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quetric t1_iyxufml wrote

Reply to comment by forte2718 in How are we sure that speed of light and other basic constants are really constants on a large cosmological scale of time and space? by The_Dark_Passenger93

How do we account for red shift without knowing distance? AFAIK the shift itself is the only way we can measure distance at cosmological scales.

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forte2718 t1_iyxz2nm wrote

>How do we account for red shift without knowing distance?

We don't. We know the distance, at least to within some margin of error that is always accounted for.

>AFAIK the shift itself is the only way we can measure distance at cosmological scales.

That isn't accurate. You probably want to do a little bit of reading into the cosmic distance ladder and how it is constructed. Redshift needs to be accounted for at all but the closest distances, and there are close to two dozen different ways of measuring differently-sized distances that cover overlapping distance ranges, and which are all in general agreement with each other within the overlapping ranges, as well as in agreement with the measured redshifts.

Hope that helps!

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mfb- t1_iyy7hip wrote

Tests of the fine structure constant compare different wavelengths from the same source. The ratio depends on the fine structure (for suitable transition choices) while redshift cancels in the ratio. The uncertainty on the redshift is far too large for the extremely precise measurements (~10^(-7) level) we can do with the ratios (/u/forte2718 ).

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