B4. Should Hubble’s Law be Renamed? Your Vote Counts!

Astronomers Edwin Hubble (left) and Georges Lemaître (right)

Astronomers Edwin Hubble (left) and Georges Lemaître (right) who first developed theories about the expansion of the Universe. Observations later made using the 100-inch Hooker Telescope on Mt. Wilson in California (upper-left) and the Hubble Space Telescope (upper-centre) supported those theories. (NASA / ESA / A. Feild (STScI))

While the discovery of the expansion of the Universe is one of the founding observations for cosmology, the history of who exactly first made it is more fuzzy. At the GA on Thursday, IAU members will vote on whether to rename the equation describing the expansion of the Universe from “Hubble’s law” to the “Hubble-Lemaître Law”, with an option to extend electronic voting to the full IAU membership.

A brief history of an expanding Universe

In 1927, Belgian astronomer Georges Lemaître published “Un Univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques”, a paper in which he rediscovered Friedmann’s dynamic solution to Einstein’s general relativity equations that describes an expanding Universe, and then derived how this implied that galaxy spectra should be redshifted proportional to their distance. Lemaître also used existing published data on galaxies to derive the rate of expansion.

In 1928, both Lemaître and the American astronomer Edwin Hubble attended the third IAU General Assembly in Leiden, the Netherlands, where they discussed the importance of redshift in observations of distant extragalactic nebulae.

In 1929, Hubble published “A relation between distance and radial velocity among extra-galactic nebulae”, a paper in which he derived the linear distance-velocity relation for galaxies. In 1931, with Milton Humason he co-authored “The velocity-distance relation among extra-galactic nebulae”, which included more detailed observations of galaxy velocities. Soon after, cosmic expansion equations were called “Hubble’s law”.

Setting the historical record straight

Between the publication and the language, Lemaître’s article was not widely read by astronomers (although it was read by Albert Einstein, who accepted the maths but rejected the concept of expansion at the time). When a translation of the paper was published in the Monthly Notices of the Royal Astronomical Society in 1931, Lemaître edited out the expansion equations, disinclined to republish work based on more tentative observations when Hubble had since published similar work using more detailed observations. His own work on galaxy velocities was “of no actual interest”, Lemaître wrote to the journal’s editor.

But now, in order to honour Lemaître’s contribution and, as the IAU’s Resolution B4 reads, to honour his intellectual integrity in valuing scientific progress more than his own visibility, the IAU is asking its members to vote on whether Hubble’s law should be renamed as the “Hubble-Lemaître Law”.

An Unexpected Controversy

But the resolution itself isn’t that simple, and it has generated lively debate. We sat down with outgoing General Secretary Piero Benvenuti to understand what’s going on with Resolution B4.

During the 2006 GA in Prague, the IAU voted on a resolution about the definition of a planet that excluded Pluto (and all exoplanets). “That has generated quite a lively discussion which is still going on,” says Benvenuti. Within the IAU, a lot of that criticism has focussed on procedures that meant only the small fraction of members who were physically present at the 2006 GA were able to vote. This led to adding the option for electronic voting into the bylaws and statutes.

But there’s a catch. “If the Executive Committee wants to propose a resolution for an electronic vote, this has to be announced at least three months in advance from the General Assembly,” explains Benvenuti. “We didn’t anticipate such a large discussion, and so we didn’t think to propose an electric vote [for Resolution B4].”

But now that the conversation is sparking up, the Executive Committee is less confident that the resolution clearly represents what IAU members want. “We see that we run the risk of voting this only locally and get similar criticism [to what] we had at the time of the Pluto affair,” says Benvenuti. The only problem is that they realised the resolution was controversial too late to meet the three-month notice period.

Instead, Benvenuti recommended that the IAU members at the GA vote on the resolution, but then request approval from the assembly to extend the vote electronically. “We don’t want to be bound by bureaucracy, and if we see that something makes sense, is logical — we want to do it,” says Benvenuti.

What happens now?

Resolution B4 was presented during the first Business Meeting last week, and will be up for vote along with several other (less controversial) resolutions during the second Business Meeting on Thursday at 16:30-18:00.

Now, Benvenuti explains, Resolution B4 will be presented at the session and opened for discussion and put to a vote, just like all the other resolutions. But what’s different about this one is that Benvenuti wants the discussion at the GA to be captured, with all the arguments in favour and against the resolution summarised in a document to be shared with the full IAU membership, along with details of the result of the vote at the GA. “People at home would have an opportunity to see it, to consider the different positions on the resolution, and then make their own judgment, then a vote,” says Benvenuti. “The final decision will be the electronic vote.”

Please note that access to the venue will be restricted on Thursday, when Resolution B4 will be voted on, due to increased security for a European Council meeting, so please allow extra time to enter the building.