On 4 January 2014 04:06, Jason Resch <jasonre...@gmail.com> wrote: > On Fri, Jan 3, 2014 at 9:21 AM, Edgar L. Owen <edgaro...@att.net> wrote: > >> Lliz, Brent and Jason, >> >> Actually Liz is correct here, by GR it is the acceleration. That is the >> physical cause of the clock time differences of the twins. >> > > In my experiment, lets say the acceleration lats for a total of 4 minutes: > one minute to accelerate up to 0.8 c, one minute to slow down at Proxima > Centauri, one minute to accelerate back up to 0.8 c toward Earth, and a > final minute to accelerate down to back at Earth. > > If the accelerations alone account for the clock discrepancies, then there > would be no need to go to Proxima Centauri at all. Pam could spend 4 > minutes whizzing around the solar system and get in all the same > accelerations. > > Is this what you are saying? > > It isn't what *I* was saying.

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My point - also made (no doubt better) by Brent - was simply that there is no reference frame in which Pam's path through space-time can be made shorter than Sam's, and this is only possible *because of *the accelerations. The accelerations themselves don't cause the ageing - we could assume they're 1G and last through the entire trip, and that would give (more or less) the same result with the clocks, though the calculations would be a bit harder. If we assume that both Pam and Sam experience the same acceleration throughout, the equivalence principle means they age at the same rate due to the acceleration alone. However, and this is the important point, the acceleration causes Pam's path through space-time to be bent. For our own convenience we simplify the calculations by assuming the acceleration period is negligible. (So we could perhaps assume Pam is in a very, very robust space ship, and stuck inside a Larry Niven style stasis field for a few minutes of million-G acceleration. Or maybe she's an AI, or...) It's just geometry - in all ref frames, Pam's path traces two sides of a triangle and Sam's traces the third side. You can't have a triangle in which two sides are shorter than the third side, and the clock discrepancy is due to the length of the paths through space-time - the shorter path experiences the longer time (the longer path "trades space for time"). It isn't rocket science! :-) -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.