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Can't be a 'preferred' frame.

  1. Jun 23, 2007 #1
    Although is against the spirit of GR, isn't the vaccumm (at QM level) a preferred frame of reference?, or if Dark Matter exist shouldn't we measure the speed of light respect to it as it was thought to be made whenever you believed in aether ?.


    Then somehow Einstein was wrong and there a pure reference frames with its own time, perhaps the changing rate of Dark Matter or the desintegration period of the particles in vaccuum is just a 'universal clock' for every observer.

    Another question is does a particle 'adquire' gravity ??, for example perhaps space-time is smooth and fine, but when it aboserbes a Graviton then curvature is created, so in the end we live in a flat space 'surrounded' by gravitons , which create the curvature,in this case at first level interaction (first order in perturbation theory) we must recover Einstein Lagrangian (this is just an speculation).
     
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  3. Jun 24, 2007 #2

    marcus

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    Cosmologists have used a preferred frame for many decades. It has its own time. as you say.

    Erwin Hubble discovered the preferred frame that they use, but now they determine it more accurately by the CMB (cosm. microwv. backgrd)

    before COBE measurement of CMB, the preferred frame was often called "being at rest with respect to the Hubble Flow"

    Now, after COBE, it is often called "being at rest with respect to CMB"

    basically it means BEING AT REST WITH RESPECT TO THE EXPANSION OF DISTANCES.

    COBE and other CMB observations found that the solar system is moving about 380 km/sec wrt CMB, in the direction of constellation Leo
    that is, the roughly uniform temperature of 2.75 kelvin has a DOPPLER HOTSPOT in the Leo direction and a DOPPLER COLDSPOT in the opposite direction.
    if we stopped moving 380 km/sec in that direction then the temperature of CMB would be roughly uniform in all directions

    But many decades before this COBE result, Hubble had found that out in the Leo direction THE GALAXIES WERE NOT RECEDING AS FAST AS THEY SHOULD and they didnt have as much redshift as his Law predicted. this was because our 380 km/second motion was "running after them" and reducing their recession speed by that amount.
    Also Hubble found that in the opposite direction the Galaxies were receding faster than the Hubble law said. The law was based on average. this was because our 380 km/sec speed was ADDING to the recession. and contributing to the redshift.

    So before COBE we did not know the speed and direction so accurately but we still had an idea that we were moving with respect to the "Hubble Flow" that is moving with respect to the expansion of the universe and the recession of the galaxies.

    IT IS THE SAME IDEA OF REST FRAME WHETHER YOU MEASURE BY THE CMB DIPOLE OR THE GALAXY REDSHIFT DIPOLE.

    Observational astronomers make it their business to correct for solar system motion, and even for earth motion.
    It comes with the job.

    this is compatible with Gen Rel because our universe is a particular solution to the equation of Gen Rel. Nobody ever said that a particular solution could not have a preferred rest frame
    the full Gen Rel theory has no preferred frame, but Cosmology which is the study of this one universe that we are in certainly does have.
    So actually Einstein wasn't wrong. He knew about Hubble results and the expanding Friedmann-LeMaitre model and all that, so he must have known about the preferred frame and I doubt it bothered him one bit :smile:
     
    Last edited: Jun 24, 2007
  4. Jun 24, 2007 #3

    russ_watters

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    "The vacuum" isn't a frame of reference, much less a universally preferred one.
     
  5. Jun 24, 2007 #4

    pervect

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    If you have an empty vacuum with a cosmological constant, the stress-energy tensor is invariant under a boost, so there isn't any preferred reference frame.

    I just checked this: diag(x, -x, -x, -x) doesn't change under a boost.

    In cosmologies with matter (for example the flat FRW cosmologies), the stress-energy tensor can vary under a boost, IIRC, but this can be attributed to the matter present in these cosmologies, not the vacuum.

    As far as your questions about gravitons goes, this is probably the wrong forum. Try the standard model forum. "Gravitons" are not part of the formalism of GR, they would be the formalism of some sort of quantum theory of gravity, i.e. not GR. So your question is not a question about GR, but a question about quantum gravity. Some authors have suggested that it is possible to recover GR from a quantum gravity model in a flat Minkowski space-time, for instance see http://xxx.lanl.gov/abs/astro-ph/0006423, but you might want to see the negative comments made by some other posters such as Chris Hillman about this approach. Basically you are getting into deep water here, you probably want to learn GR first before you start worrying about gravitons - GR doesn't really deal with them, it's a classical theory.
     
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