From: ks@forty2.physik.unizh.ch (Kurt Sonnenmoser)
Newsgroups: sci.physics
Subject: Re: Is Special Relativity a closed subject?
Keywords: radiation from charges, FAQ
Date: 17 Dec 92 22:29:47 GMT
Organization: Physics Institute University Zuerich, Switzerland


In article <Bz18EA.H4r@iat.holonet.net> parrott@iat.holonet.net
(Stephen Parrott) writes:
|
| 	Perhaps because Dirac's calculation was so complicated, some people seem
| not to recognize that it definitively solves the problem of "does an
| accelerated charge radiate".  As D. Boulware writes in 
| [Annals of Physics 124 (1980), 169]:
| 
| 	"The question of whether a uniformly accelerated charge radiates
| has been the subject of a long series of papers with some distinguished
| authors reaching the conclusion that it does, while others, equally 
| distinguished, reach the conclusion that it does not.  The most careful
| treatments are those of Fulton and Rohrlich [1] and Coleman [2] both of
| whom concluded that the charge does in fact radiate. ...
| 	[1]  T. Fulton and F. Rohrlich, F. Ann. Phys. (N.Y.) 9 (1960), 499
| 	[2]  S. Coleman, Rand Report RM-2820-RR (1961), unpublished"
| 	Note:  I believe Coleman's Rand Report was belatedly published in
| 		D. Teplitz, Electromagnetism, Plenum Press, N.Y., 1983
| 	
| 	I don't know which "distinguished authors" Boulware refers to,
| but I don't know of any paper by a recognized expert in a major journal
| which claims that a uniformly accelerated charge does not radiate.

In [1], Pauli and Von Laue are cited to have argued that a charged
particle in hyperbolic motion will not radiate.

In article <ByKwvA.FFA@iat.holonet.net> Stephen Parrott writes:
|
|   Does a Stationary Charge in a Static Gravitational Field Radiate?
| 
| 	About six months ago there were discussions about this problem
| on the net.  None of the discussions or the references given to the
| literature satisfied me (mainly because of inadequate mathematical
| development), and I resolved to work out the problem for myself.  

For my proposed FAQ entry I did not feel the need for a rigorous
mathematical treatment on the background of General Relativity.
People who ask that question on the net are usually bothered by a
seeming contradiction with the Equivalence Principle (EP) -- even for
situations where Classical Physics is adequate. My goal was to point out
that due to the locality of the EP, there is no contradiction. Maybe
section 1a (see below, for those who missed it) should be a little more
verbose about that.

			-------------------------


1a) DOES THE GRAVITATIONAL FIELD OF A STATIC MASSIVE BODY CAUSE
    RADIATION FROM A CHARGED PARTICLE AT REST ON ITS SURFACE?
    (Or: "According to the Equivalence Principle, the electron on my
    desk should radiate!")

    Answer: No, it doesn't. Reason: Static situation --> no magnetic
    fields --> vanishing field energy current, i.e. no radiation. The
    Equivalence Principle only leads you to the conclusion that if you
    put the particle on the bottom of an accelerated elevator in gravity
    free space, you will observe no radiation (in the reference frame of
    the elevator).

1b) DOES A CHARGED STABLE PARTICLE IN FREE FALL IN THE GRAVITATIONAL
    FIELD OF A MASSIVE BODY RADIATE? (Or: "According to the Equivalence
    Principle, my electron should not radiate if it falls to the
    ground!")

    Answer: Yes, it does. Reason: It's like with any acclerated motion
    of a charged particle: The acceleration causes "kinks" in the field
    lines that propagate with the velocity of light and carry off
    energy. This energy comes from the orbital energy of the particle
    and not from its mass. As before, trying to apply the Equivalence
    Principle is misleading: the free falling particle is only _locally_
    equivalent to one at rest in gravity free space, but in order to
    calculate the energy radiated off, you have to integrate the energy
    flux of the electromagnetic field over a sphere going to infinity
    (in a fixed reference frame), which is, of course, not a local
    procedure. The Equivalence Principle only tells you that if you go
    very close to the particle, you see no radiation.

1c) DOES A UNIFORMLY ACCELERATED CHARGE RADIATE? (Or: "Ok, let's forget
    about the Equivalence Principle! What happens globally?")

    Answer: David Boulware [Ann.Phys. 124, 169-188 (1980) ("Radiation
    from a Uniformly Accelerated Charge")] has shown that a uniformly
    accelerated charge in gravity-free space does in fact radiate
    (contrary to earlier beliefs, e.g. of Pauli), but also that it is
    _not_ globally equivalent to a charge at rest in a static
    gravitational field. More specifically, there are regions of
    space-time where there is no coordinate frame in which the
    accelerated charge is at rest and the gravitational field static. So
    there is no contradiction to the fact that charges at rest in a
    gravitational field do not radiate.

Kurt Sonnenmoser
Newsgroups: sci.physics