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Do photons gain mass in the presense of a black hole?

  1. Feb 6, 2012 #1
    I understand how gravity can affect photons or light waves (Einstein's equivalence principle). But I was wondering if there are any theories that predict that a photon might somehow acquire mass in the presence of a singularity.
  2. jcsd
  3. Feb 6, 2012 #2
    I'm going to assume that you mean black-hole, when you say singularity. The central point of the BH should have no relevance---unless I misunderstand you.

    Note that there isn't anything special about the gravity of a BH. If a BH's gravity somehow gave light mass, then a star, or even a planet would also.

    Nothing, however, can give a photon rest-mass. In general relativity, 'mass' (in-general) is not always well-defined. A photon will (presumably) exert a gravitational force on other-particles, regardless of the local gravity (e.g. a black-hole).
  4. Feb 6, 2012 #3
    My understanding is that light waves flatline when trying to leave a BH - they can not escape. I was not sure if this had an effect on the photons. - Thank you for your answer.
  5. Feb 6, 2012 #4
    Black-holes don't change anything about the photons themselves; instead they're drastically deforming the shape of space-time itself. At (and within) the event horizon, the photons are exactly the same, but spacetime is bent so much that nothing can move outward.
  6. Feb 8, 2012 #5
    I was not sure if this had an effect on the photons. http://www.bosin.info/g.gif [Broken]
    Last edited by a moderator: May 5, 2017
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