How can gravity escape a black hole?

[Pluto]

G'day from the land of ozzzzzz

My aim is to prove to you that not only matter escapes via jets, but in huge amounts. Jets are jets regardless of their origin.


It's late right now, so I'll be back

Some parts of the link that I posted you have read them out of context. Thats Ok no harm done.

[modest]

Originally Posted by Karnuvap

This question pre-supposes that a gravitating object "Radiates" gravity. If this were so then it would be useful to ask how that radiated 'stuff' is able to escape the black hole's event horizon.

However - this is not how Gravity works. According to General Relativity (GR) massive objects distort spacetime (the most common visualisation of this is the bowling ball on a rubber sheet) and so objects 'fall' towards heavy objects simply because it is the 'line of least resistance' to do so through spacetime that has been distorted by a mass.

Now, if that mass was 'bouncing up and down' (or in 3-D if it is orbiting another mass, as in a binary system) then the 'rubber sheet' would ripple like the surface of a pond. These ripples carry away energy from the object as either Gravity Waves or Gravitons (just different ways of looking at it). So, for example, a neutron star orbiting outside the event horizon of a black hole would radiate Gravity Waves that ought to be detectable.

However, once the neutron star has crossed the event horizon of the black hole it could merrily continue orbiting for a while yet before plunging into the singularity at the centre but now (due to the distortion of space and time axes within the black hole) the gravity waves would NOT escape - the mass of the black hole would increase and thus the diameter of the black hole would grow but it would stop radiating gravity waves.

Thus you could say that black holes do trap gravity.

Hope this helps

The Vap.

I see right where you're coming from, and very-well said.

We can ask this same question more sensibly by leaving out gravitons and focusing on charge. Black holes are certainly allowed to have charge in general relativity, in fact it is one of only three properties classical black holes are allowed to have via the no-hair theorem (mass, charge, and angular momentum).

Since we know charge is mediated by virtual photons rather than any general relativistic effect, we can ask how the virtual photons are able to escape the black hole to communicate this charge. My suspicion is that they would have to travel faster than light for both QM and GR to remain intact. I don't think this necessarily presents a problem - but I find it very interesting.

~modest

[Karnuvap]

There you go again with your faster-than-light-photons (Virtual or not). You have gotta stop with all this faster than light stuff - especially with light itself.

Faster than light photons is like saying faster than light light. If it's light then it travels at the speed of light - by definition.

I think the answer to how the charge of a black hole is 'communicated' to the outside world might have been touched on earlier in this thread by Jay-Qu when he said that one half of a virtual particle pair would preferentially fall past the event horizon if it was attracted to the charged black hole. - But wouldn't this eventually result in the neutralisation of the black hole's charge?

Of course this wouldn't apply to the virtual photons (not charged) but since they are created at the event horizon they don't need to travel faster than the speed of light. The one that doesn't fall into the black hole can escape by travelling at its normal speed (of light).

How this helps explain hairy (or bald) black holes I have no idea but it is fun debating it among people who at least have an idea what they're talking about.

[modest]

Originally Posted by Karnuvap

There you go again with your faster-than-light-photons (Virtual or not). You have gotta stop with all this faster than light stuff - especially with light itself.

Faster than light... light

Originally Posted by Karnuvap

I think the answer to how the charge of a black hole is 'communicated' to the outside world might have been touched on earlier in this thread by Jay-Qu when he said that one half of a virtual particle pair would preferentially fall past the event horizon if it was attracted to the charged black hole. - But wouldn't this eventually result in the neutralisation of the black hole's charge?

Not only that, it doesn't explain how half a pair is attracted to the hole in the first place.


