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Velocity of light remain costant in a gravitational field?

  1. Jun 23, 2008 #1
    Does the velocity of light remain costant in a gravitational field?
    In my calculation it is less than c.
  2. jcsd
  3. Jun 23, 2008 #2
    velocity is a vector quantity... it depends on its direction in relation to the field
  4. Jun 23, 2008 #3
    So c in a gravitational field is bigger than c?
    What Relativity say about this?
  5. Jun 23, 2008 #4


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    Hi Ignition! :smile:

    (You mean speed)

    In general coordinates, the speed of light depends on the metric you have chosen.

    But in local inertial coordinates, the speed of light is always c. :smile:
  6. Jun 23, 2008 #5
    well gravity can bend the path of light, and a black hole can stop light from escaping because gravity is so strong... im not sure if light slows down and turns back around when trying to escape a black hole or if it just cant be bounced back out in the first place or if it goes c out and then is reversed to c in the opposite direction from the gravity... i dont think light accelerates it just goes c... I'm not sure ive never "seen" a black hole haha
  7. Jun 23, 2008 #6
    The *magnitude* is always 'c'. The direction can change, and therefore it can "accelerate" in a given direction.
  8. Jun 23, 2008 #7
    The speed of light in vacuum remains locally the same in a gravitational field. Observers may measure a different speed due to the curvature of spacetime.

    The light is not slowing down, its wordline is curved back into the black hole, so it has nowhere to go but back.

    Light in vacuum does not accelerate since its wordline always follows a geodesic of spacetime.
  9. Jun 23, 2008 #8
    I think you meant "worldline".
    Unfortunately that is all I can contribute to this topic.
  10. Jun 24, 2008 #9
    Re: Light

  11. Jun 25, 2008 #10


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    Re: Light

  12. Jun 25, 2008 #11
    Re: Light

  13. Jun 25, 2008 #12
    Re: Light


    --You'll remember that history is full of dicarded axioms that were once believed in religiously.---

    That's the easy answer as it will always be true of any theory.

  14. Jun 25, 2008 #13
    Re: Light

    True enough.
  15. Jun 25, 2008 #14
    Re: Light

    Relativity is a convention. As it works, it is not wrong, but incomplete. It is a convention that is self sustaining because it is self consistent and therefore inescapable.
    All relativity theory must concede, accept or agree on the first instance of measure which is
    usually referred to as "proper" time, mass or length. This first "quantification" sets all subsequent
    quantification of dimension simply because space, time and mass cannot be defined
    uniquely from each other.
    Without this first premise of the constancy of dimension set by choice and sustained by
    the convention of the relativity of "proper" dimension, the equations of mechanics become
    meaningless, arbitrary expressions.
  16. Jun 25, 2008 #15
    Re: Light

    Why can't I PM shamrock5585??

  17. Jun 26, 2008 #16
    Re: Light

    I think you said it well. I like the convention thing. What is reality after all. I've been in God's pocket and I can't even find his watch, no less take it apart.
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