> It appears that Twin A goes off on one of his classical relativistic
> journeys.  And he returns to shake hands with Twin B.  Question, who
> actually made the trip?

> But not so fast.  There is a way to find out who really made the trip.
> Let there be a comparison of the twin's clocks upon being reunited.
> Twin A's clock shows 20 years less elapsed time than B's, and A's
> physiological age is 20 years less.  It is therefor concluded that the
> motion between A and B was not relative, but rather it can be said
with
> certainty that A made the trip, and not B.

> How is this conundrum resolved?

> "Daniel Weston" <daniel...@webtv.net> wrote in message
> news:24457-41C252DC-58@storefull-3134.bay.webtv.net...
> > Dean:  I am uncertain what you mean by testing to see which twin
> > accelerated.  As I understand it, neither twin when confined within
> > their lab, will be able to determine whether A is accelerating and
> > returns to B, or B is accelerating (along with the universe) and
> returns
> > to A.

> The twin that applies the force required to accelerate to turn around
> will know that they have changed direction, due to the force of
> acceleration pushing them towards one end of their lab when they turn
> around. One of them has to turn around for them to meet up again, which
> requires applying a force. The web page explains it much better than I
> can. It should be clear to you if you visit it:
> http://www.phys.unsw.edu.au/~jw/twin.html

> I mean by testing that atomic clocks have been accelerated and shown to
> have acquired the predicted discrepancy in time.

> "Dean" <anonym...@yahoo.com> wrote in message

> > "Daniel Weston" <daniel...@webtv.net> wrote in message
> > news:24457-41C252DC-58@storefull-3134.bay.webtv.net...
> > > Dean:  I am uncertain what you mean by testing to see which twin
> > > accelerated.  As I understand it, neither twin when confined
within
> > > their lab, will be able to determine whether A is accelerating and
> > > returns to B, or B is accelerating (along with the universe) and
> > returns
> > > to A.

> > The twin that applies the force required to accelerate to turn
around
> > will know that they have changed direction, due to the force of
> > acceleration pushing them towards one end of their lab when they
turn
> > around. One of them has to turn around for them to meet up again,
which
> > requires applying a force. The web page explains it much better than
I
> > can. It should be clear to you if you visit it:
> > http://www.phys.unsw.edu.au/~jw/twin.html

> > I mean by testing that atomic clocks have been accelerated and shown
to
> > have acquired the predicted discrepancy in time.

> I have won small prizes playing a lottery game but I
> don't claim as a result of this "prediction",
> special insight to the aerodynamic principles that
> affect which numbered ball will pop out of the
> lottery machine.

> If accuracy of the prediction has any importance,
> GPS clocks were predicted to APPEAR faster
> as a result of a falling photon gaining energy.

> Odd that they work then.

> "Dean" <anonym...@yahoo.com> wrote in message
> news:t_vwd.60560$QJ3.26983@newssvr21.news.prodigy.com...
> SNIP

> > > If accuracy of the prediction has any importance,
> > > GPS clocks were predicted to APPEAR faster
> > > as a result of a falling photon gaining energy.

> > Odd that they work then.

> No Dean, he didn't talk about that. The claimed cause must be *wrong*,
or
> more tactfully, "misleading" as was quite well exposed in the AJP:
"the
> photon energy is conserved in a static gravitational field" (Okun et
al, AJP
> 68, Feb.2000, p.115).
> Obviously you understood nothing of what Sue is talking about...

> "Harry" <harald.vanlin...@epfl.ch> wrote in message
> news:41c29ccd$1@epflnews.epfl.ch...

> > "Dean" <anonym...@yahoo.com> wrote in message
> > news:t_vwd.60560$QJ3.26983@newssvr21.news.prodigy.com...
> > SNIP

> > > > If accuracy of the prediction has any importance,
> > > > GPS clocks were predicted to APPEAR faster
> > > > as a result of a falling photon gaining energy.

> > > Odd that they work then.

> > No Dean, he didn't talk about that. The claimed cause must be *wrong*,
> or
> > more tactfully, "misleading" as was quite well exposed in the AJP:
> "the
> > photon energy is conserved in a static gravitational field" (Okun et
> al, AJP
> > 68, Feb.2000, p.115).
> > Obviously you understood nothing of what Sue is talking about...

> "The classical phenomenon of the redshift of light in a static
> gravitational potential, usually called the gravitational redshift, is
> described in the literature essentially in two ways: On the one hand,
> the phenomenon is explained through the behavior of clocks which run
> faster the higher they are located in the potential, whereas the energy
> and frequency of the propagating photon do not change with height. The
> light thus appears to be redshifted relative to the frequency of the
> clock. On the other hand, the phenomenon is alternatively discussed
> (even in some authoritative texts) in terms of an energy loss of a
> photon as it overcomes the gravitational attraction of the massive body.
> This second approach operates with notions such as the "gravitational
> mass" or the "potential energy" of a photon and we assert that it is
> misleading."

> The claimed cause, due to time dialation, is not contested. The
> causality is easy to support.