I thought I should make one additional short posting on this topic,
summarizing what I know so far.
A stationary charge in a gravitational field does not radiate. (That
would be a source of free energy.) But if a uniformly accelerated
charge radiates, then what of the equivalence principle?
An early suggestion in Feynman's Lecture on Gravitation is that a
uniformly accelerated charge does not radiate because the actual
formula for radiated power goes as the first * third derivative of
position (rather than second * second as follows from an integration
by parts), and the third derivative of position is zero for the
special case of uniform acceleration. To put it another way, the work
done against the radiation reaction force is zero for this case.
An alternative and more popular resolution however is that of D.G.
Boulware, "Radiation from a uniformly accelerated charge," Ann. Phys.
124:169 (1980) who argues that uniformly accelerated charges do
radiate, but that cannot be seen by a co-accelerating observer, ie.
the form of a radiation field is relative (observer dependent).
An opposing recent view is that of S. Parrott, "Radiation from a
uniformly accelerated charge and the equivalence principle,"
arXiv:gr-qc/9303025 (2004) who argues not only that a uniformly
accelerated charge radiates, but that that radiation should be
experimentally observable. He therefore feels the equivalence
principle does not hold for electric charges, and claims that doesn't
violate any known mathematical result or physical observation.
--
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5040 mailto:mungan@usna.eduhttp://usna.edu/Users/physics/mungan/