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Radiation from an accelerated charge
Radiation from an accelerated charge
According to Camila de Almeida and Alberto Saa at http://arxiv.org/PS_cache/physics/pdf/0506/0506049v5.pdf, it still seems to be an unresolved question as to whether the Einstein equivalence principle is satisfied in the comparison between a charge supported in a uniform gravitational field and a charge fixed in a uniformly accelerated reference frame. By the Einstein equivalence principle is here meant the one expressed in the Einstein lift argument, that is to say the general equivalence for all physical processes of inertia and gravity, not merely the equality of gravitational and inertial masses known to Galileo and Newton, and experimentally verified by such experiments as those of Eötvös at http://en.wikipedia.org/wiki/Lor%C3%A1nd_E%C3%B6tv%C3%B6s. It is also not clear whether such equivalence is only local and generally violated globally and therefore not a principle of physics, or whether it is generally global and therefore a principle of physics.
Till now I have failed to find empirical evidence directly bearing on this question for a charge supported in a gravitational field and a charge fixed in a uniformly accelerated reference frame. Can you advise me? Of course I would also be very interested in advice about the theoretical analysis of the matter.
Christopher
Submitted by Christopher Joh... on Sun, 2008-06-22 19:56.
Re^2 Radiation from an accelerated charge
Hi, Cornelius R. Morton.
Thank you for your helpful reply. Please excuse my late response: my computer has been out of commission for a week or so.
I have read but not yet fully absorbed the useful reference you gave.
It is striking that there seems to be little reference to empirical observations about this problem. Of course it is important to deduce, from the standard range of candidate theories, their predictions of empirical results. But also the observational results themselves must be important.
According to A. Harpaz (2007, Found. Phys. 37:763-772, "Electric field in a gravitational field"), the lines of electric field from a statically (on a table) suspended charge in a gravitational field are bent down by the gravity because they are heavy. One would naively think that such bending might be empirically measurable, and one would like to know the records from that measurement. If such a charge were radiating, naively one would expect its radiation to be mostly directed downwards to the earth or other source of the gravity, and to be detectable by a detector underneath if the table were suitably transparent. Again one would like to know the results of that detector. The description of the field in the source of Harpaz's article (A.K. Singal, 1997, Gen. Rel. Grav. 29: 1371-1390, "The Equivalence Principle and an Electric Charge in a Graviatational Field II: A Uniformly Accelerated Charge Does Not Radiate") seems to say the the electric field lines would lie on circles with two opposite senses: on the face of it this seems nonsense.
It seems that classical electromagnetic theory will have difficulty in predicting radiation if it is assumed that radiation is somehow quantised while it is still in the field, and not just virtually quantal by virtue of its detection through resonance in devices that work by the photoelectric effect, and which count electrons, not "photons" as particles themselves (see W. Lamb, 1995, Appl. Phys. B 60: 77–84, "Anti-photon"). It is not obvious how a classical electromagnetic field could be considered as radiation until it had some kind of space-time structure, likely oscillatory, that would resonate with the electrons in the detector. Would the charge on the table be in some kind of bound state with the table, and so have some kind of consequent quantum condition for its radiation? Does it make sense to speak of the quantum state of a free charged particle? Of a charged particle suspended on a table, but otherwise free? Where is the counter-charge left behind when the free charge was sent to be put on the table? Would the downwards radiation usually be absorbed by the material gravity source? Would it be the case that any non-electromagnetic force that accelerated an otherwise free charged particle would somehow need to have some kind of quantal interaction with the particle?
As you see, I remain puzzled. Please tell me if you have some more enlightenment.
Christopher
RE Radiation frm an accelerated charge
There seems to be differences of opinion as to the radiation from a charged particle undergoing linear acceleration, acceleration in a straight line. It may, it may not, possibly when acceleration starts or stops, etc. The following link to "Does A Uniformly Accelerating Charge Radiate" may help.
http://www.mathpages.com/home/kmath528/kmath528.htm
Cornelius R. Morton
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