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Does light have mass?

  1. Oct 5, 2012 #1
    Does light have mass?
    Is light affected by gravity?
    What should something have to be affected by gravity?
     
  2. jcsd
  3. Oct 5, 2012 #2

    Simon Bridge

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    No.
    yes.
    energy.

    These are questions that are well covered online though.
    The main confusion comes from trying to relate the behavior of light near a massive body and Newtonian gravity.
    Understand that Newton's gravity is wrong and has been supplanted by General Relativity, where gravity is understood in terms of local curvature in 4D space-time.
    In GR, the gravitational interaction is covered by the stress-energy tensor.
     
  4. Oct 6, 2012 #3

    Drakkith

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    No, but it has energy.

    Yes! Gravity according to General Relativity, which is our leading theory of gravity, is the result of curved spacetime. Anything traveling through spacetime will be affected, including EM radiation that is massless.

    Well, energy is one answer. But I would ask that if something has absolutely zero energy, does it even exist? Could it just be that all things are affected by gravity?
     
  5. Oct 6, 2012 #4
    Would curved space time have potential energy in same way a spring is just waiting to be relased by the release of the matter in space time?
    I ask because if gravity effects everything with energy, that would then mean it would effect itself which we know gravity doesn't effect gravity.
     
  6. Oct 6, 2012 #5

    Drakkith

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    Except that it does affect itself. This is why you cannot apply renormalization to gravity. (Or so I'm told)
    http://www.einstein-online.info/spotlights/gravity_of_gravity
     
  7. Oct 6, 2012 #6
    How does it effect itself? If gravity effects energy and gravity can have energy, wouldn't there be a infinite space curve like a black hole only not effected by mass in a small area but rather - itself.
     
  8. Oct 6, 2012 #7

    Drakkith

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    I don't know GR well enough to answer this. Check this thread though.
    https://www.physicsforums.com/showthread.php?t=640266
     
  9. Oct 6, 2012 #8

    Chronos

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    If gravity contributes to itself, you end up with free energy.
     
  10. Oct 6, 2012 #9
    Hi.

    Within accuracy in current experiment standard, no mass is observed for light.
    You can find the maximum possible value of light mass easily in books or web.

    Yes, it runs 'straight' in curved space-time.

    Gravity itself express geometry of space-time.

    Regards.
     
  11. Oct 6, 2012 #10
    Thank you all for your enlightening and educational comments.
     
  12. Oct 6, 2012 #11

    Simon Bridge

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    Do you have a reference for that?
    Did you see the reference in Drakkith's earlier post?

    Anyway - seems we have satisfied OP ;)
     
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