Date: Sun, 19 Jul 2020 22:14:22 -0500 (CDT)
From: "Stephen A. Fulling" <fulling@math.tamu.edu>
To: Acceleration Radiation Community: ;
Subject: More comments by Bob Wald

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From: Robert Wald <rmwa@uchicago.edu>
Date: Sat, 18 Jul 2020 11:26:34 -0500
Subject: Re: More comments, July 17

Below are a few quick comments with regard to Daniel's and Don's 
remarks 
[https://www.math.tamu.edu/~fulling/ar/fulling1_comments717.txt ]

                             Best wishes, Bob

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Daniel's remarks: I agree with Bill's comments. There is no such 
thing as "the physical solution"; everyone is free to consider 
any solution to Maxwell's equations that they want to consider. 
The solution people are usually most interested in is the one 
with no incoming radiation from null infinity. (If one has this 
solution, it is easy to add a homogeneous solution to account for 
incoming radiation if one wishes.) I don't see any way of arguing 
why one person's choice of initial data on a Cauchy surface would 
be "better" than someone else's choice (unless, e.g., the charges 
are known to be static for all time in the past, in which case 
the "no incoming radiation" condition would pick out a "natural" 
choice of initial data).

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Don's remarks: a) I recall that radiation from a radially 
infalling point charge in Schwarzschild was looked at and 
possibly numerically calculated in the 1970s (around the time of 
the Davis, Ruffini, Press, Price paper on gravitational radiation 
from an infalling mass). b) When I said " A stationary charge in 
a (globally) stationary spacetime, of course, will not radiate to 
infinity" I was talking about a spacetime where there is a time 
translation symmetry, including, e.g., conductor boundaries. A 
spacetime with moving conductors is not stationary, nor is a 
spacetime with black holes orbiting around each other. Radiation 
in these cases certainly should be expected.

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