Black Holes & Light: Can Gravitational Force Exceed Speed of Light?

In summary: No - nothing would be "zero inertia", because inertia is a measure of the tendency of an object to resist changes in its state of motion. There would be regions of space time where gravity was weaker, but everywhere else in the universe gravity would be the same.
  • #1
Liger20
65
0
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?
 
Space news on Phys.org
  • #2
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?

No - force and speed are different quantities. The force of gravity doesn't have any particular speed.
 
  • #3
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?

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.
 
Last edited:
  • #4
Okay, thanks, that makes sense...
 
  • #5
1 universe.
Billions of galaxies.
Each galaxy contains billions of stars.
Each star has at least one planet orbiting it.
Surely there’s more life out then us, and more intelligent
 
  • #6
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.

If gravity does propagate at c, this would mean that there could be areas of space time that were never "disturbed", wouldn't it? What would be the properties of such localities, zero inertia?
 

1. What is a black hole?

A black hole is a region in space where the gravitational force is so strong that nothing, including light, can escape its pull. It is formed when a massive star collapses in on itself, creating a singularity - a point of infinite density and zero volume.

2. How does a black hole affect light?

A black hole's intense gravitational force warps the fabric of space-time, causing light to bend and slow down as it approaches the event horizon - the point of no return. Once light crosses the event horizon, it cannot escape and is trapped within the black hole.

3. Can the gravitational force in a black hole exceed the speed of light?

No, according to Einstein's theory of relativity, nothing can travel faster than the speed of light. This includes gravitational force. However, near the event horizon of a black hole, the gravitational force is incredibly strong and can cause light to appear to slow down or even stop in relation to an outside observer.

4. Can we see a black hole?

Technically, no. Black holes do not emit any light, so they cannot be seen directly. However, we can observe the effects of a black hole on its surroundings, such as the bending of light or the movement of stars, which allows us to infer the presence of a black hole.

5. How do scientists study black holes?

Scientists use a variety of techniques and tools to study black holes, including telescopes that can detect X-rays and gravitational waves, as well as computer simulations and mathematical models. They also study the effects of black holes on their surroundings, such as the gas and dust they accrete and the stars that orbit them.

Similar threads

Replies
2
Views
745
  • Cosmology
Replies
11
Views
1K
Replies
17
Views
1K
Replies
12
Views
2K
Replies
36
Views
3K
  • Special and General Relativity
Replies
11
Views
558
  • Cosmology
Replies
30
Views
3K
Replies
2
Views
924
Replies
25
Views
2K
Back
Top