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Conservation of energy question

  1. Sep 5, 2012 #1
    Lets say we had a light source. It takes energy and turns it at some efficiency into light.

    You put the light source on say, a white dwarf. The light source, still at the same efficiency, produces light that is gravitationally redshifted and therefore lost energy.

    What happened to the energy in the light? All that happened was that we moved it around yet its energy changed?
     
  2. jcsd
  3. Sep 5, 2012 #2

    CWatters

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    Where did the energy come from to escape the star?
     
  4. Sep 5, 2012 #3

    Bobbywhy

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    The Wiki page on “Gravitational Redshift” begins with this:

    “In astrophysics, gravitational redshift or Einstein shift is the process by which electromagnetic radiation originating from a source that is in gravitational field is reduced in frequency, or redshifted, when observed in a region of a weaker gravitational field. This is as a direct result of Gravitational time dilation; frequency of the electromagnetic radiation is reduced in an area of a higher gravitational potential. There is a corresponding reduction in energy when electromagnetic radiation is red-shifted, as given by Planck's relation, due to the electromagnetic radiation propagating in opposition to the gravitational gradient.”

    Then there is a detailed description of the energy question further down the page.

    http://en.wikipedia.org/wiki/Gravitational_redshift
     
  5. Sep 5, 2012 #4
    thank you. what about universal expansion and associated redshift? where does the energy go?
     
  6. Sep 5, 2012 #5

    CWatters

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    I don't pretend to understand it or even know if this is current thinking but google found..

    http://arxiv.org/ftp/physics/papers/0407/0407077.pdf

    He's also written other papers such as..

    http://arxiv.org/ftp/physics/papers/0511/0511178.pdf
     
  7. Sep 5, 2012 #6

    CWatters

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