We can thank Janus for this gem. He quoted it in another forum:

Author: Matthew P Wiener <weemba@sagi.wistar.upenn.edu>, Steve Carlip <carlip@dirac.ucdavis.edu>

In a classical point of view, this question is based on an incorrect picture of gravity. Gravity is just the manifestation of spacetime curvature, and a black hole is just a certain very steep puckering that captures anything that comes too closely. Ripples in the curvature travel along in small undulatory packs (radiation---see D.05), but these are an optional addition to the gravitation that is already around. In particular, black holes don't need to radiate to have the fields that they do. Once formed, they and their gravity just are.

In a quantum point of view, though, it's a good question. We don't yet have a good quantum theory of gravity, and it's risky to predict what such a theory will look like. But we do have a good theory of quantum electrodynamics, so let's ask the same question for a charged black hole: how can a such an object attract or repel other charged objects if photons can't escape from the event horizon?

The key point is that electromagnetic interactions (and gravity, if quantum gravity ends up looking like quantum electrodynamics) are mediated by the exchange of *virtual* particles. This allows a standard loophole: virtual particles can pretty much "do" whatever they like, including travelling faster than light, so long as they disappear before they violate the Heisenberg uncertainty principle.

The black hole event horizon is where normal matter (and forces) must exceed the speed of light in order to escape, and thus are trapped. The horizon is meaningless to a virtual particle with enough speed. In particular, a charged black hole is a source of virtual photons that can then do their usual virtual business with the rest of the universe. Once again, we don't know for sure that quantum gravity will have a description in terms of gravitons, but if it does, the same loophole will apply---gravitational attraction will be mediated by virtual gravitons, which are free to ignore a black hole event horizon.

See R Feynman QED (Princeton, ???) for the best nontechnical account of how virtual photon exchange manifests itself as long range electrical forces.

http://sciastro.astronomy.net/sci.astro.4.FAQ

[maddog]

Pluto,

As Modest said, that is a very insightful question.

Originally Posted by Pluto

How can gravity escape a black hole if its speed is C?

This question can be answered in a few ways as below.

1. According to Qfwfq, GR has a derivation (worked out in Gravitation by
Misner, Kipp, Thorne) to show that the velocity for gravity is C (speed of
light).

2. Using M-theory the current wisdom is that gravity "leaks" into other
dimensions than the 4-manifold of spacetime. This would yield the visual
of a black hole appear to gravity as glass jar rather than opaque.

3. Gravity Radiation or Gravity Waves is just the wave nature of a graviton
the particle nature (Duality remember). Both represent the same force
traveling at the same speed. Scientist are look for either object by looking
for vibrations in the moving of massive objects. Best candidates are Pulsar
starquakes (best looking at shortest pulse candidates), were another
supernovae to occur like 1987A, Eta Carinae (the hypergiant), etc.

4. Most Radiation from any black hole rarely comes from within the event
horizon. It is light (photons) of high energy X-Rays radiated for hot gases
falling into the hole from the accretion disk. The picture in this post shows
it best. Any Radiation at or near the surface of a black hole is created by
annihilation pairs already mentioned in this post (Hawking Radiation).

5. Hawking Radiation does account for mass loss from a hole and would
only mean anything if the hole were small, say asteroid size. This could
determine the life expectancy of such a black hole.

6. Like Karnuvap implied it is ludicrous, silly and inane to consider an FTL
form of Light, so I will leave it at that.

In summary, gravity does not need to "escape" a black hole, it is the
representation of the curvature of spacetime that defines the black hole.



maddog

[Tachyon!]

Only information is restricted to slower than light speed velocities according to Einstein's theory of special relativity. Also, relativity doesn't rule out faster than light particles, aslong as they have always travled faster than light. Tachyons are faster than light particles but are still only hypothetical.
Also quantum entanglement at first seems to suggest a violation of Einstein's theory since the measurement of one particle can instantaneously affect the second even when vastly seperated. But no information is shared between the two vastly seperated particles, the particles are one in the same and their histories are so interwoven that any effect on the first particle instantaneously effects the 2nd! Anyway...no violation of special relativity occurs.
And as for gravity escaping a black hole... in close proximity to the event horizon virtual matter/antimatter particles are created and this leads to loopholes which temperarally allow faster than light particles. This does not violate the heisenberg principle as long as they disappear quickly enough.

