Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Black holes and theories of gravity

  1. Sep 10, 2009 #1
    In the perception of General Relativity a Black hole can form in wich anything (including light) is trapped inside the horizon of the Black hole and can never escape, because nothing can exceed light speed.

    However, still something escapes the Black hole, which is the presence of the gravitational field outside of the horizon of the Black hole. Since in General Relativity also gravity itself can not be faster then light speed, this is - in a sense - some kind of peculiarity.
    One could (in theory) propose that a Black hole, after it has formed, would withdraw it's presence of the gravitational field outside the horizon alltogether under the assumption that also the gravity field itself can not escape from the Black hole, and with which the Black hole would effectively disappear for outside observers, and only objects that cross the horizon (without being drawn in by the Black hole as there would be no extreme force of gravity outside the horizon), would experience the presence of the Black hole and disappear inside the horizon. A black hole would then just be a 'gap in space' without making it's presence observable for outside observers.

    Appearently, however, this is not the case, since Black holes manifest themselves by the strong gravity fields that exists outside the horizon of the Black hole, which makes a Black hole observable for observers outside the horizon. Else, we would probably not know that a Black hole exists.

    What does this mean in terms of the theory of Gravity? In so far particle physics for example predicts the existence of 'gravitons' (particles that excert the force of gravity, similar to how photons excert the electro-magnetic force), those particles can't themselves 'sense' the force of gravity, although a 'graviton' would not exceed light speed.
  2. jcsd
  3. Sep 11, 2009 #2
    A very good observation and I think this is a very strong argument against the idea of gravity being caused by any kind of wave.

    In my opinion, it reinforces the concept of gravity being caused by matter's surroundings rather than matter somehow reaching out and pulling you down, more like a pushing down by space itself.
  4. Sep 11, 2009 #3
    http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html" [Broken]
    Last edited by a moderator: May 4, 2017
  5. Sep 12, 2009 #4
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook