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Georges Lemaître
1927· Person
ProvenTested many times; part of working physics.
Georges Lemaître (1894-1966), Belgian Catholic priest and physicist who first proposed that the universe is expanding and began from a single dense state.
See it on the Science map →How it works
Lemaître solved Einstein's gravity equations and found they describe a universe that grows. In 1927 he combined that math with existing galaxy measurements and estimated the expansion rate, two years before Hubble. In 1931 he ran the film backwards and proposed a 'primeval atom': everything once packed into one hot, dense state. He kept science and faith separate, and objected when a pope implied physics had proven creation.
Why it matters
He turned expansion from a curiosity of equations into a history of the universe with a beginning. The modern Big Bang theory is his idea, refined.
How the work held up
Hubble's 1929 measurements confirmed expansion; the 1965 discovery of the cosmic microwave background confirmed a hot, dense beginning. In 2018 astronomers voted to rename Hubble's law the Hubble-Lemaître law.
Still a mystery
His primeval atom said nothing about what came before or why it existed. That question remains open; physics still cannot describe the very first instant.
Connections (3)
▸Georges Lemaître proposed The Big BangProven
The relationship
Having shown the universe expands, Lemaître ran the expansion backwards. In 1931 he proposed that everything began compressed into a single 'primeval atom' that broke apart, starting space, time and the expansion. That is the core of the Big Bang theory: a definite, hot, dense beginning, rather than a universe that has always existed.
How the link was found
Georges Lemaître, in a 1931 letter to the journal Nature, partly prompted by debates with Arthur Eddington about the universe's start.
Why it's proven
The 1965 discovery of the cosmic microwave background confirmed a hot, dense early phase. Lemaître learned of it shortly before his death in 1966.
Open questions and mysteries
His 'atom' was a guess at the first instant. Modern physics still cannot describe that instant; general relativity breaks down there.
▸Georges Lemaître predicted The universe is expandingProven
The relationship
Lemaître solved Einstein's equations for an expanding universe and predicted that galaxies should recede at speeds proportional to their distance. He then used existing redshift and distance data to estimate the rate, about 625 kilometers per second per megaparsec. That was the expansion law, two years before Hubble published it.
How the link was found
Lemaître, 1927, in a French-language Belgian journal few read. His own 1931 English translation left out the rate estimate, as historians confirmed in 2011.
Why it's proven
Hubble's 1929 data matched the predicted pattern. In 2018 the International Astronomical Union recommended calling it the Hubble-Lemaître law.
Open questions and mysteries
The law's exact rate is still disputed today, the 'Hubble tension'.
▸Georges Lemaître kept his Big Bang science separate from "In the beginning was the Word": creation by God's wordFaith & belief
The relationship
Lemaître held that the Bible teaches salvation, not physics, and that his 'primeval atom' neither proved nor denied creation. A beginning in physics, he thought, is not the same as creation in theology. So when Pope Pius XII told the Pontifical Academy of Sciences in November 1951 that modern cosmology bore witness to creation, Lemaître was dismayed.
How the link was found
Lemaître stated his view in a 1933 New York Times interview and at the 1958 Solvay conference. He reportedly worked through Jesuit astronomer Daniel O'Connell to dissuade the Pope; Pius XII's 1952 address to astronomers did not repeat the claim.
Is it proven?
Documented in his own writings and by historians such as Dominique Lambert and Helge Kragh. The Church kept him in high regard: he presided over the Pontifical Academy of Sciences from 1960 until his death in 1966.
Open questions and mysteries
Whether faith and science are fully separate realms, as Lemaître held, or should inform each other is still debated by scientists and theologians alike.