[Pluto]

G'day from the land of ozzz

I have read many papers on Black holes.

The funny thing is no one has ever seen a black hole or an eventhorizon of any form.

This is interesting reading

http://www.holoscience.com/news/img/DPS%20talk.pdf

Conference of the German Physical Society, Munich, March 9-13, 2009.
Verhandlungen der Deutsche Physikalische Gesellschaft
Munich 2009: Fachverband Gravitation und Relativit¨atstheorie
http://www.dpg-verhandlungen.de/2009/indexen.html
The Schwarzschild solution and its implications
for gravitational waves

[CraigD]

Originally Posted by Pluto

The funny thing is no one has ever seen a black hole or an eventhorizon of any form.

This isn’t, I think, “funny” or unusual. Because it studies relatively small objects at relatively large distances, astronomers commonly concludes that objects exist that cannot be directly “seen” through human eyes, through indirect means.

The detection of bodies thought to be stellar-mass black holes are an instructive example of this. In the ordinary terms of telescopes, their “disks” – their event horizons – are tiny (typically about 30000 m) their distance great (the closest known one being about 3500 LY). The angular diameter of such an object is about arcseconds, equivalent to the size of a 4 mm object, such as a pea or pebble, on the surface of Pluto as seen from Earth. This is about a billion times smaller than can be seen with the best present-day telescopes.

Until much more powerful telescopes are made, or can be sent to distant star systems, no one will be able to directly see the a black hole. However, because black holes are surrounded by large accretion disks of brightly (typically in the X-ray band) glowing matter, their existence and physical characteristics can be detected and measured indirectly.

Originally Posted by Pluto

This is interesting reading

http://www.holoscience.com/news/img/DPS%20talk.pdf

Even more interesting from Steven Crothers is this, from his personal webpage:

So if it's a fight they want then it's a fight they'll get. Pasty-faced softies however, cloistered away in universities are not much of a challenge; but there are so many of them, like cane toads in the breeding season. And so I now make no bones about how I view blokes who, like K. Thorne and Ned Wright, prance about with long pony tails and matching sandals, or wear earings and otherwise dress and behave like girls (most "male" physicsts nowadays).

“The Schwarzschild solution and its implications for gravitational waves”, strikes me as more of an ad hominem attack on David Hilbert and sundry others than a work of mathematical physics. That the significance and various uses of the Schwarzchild radius () were realized years after Schwarzchild’s death doesn’t, IMHO, discredit it, or suggest any sort of plagiarism or fraud.

I find Crothers’s writing emotionally painful to read, because Crothers seems to me deeply emotionally troubled. I hope he gets psychiatric help, as his emotional issues appear to have derailed his education and career, and may, I fear, lead him to greater life troubles.

[TheFaithfulStone]

The funny thing is no one has ever seen a black hole or an eventhorizon of any form.

How would you see something that reflects no light?

What is the sound of one hand clapping?

tfs
[koans]

[maddog]

Originally Posted by modest

Continued from this post.
...
Does this present a problem for quantum gravity? I don’t think so. Gravitons would be virtual particles and I think virtual particles are allowed to travel faster than light. Someone more familiar with QM can correct me if I’m wrong, but I think gravitons:

1. would need to travel faster than c to leave a black hole and affect distant objects gravitationally
2. can travel faster than c because they’re virtual.

Modest,

My post #25 addresses the first question (at least according to Qfwfq).

Graviton's are not intrinsically virtual nor are they required to be.

It is true for virtual particles the normal rules of causality are not made so stringent
so "borrowing" energy from the "future" or "past" is allowable. For information on this
seek out a book called "About Time", I think it is Paul Davies though I admit that I am
not sure of the author.

I apologize for such a nitpick (especially one I missed earlier).

maddog