Black Holes: Do they excert gravitational influnce?

[Obelix]

"Weird question!" you are likely to say. Kindly follow me for a moment:

 

Suppose a Quantum Theory of Gravity does hold. Then, gravitational influence of a body (call it B1) on another (call it B2) would be excerted by means of a shower of gravitons (virtual partices) B1 would emit, which would transfer momentum and energy to B2. And vice versa.

 

Those gravitons (if they trully exist) are supposed to be emitted by the MASS of B1...Any objections so far?

 

Suppose however that B1 undergoes gravitational collapse (e.g., if it is a red supergiant after the supernova phase) causing its mass to shrienk within its Schwarzschild Radius, i.e. confine itself within an "event horizon", thus becoming a Black Hole. From that point on, if the mass of B1 (now enveloped by an "event horizon") emitted any gravitons, THEY WOULD NOT BE ABLE TO MOVE OUTSIDE THAT "EVENT HORIZON" OF THAT BLACK HOLE. How would then that Black Hole excert any gravitational influence on stars, etc. outside its "event horizon"???

 

It is obvious that Black Holes (at least the ones supposed to have been observed - if they ARE indeed Black Holes!) DO excert gravitational influence on other bodies, resulting in the formation of "accretion disks" and "jets". What are we to conclude? That Gravity HAS to be described in terms of a Geometry of Spacetime ("Geometrodynamics") whereas a Quantum Theory of Gravity is impossible? Would Hawking radiation suffice for the gravitational interraction? Anything else?...

 

C'mon, make suggestions!!!

[iNow]

First, what's with the font again? I thought we'd made progress there...

 

Second, a blackhole exerts the same gravitational influence as a star of equal mass.

 

Third, I was unaware that quantum gravity had been worked out. You seem to be making several conclusions based on these supposed premises of quantum gravity. Do you have a source or peer-reviewed citation for the workings of quantum gravity? Again, I'm surprised I haven't yet heard of this amazing step forward in cosmology.

 

My concern is that you may have begun with false premises, and hence any conclusions you draw will also be false.

[Cap'n Refsmmat]

I'd imagine that gravitons, as mediators of the gravitational force, wouldn't be influenced by their own force -- i.e. gravity isn't affected by gravity.

 

That's just an uneducated guess, though.

 

iNow: I suggest you read the Wikipedia article for a little background. Gravitons are indeed hypothetical, but the question still makes sense to me.

[Obelix]

First, what's with the font again? I thought we'd made progress there...

 

Aw, c'mon! I LOVE this font! Is it so horrible to you?

 

Second, a blackhole exerts the same gravitational influence as a star of equal mass.

 

That was precisely what I wrote in the last paragraph above.

 

Third, I was unaware that quantum gravity had been worked out. You seem to be making several conclusions based on these supposed premises of quantum gravity. Do you have a source or peer-reviewed citation for the workings of quantum gravity? Again, I'm surprised I haven't yet heard of this amazing step forward in cosmology.

 

My concern is that you may have begun with false premises, and hence any conclusions you draw will also be false.

 

Read a bit more carefully: I wonder IF all the above mean that a Quantum Gravity is, after all, IMPOSSIBLE!

 

As to whether "gravity influences gravitons" ("does gravity gravitate?") this is a very much open question indeed. It is connected with the so called "Very Strong Equivalence Principle" which asserts that ALL laws of Physics (gravitational ones included) can be expressed in a Special Relativistic form, in a local freely falling frame of reference.

[Daecon]

It's questions like this that make me think gravity is an inherent feature of mass in the fabric of space/time (the rubber sheet analogy) and not composed of carrier particles like standard forces.

[Klaynos]

Cap'n Refsmmat, hit the nail on the head here.

 

The theoretical gravitons interact VERY weakly with each other, in the same way that photons interact very weekly with each other, so gravitons would 'feel' ALOT less gravity compared to other particles, many orders of magnitude less. And not even supermassive black holes are that big.

 

Also we've got observed evidence for black holes and they appear to have gravity

[iNow]

Aw, c'mon! I LOVE this font! Is it so horrible to you?

 

Yes, actually. Apparently it causes me to completely miss the accurate parts of and valid questions in your post.

[swansont]

Any problem you'd have with gravitons you'll have with the electromagnetic force as well. And perhaps worse with force carriers that have mass — do they fail to work outside the event horizon, but in a region where they are gravitationally bound and would be unable to interact with other particles at a greater r?

 

I think one needs to consider two things — the differences between how virtual and real particles behave, and that GR is a classical theory, so any introduction of quantum effects is potentially incompatible and may lead to erroneous conclusions. I'm not a GR person, so I don't know where exactly those pitfalls are located.

 

But that leads to a question — are we sure that gravitons wouldn't be emitted at the event horizon?

[gcol]

But that leads to a question — are we sure that gravitons wouldn't be emitted at the event horizon?

 

That seems such a significant, not to say fundamental question. Does it not call into question the nature and existence of gravitons? if gravitons can escape the event horizon, then one or the other is not what we are led to believe it is, surely.

