Today’s arxiv find is a historical fact that I really should have known by now. From “The linear redshift-distance relationship: Lemaître beats Hubble by two years“:
The facts are simple: Friedman (1922) was the first to publish non- static solutions to Einstein’s field equations. However, he did not extend that into a cosmological model built on astronomical observations. In 1927 Lemaître rediscovered these dynamical solutions. In the same publication he extracted (on theoretical grounds) the linear velocity–distance relationship v=Hr. Combining redshifts published by Stromberg (1925) (who relied mostly on redshifts from Slipher (e.g. Slipher 1917)) and Hubble’s distances via magnitudes (Hubble 1926), he calculated for the “Hubble constant” two values, 575 and 670 km/sec/Mpc depending on how the data is grouped. For Lemaître these results showed that the Universe was expanding. Two years later Hubble found the same velocity–distance relationship v=Hr on observational grounds from practically the same observations that Lemaître used in 1927. However, Hubble does not credit anyone for the redshifts, most of which again came from Slipher.
Why is this not more widely known? In 1931, Lemaître’s paper was translated into English with the help of Eddington, but “the two pages from the 1927 paper that contain Lemaître’s estimates of the Hubble Constant are not in the 1931 MNRAS paper”.
The standard story is that Friedman discovered the equations. Lemaître rediscovered the equations and promoted them. Hubble used Slipher’s observations to show that the expansion predicted by the equations was actually true. It seems that Lemaître did it all! And, according to Wikipedia, was one of the inventors of the Fast Fourier Transform.