How does blackhole gravity affect anything?

[monitoradiation]

Okay, here's my question - in my (very) rudimentary understanding of modern physics. each of the 4 fundamental forces have an associated particle. Like Gluons, Bosons, and Photons mediate the other three forces, Gravitons are the elementary particles associated with conveying gravity.

Now the question is:

If nothing is able to escape the event horizon of black holes, how does gravity of a black hole reach outside of the event horizon?

 

[Anachronous Rex]

Okay, here's my question - in my (very) rudimentary understanding of modern physics. each of the 4 fundamental forces have an associated particle. Like Gluons, Bosons, and Photons mediate the other three forces, Gravitons are the elementary particles associated with conveying gravity.

Now the question is:

If nothing is able to escape the event horizon of black holes, how does gravity of a black hole reach outside of the event horizon?

I'm fairly sure that the existence of gravitons has not been demonstrated.

 

[monitoradiation]

Righto.

I forgot to say that hypothetically, how would it work?

 

[Anachronous Rex]

Righto.

I forgot to say that hypothetically, how would it work?

I'm not sure if gravitons would themselves be subject to gravity either... but I'm really out of my element here...

 

[Pulsar]

I think it has to do with quantum tunnelling: some gravitons would be able to tunnel through the potential barrier.

 

[SynapticMisfire]

Okay, here's my question - in my (very) rudimentary understanding of modern physics. each of the 4 fundamental forces have an associated particle. Like Gluons, Bosons, and Photons mediate the other three forces, Gravitons are the elementary particles associated with conveying gravity.

Now the question is:

If nothing is able to escape the event horizon of black holes, how does gravity of a black hole reach outside of the event horizon?

Gravity is poorly understood at the moment, but you might find some answers here:

http://www.astronomycafe.net/qadir/q756.html

 

[Neil86]

Firstly I am only a physics student not a graduate so there is probably someone lurking with a better idea than me.

Technically speaking boson is the name for the group of particles that are force carriers not a specific force carrier but that is not important to the argument.

Correct, gravitons have not actually been proven to exist, maybe they don't and the point is moot.

There is an idea that since the time dilation effect means an outside observer never sees an object pass over the event horizon so for a distant observer the gravity is actually emitted from outside the event horizon, but this explanation has its flaws and one I can think of is that any distant observer cannot see all of the mass that fell in so should observe less gravity.

I am not satisfied by the quantum tunnelling explanation because I would expect it to mean not all gravity escapes and black holes appear lighter than they are, with the effect becoming more pronounced as the black hole gains mass.

There is also an idea based on virtual particles which I find less than satisfying, virtual particles spontaneously appear and then disappear within such a short time frame that the universe 'doesn't notice' but may interact with real particles within this timeframe, but again I have not seen anything on the subject with enough detail to explain how black holes of a given radius display the expected mass.

Or if you want a short answer, I don't think anyone actually knows yet.

 

[Nelson]

I don't know enough about GR to fully answer this question, but I think the short version is:

Gravitons are not subject to the gravitational force. Gravitons don't interact with other gravitons. Stated another way, gravitons do not follow the curvature of space-time, rather they DEFINE space-time. Gravity can't be lensed or Doppler shifted. It doesn't behave in the same way as electromagnetism. This is why it makes more sense to me to think of gravity is actual distortions in space-time rather than a stream of particles, or waves.

 

[monitoradiation]

Thanks Neil and Nelson <3 Question has been partly answered :3

 

[DeathofSpeech]

Okay, here's my question - in my (very) rudimentary understanding of modern physics. each of the 4 fundamental forces have an associated particle. Like Gluons, Bosons, and Photons mediate the other three forces, Gravitons are the elementary particles associated with conveying gravity.

Now the question is:

If nothing is able to escape the event horizon of black holes, how does gravity of a black hole reach outside of the event horizon?

The short but messy explanation goes something like this I believe.
Gravity accompanies a relativistic distortion in spacetime.
Whether gravity IS the distortion or whether it causes the distortion, I don't think is quite clear. We can measure gravity but we still have no really good universally accepted explanation for the mechanism. I think we might be close (that is the pedestrian We, I'm just a spectator)... time will tell.

