American astronomer Edwin P. Hubble has traditionally been credited with the discovery that of the expanding universe. In 1929 he published a paper which described how the more distant a galaxy is from earth, the faster it appears to move away from us, a principle now known as Hubble’s Law. Using the speed of recession as deduced from redshift data (measured by astronomer Vesto Slipher) and the distance from earth to those galaxies (measured by Hubble himself), Hubble was able to calculate the cosmic expansion rate, a constant now known as the Hubble Constant. That discovery made him a luminary in the field and resulted in the coolest telescope ever being named after him in 1983.
The only problem is he wasn’t the first to discover it. Belgian priest and astronomer Georges Lemaître published his own findings about the velocity-distance relationship, including a nearly identical cosmic expansion constant deduced from recently published redshift data, in a French-language paper in the Annales de la Société Scientifique de Bruxelles in 1927. The journal was fairly obscure and the article only translated into English for publication in the Monthly Notices of the Royal Astronomical Society in 1931. The 1931 version, however, was missing key paragraphs about the expansion constant.
The spotty translation has long been known to historians and astronomers, but earlier this year controversy erupted over whether Hubble might have had something to do with muzzling his competition. Astronomer Sidney van den Bergh suggested (pdf) that the translator had intentionally dropped the cosmic expansion paragraphs, and mathematician David Block built on that (pdf), speculating that the “fiercely territorial” Hubble, concerned that he and the Mount Wilson Observatory in Pasadena, California, receive all the credit for the expanding universe, influenced the English publication to censor the paragraphs that showed that Lemaître had gotten there first.
There was no evidence of this but neither was their evidence exonerating Hubble from the charge, until now. Mario Livio, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, has found definitive proof that Hubble had nothing at all to do with the missing paragraphs. The culprit, as it happens, was none other than Georges Lemaître.
After going through hundreds of pieces of correspondence of the Royal Astronomical Society, as well as minutes of the RAS meetings, and material from the Lemaître Archive, Livio has discovered that Lemaître omitted the passages himself when he translated the paper into English!
In one of two “smoking-gun letters” uncovered by Livio, Lemaître wrote to the editors: “I did not find advisable to reprint the provisional discussion of radial velocities which is clearly of no actual interest, and also the geometrical note, which could be replaced by a small bibliography of ancient and new papers on the subject.”
As for why Lemaître chose to censor his earlier discovery of the expanding universe, the letters don’t provide his motivation. Livio thinks that Lemaître just didn’t particularly care to claim the find. The data he had used to calculate the expansion constant had been improved on since 1927, so his old work might have looked out of date. He also might not have thought there was much of a point to including his earlier but more tentative findings since Hubble’s had already been published two years before.