Move over, Hubble: discovery of an expanding cosmos entrusted to a little-known Belgian astronomer priest | Science

Hubble's law, the cornerstone of cosmology describing the expanding universe, should now be called the Hubble-Lemaître law, following a vote by members of the International Astronomical Union (IAU), the same organization which revoked Pluto's planet status. The change aims to remedy the historical negligence of Georges Lemaître, a Belgian astronomer and priest who, in 1927, discovered the expanding universe, which also suggests a big bang. Lemaître published his ideas two years before American astronomer Edwin Hubble describes his observations that galaxies farther away from the Milky Way are retreating more quickly.

The final count of the 4060 votes cast, announced today by the IAU, was 78% in favor of the name change, 20% against and 2% abstention. But the vote was not without controversy, both in its execution and in the historical facts on which it was based. Helge Kragh, a science historian at the Niels Bohr Institute in Copenhagen, describes the briefing notes presented to IAU members as "bad history". Others argue that it is not up to IUA to rename physical laws. "It's a bad practice to change the story retroactively," says Matthias Steinmetz of the Leibniz Institute of Astrophysics in Potsdam, Germany. "It never works."

Piero Benvenuti from the University of Padua in Italy, who left his position as secretary general of the AIU in August, proposed the change last year because, historically, he did not feel well . In 1927, Lemaître calculated a solution to the general relativity of Albert Einstein. the equations that indicated that the universe could not be static but was expanding. He supported this claim with a limited set of previously published measurements of galaxy distances and velocities, computed from their Doppler shifts. However, he published his results in French, in an obscure Belgian newspaper, and thus remained largely unnoticed.

In 1929, Hubble published his own observations showing a linear relationship between velocity and distance for retreating galaxies. He became known as Hubble's Law. "Hubble was clearly involved, but was not the first," says astronomer Michael Merrifield of the University of Nottingham in the UK. "He was good at selling his story."

The text of the IAU resolution, circulated to members prior to the vote, states that Hubble and Lemaître met in 1928, at an IAU General Assembly in Leiden, the Netherlands. Low – between the publication of their two documents – and "exchanges of views" on blockbuster theory. Kragh says that this meeting "almost certainly did not take place" and that the IAU declaration "has no documented basis". Benvenuti says that historians know, thanks to the comments of Hubble's assistant, that he came back very happy from Leiden and started gathering more data. "Who else could have talked to Hubble about this problem if it's not Lemaitre?" Benvenuti asked.

The resolution was also criticized for confusing two different problems: the expansion of the universe and the distance-speed relationship for galaxies, also called Hubble's constant. Hubble never claimed to have discovered cosmic expansion, but did a lot of work of observation to determine the speed of expansion of the universe. "If the law is about the empirical relationship, it should be Hubble's law," says Kragh. "If it's cosmic expansion, it should be Lemaitre's law."

Members also criticized the IAU on the conduct of the vote. Traditionally, IAU resolutions are debated at general meetings, once every 4 years, and decided by a show of hands of the members present. But such a poll led to the unpopular vote of 2006 that reclassified Pluto as a dwarf planet. "The UAI has been badly burned by Pluto's trick," says Merrifield. As a result, IAU has put in place an online vote of all 11,000 members.

In the case of the Hubble Act, participants at the August AGM in Vienna were frustrated by a very brief debate, followed by a preliminary poll (74% in favor of the name change). The IAU Executive Committee invited others to submit questions electronically and launched the online vote in early October. Merrifield says that there was not enough time and opportunity for debate. "The AIU has presented the issue as neat and orderly, but it's a much more troubled and complicated story," he says. He added that several other researchers might apply because they were also working on the cosmic expansion and motion of galaxies at the time.

A final concern is whether the IAU is in its rights to intervene in historical affairs. "There is no warrant for naming the physical laws," says Steinmetz. The IAU has recognized and only recommends the use of the term Hubble-Lemaître law. Is it going to take? "No, I do not think so," said Kragh. "The Hubble Law has been rooted in literature for almost a century."

In any case, Merrifield says, "It does not really matter, really."