[Klaynos]

That seems such a significant, not to say fundamental question. Does it not call into question the nature and existence of gravitons? if gravitons can escape the event horizon, then one or the other is not what we are led to believe it is, surely.

 

But the gravitons wouldn't interact well with each other so *shrug* for them not being what we think they might be. But for both BHs and gravitons they're quite unknown to us, BHs beyond the even horizon we know very very little about because GR breaks down.

[timo]

The event horizon is a boundary, where no light-like or time-like paths lead out. Virtual particles are not particles, merely terms in a Taylor expansion that look akin to particles. Interactions work via a source influencing a field (in this case energy creating the gravitational field via the Einstein equations) which then influences other particles, e.g. via [math] \ddot x^\mu - \Gamma^\mu{} _{\alpha \beta} \dot x^\alpha \dot x^\beta = 0[/math] which you (Obelix) seem to know, already. There is initially no reason why the field equation should be altered when you go from the non-quantized version to a theory of quantum gravity. As a matter of fact, reproducing the classical version for classical scales (in which case spacetime outside a BH is non-Minkowskian just as if there was a non-BH object with the same mass creating the field) is a requirement for a quantum theory of gravity.

If you insist on interpreting the terms in the Taylor expansion, the virtual particles, as particles then those "particles" are not restricted to being time-like or light-like and hence you shouldn't have any problems with the EH.

Sorry for being a bit vague. It's a bit hard to make comments on a non-existing theory. The bottom line is that virtual particles are not particles and especially not required to be time-like or light-like.

 

Sidenote: The question is a classic. There should be dozens if not hundreds of good replies to the question "how can gravitons escape the event horizon" online.

[swansont]

The bottom line is that virtual particles are not particles and especially not required to be time-like or light-like.

 

Bingo. What I was alluding to a few posts ago, but stated better.

[Klaynos]

The event horizon is the point at which classical physics breaks down...

 

I bloged about it...

[Daecon]

Maybe gravitons are generated by a black hole in the same way that Hawking radiation is?

[Obelix]

The theoretical gravitons interact VERY weakly with each other, in the same way that photons interact very weekly with each other, so gravitons would 'feel' ALOT less gravity compared to other particles, many orders of magnitude less. And not even supermassive black holes are that big.

 

Also we've got observed evidence for black holes and they appear to have gravity

 

Whether gravity "gravitates" (i.e. whether it interracts with another gravitational field) is a capital question.

 

Black Holes (at least the objects that have been observed as such) do gravitate, to be sure.

 

Yet there is a difficulty in many people (myself included) to conceive the compatibility (which MUST be there!) between a geometrical theory of gravity (gravity as spacetime geometry = "Geometrodynamics") and another theory where gravity shows up as an inrerraction by a field throughout spacetime. If that compatibility had been conceived we would have the Theory of Everything!

 

In the case we are discussing here: Whatever gravitons are (provided they do not follow spacelike trajectories, i.e. they do not travel faster than light) THEY WOULD NOT BE ABLE TO ESCAPE AN EVENT HORIZON. This is a property of spacetime GEOMETRY. It is not a matter of "how strong is the gravitational pull of gravitons on gravitons".

 

A technical question: Is anyone familiar with Feynman's Integrals? If they were to work for gravitons, how would they be extended from the inside of a black hole to its outside, via its event horizon? (I'm a relativist, not quite familiar with Quantum Field Theory, so I may be asking stupid questions here...Sorry if that's so!)

 

If you insist on interpreting the terms in the Taylor expansion, the virtual particles, as particles then those "particles" are not restricted to being time-like or light-like and hence you shouldn't have any problems with the EH.

 

Once again: I'm not adequately familiar with QFT: If gravitons were spacelike, wouldn't gravity propagate faster than light?

 

Besides it's not only gravity and gravitons. There also are charged black holes (at least in theory). Electromagnetism is a well studied interraction with a very successfull QF theory of its own. How do charged black holes excert electromagnetic interraction on the rest of the universe?

 

Sidenote: The question is a classic. There should be dozens if not hundreds of good replies to the question "how can gravitons escape the event horizon" online.

 

Do you know any texts where the question is posed?

[ajb]

A gravitons are at this stage "theoretical" we have to discuss them in the context of a theory.

 

So, lets work with general relativity as an effective theory and not worry about remormalisation or anything like that. More specifically lets work with just the tree diagrams.

 

Statement; The action for general relativity is non-quadratic (in fact non-polynomial) and hence gravitons interact with each other.

 

Answer's you question?

[timo]

Once again: I'm not adequately familiar with QFT: If gravitons were spacelike, wouldn't gravity propagate faster than light?

Gravitons are supposed to be light-like. Virtual gravitons are not (in my eyes) gravitons.

 

Besides it's not only gravity and gravitons. There also are charged black holes (at least in theory). Electromagnetism is a well studied interraction with a very successfull QF theory of its own. How do charged black holes excert electromagnetic interraction on the rest of the universe?

