Gravity Waves

Discussion in 'Physics & Math' started by Little Bang, Sep 26, 2015.

  1. Little Bang Registered Member

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    If we don't find gravity waves will we have to change something about Physics?
     
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  3. brucep Valued Senior Member

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    No. If we never directly measure a gravitational wave we still have volumes of indirect evidence. The discussion is always about the sensitivity of the empirical device measuring the waves and how to filter out local natural and unnatural 'noise' which places limits on the sensitivity. Putting them in inertial freefall [jn Space] eliminates the ground 'noise'. It's taken many years to get here. Looking forward to the space experiment. The history of the potential measuring device is pretty interesting.
     
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  5. paddoboy Valued Senior Member

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    Nice answer bruce.
     
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  7. brucep Valued Senior Member

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    I think you mentioned Weber's device. The first time I saw a picture of the device. I was reading the John A. Wheeler book Geons, Black Holes, and Quantum Foam: A Life in Physics. Another great read with lots of history.
     
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  8. river

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    Gravity waves are about rotation and vibration , atomically and subatomic.

    And gravity is such a weak force it is really irrelevant force.
     
  9. Daecon Kiwi fruit Valued Senior Member

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    [Citation needed]
     
  10. river

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    Not going to happen
     
  11. Daecon Kiwi fruit Valued Senior Member

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    Tell us something we don't know.
     
  12. river

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    Post # 5
     
  13. AlexG Like nailing Jello to a tree Valued Senior Member

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    Of course not.
     
  14. Little Bang Registered Member

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    Ok so there are volumes of indirect, could you tell me about three or four?
     
  15. brucep Valued Senior Member

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  16. brucep Valued Senior Member

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    It's a good reason for your sanction. Unfortunately nonsense such as you post is appropriate for this forum.
     
  17. brucep Valued Senior Member

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    Since you have nothing but ignorant comments to offer please go away.
     
  18. Fednis48 Registered Senior Member

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    I actually saw a really good talk about this just the other day. I found out that there are two kinds of gravity wave detectors. Some use large, rigid objects (i.e. long metal bars) at extremely low temperatures and watch for passing gravity waves to excite the objects' oscillation modes. Others use laser interferometers with kilometers-long arms, and watch for the interference fringes to move as gravity waves compress one arm compared to the other. If memory serves, the metal bar detectors usually look for rotational modes, while the interferometers look for vibrational (i.e. compression/extension) modes. In both cases, the kinds of displacements they're looking for are on the atomic scale, and in the latest generation of interferometeres they're actually using some quantum mechanical tricks to cheat the Heisenberg uncertainty principle because they need to measure arm lengths to that high of precision. (Look up "squeezed vacuum" states if you're interested in more of the details.) It's really a testament to human engineering that these experiments are even in the realm of possibility, let alone in progress.

    So it's not true that gravity waves are about atomic/subatomic rotation and vibration. Quite the contrary, they're about extremely large scale rotation and vibration, and the reason we have to look at atomic distances to find them is that our biggest detectors are just barely big enough to see them at all. As for gravity being an "irrelevant" force, that seems like an odd claim from someone who was making good use of gravity to stay in his chair while he typed it.
     
  19. paddoboy Valued Senior Member

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    river has many odd claims in his repertoire, not the least being ghosts, goblins, Bigfoot, Alien craft buzzing Earth....Oh and let's not forget Plasma/Electric theory.
     
  20. Q-reeus Valued Senior Member

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    Can you provide a link - presumably YouTube?
    Resonant bar detectors are pretty much old hat nowadays. There is a third kind - hollow superconducting resonators - that have mostly taken over re acoustic mode detectors.
    Not really. The some would say bizarre logic has that there is relatively negligible strain in the arms. The assumed displacements are largely in the suspended mirrors.
    Sorry - memory problems. It's flexural modes where the overwhelming expectation for detection of GR's brand of GW's is centred. About the nearest one could come to 'rotational' is that by analogy with light, there is expected to be a general elliptical polarization of incident waves.
    Again, no. The overwhelming expectation is for GR's quadrupole mode TT-gauge GW's - which are pure shear in nature. Maybe you meant 'effective' detector modes, not GW ones?
    Not having a good day here, Fednis48

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    . Again no. Expected GW induced strains are typically of the order 10^-22. Plug that into a 4km arm, and we get ~ 4*10^-19m. By use of multiple reflections, the effective figure is improved by around two orders of magnitude. Still way, way below atomic scale. And picture is far worse again for the typically meter-sized hollow resonator detectors.
    Or a sign of desperation. Squeezed mode enhancements give only around a factor of 2 additional sensitivity.
    I was going to keep out of this thread having said my piece here.
    Anyway, as final comment this post, it should be mentioned that OP's tital 'Gravity Waves' is inappropriate, as gravitational waves are what is really being discussed. Gravity waves are very easily detected - just gaze out from any sea shore.
     
  21. danshawen Valued Senior Member

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    Oh, you read about it, did you? That's nice, brucep. I was THERE.

    Clearly, Mr. Potter, literacy, like fame, isn't everything.
     
    Last edited: Sep 28, 2015
  22. BrianHarwarespecialist We shall Ionize!i Registered Senior Member

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    You seem to have some quite unique experiences Dan Shawen.
     
  23. sweetpea Registered Senior Member

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    So was the janitor, I bet the janitor's posts would show more understanding of gravitationals waves than your posts on the other thread “LIGO's "New Ear for the Universe"

    And after reading some of your posts... being THERE clearly isn't everything either.
    Ps paddo notice three dots only.

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