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Old Apr 25th 2018, 12:57 PM   #1
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General Relativity and the Principle of Reversibilty of Light.

Does GR imply that the Principle of Reversibiltiy of Light does not hold in our universe?
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Old Apr 25th 2018, 02:39 PM   #2
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Originally Posted by studiot View Post
Does GR imply that the Principle of Reversibiltiy of Light does not hold in our universe?
I'm not certain but bet that it does hold given GR. Light moves on geodesics which under he right circumstances means it should hold under the Principle of Reversibility of Light.
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Old Apr 25th 2018, 04:03 PM   #3
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Thanks for the reply

It's geodesics that are the problem.

Take a simple example.

A survey sets up a theodolite at point A on the earth's surface and sight point B.
He then sets out a line of pegs leading to B

Another surveyor sets up at B and does the same thing.

This produces two rows of pegs leading from A to B and B to A.

This is well known and derives from the fact that gravity at A and B point to slight different centres since the Earth is not a true sphere.

I am trying to get my head around the more difficult question of the universal spacetime manifold, which does the same thing on a much grander scale than the 2D manifold of the Earth's surface.
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Old Apr 25th 2018, 10:04 PM   #4
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Smile GR

Congratulations
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Old Apr 26th 2018, 02:00 PM   #5
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Originally Posted by htam9876 View Post
Congratulations
Why?

-Dan
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Old Apr 27th 2018, 11:26 AM   #6
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So it has been suggested to me that even if light is emitted from both ends of a given path it is not possible to actually reproduce that path, starting from each end since the time coordinates will not be the same.
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