Re: Relativity question

From: Schoenfeld (schoenfeld1_at_gmail.com)
Date: 03/19/05 

Date: 18 Mar 2005 17:34:25 -0800

Neil - Salem, MA USA wrote:
> "John Smith" <no@way.net> wrote in message
> news:d1dh35$9t5$1@rainier.uits.indiana.edu...
> > If me moving away from the earth is the same thing as the earth
moving
> > away from me why then does time slow down for me but not for
earthlings?
> > Many thanks.
>
> Before I give you my two cents on this question, let me first give
you my
> disclaimer: I am far from being even half way competent on the
subject of
> relativity. That said, this is the simple answer I was given
concerning
> this apparent paradox. The space traveler who leaves Earth and
travels at
> velocities approaching the speed of light and then returns to Earth
will
> indeed have aged less than those on Earth because of the acceleration

> involved in his trip (accelerating away from the Earth, turning
around, and
> decelerating when he arrives back at Earth).

The "present" of an observer in an inertial frame is the set of
simultaneous events measured by the observer in that frame. When an
observer switches frames, the "present" also switches. Mathematically,
the present is a 3d plane in Minkowski space (simultaneity plane) and
acceleration by the traveller causes the traveller to smoothly switch
frames which rotates the simultaneity plane by some angle. After the
u-turn finishes the travellers "present" matches up with earths
"future" thus when he arrives the earth will appeared to have rapidly
aged. The only frames capable of rotating an observers present to match
up with Earths past are superluminal ones, which are strictly
prohibited in SR.

> Speaking of dilations of time, there was a humorous story in the news
years
> ago when, after a NASA space mission, the astronauts submitted a bill
to
> NASA for overtime. Someone calculated that the astronauts had aged
more
> than those on Earth, perhaps because time runs slower on the surface
of the
> Earth (due to the gravity of Earth) than it does in outer space.

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