paradoxical twins Article-I.D.: sri-unix.3302 Posted: Thu Sep 16 08:24:26 1982 Received: Fri Sep 17 03:18:44 1982 From: John G. AspinallDate: 15 Sep 82 19:28:39-PDT (Wed) From: harpo!ihps3!houxi!deimos!ariel!houti!trc at Ucb-C70 Article-I.D.: houti.154 Via: Usenet; 16 Sep 82 4:08-PDT Now that simultaneity has been settled (I hope) how about the good old twins paradox? My question here is, if both frames of reference are equally good, then why should one twin age differently than the other? In fact, it would seem to me to be reasonable to argue that, there is in fact a prefered (stationary) frame of reference, but that the only way to detect the difference is to check the relative time dilation effects between two frames. I have heard it argued that the difference is that one undergoes acceleration and the other doesnt, and that this somehow explains the effect. However, the difference in ages doesnt occur during the acceleration, for the most part, but rather during the long period of free fall. Sigh. You have just invoked simultaneity again. That is, you have compared their ages ("at the same time") when they're in different inertial frames. The "stay-at-home" twin stays in one inertial frame, the "rocket-traveller" twin switches from one inertial frame to another. I hate to end this here, but a good explanation would take more time and effort than I have available. I highly recommend French's explanation in "Special Relativity" (Norton, MIT Introductory Physics Series, 1968) on pages 154-159. He makes the asymmetry between the twins clear, and also shows that special relativity is adequate for handling the problem. John Aspinall.