[EPS12-pl] Prof Schaefer's answers to György Szondy's questions

[Horvath Dezso]

> > > ---------- Forwarded message ----------
> > > Date: Wed, 21 Aug 2002 13:28:53 +0200
> > > From: György Szondy <gyorgy_szondy@hotmail.com>
> > > To: EPS12-plenary@lists.kfki.hu
> > > Subject: to Prof. Schafer: GPS and Celestial Mechanics
> > > Resent-Date: Wed, 21 Aug 2002 15:57:00 +0200 (MEST)
> > > Resent-From: eps12-plenary-admin@lists.kfki.hu
> > > Resent-To: eps12-plenary-owner@lists.kfki.hu
> > >
> > > to Prof. Schafer:
> > > Question about the relation of GPS and General Relativity based Celestial
> > > Mechanics.
> > >
> > > BACKGROUND:
> > > -----------
> > > Kovalevsky stated about solving problems in a general fashion in the
> > > framework of Einstein's theory of gravity that it is conceptually possible,
> > > "but the mathematical difficulties encountered have by far not yet been
> > > solved"[1]
> > >
> > > GPS is the most common usage of high precision relativistic calculations.
> > > Relativistic corrections used in GPS are qiuite simple. It is usually said
> > > to be based on Special and General Relativity (GR), however it is quite far
> > > from GR as the phenomenon of time is defined differently. "Time" in GPS
> > > measurements refers to coordinate time while in General Relativity "time" is
> > > proper time. Proper time in GPS measuremets is called "clock rate". A usual
> > > statement here sounds like: "clocks run at different rates when they are at
> > > different distances from a center of gravitation attraction." [2][3][4]
> > >
> > > QUESTIONS:
> > > ----------
> > > - Why do you think mathematical method used in GPS calculations is not
> > > really identified yet as a base of different theoretical description of
> > > gravitation?
> > > - Which benefits that are expected from this approach [5] do you agree with?
> > > (no gravitational red-shift, synchronisation, lower mathematical complexity,
> > > linear addition of mass and energy)
> > > - What do you think can make phisicists to deal with the theoretical
> > > background of GPS calculations? When will be worked out?
> > >
> > > Thank you,
> > > György Szondy
> > >
> > > REFERENCES:
> > > -----------
> > > [1] J Kovalevsky, 2000, Celestial Reference Systems - An Overview,
> > > Proceedings of IAU Colloquium 180
> > > http://aa.usno.navy.mil/colloq180/Proceedings
> > > [2] R. A. Nelson, Relativity Fundamentals for Time Scales and Astrono=
metry
> > > http://ad.usno.navy.mil/ad/forum/nelson.pdf
> > > [3] Project A - Global Positioning System,
> > > http://www.eftaylor.com/pub/projecta.pdf
> > > [4] Tom Van Flandern - What the Global Positioning System Tells Us about
> > > Relativity, http://www.metaresearch.org/cosmology/gps-relativity.asp
> > > [5] Linear Relativity as the Result of Unit Transformation, 2001,
> > > physics/0109038
> > >
> > >
> > >
> > > György Szondy
> > > gyorgy_szondy@hotmail.com
    [ Part 2: "Attached Text" ]

Dear Mr. Szondy,

please find below my answers to your questions.

- Full general relativity needs a geometric language
to clearly identify physical effects. Thus the GPS
calculations you have in mind will not prove useful
as a base of different theoretical description of gravitation.

- Coordinates in which g_00 = -1, and even g_0i = 0, hold
are well known in general relativity (Gaussian coordinates).
However, they do relate to freely falling observers and are
thus often not appropriate. In those coordinate systems
the three-dimensional metric is time dependent in general
(e.g. see Landau/Lifshitz textbook on the Classical Theory
of Fields).  Your approach I cannot support.

- Nothing, I think.

Sincerely yours,
G. Schaefer