Georges Lemaître

Belgian physicist

• Born: July 17, 1894; Charleroi, Belgium
• Died: June 20, 1966; Louvain, Belgium

The Belgian physicist Georges Lemaître established the foundation for modern cosmology. He was the first to theorize the big bang, the idea that the universe came into being at a specific point in time and expanded outward.

Primary field: Physics

Specialties: Astrophysics; relativity; cosmology

Early Life

Georges-Henri Lemaître was born in Charleroi, Belgium, on July 17, 1894, into a devoutly Catholic family. After attending a Jesuit school for his early education, he began studying civil engineering at the Catholic University of Louvain, Belgium, but his university studies were interrupted by the outbreak of World War I. He served in the Belgian artillery during the war, earning several military honors.

Following the end of the war, Lemaître abandoned the study of engineering and entered the seminary. He was ordained a priest in 1923 and, among other honors, later served for several years as president of the Pontifical Academy of Sciences in the Vatican. Throughout his theological training, Lemaître also pursued his interests in mathematics and physics, in which he earned his doctorate in 1920. The same year he was ordained, Lemaître received a fellowship to the University of Cambridge in England, where he focused on the theory of general relativity proposed by German physicist Albert Einstein in 1916. Basing his research on Einstein’s calculations, Lemaître began formulating his own calculations about the universe.

Lemaître spent the next two years pursuing postgraduate studies in astrophysics in the United States, at Harvard University and the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts. Lemaître was appointed a professor of astrophysics at the Catholic University in Louvain in 1925. He became a full-time professor in 1927, a position he retained until his retirement in 1964.

Life’s Work

In 1927, Lemaître published the results of the calculations he had begun at Cambridge in the Annales de la Société scientifique de Bruxelles (Annals of the scientific society of Brussels). In his paper, he postulated that the universe is expanding in all directions. Einstein had proposed an unknown cosmological constant that lent support to the idea of a static universe, one that has always existed and will continue to exist endlessly in more or less the same form. However, Lemaître’s calculations showed that the universe is either shrinking or expanding. After observing redshift in galaxies outside the Milky Way—the phenomenon of lengthening light waves that, according to the Doppler effect, indicates the light source is moving away from the observer—Lemaître concluded that the universe is expanding.

Given that most scientists at the time—including Einstein—believed in a static universe and that Lemaître did not have substantial proof to support his theory, his 1927 paper was at first largely ignored by the scientific community. Then, in 1929, American astronomer Edwin Hubble confirmed the redshift of galaxies. This led British astrophysicist Arthur Eddington to publish an English translation of Lemaître’s paper in the Royal Astronomical Society’s Monthly Notices in March 1931. Lemaître himself continued to publish papers elaborating on his cosmology during the 1930s. In these, he proposed that the universe had had a definite beginning, wherein all matter was condensed into a single point.

In the early 1930s, scientists took note of and challenged Lemaître’s theory. They generally accepted the concept of an expanding universe, but not the idea of its beginning. It was one of Lemaître’s rivals, British astrophysicist Fred Hoyle, who later coined the term “big bang” to differentiate it from his steady-state theory. The steady-state viewpoint essentially reworked the theory of an infinite and eternal universe. It held that, as the galaxies move further and further apart, the universe continuously generates new matter to compensate for density lost through cosmic expansion. This process thus maintains the universe in a stable condition.

Lemaître’s critics included, at least initially, Einstein. By the time Einstein encountered Lemaître’s theory of cosmic expansion, he had already rejected a similar argument put forth earlier, unbeknownst to Lemaître, by the Russian mathematician Aleksandr Friedmann.

Both Friedmann and Lemaître had used Einstein’s discovery that space and time are flexible, described as part of his theory of general relativity, to reach the same conclusion: The fabric of space had to be either stretching or shrinking, and it was incapable of maintaining fixed dimensions. Einstein was well aware of the implications of his own mathematics. Tied, however, to the traditional notion of a static universe, he altered his methods to make his equations reflect this assumption rather than evidence to the contrary. After Hubble’s confirmation of redshifts emerged and thus supported Lemaître’s theory, Einstein conceded Lemaître’s hypothesis.

Lemaître believed that his theory was testable. If the big bang had really occurred as he described it, it should have produced a number of lasting, observable effects. Lemaître and other supporters of his theory predicted two consequences in particular. First, they believed that the big bang would have caused the universe to enter a state of continual expansion as its components raced away from the epicenter of the original explosion. And second, they claimed that it should be possible to trace the afterglow of the big bang in the form of a particular type of cosmic microwave background radiation (CMBR) left over from the initial explosion.

When Lemaître first proposed his controversial hypothesis, he could only make theoretical predictions, lacking the technology to carry out the necessary observations and measurements. Scientists spent the decades up through the 1960s testing Lemaître’s theory as well as several other competing models without arriving at a consensus. But in 1965, American physicists Arno Penzias and Robert Wilson confirmed the existence of CMBR. The discovery bolstered the credibility of Lemaître’s ideas, which came into wide acceptance by the late 1960s.

Throughout his career, Lemaître perceived no conflict between his pursuit of mathematics and physics to explain cosmological mysteries and his Catholic faith. He held the view that God had endowed humans with an intellectual capacity to contemplate all the wonders of what he believed to be a divinely created universe. Yet Lemaître’s detractors charged that his belief in a creator represented a bias causing flaws in his scientific thinking. Others pointed out that the theory of the big bang contradicted the biblical account of creation. Lemaître, who believed that the big bang theory was compatible on some level with the story told in Genesis, had little patience for these critics.

Lemaître died in Louvain on June 20, 1966, at the age of seventy-one.

Impact

Lemaître’s theory of the big bang established the foundation for modern cosmology, the study of the origins, structure, and nature of the universe. Since Lemaître first proposed his theory, astrophysicists have been investigating the credibility of the theory and explanations of the first few minutes of universal history. The nature of the primordial atom, the particles that constituted the atom, and the reaction of the particles in the first few minutes after the explosion were topics Lemaître left unaddressed. Also unexplained were the cause and nature of the explosion.

The big bang theory has brought about an examination of the universe on both the grand and the microscopic scales. Astronomers have scanned the heavens for background radiation, resulting in discoveries of cosmic rays and other forms of radiation. Physicists have explored the inside of the atom, hoping to discover clues that might lead back to the first few minutes of history. Their search has required the building of particle accelerators in an effort to duplicate the energy of the initial explosion. Following this development, the scientific community began exploring the subatomic world, which turned out to be full of unknown particles. Whether or not Lemaître’s theory is correct, it has led scientists to fit antimatter, quarks, and other newly discovered forms of matter into the picture of the early universal theory.

Bibliography

Bartusiak, Marcia. The Day We Found the Universe. New York: Vintage, 2009. Print. A history about discovering the universe, centered on the early 1900s. Includes discussion of Lemaître and the big bang theory.

Farrell, John. The Day Without Yesterday: Lemaître, Einstein, and the Birth of Modern Cosmology. New York: Avalon, 2005. Print. A biography of Lemaître, detailing his work on the big bang theory.

O’Connell, Jason R., and Alice L. Hale, eds. The Big Bang: Theory, Assumptions, and Problems. Hauppauge, NY: Nova Science, 2012. Print. Up-to-date research into the big bang theory covering various topics, including problems with the theory.