Variation of alpha vs cosmological expansion

[fhenryco]

hello,

My question will be quite naive for experts and reflects the fact that I'm new to the subject of varying the fine structure constant alpha and mainly need an introductory reference ... so if someone has a good one to advice ...thanks a lot

i just don't understand the basics: how people can distinguish pure expansion effects (that should shift absorption ray wavelengths, let say Lambda1 and Lambda2 by the same factor so also the difference Lambda1-Lambda2 by the same factor ) from time variations of the fine structure constant alpha that also modifies Lambda1-Lambda2 ?

It's because i don't understand how the modification of alpha could modify Lambda1-Lambda2 by some factor F without modifying also Lambda1 and Lambda2 individually by the same factor F , which would make it indistinguishable from a pure expansion effect...i guess (?)

thanks in advance

 

[mfb]

A variable fine-structure constant would change $\lambda_1 / \lambda_2$ (via the fine-structure, which depends on higher powers of $\alpha$), the expansion of space does not. Spectroscopy therefore allows to measure both at the same time, and there are good upper limits on any possible shift of the fine-structure constant.

 

[fhenryco]

A variable fine-structure constant would change $\lambda_1 / \lambda_2$ (via the fine-structure, which depends on higher powers of $\alpha$), the expansion of space does not. Spectroscopy therefore allows to measure both at the same time, and there are good upper limits on any possible shift of the fine-structure constant.

Thank you very much ! i suspected something like "higher powers of alpha" involved ! this is much more clear now ! it's very difficult to find such a basic crucial information in vulgarisation sites while in scientific publications it is often buried in the formalism. so thank you again for helping me save my time.