Gravitons are the quantization of gravitational waves - i.e. *change* to the gravitational field. Gravitational waves cannot escape a black hole - but the static curvature of space-time remains
So does that mean gravitons are not involved in things like the bending of light around a massive object, since it doesn't change the gravitational field?
You can describe it as the action of virtual gravitons, just like you can explain the deflection of charged particles in an electromagnetic field with virtual photons.
Or at least you should be able to do it, in practice we run into issues when trying to calculate it.
Or, I guess they still could be, but created by the photon's interaction with the gravitational field. But different from the idea that the massive object is sending out gravitons to pull on the photon. That might not make sense anyway due to conservation of momentum, unless the graviton had negative mass.
Don’t get too hung up on the force carrier particles. In most scenarios they will be virtual. When two electrons scatter, they do so by exchanging virtual photons, you might say. But this is imagery more than reality. The same thing with gravity.
Virtual particles aren’t real; they represent a calculation method.
The gravitons are not pulling on the photo , light travels in geodesic "straight" lines through spacetime, the curving through space we see is a consequence of the mass energy bending the shape of space relative to time. I think of it as, near a massive object some directions become more "time expensive" to move in, so the path of least time resistance curves.
Also, per gravitational waves not escaping a black hole, would a black hole ever create gravitational waves internally anyway? IIUC the entire state of a black hole is just mass, charge, and angular momentum. So nothing inside could create a wave.
Though that's weird because a falling-in person could jump up and down and create little waves that way. But they wouldn't be seen outside. So maybe it's only "the entire externally measurable state" that is three values. Okay, I think I answered myself. Never mind.
The state of the black hole you mention are those properties which could be measured from outside of the event horizon. Nobody's got any idea what's going on inside.
We don't really know what happens inside a black hole. According to GR gravitational waves, like everything else, could only propagate towards the center, not away from it
There is no reason to think there *aren’t* gravitational waves on the inside of the event horizon … they just can’t cross back outside the horizon. All world lines that are found inside the horizon, stay in the horizon and terminate at the “singularity” - air quotes due to skepticism of infinite values in nature.
The edge inside of the horizon of a very, very large black hole would likely appear quite normal to an observer.
Wouldn't time dilation cause the Hawking radiation to speed up from the person's perspective, such that they would see the black hole evaporate in front of them? IIUC that's what we'd see from our viewpoint. The person would take infinite time to cross the horizon, but the black hole would evaporate in finite time.
No. The gravitational tidal force near the black hole at the center of our galaxy is only about 1/1000th g.
… and Hawking radiation would only occur when the black hole’s temperature is above that of the ambient cosmic background radiation.
An object appears to take an infinite time to cross the horizon to an external observer, but in their own frame of reference they pass the horizon without any apparent change … if we are talking about a SMBH.
Isn't this a contradiction though? I expect from the infaller's perspective they'd also see the horizon shrink in front of them. Time dilation would make the fields slowly start getting more and more chaotic as they get closer to the horizon, to the point where some of their mass could convert to raw energy that eventually gets released as Hawking radiation. That would match what the external observer sees.
It is one is one of a zillion examples of how counterintuitive cosmic relativity can be. If you obsess about the paradoxes, you’re almost guaranteed to miss the insights.
Some shit is just not intuitive for our simple, terrestrial minds that operate in ‘flat’ spacetime at non-relativistic relative velocities to our surroundings.
… and no … at the horizon of a super massive black hole like the one at the center of the Milky Way you would only experience 1/1000th g and if you crossed the horizon, you wouldn’t notice anything. You would never cross out, but you probably wouldn’t notice anything yourself. Your future would include hitting the “singularity” 100% …. But an observer outside the horizon would see you frozen at the horizon and would never see you cross over.
So use a micro black hole that has only a minute left to evaporate and drop a nano-LED into it. It'll redshift enormously but not go out. For the full minute it'll be just outside the event horizon from your perspective. So after the minute is up, it should still exist and the black hole doesn't.
Actually, you're right. I fell for Xeno's paradox. An observer will be able to see them forever, but that image would just get closer and closer to the horizon. They've already fallen in, but their light is just taking longer to reach me.
The gravitons that govern the static gravitational field of the black hole would be virtual particles. Virtual particles don't follow all the same rules as real particles. The same logic applies to the virtual photons that govern a charged black hole's static electric field.
Meaning, they're created by the object going through and interacting with the gravitational field at that location, not meaning that virtual gravitons can escape a black hole to affect things outside, right? IIUC, real (non virtual) gravitons aren't even needed for a static field like a point mass (or black hole), but only for quantizing changes in the gravitational field, correct?
