Who proposed the velocity-distance relation two years before Hubble's 1929 confirmation?

Georges Lemaître proposed the velocity-distance relation two years before Hubble’s 1929 confirmation.

In a 1927 paper, the Belgian priest, physicist, and astronomer derived a relationship in which a galaxy’s recession velocity increases with its distance. He used general relativity and available astronomical measurements to argue that the universe was expanding. His work appeared in French in a Belgian scientific journal and initially attracted little attention.

Edwin Hubble published his observational distance-velocity relation in 1929, using galaxy distances and redshift measurements. Hubble’s paper made the relationship famous, but Lemaître had already derived it and estimated a value for the proportionality constant now associated with the Hubble constant.

The historical credit is therefore more nuanced than the familiar name “Hubble’s law” suggests. In 2018, the International Astronomical Union recommended “Hubble–Lemaître law” to recognize Lemaître’s contribution. Alexander Friedmann had independently obtained expanding-universe solutions from Einstein’s equations in 1922, but Lemaître was the figure who connected the theory to the observed velocity-distance relation.