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Does wavelength play a role in cosmological redshift? Do we see certain wavelengths affected less by expansion or notice any delay in arrival of certain wavelengths?

How accurate are any observations?

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Standard cosmological models predicts that the cosmological redshift and the speed of light are wavelength-independent. This result is confirmed observationally e.g. by Ferreras & Trujillo (2016), who used $\sim500\,000$ SDSS galaxy spectra down to a precision of $\Delta z \sim 10^{-6}$ and $\Delta z \sim 10^{-5}$ for galaxies at $z<0.1$ and $z>0.1$, respectively.

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    $\begingroup$ Wow, it always amazes me to see the precision to which scientists test things, especially things someone generally takes for granted or assumes to just be true. $\endgroup$
    – zephyr
    Sep 8, 2017 at 13:05
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    $\begingroup$ It's a good point, @zephyr. You often hear a statement about science like "It's just theory". But science is, in fact, not just theory. No model is accepted as a theory without substantial observational/experimental evidence. $\endgroup$
    – pela
    Sep 9, 2017 at 7:51

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