Absorber Theory, Retarded and Advanced Potentials

[FourierFaux]

Hello. I've been reading an interesting article by a pair of smart fellows...

http://rmp.aps.org/pdf/RMP/v21/i3/p425_1

J. A. Wheeler, R. P. Feynman. "Classical Electrodynamics in Terms of Direct Interparticle Action". Reviews of Modern Physics. Volume 21. Number 3. 1949.

I haven't actually taken Quantum Field Theory myself, but I've been trying to wrap my head around the idea of Retarded and Advanced Potentials. From what I've been able to piece together... a retarded potential is one which propagates at a finite speed. An advanced potential is one that propagates instantaneously?! Do I have these definitions correct?

This article may be out of date... but it's interesting to hear his (Wheeler's) voice, the way he thinks...

 

[skippy1729]

... a retarded potential is one which propagates at a finite speed. An advanced potential is one that propagates instantaneously?! Do I have these definitions correct?

Close, but no cigar!

Retarded potentials travel from the past to the future an a finite speed.

Advanced potentials travel from the future to the past at a finite speed.

For example, an accelerated charge, A, at T1 radiates an retarded wave into the future which scatters another charge, B at T2 > T1. The acceleration of B radiates an advanced wave into the past which arrives at A at precisely T1. So the radiation reaction of charge A due to charge B is felt instantaneously by A. The article you quote was preceded by:

http://authors.library.caltech.edu/11095/1/WHErmp45.pdf

which extensively discusses these advanced and retarded solutions.

Skippy

 

[FourierFaux]

Oh. Thanks Skippy! :)