Re: Equivalence Principle

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

On Mon, 16 Feb 1998, A. R. Marlow wrote:

> Apropos the continuing appeal to the equivalence principle to try to
> justify the inclusion of fictitious forces in physics, the clear and
> cogent analysis of the principle by Edward A. Desloge (Nonequivalence of a
> uniformly accelerating reference frame and a frame at rest in a uniform
> gravitational field, Am. J. Phys., 57, 12, December, 1989, Pp. 1121 -
> 1125) should definitely be read by anyone interested in the issue.
> ...
> The new emphasis in the paper is on the fact that *uniform* gravitational
> fields both exist (contrary to claims made sometimes) and can be
> distinguished from acceleration in a field free space.

I recall reading and being disturbed by this paper when it first 
appeared.  Despite the author's very specific conclusions, I still 
can't understand on physical grounds how one could possibly 
distinguish between a uniform gravitational field and uniform 
acceleration.  Doesn't it seem simply a matter of definition that 
any observation that would contradict the hypothesis that one 
moves with uniform acceleration through a flat space would equally 
contradict the hypothesis that space is filled with a uniform 
gravitational field?  Unfortunately, I am far too much of a 
dilettante in these matters to completely follow the exposition, 
much less, to find errors in it.  In the end, with regret, I 
simply filed the paper away and hoped for the "Comment on ..." 
follow up that never appeared.  So, now may be an auspicious time 
to get the answers I should have sought back then.  

I can't help but think that the distinctions the author makes must 
ultimately be nothing more than nonphysical artifacts of using 
different definitions for the coordinates in each case or 
something similar.  Can any other impartial observer (Paul?, 
David? ...) confirm for me the validity of Desloge's analysis and, 
if so, possibly give me a way of understanding, on more conceptual 
grounds, how one might understand the distinction between uniform 
gravity and uniform acceleration?

John
-----------------------------------------------------------------
 A. John Mallinckrodt      http://www.intranet.csupomona.edu/~ajm
 Professor of Physics    mailto:ajmallinckro@csupomona.edu
 Physics Department       voice:909-869-4054
 Cal Poly Pomona            fax:909-869-5090
 Pomona, CA 91768-4031   office:Building 8, Room 223