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Redshift Energy Conservation

  1. Feb 6, 2009 #1


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    This is my first time on physics forums, and I am glad to have the chance to participate. My questions have been asked many times by others, but after lots of research, including among these threads on physics forums, especially “hurk4” on Feb 14-07 and Will Kastens, I can find no definitive answers.

    Einstein wrote (The Principle of Relativity”, Dover, 1952, p.71): “…radiation conveys inertia between the emitting and the absorbing bodies.” Each photon subject to the cosmological redshift apparently conveys less energy to the absorber than it had when it was emitted.
    Question. # 1. Since energy is always conserved, where has this difference in energy gone?

    The following references are relevant:
    Misner, Thorne, Wheeler (Gravitation, section 29.2): “A detailed analysis focuses attention on three processes: emission, propagation, and absorption. Emission and absorption occur in the proper reference frames (orthonormnal tetrads) of the emitter and receiver; they are special-relativistic phenomena. Propagation, by contrast, is a general-relativistic process: it is governed by the law of geodesic motion in curved spacetime.”

    Sten Odenwald and Rick Fienberg (“Sky and Telescope”, February 1993, “Galaxy Redshifts Reconsidered): “Steven Weinberg and Jaylant Narlikar and John Wheeler, “The frequency of light is also affected by the gravitational field of the universe, and it is neither useful nor strictly correct to interpret the frequency shifts of light...in terms of the special relativistic Doppler effect.” In fact, general relativity allows the Conservation of Energy to be suspended so that matter and energy may be created quite literally from the nothingness of curved spacetime.”

    Peebles (Principles of Physical Cosmology, 1995, p. 139): “Where does the lost energy go? ... The resolution of this apparent paradox is that while energy conservation is a good local concept ... and can be defined more generally in the special case of an isolated system in asymptotically flat space; there is not a general global energy conservation law in general relativity theory.”

    Whereas Einstein wrote (The Principle of Relativity”, Dover, 1952, p. 150): “Thus it results from our field equations of gravitation that the laws of conservation of momentum and energy are satisfied.”

    Questions # 2. The object which emitted Gamma Ray Burst 080913 was measured to be at a redshift of 6.7, or at a distance of 12.8 Billion light-years. Since all e-m radiation is subject to the cosmological redshift, and the Swift satellite detector received gamma rays, how much energy did that radiation have when it was emitted? Do we need a new name for it?
  2. jcsd
  3. Feb 7, 2009 #2


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    1. The key word you are missing in that Einstein quote is "apparently". Kinetic energy and momentum are frame of reference dependent (in both Einstein's and Galileo's relativity), so they can be different in one frame than another. There is no violation of COE.

    2(b). Gamma rays are anything above 10^19 hz, so no, there wouldn't ever be a need for another name for a band above them.
  4. Feb 7, 2009 #3


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    Those are great quotes!
    I put the nested quotation from Weinberg et al in italics to help distinguish the two levels. Hope I got it right. The main message, that GR allows COE to be suspended, is I think in Odenwald Fienberg's words.

    BTW welcome to Physicsforums!
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