The result though is that at the event horizon, the only way to leave is to go backward in time.
The event horizon is not a physical surface, but is the radius from the singularity at which spacetime gains an irreversible direction for time. Returning to the outside, would require moving backward in time as well as physically through space.

It is similar to falling down a well in 4 dimensions. The further you fall the further the top of the well recedes into the past. Climbing out of a normal well involves moving forward in time as you progress upward out of the well. With a black hole however climbing upward still carries you forward in time, further into the black hole. If you moved as fast as possible, C, you would still be moving forward in time into the black hole. The longer it took to climb up, the deeper into the well you would fall. If the fastest you could climb up was the speed of light, the well would still get deeper faster than you could climb out.
Whether gravity is a spacetime distortion, or the spacetime distortion has some other underlying cause doesn't really matter. The distortion only becomes the event horizon at the point that the well gets deeper faster than light can climb out, but the distortion in spacetime also extends away from the black hole rather like a funnel.

Take a household funnel and make a mark in the conical portion and let's just call that the event horizon. You might be able to leave the funnel so long as you never pass below that point, but the funnel still slopes toward the event horizon even outside the event horizon.

Spacetime like the funnel, still slopes inward toward the event horizon and the event horizon becomes sort of like the mark inside that kitchen funnel. It is only the point that once you pass it you can't come back. A statement then that a static gravity well has a "speed." would be like saying "Speed of Funnel." The funnel doesn't have to move to have an inward slope. It is unlike the kitchen funnel though in that the slope inward extends in all directions at once.

I hope I've made a fair account of my answer and that it is more helpful than confusing.
Good question though and in all probably better than my answer.

 

[simonecuttlefish]

in my (very) rudimentary understanding of modern physics.

I'd like to know 1/2 what you do I don't even know why black holes even work. Like, when a star collapses, how does it magically end up with enough gravity to suck light/time/it's surrounding solar system into it, if it didn't have that much gravity in the 1st place. And even if it did "eat" it's local planets, then the sum total gravity wouldn't be any stronger than what was there before the star collapsed, so why do they start eating everything. Or perhaps I pay too much attention to special effects from dumb movies.

 

[SynapticMisfire]

in my (very) rudimentary understanding of modern physics.

I'd like to know 1/2 what you do I don't even know why black holes even work. Like, when a star collapses, how does it magically end up with enough gravity to suck light/time/it's surrounding solar system into it, if it didn't have that much gravity in the 1st place. And even if it did "eat" it's local planets, then the sum total gravity wouldn't be any stronger than what was there before the star collapsed, so why do they start eating everything. Or perhaps I pay too much attention to special effects from dumb movies.

An object will experience the greatest acceleration due to gravity at the surface of the Sun, and if it enters the Sun, the gravitational acceleration will decrease, since the deeper it goes, the less mass there is to pull it into the Sun and the more mass there is on the other side of it, pulling it in the opposite direction, and pulling at it from the sides. If the object reached the core of the Sun, it would experience no gravitational acceleration, since the Sun's mass would be pulling on it equally from all directions.

If the Sun collapsed into a black hole (which it won't), the gravitational force acting on the rest of the objects in the solar system would remain unchanged; the Earth and all the other planets would continue in their orbits just as they had done when the Sun was an ordinary star and wouldn't be sucked in and 'eaten', however an object which passes the point where the surface of the Sun used to be would still have the entire mass of the Sun pulling it in the direction of the black hole, rather than having a portion of that mass pulling it in the opposite direction and from the sides.

Thus, instead of the gravitational acceleration decreasing as the object approaches the black hole, it keeps getting stronger until eventually even light is unable to escape.

For an object at the surface of the Sun, the gravitational acceleration would also be reduced by the fact that some of the mass of the Sun would be 1,392,000km away, due to the large size of the Sun, and would have less gravitational pull than mass that was closer to the object. With a black hole, it's possible to get much closer to all of the mass at once, rather than only being able to get close to some of the mass.

*Edit* The gravitational acceleration would be greatest at the surface of the Sun if the Sun was of uniform density, but since it gets denser towards the centre, the greatest acceleration will be at a certain depth inside it.

 

[AndromedasWake]

Okay, here's my question - in my (very) rudimentary understanding of modern physics. each of the 4 fundamental forces have an associated particle. Like Gluons, Bosons, and Photons mediate the other three forces, Gravitons are the elementary particles associated with conveying gravity.

