If photons can't escape a black hole, how come gravitons can?

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  • #1
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It would seem that they both must observe the laws of General Relativity.
 

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  • #2
Drakkith
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As a force mediating particle, gravitons would come as virtual gravitons, just like virtual photons are the force exchange particles of the EM force. Virtual particles cannot be said to 'travel' anywhere. That is, they aren't created at one particle just to travel to another and 'exchange' forces between them. So one answer to your question is that nothing comes out of the black hole at all. No gravitons move from the black hole to the outside world.
 
  • #3
swampwiz
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So one answer to your question is that nothing comes out of the black hole at all. No gravitons move from the black hole to the outside world.

So if no gravitons move from the black hole, how does gravity work from there?
 
  • #4
Drakkith
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So if no gravitons move from the black hole, how does gravity work from there?

No virtual photons move in between two interacting charged particles either. The idea that virtual particles must move between two particles in order for a force between them to exist is incorrect. Virtual particles don't even 'move' in the normal sense. Unfortunately it's difficult to explain how virtual particles work, as they don't act like normal particles at all. They are better described as transient fluctuations of an underlying field that happen to be described by the same math that describes real particles.

Give this article a read: https://profmattstrassler.com/artic...ysics-basics/virtual-particles-what-are-they/
 
  • #5
lomidrevo
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It would seem that they both must observe the laws of General Relativity.

Graviton is a hypothetical particle in theory of quantum gravity. General Relativity says nothing about gravitons. GR rather describes spacetime as continuum.
 
  • #6
snorkack
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Virtual photons also freely get out the way real photons cannot. A black hole is allowed to have an electric charge.
Is a colour a legal hair of a black hole?
 
  • #7
swampwiz
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Graviton is a hypothetical particle in theory of quantum gravity. General Relativity says nothing about gravitons. GR rather describes spacetime as continuum.

So what you saying is that there is "graviniferous ether" for gravitons?
 
  • #8
Vanadium 50
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So what you saying is that there is "graviniferous ether" for gravitons?

Nobody said such a thing.

Neither photons, gravitons, black holes nor General Relativity behaves in the way you suggest in your opening post.

Fundamentally, the problem with this thread is that even the question was rife with misconceptions, and to make it worse you posted it at an A-level, making people think you want a graduate level explanation.
 
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  • #9
lomidrevo
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So what you saying is that there is "graviniferous ether" for gravitons?

No, I am just saying that within the framework of GR, nothing like graviton exists. Therefore you cannot expect to get any meaningful answer based on "laws of GR". In GR, the gravity is not a force. It is interpreted as a consequence of curved spacetime (a continuum). This is not very compatible with a view that there exists a particle (graviton) that mediates the force of gravity.

The concept of graviton comes from theory of quantum gravity, which is beyond the GR model, and which is not complete, to my best knowledge. Maybe "Beyond Standard Model" is more appropriate section to post your question, to get more involved answers.
 
  • #10
lpetrich
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A black hole's gravitational field is frozen in place, so nothing has to escape it to make its field. Changes in it are a different story, however.

As to gravitons, gravitational waves will propagate like electromagnetic ones, and will be unable to escape from inside the BH's event horizon.
 
  • #11
davenn
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A black hole's gravitational field is frozen in place, so nothing has to escape it to make its field. Changes in it are a different story, however.

No, not correct ... It has a gravitational field just like any other mass
 
  • #12
swampwiz
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A black hole's gravitational field is frozen in place, so nothing has to escape it to make its field. Changes in it are a different story, however.

As to gravitons, gravitational waves will propagate like electromagnetic ones, and will be unable to escape from inside the BH's event horizon.
So you saying that gravitons eminate from mass within the black hole, but those are subject to GR, and so stay within the black hole? I wonder if the gravity waves on the return back (i.e., like an ICBM coming down after reaching maximum altitude within the Earth gravity well) somehow reinforce each other in some type of resonance.
 
  • #13
lpetrich
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Yes, that's it.
 
  • #14
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We have no complete theory of gravitons, so it is a little speculative to talk about them anyway. But the bottom line is that all gravitational effects in GR arise from stress energy in the past light cone.
 
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  • #15
lpetrich
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In the absence of a full quantum theory of gravity, we can quantize perturbations of a classical-limit gravitational field. Even without that, we can work with such perturbations in the classical limit. One finds that they travel on null geodesics, just like photons. This means that if a gravitational wave originates inside a black hole's event horizon, then it will not escape.
 
  • #16
Mister T
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It would seem that they both must observe the laws of General Relativity.
Gravitons are not part of general relativity. General relativity ignores quantum theory and the graviton is a purely quantum particle.
 
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  • #17
davenn
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In the absence of a full quantum theory of gravity, we can quantize perturbations of a classical-limit gravitational field. Even without that, we can work with such perturbations in the classical limit. One finds that they travel on null geodesics, just like photons. This means that if a gravitational wave originates inside a black hole's event horizon, then it will not escape.


You continue to make claims that don't align with the facts, please show some links to reliable sources
 
  • #18
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In the absence of a full quantum theory of gravity, we can quantize perturbations of a classical-limit gravitational field.
Yes, but then the background spacetime is not composed of gravitons since the “gravitons” are perturbations. In other words, a static black hole is not producing its gravity by emitting a stream of gravitons in such an approach.

That is usually the implicit or explicit assumption of questions like this, so I am not sure how valid such perturbative approaches are for answering this type of question. The question and the answer have different assumptions and it is not clear that one set of assumptions is better than the other since there is no fully developed theory to compare them to.
 
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  • #19
Mantuano
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A black hole's gravitational field is frozen in place, so nothing has to escape it to make its field. Changes in it are a different story, however.

As to gravitons, gravitational waves will propagate like electromagnetic ones, and will be unable to escape from inside the BH's event horizon.
As you may know, the only grav-waves detected up today have been originated outside black holes, and neutron star collisions, both from the dissipated energy of their movements, and consequently their gravitatory effects on the spàce-time geometry.

Nobody is talking of waves crossing the black hole horizon from its inner side.
In the same way, the gravity deformation and field differential does not disappear at the outer side of the black hole event horizon, so the answer maybe is that gravity field differential is the force generator and not just a phantom particle which has not even been considered in the RGT.
 
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