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Gravity and LIGO

  1. Jun 28, 2004 #1
    What is the wavelength and amplitude of the gravitational waves that LIGO is trying to detect? Are these waves made of gravitons (as light waves can be made of photons) and how much energy do they carry?
  2. jcsd
  3. Jun 28, 2004 #2
    The detector must be optimized for the type of gravity wave source one is trying to detect. See a blurb here: http://www.ligo.caltech.edu/~mours/audio.html

    LIGO currently is in the frequency range of around 10*2 to 10*3; but I believe it is being reconfigured to a much lower frequency, especially in light of its so far null results. As you can imagine the amplitudes of GW's are very small.

    A typical a formula for the power radiated by GW's from a spinning (non symmetric) mass source would not only be proportional to the moment of inertia (squared) but also to the sixth power of the frequency! :eek: but unfortunately also to the inverse 5th power of c. :frown:

    LIGO does have the ability to detect these tiny amplitudes; however so far the results are nill, even though I believe there are plenty of qualified sources. My opinion is that, like Michelson-Morley, I predict a null result (due to the fundamental physical basis for the LIGO apparatus); and we may learn more about nature from that null result than actual detection. :wink:

    Last edited: Jun 28, 2004
  4. Jun 28, 2004 #3


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    Actually, LIGO's currently null result is expected. The current version is pretty much there to work out bugs. Nobody expects to see anything (and never did) until the upgrades are done in a few years. And then it might take a couple years of observing to find some good sources. LIGO et al pushes the boundaries of experimental precision many orders of magnitude beyond where it was before, so there are a lot of uncertainties to face.

    As to your graviton question, I'll point out that there is currently no good theory in physics which contains gravitons. They are therefore ill-defined conceptualizations. There's no point in talking about them. On a purely conceptual level, I find that waves are much simpler to think about than particle-wave hybrids even in the electromagnetic case (where photons are of course well-defined).
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