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Does Hubble's Expansion voilate conservation of energy by redshifting EM waves?

  1. Feb 20, 2012 #1
    I am assuming the answer to my question is no, but what am I missing?
    My reasoning is very basic: E=hf, therefore as the universe expands the wavelength of all the far traveling radiation is increased and due to constant velocity c their frequency must decrease which translates into them losing energy.
    I would appreciate if somebody could shed some light on this for me, please.
    (bad puns are bad... :P)
  2. jcsd
  3. Feb 20, 2012 #2
    Similary, some galaxies are now receding apart @ velocities > c (in stark contadiction to Einstein's posit).

    To answer your question;- both red-shift and corresponding velocitiy are due to spatial expansion .... it's not that the galaxies are shifting, merely the space inbetween is.

    There's no law regarding the speed limit of space itself, is there?
  4. Feb 21, 2012 #3
    I don't believe you read my question properly. It has nothing to do with velocity; I'm concerned with the energy of the waves.

    If a photon is created with the frequency of 100 Hz and after travelling between two distant galaxies due to the expansion of the universe it's frequency drops to 10 Hz it should have lost 90% of it's energy.
  5. Feb 21, 2012 #4


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    The easy answer is that conservation of energy does NOT apply in General Relativity. Energy is not a well defined quantity in GR either. (Or so I've been told)
  6. Feb 22, 2012 #5
  7. Feb 22, 2012 #6


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    Ah, a nice read. I love the opening lines.
    Pretty much what I've been told.
  8. Feb 22, 2012 #7
    Thank you, that was a useful link.

    ''Those who harbor no qualms about pseudo-tensors will say that radiant energy becomes gravitational energy.''
    That's what I thought about as well, though I am not entirely satisfied with it as an answer and I guess that until I cover GR in more depth I probably won't be satisfied anyway.
    Although it would seem that even the people who concern themselves with GR still struggle to come up with a coherent and verifiable answer to this problem.

    Edit: I found similar topic in the archive - https://www.physicsforums.com/archive/index.php/t-156255.html

    EDIT2: I found this paper online on this same exact topic: http://arxiv.org/ftp/arxiv/papers/1111/1111.2331.pdf
    Could anyone comment on it's credibility? The author is implying a static universe which I know to be a very unorthodox idea in today's cosmology so I holding to my skepticism for now but if someone with more experience in scientific process and literature could comment on this I would greatly appreciate it.
    Last edited: Feb 22, 2012
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