On 21/04/30 12:07 AM, john mcandrew wrote:
There's a post in the newsgroup sci.physics.relativity called: "Jefimenko on Causality and Physical Laws" where Tom Roberts makes the important point that the fields can also be expressed in terms of the advanced solution to Maxwell's equations:
https://groups.google.com/g/sci.physics.relativity/c/KEV9NN6ObHc/m/GRumQHEnBAAJ
Does Jefimenko mention the advanced version of his equations in any of his papers or books?
Good question. (The difference can be nothing more than a few
minus signs here and there, of course.)
On a more fundamental level, I doubt that Jefimenko's equations
give more insight in past-and-future questions than the other
approaches to electrodynamics. He just expresses the fields
directly in terms of the sources in a closed-form expression,
whereas the alternative is to first use an equation for the
potentials and from there derive the fields, so it is nothing
but a substitution exercise (although it is surprising that
the result are still fairly concise and readable equations!)
On the other hand, you could argue that Jefimenko's elimination
of for potentials and therefore of the arbitrary gauge choice may
be important. But classically, this gauge is just a completely
arbitrary function of space and time, which is not determined by
the past or the future at all, so for past-and-future questions
also that will not help, I guess (and anyhow the analysis should
then be QM-based in view of the Aharanov-Bohm effect.)
--
Jos
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