Expert: Jayendra Upadhye - 2/13/2005

Question
If nothing can escape a black hole, where does the gravity come from?

(This question is intentionally naive. Which fundemtal forces 'escape' black holes? What does that distinction tell us about the nature of black holes?)

Answer
Hi John,
Strange that i answered your question yesterday but it somehow did not register as answered and appears pending today!
So I will say what i said yesterday.
Hopefully this time it will go thru.

Actually, relativity, and strong and weak fundamental forces is not my cup of tea, especially what happens inside the event horizon of the hole.

But we can attempt to understand things in another fashion.

1 - Say a planet is orbiting a massive star that is about to go supernova, at many A.U from it.
   On fine day, the star goes supernova, and leaves behind a black hole.
   The planet's orbit is somewhat disturbed by the event (change of mass of parent star due to mass ejected as supernova ejecta), and also somewhat due to the fury of the blast!
   Eventually we find the planet is still held captive by the gravity of the hole.
   This is so, because gravity is a "point field" like the electrostatic and magnetic fields.
   The difference with teh electrostatic field being there is no magnetic mon-pole and no gravitational +ve/-ve polariy we know of.
   Otherwise like the other two fields, gravity is a conservative field too.
   Due to absence of "point of origin", we say that the gravitational field is simply warping of space and time when the curvature is very strong, centered around the "cause of warp".
   But gravity does not "emanate" from the hole in the sense that electromagnetic disturbances such as light does.
   So there is no question of gravity "bending in on itself" and leaving the environs of the hole outside the event horizon, "gravity-less".
   The warping of space persists as long as the "cause" (black or white!) is there.
   This is the reason, that gravity continues to be felt by objects in the balck holes vicinity, and which eventually become part of the accretion disk.

The question of strong (but extremely short range) fundamental forces does not arise here, as they come into play at atomic levels only, while dealing with subatomic particles.

Does my explanation sound ok?
Jayen