"Jeff Root" <jeff5@xxxxxxxxxxxx> wrote in message
> Greg Neill replied to Jeff Root:
> >> > photons are practically oblivious to electric and
> >> > magnetic fields; photon-photon interactions have an
> >> > incredibly small cross section. The interaction,
> >> > according to quantum theory is, if memory serves, a
> >> > third order effect which is practically nil.
> >> How might I coax two photons to interact?
> > The simplest way is to have them do so in the
> > presence of a particle. Alone, two photons very
> > rarely interact.
> What maximizes the probability of two photons interacting
> without a particle? They both have to exist at the same
> time. What else? Should they collide perpendicularly?
> Head-on? With the fields aligned? Or opposed? Or...?
I'm no expert in Quantum Theory, but my gut feeling
would be to duplicate the conditions of a matter-
antimatter annihilation in reverse, that is, have
two equal energy photons meet head-on. I would
welcome input from more knowledgeable sources.