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I Light acceleration

  1. Sep 20, 2016 #1
    A beam of light bends when near a star. Since velocity is a vector, although the path still follows a null geodesic, a change in direction implies that acceleration is present. Light does then, in fact, accelerate. Is this correct ?:frown:
     
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  3. Sep 20, 2016 #2

    A.T.

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    Coordinate acceleration.

    It can have coordinate acceleration. Geodesic world-line corresponds to zero proper acceleration.
     
  4. Sep 20, 2016 #3

    phinds

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    No it is not correct. A geodesic is followed BECAUSE there is no force being applied to the light. The geodesic is "bent" if looked at via Euclidean geometry, which would imply a force on the light, but space-time does not follow Euclidean geometry, It follows Riemann geometry and the geodesic is a straight line implying no force.

    To restate: the light is not changing direction. It is going in a straight line.

    EDIT: I see AT beat me to it and gave a more complete answer.
     
  5. Sep 20, 2016 #4

    Orodruin

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    Just to be specific:
    Pseudo-Riemannian geometry. In Riemannian geometry the metric is positive definite.
     
  6. Sep 20, 2016 #5

    phinds

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    OK. Thanks
     
  7. Sep 20, 2016 #6

    A.T.

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    The spatial path of light is curved and the propagation direction does change. Only its world-line is a geodesic (locally straight).
     
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