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

Gravitational waves?

  1. May 19, 2010 #1
    Do Gravitational waves bend like light in the presences of a strong gravitational field.
  2. jcsd
  3. May 19, 2010 #2
    Yes, crager; General Rel. can be used to predict refraction of gravitational waves (wave fronts) by massive sources similar to gravitational "lensing" of light.....
    I believe Kip Thorne did a calculation briefly that the showed that the sun 'focuses' GW's out to about the orbit of Jupiter.

    However, to get any sort of appreciable intensity amplification a massive black hole would probably be necessary.
    Ruffa gave an interesting calculation of a GW passing through a massive black hole at the center of our galaxy and focusing it at the location of earth...
    see: http://iopscience.iop.org/1538-4357/517/1/L31/fulltext

  4. May 19, 2010 #3
    So if light can't escape a black hole , can a GW escape a black hole . And are we saying that gravitons interact with other gravitons.
  5. May 19, 2010 #4


    User Avatar
    Science Advisor

    Since GR is a nonlinear theory, I would say definitely yes.
  6. May 20, 2010 #5
    so its different then light , This may be a dumb question but if the G field of a black hole is so strong that light can't escape it , then how does the G field exist past the event horizon , can a gravitational wave travel out side the event horizon.
  7. May 20, 2010 #6
    I hope I wasn't vague in my post, crager. I wasn't referring to gravity waves oiginating in the black hole, but rather the black hole diffracts a gravity wave that passes through the region of the black hole. Isn't that what you were concerned with?

    BTW, generally these calculations are done using wave mechanics, not gravitons.

  8. May 20, 2010 #7
    you were talking about the GW traveling by the black hole and getting bent , but i am still curious if a gravitational wave can escape a black hole .
  9. May 20, 2010 #8
    Gravity Waves are "still" theoretical, correct?

    I recently had a Gravity Wave conversation with Physics Professor Gowdy,(Virginia Commonwealth University).

    Gowdy, was with "Weber" when he constructed his (Aluminum Mass)"Gravity Antenna". Gowdy said initially it "seemed" to work, but could never be duplicated or verified, even by more sophisticated laser based methods.

    Weber's Gravity Antenna, was once, on display at the Smithsonian.

    I'm not an expert on this subject, I've just had casual conversation with one who was. Any relevant information would be appreciated.
  10. May 21, 2010 #9
    Not according to Joe Weber. ;))

    Hi jmatejka;
    I really like Weber; bold and innovative, creative , and willing to withstand the inevitable criticism for those "do it firsters". Yes, he is controversial....but I really like his results, even though no one wants to admit they are GW's, the "cause" of his signals are still somewhat a mystery.
    The facinating thing to me is that he did get a great number of coincident signals from several detectors....and more importantly they had a sidereal time anisoptropy that is still inexplicable without assuming 'something' was orignating from the galactic center. I think you should ask Prof Gawdy what he thinks of the sidereal data;

    I'll try to discuss more of the nature of this later if you are interested.

    Last edited: May 21, 2010
  11. May 21, 2010 #10


    User Avatar
    Science Advisor

    Gravitation waves do not escape a black hole. What exists outside a black hole is the (static or stationary) gravitational field. And this field already existed prior to the collaps. During a perfectly spherically symmetrc collaps the field of the collapsing star does not change; no gravitational waves are emitted.

    And please do not confuse the gravitational field with gravitons. In most contexts gravitons are something like "quantized ripples on pre-existing geometry", that means a purely perturbative concept which does not help to explain strong gravitational fields. Look at an electric field: it cannot be explained based on perturbative photons only.
  12. May 21, 2010 #11
    Fascinating! Ill update Gowdy in few weeks on a book I'm writing. Ill pass the text of this message on to him, and see what he has to say. Ill be at the SSE conference in a couple weeks, Physics Professor Richard Blade will be there. Richard attended some of Weber's lectures. Ill get Richard's opinion as well, then update this thread

    Very interesting............................Gowdy implied, "it seemed real enough to him also"

    Thanks, I'm always interested in more on this subject.
    Last edited: May 21, 2010
  13. May 21, 2010 #12
    Just to be clear is the graviton the excitation of the G field , is the graviton the same relation to its field , as what the photon is to the magnetic field. or is this incorrect .
  14. May 22, 2010 #13


    User Avatar
    Science Advisor

    The graviton is a mathematical concept, analogous to the photon for the electromagnetic field.

    The problem is that we know that a) the purely perturbative photon concept fails already in many situations, e.g. in QCD; the gluon as a single quantum particle cannot explain confinement; the non-perturbative gluon field can. And we know b) that the construction of a quantized graviton field fully analogous to the quantization of the photon field is doomed to fail due to mathematical problems in pertubative quantum gravity.

    So there can be some field g(x) which can be called graviton field, but its properties will be totally different from the photon field.
  15. May 22, 2010 #14
    thanks for your answer tom.stoer , you seem to really know what you are talking about .
    Last edited: May 22, 2010
  16. May 22, 2010 #15


    User Avatar
    Science Advisor

    thanks :-)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook