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The Radial Velocity...

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Posted by Bruce on January 19, 2002 23:16:28 UTC

of light with respect to the GR bookkeeper (far away observer at rest in flat spacetime) is

dr/dt = 1-2M/r so as r -> 2M then dr/dt -> 0.

Because of the equivalence principle we do all the local physics using SR and it can be shown that the local coordinate speed of light is always measured at c.

The local radial velocity of light.

drshell/dtshell = + or - 1

The equations of motion for radial and tangential motion of light are a little more complicated because there is another term, b = impact paramenter, accounted for. But when b = 0 the equations are equivalent to the two I mentioned.

The gravitational redshift is due to a loss of energy as the light 'climbs out' of the gravitational field.

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