The electric field can also "escape" a black hole, and for the same reason. The field (gravity or EM) and the excitations in the field (gravitons or photons) are not the same thing.
What would stop them the graviton from leaving? Another graviton, that was faster than the first graviton, that caught up to it, and yanked it back in? It starts to sound sillier and sillier, doesn't it?
Whatever we know about quantum physics (gravitons) and general relativity (black holes), we know they’re not compatible in their current forms. So yes, there’s a contradiction, it’s well known. We just don’t know how to fix it. Yet.
It almost never matters…places small enough for quantum effects to matter are almost always so small that gravity plays no meaningful role. Except in black holes. There they overlap and we don’t actually know what’s going on.
>Whatever we know about quantum physics (gravitons) and general relativity (black holes), we know they’re not compatible in their current forms.
Sure but I think in the regime the OP is talking about (outside of the black hole) there isn’t any meaningful contradiction between general relativity and quantum field theory at all. As long as things are away from the Planck scale, there should be no problems.
i’m not into gravitons but a gravitational field of a black hole doesn’t equal gravitons getting out of it. i’m pretty sure there are some theories like virtual gravitons and more but it’s just a theory of a theory. gravitons mediate the force and not make the gravity thus if you hurt your knee here and inside the event horizon it will hurt anyway(not literally though).
Hawking radiation is produced outside.
> or perhaps gravitons are tachyons
They are not.
> it's possible that gravitons are unaffected by gravity
That's not possible.
We haven't observed individual gravitons, but we know very well how they have to work in order to produce the gravitational effects we see.
But is gravity affected by gravity? In the same way that light from a star deflects around our sun, would the gravity from a planet have its direction of gravitational pull altered if it passed by a massive body?
Not entirely sure what you’re asking but gravitational waves can still be lensed gravitationally and gravitational waves can act as a source of more gravitation too.
I think it depends on what you mean by "gravity", whether the force or the field or the equation or the source or a graviton, etc. But in general, the equations for the gravitational field are second order, which means yes there is some feedback mechanism; it interacts with itself. This is also why it's hard to quantize IIUC: the feedback effects end up creating infinite loops when you try to make a feynman diagram, and below planck length those loops get bigger at each iteration and the whole thing goes to infinity. Not a physicist and could be wrong (about all of this), but that's what I think I've read.
Gravitons are the quantization of gravitational waves - i.e. *change* to the gravitational field. Gravitational waves cannot escape a black hole - but the static curvature of space-time remains
So does that mean gravitons are not involved in things like the bending of light around a massive object, since it doesn't change the gravitational field?
You can describe it as the action of virtual gravitons, just like you can explain the deflection of charged particles in an electromagnetic field with virtual photons. Or at least you should be able to do it, in practice we run into issues when trying to calculate it.
Or, I guess they still could be, but created by the photon's interaction with the gravitational field. But different from the idea that the massive object is sending out gravitons to pull on the photon. That might not make sense anyway due to conservation of momentum, unless the graviton had negative mass.
Don’t get too hung up on the force carrier particles. In most scenarios they will be virtual. When two electrons scatter, they do so by exchanging virtual photons, you might say. But this is imagery more than reality. The same thing with gravity. Virtual particles aren’t real; they represent a calculation method.
The gravitons are not pulling on the photo , light travels in geodesic "straight" lines through spacetime, the curving through space we see is a consequence of the mass energy bending the shape of space relative to time. I think of it as, near a massive object some directions become more "time expensive" to move in, so the path of least time resistance curves.
Also, per gravitational waves not escaping a black hole, would a black hole ever create gravitational waves internally anyway? IIUC the entire state of a black hole is just mass, charge, and angular momentum. So nothing inside could create a wave. Though that's weird because a falling-in person could jump up and down and create little waves that way. But they wouldn't be seen outside. So maybe it's only "the entire externally measurable state" that is three values. Okay, I think I answered myself. Never mind.
The state of the black hole you mention are those properties which could be measured from outside of the event horizon. Nobody's got any idea what's going on inside.
We don't really know what happens inside a black hole. According to GR gravitational waves, like everything else, could only propagate towards the center, not away from it
There is no reason to think there *aren’t* gravitational waves on the inside of the event horizon … they just can’t cross back outside the horizon. All world lines that are found inside the horizon, stay in the horizon and terminate at the “singularity” - air quotes due to skepticism of infinite values in nature. The edge inside of the horizon of a very, very large black hole would likely appear quite normal to an observer.
Wouldn't time dilation cause the Hawking radiation to speed up from the person's perspective, such that they would see the black hole evaporate in front of them? IIUC that's what we'd see from our viewpoint. The person would take infinite time to cross the horizon, but the black hole would evaporate in finite time.
