🚀 go-pugleaf

In article <mcirvin.718405900@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:

> >I don't really mind statements to the effect that static fields (of
> >any sort) don't propagate. 
> 
> I reminded myself after I posted this that the fields in the solar
> system aren't static.  "Radiation-free" is a better term.

In my opinion, "radiation-free" isn't too bad a definition of
"static."  

After all, just think of the electromagnetic field produced by a
nonaccelerating point charge; the fields are time-varying if it is
moving in the lab frame, but they aren't if it is at rest in the lab
frame.  That is: whether or not the fields are time-varying is not a
Lorentz-invariant distinction.

(And, of course, the electromagnetic "field lines" from a point charge
moving with constant velocity will always point to the present, not
retarded, position of the charge.  This does not mean that
electromagnetic forces travel faster than light.)
--
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