The discussion revolves around the nature of gravitational force in relation to black holes and the speed of light. Participants explore whether the gravitational force of a black hole can exceed the speed of light, particularly in the context of light being unable to escape a black hole's gravitational pull. The conversation includes conceptual clarifications and speculative reasoning about gravitational fields and their properties.
Participants express differing views on the relationship between gravitational force and the speed of light, with no consensus reached on the implications of black holes on this relationship.
The discussion includes assumptions about the nature of gravitational fields and their interaction with light, which remain unresolved. The implications of gravitational propagation and its effects on spacetime are also not fully explored.
Liger20 said:Black holes exert such a powerful gravitational force that even light cannot escape its grip. But doesn't this imply that the rule about how nothing can exceed the speed of light has been violated? If a black hole can suck in light, then doesn't that mean that the gravitational force of a black hole can exceed the speed of light?
Liger20 said:Black holes exert such a powerful gravitational force that even light cannot escape its grip. But doesn't this imply that the rule about how nothing can exceed the speed of light has been violated? If a black hole can suck in light, then doesn't that mean that the gravitational force of a black hole can exceed the speed of light?
marcus said:Mathman gave you a correct answer. However I am interested in what I think is your mental picture. It seems as if you imagine the Force having a speed, as if it consisted of little force particles running after the light particles, trying to catch them! And these force particles have certain speed, limited by the usual speed limit.
If the Force police actually WAITED until a light particle tried to make a run for it, then I think you would be right! The force would never catch up and haul them back!
But actually the force is embodied in the GRAVIATIONAL FIELD that is already out there around the black hole.
You can think of it either as a force field or as a curvature of the GEOMETRY of spacetime, which GUIDES almost every outgoing lightray back into the hole.
With almost no exception, all the geodesics---the straightest lines light can follow in the curved geometry---lead back to the hole.
Or if you don't like geometry, think "force", but it is the same in gravity case. Changes in the field do propagate like waves, it is thought, probably at the speed of light. But for a steady black hole the field is not changing and it doesn't have any speed. THE FIELD IS ALREADY OUT THERE ready to send the light back.