Depending on preferred view, either:

- via virtual particles, that can cross the EH.

- via the field, which clearly (at least for the gravitational field) exists outside the EH.

 

Do you know any texts where the question is posed?

No, but Google gives e.g. these results:

- http://www.physicsforums.com/showthread.php?t=65583 : Didn't read it, but Janus has the habit of knowing what he sais.

- http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980601a.html, http://www.fnal.gov/pub/inquiring/questions/blackholes.html : I somewhat dislike the heavy use of the term virtual particles that sounds like circumventing problems by usage of misleading but undisputed terminology. But Nasa and Fermilab should be relatively serious sources.

[Riogho]

The problem with the graviton theory is that gravity DOES interact with itself, meanign the gravitons will interact with other gravitons. This si why it is so much harder to analyze then something like the electromagnetic force where photons pretty much stay to themselves.

 

However, we know to a very close approximation the fields of a graviatonal body add verym uch like the electromagnetic field.

 

I.E. if you had one point charge, and the field it created was E1, and another charge a little farther off and it created E2, etc etc, The charge at any given point would be

 

E = E1 + E2 + E3. . .

 

It works the same way for the gravitational force. Mostly.

[ajb]

The event horizon is the point at which classical physics breaks down...

 

I bloged about it...

 

This isn't true.

 

If we are talking about the Schwarzschild black-hole in general relativity then the apparent singularity at the event horizon is not a true singularity but a coordinate singularity. That is it reflects out bad choice of coordinate system to describe that region.

 

You can continue across the horizon smoothly by changing coordinates.

[abateNth]

"Weird question!" you are likely to say. Kindly follow me for a moment:

 

Suppose a Quantum Theory of Gravity does hold. Then, gravitational influence of a body (call it B1) on another (call it B2) would be excerted by means of a shower of gravitons (virtual partices) B1 would emit, which would transfer momentum and energy to B2. And vice versa.

 

Those gravitons (if they trully exist) are supposed to be emitted by the MASS of B1...Any objections so far?

 

Suppose however that B1 undergoes gravitational collapse (e.g., if it is a red supergiant after the supernova phase) causing its mass to shrienk within its Schwarzschild Radius, i.e. confine itself within an "event horizon", thus becoming a Black Hole. From that point on, if the mass of B1 (now enveloped by an "event horizon") emitted any gravitons, THEY WOULD NOT BE ABLE TO MOVE OUTSIDE THAT "EVENT HORIZON" OF THAT BLACK HOLE. How would then that Black Hole excert any gravitational influence on stars, etc. outside its "event horizon"???

 

It is obvious that Black Holes (at least the ones supposed to have been observed - if they ARE indeed Black Holes!) DO excert gravitational influence on other bodies, resulting in the formation of "accretion disks" and "jets". What are we to conclude? That Gravity HAS to be described in terms of a Geometry of Spacetime ("Geometrodynamics") whereas a Quantum Theory of Gravity is impossible? Would Hawking radiation suffice for the gravitational interraction? Anything else?...

 

C'mon, make suggestions!!!

 

Gravinometric studies indicate, virtual/mysterious forces are a know unknown. Huh?, there's forces unaccounted for, that are known to exist. We know not of everything. Influences on bodies observable are often highly unpredictable. This is known now, due to NEARs studies.

Near Earth Objects as they are called are unwieldy. As, they tend to force vectors we cannot determine. It's all about prediction.

 

So, within the confines of you determination, as best I can see: It's virtual fits of the "gravitons ' into your theory of Relative Mass. Which is, of course, the source, I may freely assume, yes.

If a Black Hole emitted/bounced/absorbed such, and an energy flux resulted so the acceleration/deceleration were achieved, then there may be this collapse, as you suggest.

 

Furthering, if say given graviton = F(Ma)*G/d^2

the classic we're allowed of such, where G is gravitational constant, distance represented by d.

Then, plugging in, for given that G(rav) is your phantom gravitons then we might deduce angular momentum. Here we go:

 

F(Ma)*G/d^2 + F(F(Ma)*G(G+G(rav))/d^4*(4/3)R/Dm*pi

Given: R=mean radius for center of mass,

Dm=Speculated radii of difference of above, due to influence:Typ=d^4

pi=constant pi. ~3.1415927 at 8 significant digits, truncate

 

Going on,

You're Graviton is going to have influence in observation one of two ways.

Either magnitude or appearance then removal. Calculation versus exotic, I'll assume the latter for you:

 

Given (+/-) effect, reciprocal of the above derivation induces an interesting phenomenon. Pulsating, not unlike the Quasar, a little known of unknown producer.

 

Positive Plane to negligible then reversal to Negative Plane: Pops. Yes, them explosions.

Infinite to Zero: Elimination, Bye Bye

Negative/Positive Effects: Mainly unknown, possible light producer.

 

Tonight, let us go outside, focus upwards, and observe. Might see sumpin'.