starship-design: Re: The "So-called" Twin Paradox, cont'd

[TLG.van.der.Linden@tip.nl (Timothy van der Linden)]

Timothy replies to Rex writing:

>The difference in trip time could also be attributed to different
>paths through *space*, but relativists don't like absolutes.  (I
>see the idea of an absolute frame of reference in Timothy's
>comment, in his email of 1/26 at 10:12 EST, "So to find the
>symmetry breaking factor in the Twin Paradox you *need* to look at
>a global (non-homogeneous) environment.")

I really did not mean to touch the idea of an absolute reference frame.
Actually I don't understand how you did derive that from what you quoted
directly above.
I wanted to emphasize the fact that one needs to look at more than just one
point in space, in order to realize relativity (since it means that on
compares between multiple points).
I got the impression that Steve said the same only in much more words (which
to me seemed to obscure the core of the problem).

>But, one relativist,
>Einstein himself (on p. 56 of his "The Meaning of Relativity,"
>Fifth Edition, Princeton, 1956), raises the possibility of an
>absolute frame by citing "Mach's Principle," which postulates that
>"a material particle [moves] relatively to the centre of mass of
>the universe."  [See also Holstein and Swift, Amer. J. Phys. 40,
>p. 749 (1972).]

Why should the centre of mass of the universe be more an absolute frame,
than for example the center of the Sun?
Or rephrased: What are the "special" properties of an absolute frame of
reference?

>However, if the "observations...entirely between themselves" are
>composed of Doppler-shift measurements by each of light from the
>other, they both measure exactly the same shift (as the Special
>Theory stipulates) and can't tell which one is "moving."  But they
>*can* determine which one is moving by looking at the Doppler
>shift of light from the "fixed stars."  That was my point that I
>may have oversimplified a bit in my 11/29/96 response to Nick.

The word fixed is really not necessary, they may move or accelerate as much
as they want, they are the same as Steve's 3th observer and the same as my
global environment. As a result there are several other ways than Doppler
shift alone to determine who intertally accelerates.

Timothy