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Gravitational Waves

  1. Oct 31, 2014 #1
    Have "we" (the scientific community) found any proofs of gravitational waves? I read about an experiment including a couple of mirrors very apart from each other and a laser that aimed to somehow measure the possible existence of gravitational waves, but as far as I understood (clearly not much) at the time of that article, it was unsuccessful.
    Could you please give some information about this? Are there real measurements of GW?
    Also, could you please explain the basics of the experiment?
    Thanks and best regards,
     
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  3. Oct 31, 2014 #2

    phinds

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    By "proof" I assume you mean experimental evidence. That's really a demonstration of existence, not a proof.

    At any rate, the little boogers are believed to exist but have yet to be demonstrated to exist.

    It would be great if they could be detected because that's one of the ways that we might be able to look past the surface of last scattering, but so far all we know is that they either do not actually exist or (more likely) they are too subtle for our current technology to detect.
     
  4. Oct 31, 2014 #3
    So they have not been detected yet?
    What about the experiment? I think they’re called “gravitational waves antennas” (?)

    Also, what is the theoretical range of frequencies for a gravitational wave?

    This might sound rather stupid but, isn’t it possible to easily create a gravitational wave in a laboratory by rotating a heavy load eccentric relative to the axis of rotation?

    Thanks,
     
  5. Oct 31, 2014 #4

    phinds

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    I can't help w/ that but someone here probably will.

    Sure, that will produce gravitational waves (assuming they exist) but those would be so utterly tiny that there may NEVER be any equipment that could detect something THAT small.
     
  6. Oct 31, 2014 #5
    That is exactlymy point: A graviational wave created in your lab 2 meters aways from a detector with a "considerable big mass" is expected to be much smaller than a graviational wave coming from a Super Nova (I've read that supernovas create GW) comming from a distance of several light-years?
     
  7. Oct 31, 2014 #6

    jtbell

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  8. Oct 31, 2014 #7

    Orodruin

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    As with electromagnetic radiation, you can have gravitational waves of essentially any frequency. It simply depends on the source.

    The only confirmed evidence in favor of gravitational waves thus far is that binary pulsars seem slow down at a rate which is compatible with the one predicted from the emission of gravitational waves. We have so far not detected gravitational waves directly.
     
  9. Nov 4, 2014 #8

    PAllen

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    It is worth adding that plausible models of sources of gravitational waves suggest that our currently operational detectors should have null results. That is the impetus for next generation increases in sensitivity.

    On the other hand, the binary pulsar evidence is quite strong - precise quantitative agreement with predicted orbital decay due to gravitational radiation per general relativity.
     
  10. Nov 4, 2014 #9
    I'm curious how this relates to the "graviton" in particle physics. Would the wave-particle duality imply that a gravitational wave and a graviton are two aspects of the same phenomenon?
     
  11. Nov 4, 2014 #10

    PAllen

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    Same relation (per majority guess - which is all there is now) as between photon governed by QED and Maxwell's equations for EM fields/waves.
     
  12. Nov 26, 2014 #11
    Hi, I’m back after a while.. I took some days off to read about gravitational waves and other phenomena in physics, and I have a new question related with gravitational waves. I decided to post it in this same thread, but I think that maybe it could be valid to start a fresh new thread about this. Anyway, since I already have many threads open, I’ll leave it here:
    Doesn’t the prediction of gravitational waves implies the emission of some kind of energy? I came to this idea with the analogy of the electromagnetic waves produced by a moving electric charge. For a moving electron for example, energy is emitted through photons (am I right?). What about the movement of mass? I don’t mean to talk about the emission of a particle (like the already mentioned graviton). I just wonder if a gravitational wave has intrinsic energy. And what about conservation of energy in a planetary system? For example, does the orbital movement of the earth around the sun produce gravitational waves (theoretically)? I think it should. In that case, isn’t it an implication of the conservation of energy that the earth should slow down or the radius of the orbit should be reduced?

    I confess that, by bringing the electromagnetic wave analogy, I feel suspicious of being wrong by trying to mix the gravitational laws of General Relativity with quantum physics (which I understand are, ‘til the date, unmixable), so maybe that is not the best analogy for my idea. However, I can’t help to associate the existence of a GW with a form of energy, and what consequences could that have regarding specifically the reduction of distance between the earth and the sun.
    Thanks again and best regards,
     
  13. Nov 26, 2014 #12
    good thinking!
     
  14. Nov 26, 2014 #13

    mfb

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    Yes. Emission of gravitational waves is not linear with mass and other relevant quantities. A star with a mass of 10^30 kg will not emit 10^27 times the power of your 1000kg bar, but more like 10^54 times.

    This is exactly the type of indirect evidence we have for gravitational waves: orbiting pulsars lose energy, and the rate is well in agreement with the predictions for gravitational waves.
    Yes, about 300 W. This is tiny compared to various other effects on our orbit.
     
  15. Nov 27, 2014 #14
    300 W? You mean 300 Watts, as in "the Earth is losing 300 joules per second"? Where does this energy comes from? Kinetic energy? Reduction of the orbit?
    Also, probably non related with GW, but out of curiosity… what other effects act in our orbit? And what are their consequences?
     
  16. Nov 27, 2014 #15

    PAllen

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    It comes from orbital decay, if you need to think of a source. In many times the life of the universe, the earth would spiral into the central mass, and (on merger of bodies), the GW would cease.
     
  17. Nov 27, 2014 #16

    mfb

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    Orbital decay. About a femtometer (diameter of an atomic nucleus) per year if I remember the number correctly.
    Material coming from the solar system and hitting the atmosphere (or even the ground, in rare cases), gravitational forces from the moon, other planets and various other objects. Pressure from solar wind and radiation and its interaction with the magnetic field of earth. General relativity has other effects that lead to non-elliptical orbits.
    Even our space programs have a larger influence on the orbit of earth than gravitational waves have (but those numbers are not so far away from each other).
    The consequences are negligible. The orbit won't change significantly within the next few billion years (assuming no large-scale engineering from humans). The earth is just too massive.
     
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