Hubble's famous plot, showing the linear relationship between galaxies' distance and radial velocity (from Hubble, 1929)

The name of Edwin Hubble is ubiquitous in modern astronomy. Telescopes, constants, laws, galaxy classification schemes are named after the famed astronomer, considered to be the godfather of modern astronomy. If he were alive today, he would have appeared on The Simpsons, Southpark and Saturday Night Live. But a number of recent papers posted to the Arxiv and presented at conferences are calling into question Hubble’s claim to fame, and even his integrity as a scientist.

At the root of these questions lies the work of a well-known Belgian astronomer, Georges Lemaître. As a semi-Belgian I felt it my duty to look into the story and blog (and thanks to fellow Belgian astronomer Geert Barentsen for the tip).

Hubble published his seminal result showing a linear relationship between the distance to galaxies (or extra-galactic nebulae, as they were still known then) and their radial (i.e. recession) velocities in a 1929 paper in the Publications of the National Academy of Sciences, carrying the title “A relation between distance and radial velocity among extra-galactic nebulae”. He uses a decade of observations at Mount Wilson Observatory to derive the fundamental relationship empirically. As a result, Hubble is widely credited as the first scientist to show incontrovertibly that the Universe all around us is expanding.

But was he really the first?

In early June, Sydney Van den Bergh, an astronomer based in Victoria, Canada, posted a short note to the Arxiv, recalling a meeting with Georges Lemaître, a Belgian priest and theoretician based at the Catholic University of Louvain. In 1927, two years earlier than Hubble, Lemaître published a paper in which he demonstrates the expansion of the Universe from both observations and theory. Using published distances and velocities, he derives the constant of proportionality between galaxies’ distance and velocity, the number now known as Hubble’s constant H0.

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