# Does wavelength affect redshift caused by the metric expansion of space?

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?

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.

• 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. – zephyr Sep 8 '17 at 13:05
• 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. – pela Sep 9 '17 at 7:51