🚀 go-pugleaf

metares@well.sf.ca.us (Tom Van Flandern) writes:

>     Ignore T2.  As T1 travels from Earth to AC, he ages 7 months in his
>inertial frame, while people on Earth and AC are aging 4 years in their
>inertial frame.  Why isn't T1 just as entitled to say that he stood still
>while Earth and AC passed by him at 0.99 c; and therefore Earth and AC should
>have aged less than T1 between these two events?

This is your basic simultaneity problem.  What do you mean "while people
on Earth and AC are aging 4 years in their frame"?  Between when and when?
Between the time of an event here and the time of an event over there.
But the time of a event over there is poorly defined.  The person on T1,
on the other hand, is measuring the well defined time between two local
events.  There is no symmetry between what you are having T1 measure
and what you are having Earth and AC measure, so you can't expect a
symmetrical result.  Adding T2 does not add symmetry unless you allow
for the proper length of all sides of the parallelogram defined by their
world lines to be the same length and you only measure the proper times
between well defined events.  That symmetry only comes about if T1 and T2
are separated by 4 light years *in their own frame* just as Earth and AC
are separated by 4 years *in their own frame*.  And once you really do
make the problem completely symmetrical, everybody ages the same amount
(7 months) between encounters with the 2 travelers in the other frame.
You are expecting symmetry to still exist after explicitly breaking the
symmetry by insisting on making one branch of the parallelogram be 4
years long or by insisting on measuring times between local events on
the one hand and time observed in a particular global coordinate system
between a local event and a remote event.

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