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Lightspeed and 0 mass

  1. Mar 20, 2012 #1
    So, an object can move with c if and only if it has 0 mass.So howcome that light is bended by gravity? How can smth with 0 mass be bend by gravity?


    Ty
     
  2. jcsd
  3. Mar 20, 2012 #2
    Well,I think when the 0 mass moves,it's mass is no longer 0 according to the formula E=m*c^2
     
  4. Mar 20, 2012 #3

    Bill_K

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    Because gravity couples to energy (and momentum, and stress), not mass. A photon has zero mass but nonzero energy.
     
  5. Mar 20, 2012 #4
    ty for your answers .I haven't studied relativity in school yet but from what i know gravity is mass times gravitational acc.,but.if u apply that here m is zero so G is zero

    Are the formulas from classic mechanics applicable in any relativistic situation?
     
  6. Mar 20, 2012 #5
    The bending of light around objects with mass, gravitational lensing, occurs because the spacetime around a massive object (such as the sun, a galaxy, etc.), is curved, and distorts the path of the light travelling near that object.

    See this image for an example:

    http://scienceblogs.com/startswithabang/upload/2010/07/see_a_quasar_gravitationally_l/gravitational-lens-01.jpeg [Broken]

    As Bill K said, it is the momentum of the photons that determines how dramatically they are curved away from their original path.
     
    Last edited by a moderator: May 5, 2017
  7. Mar 20, 2012 #6

    jtbell

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    Staff: Mentor

  8. Mar 20, 2012 #7

    HallsofIvy

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    Only as approximations in the "v much less than c" case.
     
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