No Foam (quantum)


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MarkF
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Message 26465 - Posted 3 Feb 2006 21:57:18 UTC

    Last modified: 3 Feb 2006 22:13:43 UTC

    [url=http://www.sciencemag.org/cgi/content/full/311/5761/594a]Science online news[/quote]
    The "Airy ring" around quasar PKS 1413 135 may eliminate one proposed form of quantum gravity.
    I will post a more accessible link if I can find one.
    Haven't found any other info: for those without Science online access the author's name is Yee Jack Ng

    Profile Chipper Q
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    Message 27691 - Posted 6 Mar 2006 19:40:13 UTC

      Hi Mark. I found this one: "How Foamy is Spacetime?"

      Some interesting comments in other threads regarding the implications of not directly detecting GW radiation with LIGO, and I was wondering what reasons there might be for that; as if GW radiation is somehow scattered, absorbed, or otherwise transformed into a different form of energy, by spacetime itself over long distances. If spacetime is discrete, and if the geometry of it is changed in a gravitational field, then might it be heated by this action (as in virtual particles acquire some energy)? Is the expectation for detection of GW with LIGO related to how 'foamy' spacetime is?

      MarkF
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      Message 27697 - Posted 6 Mar 2006 22:43:15 UTC

        Last modified: 6 Mar 2006 22:51:07 UTC

        Hi Chipper Q, thanks for finding and posting the link.

        I can't answer you question about why LIGO is showing a null result. Some form of GW should exist given what we know about gravity. I an not concerned yet but that might change if S5 is completed and we still have a null result.

        If I understand this article than the quantum courseness is insufficient to seriously disrupt the light from the quasar. I would think the same argument would hold regarding GWs.

        Profile Ben Owen
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        Message 27777 - Posted 8 Mar 2006 1:04:44 UTC

          Folks,

          The waves LIGO is looking for are very macroscopic in scale. Quantum gravity will not have much effect on them in the modern universe. Quantum gravity undoubtedly affects the shape of the early universe, and some signature of it may be imprinted on the stochastic background of gravitational waves. But it will be tricky detecting that with LIGO because in its frequency band the background from lots of distant "normal" sources (neutron stars etc) is probably louder.

          The non-detection of gravitational waves so far isn't a surprise. At the current sensitivity (S5 data run), we have a fighting chance of seeing something in the next couple of years. After that there will be upgrades and it will get much better. If we find nothing in S5, that starts to say something astrophysically interesting about some neutron stars and other things, but doesn't get anyone worried about Einstein's theory not describing gravity well.

          Keep on crunching,
          Ben
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          This material is based upon work supported by the National Science Foundation (NSF) under Grants PHY-1104902, PHY-1104617 and PHY-1105572 and by the Max Planck Gesellschaft (MPG). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the investigators and do not necessarily reflect the views of the NSF or the MPG.

          Copyright © 2014 Bruce Allen