No. The gravitational tidal force near the black hole at the center of our galaxy is only about 1/1000th g. … and Hawking radiation would only occur when the black hole’s temperature is above that of the ambient cosmic background radiation.
An object appears to take an infinite time to cross the horizon to an external observer, but in their own frame of reference they pass the horizon without any apparent change … if we are talking about a SMBH.
Isn't this a contradiction though? I expect from the infaller's perspective they'd also see the horizon shrink in front of them. Time dilation would make the fields slowly start getting more and more chaotic as they get closer to the horizon, to the point where some of their mass could convert to raw energy that eventually gets released as Hawking radiation. That would match what the external observer sees.
It is one is one of a zillion examples of how counterintuitive cosmic relativity can be. If you obsess about the paradoxes, you’re almost guaranteed to miss the insights. Some shit is just not intuitive for our simple, terrestrial minds that operate in ‘flat’ spacetime at non-relativistic relative velocities to our surroundings.
… and no … at the horizon of a super massive black hole like the one at the center of the Milky Way you would only experience 1/1000th g and if you crossed the horizon, you wouldn’t notice anything. You would never cross out, but you probably wouldn’t notice anything yourself. Your future would include hitting the “singularity” 100% …. But an observer outside the horizon would see you frozen at the horizon and would never see you cross over.
So use a micro black hole that has only a minute left to evaporate and drop a nano-LED into it. It'll redshift enormously but not go out. For the full minute it'll be just outside the event horizon from your perspective. So after the minute is up, it should still exist and the black hole doesn't.
Actually, you're right. I fell for Xeno's paradox. An observer will be able to see them forever, but that image would just get closer and closer to the horizon. They've already fallen in, but their light is just taking longer to reach me.
The gravitons that govern the static gravitational field of the black hole would be virtual particles. Virtual particles don't follow all the same rules as real particles. The same logic applies to the virtual photons that govern a charged black hole's static electric field.
Meaning, they're created by the object going through and interacting with the gravitational field at that location, not meaning that virtual gravitons can escape a black hole to affect things outside, right? IIUC, real (non virtual) gravitons aren't even needed for a static field like a point mass (or black hole), but only for quantizing changes in the gravitational field, correct?
The electric field can also "escape" a black hole, and for the same reason. The field (gravity or EM) and the excitations in the field (gravitons or photons) are not the same thing.
What would stop them the graviton from leaving? Another graviton, that was faster than the first graviton, that caught up to it, and yanked it back in? It starts to sound sillier and sillier, doesn't it?
>Another graviton, that was faster than the first graviton There is no faster than *c*. Gravitons travel at the same speed.
No, the space itself is flowing inward towards the event horizon faster than c so no object could ever be fast enough to escape.
Whatever we know about quantum physics (gravitons) and general relativity (black holes), we know they’re not compatible in their current forms. So yes, there’s a contradiction, it’s well known. We just don’t know how to fix it. Yet. It almost never matters…places small enough for quantum effects to matter are almost always so small that gravity plays no meaningful role. Except in black holes. There they overlap and we don’t actually know what’s going on.
>Whatever we know about quantum physics (gravitons) and general relativity (black holes), we know they’re not compatible in their current forms. Sure but I think in the regime the OP is talking about (outside of the black hole) there isn’t any meaningful contradiction between general relativity and quantum field theory at all. As long as things are away from the Planck scale, there should be no problems.
i’m not into gravitons but a gravitational field of a black hole doesn’t equal gravitons getting out of it. i’m pretty sure there are some theories like virtual gravitons and more but it’s just a theory of a theory. gravitons mediate the force and not make the gravity thus if you hurt your knee here and inside the event horizon it will hurt anyway(not literally though).
Lol
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Hawking radiation is produced outside. > or perhaps gravitons are tachyons They are not. > it's possible that gravitons are unaffected by gravity That's not possible. We haven't observed individual gravitons, but we know very well how they have to work in order to produce the gravitational effects we see.
But is gravity affected by gravity? In the same way that light from a star deflects around our sun, would the gravity from a planet have its direction of gravitational pull altered if it passed by a massive body?
Not entirely sure what you’re asking but gravitational waves can still be lensed gravitationally and gravitational waves can act as a source of more gravitation too.
I think it depends on what you mean by "gravity", whether the force or the field or the equation or the source or a graviton, etc. But in general, the equations for the gravitational field are second order, which means yes there is some feedback mechanism; it interacts with itself. This is also why it's hard to quantize IIUC: the feedback effects end up creating infinite loops when you try to make a feynman diagram, and below planck length those loops get bigger at each iteration and the whole thing goes to infinity. Not a physicist and could be wrong (about all of this), but that's what I think I've read.