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## Gravitionel redshift – How is it working?

 Quote by Naty1 pervect: Yuiop that's a logical conclusion at the least. And isn't the cosmological constant invarient??? How can that phenomena be a coordinate choice?? Also from a recent discussion in these forums: in brief: redshifts vary over time with the evolution of the universe..... That seems difficult to interpret merely as coordinate choice.....
Redshift measurements are not coordinate dependent. In a lambda-cdm model, lambda is invariant. However, 'expanding space' is an interpretation which comes from a coordinate choice. Note that the Milne coordinates in flat Minkowski space lead to 'expansion of space' without changing the manifold geometry (or, obviously, any observations). None of this is really surprising, because there is no global definition of distance in GR. Any definition of distance is coordinate dependent - thus also, any claimed expansion of distance. The particular aspect of coordinate choice that pins down distance is the choice of spacelike slices used (referred to as a foliation). Given these, distance along 3-geodesics of the chosen surfaces (using the induced 3-metric) give distances for the chosen foliation. Often, one wants a foliation such that 3-geodesics are also spacelike 4-geodesics, but this is not necessary.

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Pallen posts:

 Redshift measurements are not coordinate dependent.
you mean cosmological redshift, not gravitational, right...?? I'm not sure I really understand that observation....in flat spacetime??

 In a lambda-cdm model, lambda is invariant......
What conclusion should I draw regarding these comments....thats why it's the cosmological CONSTANT right....?? you mean the redshifts in the model don't vary over time??

 ..None of this is really surprising, because there is no global definition of distance in GR. Any definition of distance is coordinate dependent - thus also, any claim expansion of distance.
good point....always helps to keep the fundamentals in mind....I failed that criteria a few times in this discussion.....

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