Thomas Smid wrote:
Note: this thread has been started in sci.physics.research under
http://groups.google.co.uk/group/sci...faf882621f739e
, but my reply appears to be kept ignored by the moderators (I have
submitted it already three times without getting a response of any
sort). I am therefore posting my reply here (also the initial post; any
further reference is to posts in the original thread):



Eugene Stefanovich wrote:
I was wondering lately if light can be deflected by static electric
field in a manner similar to the light deflection by gravity fields.

Suppose that we shine a laser beam close to the surface of a highly
charged metal ball (e.g., in the van der Graaf generator).
Will the beam change its direction?
Did anybody hear about such experiments?

It seems that classical electrodynamics predicts that there will
be no deflection. The electromagnetic field in the laser beam
and the static electric field of the ball do not interact with
each other (E&M theory is linear). On the other hand,
quantum electrodynamics has interactions between charges and photons
(i.e., those responsible for the Compton effect).
My best guess is that these interactions will result in the beam
deflection when passing near charged object or between capacitor plates.

Thanks.
Eugene.


I do not see any theoretical reason why light should not be deflected
by electric (or magnetic) fields. The point is that in the theory of
Classical Electrodynamics the speed of light in vacuum is effectively a
free parameter which can only be determined through experiments. In
this sense it is theoretically possible that the speed of light depends
on the electric or magnetic fields present. If you have a field
gradient this would then produce a kind of refraction effect i.e. light
would be deflected.

I personally think such an explanation could actually explain the well
known 'gravitational bending' because the sun (or other astrophysical
objects) is surrounded by a plasma halo which, due to its radial
inhomogeneity, must be associated with an electric plasma polarization
field gradient (on the other hand, I am not aware of any gravitional
bending observations and experiments where one could rule out the
existence of a plasma halo).

By the way, I do not agree with Murat's interpretation above: it would
be completely inconsistent with Electrodynamics to describe light as a
charged particle in the limit of zero charge and mass (anyway,
charge/mass is not a number but has a physical dimension).

It is true that charge/mass is not a number but has a physical
dimension in the presently used conventional units. However, one
can always measure the electric charge in kilograms at the expense
of changing the numerical value and dimension of the Coulomb
constant k. This then makes charge/mass a dimensionless number
just like (gravitational mass/inertial mass). One should also
note that if charge/mass ratio for light turns out to be 1
experimentally, it does not mean that the actual physical
electric charge of the photon is different from zero...

Murat Ozer


The experiments quoted by Eugene may rule out that light has a charge,
but not necessarily that light is not deflected by electric or magnetic
fields, because, as I indicated above, what one requires for this
'field refraction' is a field gradient (in the same way as one needs a
density gradient for ordinary refraction).

Thomas

http://www.physicsmyths.org.uk