starship-design: Re: Twin paradox

[Steve VanDevender <stevev@efn.org>]

DotarSojat@aol.com writes:
 > Hi Nick
 > 
 > Twin Paradox?  There really isn't any.
 > 
 > All you have to do to dispel the notion that there is a "paradox"
 > is to ask: What does each twin see when he looks out his window
 > during the "trip?"  The one who sees the UNIVERSE "moving" will be
 > the younger at the end of the trip.

However, the Twin non-Paradox would still happen even if one twin stayed
on a fast-moving spaceship while the other took a relativistic jaunt in
the ship's shuttlecraft; the one who left and came back on the
shuttlecraft would be younger.

The critical issue is acceleration, not apparent motion of the
Universe.  The twin in the rocket experiences acceleration, because in
order to make a round trip he must accelerate, turn around, and
accelerate back, and this is the fundamental asymmetry, because the
stay-at-home twin does not experience a change in acceleration.

Once can even construct a similar "paradox" where both twins take
round-trips with different accelerations; the twin who experiences the
greater self-measured acceleration will be younger when they meet
again.

At the risk of repeating an often-repeated suggestion again, get
_Spacetime Physics_ by Taylor and Wheeler, which has a simple, clear
explanation of the Twin Paradox and its resolution.