Re: POE summary (was Re: Work/Energy theorem?)

[SCIAMANDA@edinboro.edu]

John wrote:
> The POE says that *all* local gravitational fields are, in some sense, 
> "fictitious."  This is not to say that they are not useful.  They are 
> *very* useful but should be understood to lie in the same conceptual 
> category as centrifugal force--another useful concept.

> The POE says that *all* local gravitational fields are the result of 
> reference frame acceleration with respect to local inertial (free fall) 
> frames.
> . . .
> The POE says that, *whenever* we accelerate with respect to local 
> inertial frames for *any* reason, we "produce" local gravitational 
> fields. . . . 
> John Mallinckcrodt . . . 

John,
     This is precisely where my problem lies; I think it is because, 
being an old _art, my acquaintance with GR comes from older writings. 
Perhaps things have changed and I am out of date!  I just checked some 
writings of Einstein, Gamow, Bondi, and Reichenbach.  They all take 
something like the following viewpoint:

1) GR abolishes the preferred position of the Newtonian class of inertial 
frames (the "fixed stars" being one) by allowing an observer to transform 
away his (Newtonian) acceleration by taking account of dynamic, covariant
gravitational fields with identifiable sources (including the distant 
stars). Here we are transforming away acceleration in favor of gravitation.

	Your (more modern?) viewpoint :

2) The only inertial frame worthy of the name is the local free fall frame. 
The observer in that frame is neither accelerating nor gravitating.
Departures from that frame are produced by accelerations (relative to 
that frame).  An observer thus accelerating will see kinematical effects 
which will be identical to the effects of a gravitational field, but 
this field is fictitious and has no source beyond his acceleration 
itself. Here we are transforming away gravitation in favor of acceleration.

Please comment (and be gentle!)

Bob Sciamanda           sciamanda@edinboro.edu
Dept of Physics         sciamanda@worldnet.att.net
Edinboro Univ of PA     http://www.edinboro.edu/~sciamanda/home.html