Edwin Hubble is that relatively rare thing among dead astronomers — a global household name. He owes his status mainly to the NASA space telescope named in his honour. So when researchers suggested this year that Hubble might have censored the work of a rival to secure credit for the groundbreaking discovery that the Universe is expanding, they triggered a fuss that was far removed from the usual arcane wrangling over historical research priority.
In an admirably thorough Comment on page 171, Mario Livio, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, clears Hubble of wrongdoing. As a result, NASA and a generation of researchers whose careers are closely tied to the Hubble brand can look skywards with some relief.
The charges against Hubble certainly warranted examination. In 1927, the Belgian astronomer Georges Lemaître published a French-language paper in the Annales de la Société Scientifique de Bruxelles that laid out the essentials of a picture of galaxies expanding away from one another, and derived an expansion parameter on the basis of then-recent observations. In 1929, Hubble independently put forward and confirmed the same idea, and the parameter later became known as the Hubble constant. In 1931, Lemaître's paper was translated into English and published in the Monthly Notices of the Royal Astronomical Society, but most English speakers probably learned of Hubble's contribution before they learned of Lemaître's.
Suspicions of foul play emerged earlier this year, when amateur historians noticed that the derivation of the expansion constant is missing from the English translation of Lemaître's work. Knowing that Hubble was concerned that he, and the Mount Wilson Observatory in Pasadena, California, at which he made his observations, should get ample credit for confirming the expansion of the Universe, it was tempting to speculate that he had a hand in the editing of the Belgian's paper. But motive alone doesn't build a case, and professional historians, who had known of the irregularity for years, remained sceptical.
Livio's research suggests that they were right to hesitate. After reviewing hundreds of documents in the archives of the Royal Astronomical Society in London, Livio found a copy of a 1931 letter by Lemaître in which he said that in translating his paper, he had deleted discussion of the velocities of galaxies because it was “of no actual interest”. Why exactly Lemaître thought this is unclear, but it seems that he was not very concerned about getting the credit for his work in the way that modern followers have assumed; instead, he may have worried more about seeming out of date, given that the data on which the expansion constant was based had been improved since 1927.
The idea that the accuracy of papers and their relevance to colleagues ought to be more important than ensuring priority at every step may seem fantastic in today's cut-throat world of science. And perhaps it was then, too. Perhaps Lemaître was simply so flattered to be invited to translate his paper that, aware of Hubble's importance among English-speakers and fearful of repercussions, or eager to join the Royal Astronomical Society, he self-censored. The case against Hubble is closed, but there may still be a story for motivated historians to look into.
Space agencies should also take note. Whether or not Hubble deliberately censored Lemaître, the fact is that in the English-speaking world, Lemaître has lost — to Hubble — priority for his contributions. The Belgian's name is a worthy candidate for the title of a future space mission.