Remarkable Astronomers: St Edmund's College, Georges Lemaïtre (1894-1966) , and the Big Bang

In October 1923 a handsome priest, recently ordained in Malines, Belgium, arrived at St Edmund’s House, Cambridge (now St Edmund’s College) where he resided for nine months. His name was Georges Lemaître. The research he began in Cambridge had enormous consequences for our understanding of the universe.

Lemaître was attracted by Arthur Eddington, the director of the Cambridge Observatory in Madingley Road. In 1919 Eddington had confirmed one prediction of Einstein’s general relativity. He did this by measuring the shift in the positions of stars during a total eclipse of the Sun, a result that produced instant worldwide fame.

Under Eddington’s supervision in 1923-24, Lemaître worked on applying relativity theory to models of the universe. After a year in Cambridge, Lemaître progressed to study at Harvard and MIT, where he earned his PhD in 1926. Lemaître mixed with observational astronomers in the USA, including Edwin Hubble, who had made the first reliable measurements of the distances of galaxies. It was already known that galaxies were receding. However, Edwin Hubble did not at first attribute this to the expansion of the universe.

When Lemaître returned to Belgium he continued to work on solutions to Einstein’s equations. In 1927 he made what is perhaps the greatest discovery in modern cosmology — our universe is expanding. However, this paper was written in French, published locally, and was not known about in the USA. Later that year, when Lemaître and Einstein met in Solvay, Brussels, famously said: “Your maths is correct, but your grasp of physics is abominable.”

Meanwhile, Hubble was analysing data on galactic distances. Using much the same raw data as Lemaître, he found the relationship between galactic velocities and distances that is now known as Hubble’s Law. It’s important to understand that Hubble did not claim to have discovered expansion. In fact, some scholars suggest that Hubble rejected this interpretation to the end of his life (1954).

Eddington was so impressed by Lemaître’s 1927 paper that he arranged for a translation of it to be published in 1931 by the Royal Astronomical Society (RAS). Curiously that paper omits certain key paragraphs about the expanding universe. Over the years a conspiracy theory gradually gained ground, as sceptics asked: did Edwin Hubble censor the 1931 translation in order to hold on to the credit of discovering the expanding universe? This riddle was finally solved in 2011 when two letters by Lemaître were found in the archives of the RAS. He writes that he removed material on “the provisional discussion of radial velocities which is clearly of no actual interest.”

Lemaître was invited to London in 1931 to present his theory at a meeting of the British Association, where he floated the idea of a “Primeval Atom” from which the universe expanded. Eddington had had similar ideas, but it was Lemaître who developed this concept. He termed it a “Fireworks Universe”, but the expression that stood the test of time was Fred Hoyle’s metaphor of 1949 of a Big Bang.

At a more technical level there is an even bigger story. In order to arrive at a static model of the universe Einstein had modified the equations by introducing a term that he called the cosmological constant. The discovery of the expanding universe changed things: the universe was not static, so it did not need this arbitrary constant. Lemaître made a daring move in 1933 when he identified Einstein’s rejected constant with the intrinsic energy of the vacuum. This was the first time that the expanding universe was related to vacuum energy. In 1999 astronomers discovered that the expansion of the universe is speeding up, and they proposed that dark energy was the cause. It is now believed that 73% of the mass-energy in the universe is in the form of dark energy.

This article is copyright Total Astronomy Ltd http://www.totalastronomy.com
It was prepared by Simon Mitton
It is the first of a series of articles on Remarkable Astronomers that will be published on this blog in the next few months