Quote:
An additional thought:
.....Consider a black hole, from which no light can escape. It's not that the massless photon is "pulled on" by gravity, it's that the curvature of spacetime is so tight that any path the photon takes curves back inside the black hole......
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Without wishing to come across as pedantic this is only true if the black hole mass is fairly small. The radius of the event horizon is proportional to the black hole mass. For small masses, the radius is close enough to the physical singularity for space-time curvature (and other nasties such as tidal forces) to be significant.
For massive black holes such as the billion plus solar mass at the centre of our galaxy the event horizon is so far out that space-time curvature is very small.
To explain why photons cannot escape from inside the blacks holes horizon irrespective of its mass requires the use of
Minkowski space-time diagrams.
Unfortunately a full blown explanation is beyond the scope of this forum as well as the science forum and probably requires at least third year applied maths or physics to make sense of it.
I'll try to explain it as non mathematically as possible.
Using the attachment as a reference an observer is located in the present on a hypersurface. Anything above the plane is in the observers future, below it is in the observers past.
The light cones are analogous to an intense light flash which starts off as a point initially (in the present) and spreads out as time increases. This is the future light cone. The past light cone is simply running the flash backwards in time.
A photon can also be considered to be an "observer" in this case.
A property of the past and future light cones is that well away from a black hole horizon the cones are aligned "vertically". As a photon approaches a black hole the future light cones progressively tilts towards the event horizon. On the event horizon, the photons future light cone is inside the horizon, the past light cone points outwards. Essentially what it means for any object, photon or otherwise inside the event horizon, it would have to travel backwards in time in order to escape.
For an observer outside the horizon this is course will never be seen.
Regards
Steven