Is the cosmological redshift real, or is it an optical illusion caused by dust ?
The cosmological redshift seems to be real enough. For more about it see my article in Sky and Telescopemagazine, February 1993, which gives some background on how to interpret this phenomenon. As the article explains, there are three ways that nature seems to be able to shift the wavelengths of spectral lines from atoms. The familiar Doppler shift is the one we all know from the passing siren. When it approaches, its pitch is higher than when it moves away from us. What works for sound waves also works for light waves, and we can see the Doppler shifts in the light from stars that orbit one another in space. Einstein’s theory of general relativity predicts two new ways of doing the same trick that don’t involve motion as we normally think of it. The gravitational redshift happens when light tries to escape from a gravitational field. This is actually a phenomenon that you can explain using ordinary newtonian physics. Thanks to Einstein’s famous E= m c squared, and Planck’s equally fam
