The Naked Scientists

The Naked Scientists Forum

Author Topic: Graviton  (Read 4443 times)

Offline Sandwalker

  • Full Member
  • ***
  • Posts: 83
    • View Profile
Graviton
« on: 09/10/2004 22:19:37 »
Why is the graviton not caught in the gravity well of a black hole?


 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: Graviton
« Reply #1 on: 10/10/2004 02:47:03 »
How do you know there is a graviton? Maybe the black hole doesn't know either.

http://curious.astro.cornell.edu/question.php?number=264
 

Offline Sandwalker

  • Full Member
  • ***
  • Posts: 83
    • View Profile
Re: Graviton
« Reply #2 on: 14/10/2004 01:44:36 »
Thanks for the link gsmollin.

Classical curved space I get. QED and the Uncertainty Principle, these I get (I think), but will these allow the field to manifest itself to its full potential.

Yeah I know the Graviton is hypothetical, but then by default so is this question.

 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: Graviton
« Reply #3 on: 14/10/2004 22:40:24 »
Well, I'm not sure, and I don't feel too bad about that. This is a question that may not be answerable with our present physics. General relativity predicts a singularity at the center of a black hole, and so it does not describe the nature of the black hole, although it does a good job at the event horizon. QM has the graviton, a massless particle that travels at c. Since photons clearly cannot pass the event horizon in the outward direction, why should the graviton?

General relativity may provide the answer in time dilation. As the original mass (say a large star) collapsed into the black hole, it accelerated to c. Then time dilation slowed to 0. We experience what was left at that moment, the star's mass is frozen at the event horizon by time dilation.

It still doesn't sit as well as the pictures of interacting particles sharing force bosons, especially with that damned event horizon blocking the two-way passage of gravitons.
 

Offline qpan

  • Sr. Member
  • ****
  • Posts: 260
    • View Profile
Re: Graviton
« Reply #4 on: 14/10/2004 23:00:53 »
Whether or not there is a graviton will depend on the speed of gravity. If gravity is found to act at light speed, then a graviton will be a likely candidate for causing the effect. If the effect is found to be instantaneous, then all hell will break loose and we will have to rethink all current theories. But if it is instantaneous, it could explain how (if a graviton exists) they can escape from black holes.

However, the speed of gravity is unlikely to be instantaneous as it will violate relativity in that it will be a method capable of sending information at faster than light speed.

gsmollin - do you have any idea what current theories are on the speed of gravity? I know an experiment was conducted a few years ago and concluded that the speed of gravity was the same as the speed of light, but the result was disputed due to some people not being convinced that they had measured the speed of gravity and that they instead measured the speed of light.

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: Graviton
« Reply #5 on: 15/10/2004 03:09:34 »
No, I'm not aware of the state of this art. I am quite certain that relativity requires the effects of gravity to be transmitted at c. If not, then gravity waves could be transmitted at greater than c, and yes, that would violate the laws.

I know that gravitational detectors have been searching for gravity waves for years. I know what kind of events they seek, those with gravitational quadrupoles, but I don't have recent results of this research. Part of this problem is getting such an event that produces a gravitational shock wave detectable at multiple detectors coincident with an electromagnetic event detectable by ordinary means.

The irony of all this is that such an event is probably a rotating black hole swallowing a star. The two masses could orbit each other at relatavistic velocity before the star rips apart and shoots out synchrotron radiation, maybe a gamma ray burst. It would be great to be able to measure the gravity waves radiated from the rotating quadrupole-moment just before the gamma ray burst. Its the answer to a physicists dream, but I think its just a dream right now.
 

Offline qpan

  • Sr. Member
  • ****
  • Posts: 260
    • View Profile
Re: Graviton
« Reply #6 on: 15/10/2004 21:54:12 »
A gravitational quadra-what?

Sounds interesting - can you enlighten me further on this subject gsmollin?

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: Graviton
« Reply #7 on: 16/10/2004 02:04:29 »
I've put some links about GR at the bottom. The quadrupole form is hard to find. Its in the last link. Physically, Einstein derived this form of the GR equations for a dumb-bell mass rotating about its center of mass. This is the quadrupole, the simplest radiating form for gravity. It is analogous to the dipole form in electromagnetics, which is the simplest radiating configuration in EM.

One of the major challenges was to show that agravitationally-bound system like a binary star system would also radiate gravitational waves. This was proven in the 70's, and a Nobel prize followed.


http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GenRelativity.html
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GravWaves.html
http://www.ligo.caltech.edu/
http://www.davis-inc.com/relativity/
 

The Naked Scientists Forum

Re: Graviton
« Reply #7 on: 16/10/2004 02:04:29 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums