So we know that Hubble found evidence that the universe was expanding through finding redshift / blueshift of light from distant stars.
My question is, was he using the relativistic or classical Doppler effect in his calculations? Would you get similar results if you used either?
Taken from Wikipedia:
Although widely attributed to Edwin Hubble, the law was first derived from the general relativity equations by Georges Lemaître in a 1927 article where he proposed the expansion of the universe and suggested an estimated value of the rate of expansion, now called the Hubble constant.
Two years later Edwin Hubble confirmed the existence of that law and determined a more accurate value for the constant that now bears his name. Hubble inferred the recession velocity of the objects from their redshifts, many of which were earlier measured and related to velocity by Vesto Slipher in 1917.
So it was first predicted using GR by Lemaitre and then measured by Hubble. It's not Doppler effect because there's not a notion of relative velocity in General Relativity (unless the two object are close and in a region with negligible curvature ).
Hubble's recession speeds were less that $1000$ km/s which is much less than the speed of light, $300,000$ km/s, and so any relativistic correction would have been insignificant.
On reading Hubble's original paper you will realise that the errors in his experimental data were much more significant.
