From: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
Newsgroups: sci.math,sci.crypt,sci.physics
Subject: Re: GPS; was G.H. Hardy: Shortsighted or Disingenuous?
Date: 6 Aug 1998 13:34:43 GMT

In article <35C95129.B4795D16@cyc.com>, Fritz Lehmann <fritz@cyc writes:
>Paul Rubin wrote:

>> The Global Positioning System uses general relativity to do its
>> position calculations, from what I hear.

>I once heard the opposite, namely that although there are corrections
>in GPS clocks for special relativity, the expected corrections for
>general relativity were not found to be needed, and that the
>theoretical implications could be noteworthy, since this result
>refutes general relativity if it is not explainable as some sort of
>measuremant error or other error.

GPS was installed with a GR-switch, default off, since the engineers
refused to believe the GR effects would be necessary.  The system was
off by exactly the amount the theorists warned them, and the GR-switch
was turned on.  It's been on ever since.

>				    I heard this from someone working
>on GPS at the University of Maryland at College Park Physics
>Department a couple of years ago, in casual conversation.

More casual than you think.

>							    I think
>they had an article in Science News on something related to this, but
>I haven' seen anything on it since then.

Science News?  Wooo.

Here is your basic reference:

B.W. Parkinson, J.J. Spilker, Jr. (eds) THE GLOBAL POSITIONING SYSTEM:
THEORY AND APPLICATION, American Institute of Aeronautics and Astro-
nautics, (1995).
-- 
-Matthew P Wiener (weemba@sagi.wistar.upenn.edu)