Lemaître Proposes the Big Bang Theory Summary

  • Last updated on November 10, 2022

Georges Lemaître proposed that the universe was once a giant atom that exploded and continues to expand.

Summary of Event

In the early twentieth century, astronomers and physicists were eager for new discoveries about the macrocosm of universal life. Although these sciences often worked together, an individual did not need to have a full understanding of one field in order to contribute successfully to research or theory in the other. Often, astronomers would observe the physical world and puzzle about unknown or unexplained phenomena, and then physicists would resolve the issues raised in terms of their theories and equations. Conversely, physicists might develop new theories about the nature of the universe without having any observational data. In such cases, astronomers would proceed to seek out the projected physical realities the physicists proposed from their equations. The big bang theory is an example of this discovery method: equation first, observation second. [kw]Lemaître Proposes the Big Bang Theory (1927) [kw]Big Bang Theory, Lemaître Proposes the (1927) Big bang theory Universe;expansion Astronomy;big bang theory [g]Belgium;1927: Lemaître Proposes the Big Bang Theory[06780] [g]United States;1927: Lemaître Proposes the Big Bang Theory[06780] [c]Science and technology;1927: Lemaître Proposes the Big Bang Theory[06780] [c]Astronomy;1927: Lemaître Proposes the Big Bang Theory[06780] [c]Physics;1927: Lemaître Proposes the Big Bang Theory[06780] Lemaître, Georges

Georges Lemaître’s formal training was theological and clerical, leading him to a career in the Catholic Church as a monsignor. Similar to other religious men who pursued interests in science as a hobby (such as Gregor Mendel in genetics), Lemaître’s interests included theoretical mathematics and astronomy. In 1923, Lemaître left Belgium for an extended time of study and travel in the United States. During this visit, Lemaître pursued his own interest in science and math instead of formal church-related matters. Lemaître stayed in Cambridge, Massachusetts, at Harvard University, where he studied astronomy as a research student. Albert Einstein’s Einstein, Albert [p]Einstein, Albert;gravitation theory theory of gravitation, now accepted over Sir Isaac Newton’s, had been confirmed four years prior to Lemaître’s visit to Harvard. Edwin Powell Hubble’s Hubble, Edwin Powell discovery of independent galaxies was still a year away. The following year, 1924, Lemaître, on an official trip for Harvard, went to the Mount Wilson Observatory Mount Wilson Observatory in Southern California to observe the work in which Hubble and others were engaged. During that year, Hubble would confirm that independent galaxies did indeed exist; however, the full ramifications of that discovery and the accompanying data were not fully developed at the time of Lemaître’s visit. Lemaître was therefore unable to call on these data when he first proposed the big bang theory.

During his visit to the United States, Lemaître began exploring Einstein’s equations of gravitation. Gravitation theories When Lemaître solved these equations in the simplest manner, he discovered that they described an expanding universe. The long-held view of the universe prior to Lemaître’s discovery was that it was homogeneous, isotropic, and static. Although Lemaître still believed the universe to be homogeneous and isotropic, he now discarded the static view of the universe for a view of the universe as expanding. In 1927, Lemaître’s first paper on the homogeneous but expanding universe was published. He affirmed his belief in a universe that is the same in all directions in terms of its physical makeup and the physical laws by which it is governed; however, he denied that it is a fixed universe. He argued that the simplest solution to Einstein’s theory of gravitation demanded that the universe be expanding. At that time, there were no observational data to support Lemaître’s claim. Einstein was reluctant to endorse the proposed theory until he had investigated Lemaître’s solutions to the gravity equations. Unknown to most of the scientific community of the Western world, a Soviet meteorologist, Aleksandr Friedmann, Friedmann, Aleksandr had discovered the same solutions to the gravity equations and proposed the same view of an expanding universe in 1922. Both men came to the same conclusion independently and without any experimental data.

At Mount Wilson Observatory in 1929, Hubble discovered that the galaxies he was observing were moving away from Earth at incredible speeds; furthermore, those galaxies farther out in the universe were moving more rapidly than those galaxies that were closer. Hubble made his discovery unaware of Lemaître’s theory of an expanding universe and rejection of the traditional static view. There now existed observational data to support Lemaître’s view of expansion. In papers published in 1931 and 1933, Lemaître used Hubble’s discovery to support his theory. Lemaître’s argument was simple: Hubble had discovered that the galaxies in the universe are hurling themselves away from some central point at incredible speeds; therefore, if one were to “reverse the film,” one would see these galaxies rushing in toward one another at some central point. Furthermore, the well-established law of entropy (an organized unit becomes more disordered as time passes) suggested that the universe, which was becoming more disorderly, must at some point have been very orderly. These two arguments led Lemaître to suggest the existence in history of some large primordial atom that contained all the matter of the universe. Lemaître’s view of the universe is well described as follows: Imagine a deflated balloon covered in spots. As the balloon inflates, the spots move away from one another but continue to be the same relative distance apart. Dots far apart, such as two dots on opposite sides of the balloon, would be moving away from each other at a greater speed during the inflating than would two dots that are adjacent to each other. When the balloon is deflated, the dots rush back to a central point.

Hubble’s research provided Lemaître with the observational data to support his theory, and Einstein agreed that Lemaître’s solutions were indeed the best solutions to the gravitational equations. As a result of this support, scientists began to investigate Lemaître’s theory, which the scientific community would label the big bang theory. For a short time, Lemaître continued to develop his ideas about the theory and its effects. He made some predictions about the effects of the big bang that should be evident if indeed that was how the universe began. These proposals suggested areas that scientists could investigate in an effort to confirm the theory. The idea most pursued was the existence of some type of background radiation that must have been given off by the primordial atom when it exploded. Lemaître was confident that some type of background radiation would be discovered. After the theory became the property of the scientific community and several research projects were undertaken to examine it, Lemaître faded from the field to pursue other studies and problems of science that intrigued him. Until his death in 1966, he was still lecturing on the theory of the origins of the universe, although he did not actively engage in the current investigations.


