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Pyter

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- TL;DR Summary
- Speed light modulo changes to allow ligth ray bending in non-inertial frames.

Hi all,

I need help understanding the light ray bending in the original GR 1916 paper,

First of all, Einstein states the ##c## is not an invariant in GR.

In fact, from (70) and (73), it stems that $$\gamma = \sqrt{ -\frac {g_{44}}{g_{22}} }, $$ where ##\gamma## is ##|c| <= 1## (in relativistic units), and =1 in a Lorentz frame when ##g_{44} = -1## and ##g_{22} = 1##.

Then Einstein proceed to compute the light ray curvature using the partial derivative of ##\gamma##.

Questions:

I need help understanding the light ray bending in the original GR 1916 paper,

*Die Grundlagen...*.First of all, Einstein states the ##c## is not an invariant in GR.

In fact, from (70) and (73), it stems that $$\gamma = \sqrt{ -\frac {g_{44}}{g_{22}} }, $$ where ##\gamma## is ##|c| <= 1## (in relativistic units), and =1 in a Lorentz frame when ##g_{44} = -1## and ##g_{22} = 1##.

Then Einstein proceed to compute the light ray curvature using the partial derivative of ##\gamma##.

Questions:

- If the computed ##|c|## in a frame subjected to gravity is generally ##<= 1##, how come when an observer measures it, it's always 1?
- Since the ##g_{**}## are not unitary in an accelerated frame not subjected to gravity, this means that the invariance of ##c## doesn't apply also in this case, i.e. mass-less flat space?
- Can you explain the following equations where E. computes the total curvature, in particular $$curvature = -\frac {\partial {\gamma}} {\partial n}$$? He talks about the Huygens principle, but that formula doesn't seem a direct consequence.