Re: Curvature of Space

[Leigh Palmer <palmer@sfu.ca>]

> Hi Leigh-
> 	I disagree.
> *********************************************
> The symmetry argument is simple: If there is a force acting on the
> photon due to an electric field, what is its direction? Let me
> point out in advance that a cross product does not have an
> intrinsic direction. That should save some time.
>
> If no direction can be determined then the deflection is nil.
> *********************
> 	If no direction can be determined then the deflections
> must be symmetric around zero.  This, of course, obviates the possibility
> of a classical "force" associated with the electric field.

Deflections must be symmetric around zero, but I will ask what
happens to a single photon in an electric field. The only way
its deflection can be symmetric about zero is for its
deflection to *be* zero. In order for something like the
Stern Gerlach splitting to occur there must be a property of
the photon that the field can hook onto. The only property I
can think of is the angular momentum, and the photon is two-
fold degenerate with respect to that quantum number, so I
guess it is conceivable. The cross product of the angular
momentum with electric field is a vector since the angular
momentum itself is a pseudovector (what I've taken to
calling a "bivector").

OK, you've talked me out of my symmetry argument. Thanks.
Now I have to think harder. If there is a classical effect
then one should look for deflection of a circularly polarized
beam in a direction perpendicular to the plane determined by
the field direction and the propagation direction. The
deflection should reverse when the polarization reverses.

I'm way out of my depth here, but let me ramble for a moment
with semiclassical QED ideas. A photon, I'm told, spends some
of its (our) time as virtual electron-positron pairs. It would
not surprise me to learn that a circularly polarized photon
has an alias as a spin-parallel pair, both particles having
the helicity which would make up the angular momentum of the
photon. In that case the magnetic dipole moment of this beast
would be zero, as would the electric monopole moment. I don't
see a handle for deflection in the lowest order term.

You see what can happen when I get less than four hours' sleep
on a teaching day. Perhaps this will stimulate someone who
knows what he's talking about to suggest a mechanism.

Leigh