On Sun, Jan 28, 2018 at 6:58 PM, <mix...@bigpond.com> wrote:

This would be true if gravity was actually a force. If OTOH it is merely a
> distortion of spacetime, then as far as the photon is concerned it is just
> going
> "straight ahead". IOW it just follows the shape of the space it is
> traversing.

Another thought experiment for anyone bothered by the assumption of a loss
of gravitational attraction in the conversion of matter/antimatter into

You have an electron-positron pair that annihilate in two different
scenarios, creating 511 keV annihilation photons.  In the first scenario,
they are attracted towards a black hole and annihilate outside of the event
horizon.  The boundary that includes the black hole and the pair of
escaping photons now has less mass and hence less gravitational pull (by
assumption).  Now let the electron and positron stray over the event
horizon at time t=0 and annihilate at time t=1.  At t=0, the black hole now
has M + 1.022 MeV mass.  At t=1, the black hole is back to its previous
mass of M, even though an electron and positron have been added to it, and
even though the annihilation photons have not escaped.

One of the things that is bothering me about the second scenario is that
there probably is no baryonic matter in the black hole to begin with, so it
feels arbitrary to distinguish between the captured annihilation photons
and whatever else is there.  (What if it's all photons?)


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