Find Gravitational Force of Photons: Equations & Potential Energy

[Dmitry67]

Finally, in very early Universe the density of matter was negligible in comparison with density of radiation. So at some époque, most of the gravity of the Universe came from photons, slowing down the expansion.

 

[Dale]

Agreed to all, but here's the relativity forum. Please understand my statements as referring to a wave packet with negligible spatial extension, not zero extension. I think that's what is meant by a "photon" in a classical relativistic thought experiment (a null geodesic).

For such a pulse of light the correct spacetime is the http://en.wikipedia.org/wiki/Aichelburg%E2%80%93Sexl_ultraboost" that I mentioned earlier.

 

[sweet springs]

Hi.

A group of photons surely generates gravity. e.g. electromagnetic radiotion closed in a hollow body has energy called black body radiation. Its electromagnetic energy momentum tensor appear in the right hand side of Einstein's gravity equation. QM says that photon wavelength lamda gives its position uncertainty. So the gravity source position has uncertainty of wavelength.
Schwartzshild's radius of photon is 2Gh / (c lamda). In the case the disance between the two photons are much larger than both lamda and Schwartzshild's radius, I expect a photon motion influenced by the gravity generated by another photon can be evaluated approximately at least. In other cases e.g. two photons are in the same wave train of a laser beam we must face unknown quantum gravity.

Regards.