🚀 go-pugleaf

A. Satish Pai <Pai-Satish@CS.Yale.Edu>  writes:

>In what form is the energy circulating, then? Are the fields in motion even
>though they are being maintained by static sources? If not, what is moving? 
>Are the potentials time-varying? Are there any photons corresponding to this
>energy flux? Can the energy circulation be detected by any means?  

It has been a long time since I studied this, and I don't follow a lot of
the discussion below.  However, it is perhaps worth saying that I did not
imagine the e&m *fields* to be in motion.  It is not even clear what that
would mean.  What is circulating, if anything, is a sort of ghostly,
abstract *energy* that pervades the space.  It would seem that only
suitable integrals of this flux can be measured.  It is, however, very
cute, not to say startling, that one of them, namely the one for the
angular momentum, gives the right answer -- and that this angular momentum
is hidden in the sense that it is nonzero in a system in which nothing is
moving.  Marianne Moore demanded that poets produce "imaginary gardens with
real toads in them", but it appears that physicists can do the trick too.

%^)  Joe  jcf@world.std.com