There is something I have to ask. If photons exert no gravitational
force, then how is force conserved? It would seem that if photons are
affected by gravity but don't have gravity to affect others, that this
would lead to an imbalanced equation for force.

Yet, at the same time, if energy had gravity, then that would mean
black holes could form simply from energy itself. This would violate
special and general relativity, since black holes can't form simply
from a subatomic particle going too fast.

It seems that there's a contradiction here. How do we resolve it?

(...Starblade Riven Darksquall...)

Starblade Darksquall wrote in message
om...
There is something I have to ask. If photons exert no gravitational
force, then how is force conserved? It would seem that if photons are
affected by gravity but don't have gravity to affect others, that this
would lead to an imbalanced equation for force.

Yet, at the same time, if energy had gravity, then that would mean
black holes could form simply from energy itself. This would violate
special and general relativity, since black holes can't form simply
from a subatomic particle going too fast.

It seems that there's a contradiction here. How do we resolve it?

In the center of momentum reference frame, which for light
necessarily involves two or more photons, total system energy
gravitates according to M = E / c^2.

For a single photon in the gravitational field of a spherically
symmetric mass distribution, the photon's effective potential
is proportional to [1 / r^3] rather than the [1 / r] proportionality
of the Newtonian potential for a massive particle. Unlike
massive particles, the photon follows a "null geodesic". Old
Man interprets this to mean that a single photon does not
produce a gravitational field. [Old Man]




(...Starblade Riven Darksquall...)