Georges Lemaître: Discovered the Expansion of the Universe


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Monsignor Georges Lemaître: Image courtesy of Katholieke Universiteit Leuven

In 1927, Belgian priest and physicist Georges Lemaître made what is perhaps the greatest discovery in modern cosmology — our universe is expanding. Four years later, he proposed that the universe began with a “single quantum” — what we now call the big bang. Yet the public and many scientists remain unaware of Lemaître’s seminal achievements.

Early Life of Georges Lemaître

Georges Lemaître (1894-1966) was born on July 17 in Charleroi, Belgium. It was at his Jesuit secondary school where he first felt the calling to become a priest — and the desire to become a scientist. At age seventeen, he entered the engineering school at the Catholic University of Louvain. His education was interrupted with the German invasion of Belgium in August of 1914. Twenty-year-old Georges immediately volunteered for the Belgian army, where he witnessed four years of horrific trench warfare.

After the war, Lemaître returned to Louvain and earned his doctorate in mathematics in 1920. He then enrolled in the Maison Saint Rombaut seminary and was ordained a Catholic priest in 1923. Lemaître then studied astronomy at Cambridge University with Arthur Eddington in England, and the U.S. at Harvard College Observatory and M.I.T. After earning a second doctorate in 1927, Lemaître returned to Belgium and became a professor at Louvain.

Lemaître and the Expansion of the Space

The first hints that the universe is expanding came in 1917 when Albert Einstein applied his new general theory of relativity to the universe as a whole. To Einstein’s surprise, his field equations showed the universe was either expanding or contracting. Since there was no evidence for this at the time, Einstein added his famous cosmological constant to model an eternally static universe — one that has always been and will always be the same size. He later called this “the greatest mistake of my life”.

In 1922, Russian physicist Alexander Friedmann developed his own dynamic solutions to Einstein’s field equations.

Then, in an obscure 1927 paper (written in French), Georges Lemaître independently published his solution to Einstein’s equations. From his model, he proposed a linear relationship exists between a galaxy’s distance and its redshift. In general, the further away a galaxy is, the greater its light is shifted towards the red end of the spectrum (lower frequency). Lemaître reasoned that on its long journey to the Earth, a galaxy’s light is stretched in frequency by the expansion of space itself. The longer the light’s journey, the more the universe has expanded — thus the greater the light’s stretching or redshift. Lemaître backed up his claim by correlating published redshift data from Strömberg and Slipher with galaxy distance measurements by Hubble and Humason.

The universe continues to expand: Image credit NASA

That same year, Einstein was in Brussels to attend the Solvay Conference. Lemaître collared the great physicist to explain his model. Einstein responded: “Your calculations are correct, but your grasp of physics is abominable.”

Two years later, Edwin Hubble — who, like most scientists, had not read Lemaître’s paper — came up with the same redshift/distance relationship using nearly the same data. Ignorant of Lemaître’s precedence, physicists later labeled it “Hubble’s Law”. The discovery of the expansion of the universe is still generally credited to Hubble, even though he reportedly rejected this explanation for galaxy redshift to the end of his life.

The Cosmic Egg

In 1931, Monsignor Lemaître proposed an even more radical idea — the universe began as a “single quantum”. The expanding universe must have been smaller and smaller in the past, he reasoned. Thus it must have had a finite beginning.

How was Lemaître’s idea received? Many physicists were suspicious of a beginning of the universe proposed by a Catholic priest. The idea was too close to the Genesis story in the Bible. To make matters worse, Pope Pius XII latched onto Lemaître’s theory as confirmation of the biblical description of creation. Lemaître argued it was just a scientific theory and nothing more — neither confirming nor denying religious beliefs. He said:

As far as I can see, such a theory remains entirely outside any metaphysical or religious question . . . It is consonant with Isaiah speaking of the hidden God, hidden even in the beginning of the universe.

In 1933, Lemaître and Einstein gave a series of lectures in California. Recanting his earlier objections, Einstein now called Lemaître’s theory “the most beautiful and satisfactory explanation of creation to which I have ever listened.”

The expanding universe (Click for larger view): Image credit NASA

Honors and Vindication in Later Years

Lemaître defended his views to other physicists with great conviction, but never sought personal fame. Nonetheless, he received recognition from his country, his church, and his colleagues. In 1934, Lemaître received the Francqui Prize, his country’s highest scientific honor. Pope Pius XI inducted him onto the Pontifical Academy of Science two years later. He was elected to the Belgian Royal Academy of Science and Arts in 1941, and was the first to receive the Eddington Medal in 1951.

Lemaître’s ideas were vindicated in 1964 with the discovery of the cosmic microwave background — the residual radiation from the big bang. His assistant told him of this discovery in 1966 while Lemaître was in Hospital Saint Pierre suffering from a heart attack. The man called “the father of the big bang” died two weeks later at the age of seventy-one.


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