Quote:
Originally Posted by sjastro
A couple of issues here.
(1) Since photons are there own anti-particles a photon (antiphoton) will behave the same in the field of matter (antimatter). In other words both will travel along null geodesics.
(2) I'm not sure why it is assumed antimatter will produce a "divergent" spacetime.
Consider the spacetime around a large mass antimatter object. A small mass antimatter object will move in a geodesic path equivalent to both objects being made from matter. In other words spacetime is "convergent".
Spacetime is still "convergent" if we replace the small antimatter mass with a small mass since spacetime curvature is determined by the larger mass.
What happens to spacetime if we have small antimatter and matter masses in the presence of the larger antimatter (or matter) mass?
For those that know GR if both masses are either antimatter or matter, Einstein field equations simply reduce to the Ricci tensor R(u,v)=0.
In the case of a large antimatter mass/ small matter mass (or vice versa) perhaps we should consider what happens if we have a large and small mass where both masses are carrying a postive or negative charge. We have a scenario that "resembles" the hypothetical matter/antimatter repulsive force.
In this case we a strong electromagnetic field acting with the gravitational field and a repulsive Lorentz force acting on the smaller mass.
The electromagnetic field becomes part of the field equations.
The field equations take the form G(u,v) = (-8*pi*G)/c ^2*T(u,v)+F(....)
G(u,v) is the Einstein tensor.
G is the gravitational constant.
T(u,v) is the matter energy tensor.
F(.....) is a long winded term for an electromagnetic tensor. 
I would imagine the the repulsive force between matter and anti matter would be treated in a similar way. 
Regards
Steven |
Normally, everything you have said would be the case, but what I and Rob said is what if the photons were behaving as normal photons and not as antiphotons, for whatever reasons, within that region of antimatter space, as the journal article mentioned. If there was this repulsive gravitational force present, because the CPT symmetry of those photons would be opposite to the region they were in, they would act in accordance with that...i.e. they would move in divergent paths within the antigravitational field (in their experience), away from the lensing mass. Off course, antiphotons would behave normally and you'd see the same results of the lensing that we would. However, that's not what we see, so the theory proposed is just a simple thought experiment and has no basis in observation.