Here are, very briefly, the background facts that are most relevant for this debate.

By February 1922, astronomer Vesto Slipher had measured the radial velocities (velocities along the line of sight from us) for forty-one galaxies. In a book published in 1923, Arthur Eddington listed those velocities and remarked, “The great preponderance of positive [receding] velocities is very striking; but the lack of observations of southern nebulae is unfortunate, and forbids a final conclusion.” (Galaxies were initially called nebulae [from Latin for “mist,” or “cloud”] because of their fuzzy appearance.) In 1927 Georges Lemaître published (in French) a remarkable paper whose title read (in its English translation): “A Homogeneous Universe of Constant Mass and Increasing Radius Accounting for the Radial Velocity of Extra-Galactic Nebulae.” Unfortunately, it was published in the little-read Annals of the Brussels Scientific Society. In it, Lemaître first discovered dynamic (expanding) solutions to Einstein’s general relativity equations, from which he derived the theoretical basis for what is now known as Hubble’s law: the fact that the velocity of recession is directly proportional to the distance. But Lemaître went beyond mere theoretical calculations. He actually used the velocities of the galaxies as measured by Slipher—and approximate distances as determined from brightness measurements by Hubble in 1926—to discover the existence of a tentative “Hubble’s law” and to determine the rate of expansion of the universe. For the numerical value of that rate, today called the Hubble constant, Lemaître obtained 625 (in the common units of kilometers per second for every 3.26 million light-years of distance). Two years later, Edwin Hubble obtained a value of about 500 for this same quantity. (Both values are known today to have been wrong by almost an order of magnitude.) In fact, Hubble used essentially the same recession velocities—the ones determined by Slipher—without ever mentioning in his paper that these were the latter’s work. Hubble did use superior distances, which were based in part on better stellar distance indicators. Lemaître was fully aware of the fact that the distances he had used were only approximate. He concluded that the accuracy of the distance estimates available at the time seemed insufficient to assess the validity of the linear relation he had discovered.

Based solely on what I have described so far, I think most people would agree that it seems only fair to attribute the discovery of the expanding universe and of the tentative existence of Hubble’s law to Lemaître, and the detailed confirmation of that law to Hubble and Humason. The subsequent, truly meticulous observations of Hubble and Humason extended Slipher’s velocity measurements to greater and much more accurate distances. Here, however, is where the plot thickens.

The English translation of Lemaître’s 1927 paper was published in the Monthly Notices of the Royal Astronomical Society in England in March 1931. However, a few paragraphs from the original French version were deleted—in particular, the paragraph that described Hubble’s law and in which Lemaître used the forty-two galaxies for which he had (approximate) distances and velocities to derive a value for the Hubble constant of 625. Also missing were one paragraph in which Lemaître discussed the possible errors in the distance estimates, and two footnotes, in one of which he remarked on the interpretation of the proportionality between the velocity and distance as resulting from a relativistic expansion. In the same footnote, Lemaître also calculated two possible values for the Hubble constant: 575 and 670, depending on how the data were grouped.

Who translated the article? And why were these paragraphs deleted from the English version? Several history-of-science amateur sleuths suggested in 2011 that someone had deliberately censored those parts of Lemaître’s paper that dealt with Hubble’s law and the determination of the Hubble constant. Canadian astronomer Sidney van den Bergh speculated that whoever did the “selective editing” did so to prevent Lemaître’s paper from undermining Edwin Hubble’s priority claim. “Picking out part of the middle of an equation must have been done on purpose,” he noted. South African mathematician David Block went even somewhat further. He suggested that Edwin Hubble himself might have had a hand in this cosmic “censorship” to ensure that credit for the discovery of the expanding universe would go to himself and the Mount Wilson Observatory, where he made the observations.