Lemaître’s bold new insight into an expanding universe sent astronomers and physicists delving into their observations and calculations, hoping to unravel the mysteries of the origin of the universe. The big bang theory brought physics and astronomy together to create a joint science known as astrophysics, which investigates the credibility of the theory and seeks an explanation of the first few minutes of universal history. Although Lemaître explained how the universe started, his theory and calculations told little about the nature of that early universe, aside from the idea of the primordial atom. The nature of that atom, the particles that constituted the atom, and the reaction of those particles in the first few minutes after the explosion were questions unanswered by Lemaître or his theory. Also unanswered were the cause and nature of the explosion that sent matter hurling through space.

The big bang theory required the examination of both the macrocosm and the microcosm. Astronomers and many physicists, focusing on the macrocosm, began to study the current universe in the light of the big bang in an effort to gather data about the first few minutes of history. Using Lemaître’s idea of running the film backward from where the universe currently is to where it was, these scientists searched for clues. This search included scanning the heavens for the background radiation; such discoveries as cosmic rays and other forms of radiation resulted. In the microcosm particle, physicists began to explore the inside of the atom hoping to discover clues there that might lead back to the first few minutes of history. Their search required the building of particle accelerators in an effort to duplicate the energy of the initial explosion, which brought the scientific community into the subatomic world full of unknown particles. Lemaître’s theory required scientists to fit antimatter, quarks, and other new forms of matter being discovered into the picture of early universal history.

Although Lemaître’s theory is a theory of science, it had many philosophical ramifications. If it is possible to run the film backward and understand the cause-and-effect beginning of the universe, would it then be possible to project forward with certainty where the universe would be in any number of years? Did this theory then support a deterministic view of reality? How did creatures with free will fit into the picture? Another philosophical and scientific question centers on the cause of the explosion and time. Einstein proved that time is relative to space and speed, but if the universe was once contained in one large atom taking up nothing defined as space and traveling at no speed, what was the cause of the explosion? The explosion could not be the result of changing circumstances over time, because time did not exist. The search for all the answers of the early history of the universe has been successful back to the first few thousandths of a second after the explosion. What nature was like in those fractions of a second and before requires a grand theory that unifies all of physics. Big bang theory Universe;expansion Astronomy;big bang theory

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Abell, G. O., and G. Chincarini, eds. Early Evolution of the Universe and Its Present Structure. Boston: D. Reidel, 1983. Collection of papers presented at a symposium of the International Astronomical Union in Kolymbari, Crete. Topics include cosmology, early history of the universe, and conjecture as to where the universe could be heading. Presents a detailed discussion of the current structure of the universe and how this informs the science of the past. Includes bibliographies and indexes.
  • citation-type="booksimple"

    xlink:type="simple">Berger, A., ed. Big Bang and Georges Lemaître. Boston: D. Reidel, 1984. Compilation of papers delivered at the International Symposium on Georges Lemaître represents an excellent source of biographical information, information on the development of Lemaître’s theory, and an overview of work in cosmology up to 1984. Includes many equations, illustrations, and bibliographies.
  • citation-type="booksimple"

    xlink:type="simple">Contopoulos, G., and D. Kotsakis. Cosmology: The Structure and Evolution of the Universe. Translated by M. Petrou and P. L. Palmer. 2d ed. New York: Springer-Verlag, 1987. Presents various explanations of the big bang theory and the implications of the differing interpretations of the theory. Includes some equations and technical diagrams, but is written for the beginning student of cosmology and provides excellent explanations of some complicated issues.
  • citation-type="booksimple"

    xlink:type="simple">Gribbin, John. In Search of the Big Bang: The Life and Death of the Universe. Rev. ed. New York: Penguin Books, 1998. History of modern cosmology presents the story of the discovery of the nature of external galaxies. Intended for the general reader. Includes illustrations, bibliography, and index.
  • citation-type="booksimple"

    xlink:type="simple">Silk, Joseph. The Big Bang. 3d ed. New York: W. H. Freeman, 2000. Excellent historical account of the big bang theory from Lemaître and Friedmann through Hubble’s discoveries to the end of the twentieth century. Explains how the discoveries were made, their implications, and the reactions of the scientific community. Also traces the history of the universe using the big bang model. Includes glossary and index.
  • citation-type="booksimple"

    xlink:type="simple">_______. On the Shores of the Unknown: A Short History of the Universe. New York: Cambridge University Press, 2005. A history of the universe and the development of humankind’s knowledge about it that is accessible to lay readers. Includes illustrations and index.
  • citation-type="booksimple"

    xlink:type="simple">Trefil, James S. The Moment of Creation. New York: Charles Scribner’s Sons, 1983. Begins with the premise that the big bang theory is correct, so does not mention Lemaître or attempt to defend the theory. Explains how science has come to an understanding of the first few minutes of history, using examples of discovery such as Hubble’s work at Mount Wilson. Also proposes what the universe might have looked like in the first few milliseconds after the explosion. Includes illustrations and bibliography.

Hale Establishes Mount Wilson Observatory

Kapteyn Discovers Two Star Streams in the Galaxy

Slipher Presents Evidence of Redshifts in Galactic Spectra

Hubble Determines the Distance to the Andromeda Nebula

Hubble Shows That Other Galaxies Are Independent Systems

Hubble Confirms the Expanding Universe

Categories: History Content