Now the question is:

If nothing is able to escape the event horizon of black holes, how does gravity of a black hole reach outside of the event horizon?

I can see there have been many answers to this question already. I just wanted to add a couple of points.

The first is that in GR, there is no inconsistency with gravity "escaping" a black hole. Treating the gravitational field as spacetime curvature gives you a solution for the field around the black hole - the source - which just exists. In GR the gravity does not need to radiate off the surface to be felt by an object outside the black hole.

This treatment is elegant, but obviously leads to the counter intuitive solution that space is somehow changing shape. Of course if gravitational waves are detected (which propagate like EM radiation in an EM field) then Einstein's view of space as a gravitational field will once again prove to be the most accurate. The theory does not need to provide any real ontology of space to describe its relationship to mass, but we do know that this classical treatment of black holes is incomplete, since black holes themselves are gravitational singularities (read: unsolvable regions of a gravitational field)

Secondly, and more relevant to your question, is quantum mechanics. Invoking a graviton particle is one solution, and if it's correct, then the quantum description will be very similar to that of the EM radiation emitted by a charged black hole. In this case, virtual particles are free to flip-off the laws of nature (as long as nature doesn't notice, and nature's awareness is set by the Uncertainty Principle), cross over the event horizon like it doesn't exist and mediate the electromagnetic force.

It's silly, but it's correct. And that's quantum mechanics for you.

 

[Master_Ghost_Knight]

I allways taught that if you used the graviton as the hypotesised solution of quatum mechanics then GR sort of takes the bin since gravity is now caused by a carrier particle instead of a destortion of space. And with quatum mechanics blackholes could eventualy let somestuff comeout of the blackhole (since gravity is a descrete event) where as in GR if you travel trough conventional space you are just stuck there.

 

[AndromedasWake]

I allways taught that if you used the graviton as the hypotesised solution of quatum mechanics then GR sort of takes the bin since gravity is now caused by a carrier particle instead of a destortion of space. And with quatum mechanics blackholes could eventualy let somestuff comeout of the blackhole (since gravity is a descrete event) where as in GR if you travel trough conventional space you are just stuck there.

Well, this is part of the problem. Even if a good quantum description of gravity is obtained, it will need to be compatible with GR, which has the monopoly on large scale observations. This is the problem with cobbling together theories which apply at radically different scales. There is certainly progress being made in QM to determine the boundary between the quantum domain and the classical domain (see decoherence) but due to the existence of that boundary, it is necessary to have two formulations of gravity and find some kind of unification. This by no means makes the current work useless. Whatever supplants our current models of gravity will look back on QM and GR as necessary starting points, as they provided the insights which describe gravity to a first, second or third approximation.

Remember that quantum mechanics provides loopholes for things like virtual particles, but that's precisely the reason why it's problematic. Virtual particles are an attempt to develop an intuitive understanding of certain quantum interactions, but the process has not been realised. Likewise, GR separates gravity from the other forces by its very treatment of space and time, which is only possible to visualise geometrically. In other words, we can talk about the distortion of geometry, but not the substance of space (at least not yet). New theories of particles physics such as String or E8 might be able to provide a consistent ontological description of matter/energy/space and the way it interacts. That's what makes these theories very important.

On the other hand, it could be that what's really going on is simply too strange to work out, but it's not in the interest of any pragmatic scientist to adopt that position.

 

[simonecuttlefish]

To SynapticMisfire

Fantastic. Thank you. I had not thought about the gravitational pull of an object being spread over the distance across the object, thus lowering the effect of the gravity being exerted by it's 'furthest' edge on something on the other side ............ if I got that right. Thanks again, and my apologies to the OP monitoradiation for asking this here and not starting another thread.

 

[monitoradiation]

To SynapticMisfire

Fantastic. Thank you. I had not thought about the gravitational pull of an object being spread over the distance across the object, thus lowering the effect of the gravity being exerted by it's 'furthest' edge on something on the other side ............ if I got that right. Thanks again, and my apologies to the OP monitoradiation for asking this here and not starting another thread.

No need to apologize :3 Some interesting points have been raised in addition to answering my OP.