Georges Lemaître and the Big Bang. No prejudices please

Author: Eduardo Riaza Molina
Author of the blog Georges Lemaître and of "La historia del comienzo. Lemaître, father of the Big Bang" (meeting, 2010)
Published in: Nuestro Tiempo 2013; 681: 24-9.
Publication date: October-December 2013

It is difficult to be an astrophysicist and a priest. Even more so if you propose a theory that challenges Albert Einstein's research and revolutionises astronomy. This happened to Georges Lemaître, the father of the theory of the origin of the cosmos.

One of the main problems of post-modern society is the mistrust of knowledge human beings. Thus, there is no shortage of people who believe that man often lets himself be dragged along by them in everything he does. Others question scientific certainty, believing that its models are subject to change. However, experimental science provides a reliable knowledge because its models can be demonstrated, and its limitations do not detract from scientific advances and the rational capacity that makes them possible.

Science is a privileged way to seek and find the truth, even if it is partial. One of the most popular physical theories is the Big Bang or expansion of the universe, proposal , initially proposed by the astrophysicist and Catholic priest Georges Lemaître to explain the origin of the world.

The theory of relativity

It all began in 1915, when Albert Einstein published the theory of General Relativity. Although almost all of Europe was involved in the Great War, his writings jumped to the other side and found their way into the hands of Arthur Eddington. The British astronomer was so enthusiastic that he translated the German physicist's work into English and did not fail to take advantage of the solar eclipse of 1919 to test some of the predictions of the theory. From then on, Einstein was to acquire great popularity because the theory of relativity not only modified the conception of space and time, but also made it possible to explain the Universe as a whole.

Einstein was the first to be surprised to find that the solution to his equations gave as result a changing world, a Universe that he himself initially estimated to be contracting. As this was beyond him, he introduced a term into the equations to counteract the gravitational effect: a repulsive force, which he called the cosmological constant. This constant endowed empty space with a pressure that kept the stars apart, thus achieving a world in accordance with his thinking: static, finite and eternal. Years later, Einstein would comment that the introduction of this constant in his equations had been the biggest mistake of his life.

Meanwhile, in 1917, the Dutch astronomer Willem de Sitter obtained a solution to the German scholar's equations, suggesting the possibility that the Universe was infinite. On the other hand, the Russian mathematician Alexander Friedmann obtained in 1922 several solutions to these equations, proposing universes that contracted or expanded, depending on the values taken by the cosmological constant. When his work was published in Germany, Einstein responded with a grade in the same journal, presuming a mathematical error. The error eventually turned out not to exist, but Einstein was slow to rectify it, so Friedmann's proposal fell into oblivion.

In Cambridge, next to Eddington

Georges Lemaître arrived as a scholarship student at postgraduate program. He was born at the end of the 19th century in the south of Belgium and was the eldest of four brothers. His father had studied law at the Catholic University of Louvain (UCL) and owned a glass factory.

Georges began his studies in Mining Engineering in Leuven, but his programs of study was interrupted by the outbreak of World War I, in which he participated as a gunner. programs of study At the end of the war, he returned to the classroom, but not to continue his engineering studies, but to begin his studies in Physics and Mathematics, where he received his PhD in 1920. That same year he joined the seminar in Mechelen, and in 1923 he received holy orders. His status as a priest was not an obstacle to continue with his scientific degree program and he applied for admission as a student researcher in Astronomy at Cambridge University for the 1923-24 academic year. There he was student of Arthur Eddington, who taught him how to combine astronomy and the theory of relativity.

Both scientists understood science and religion as two paths to the truth and soon became sympathetic. According to Eddington, "concern for truth is one of the ingredients of the spiritual nature of the human being [...] In science as in religion, truth shines ahead like a beacon showing the way". He also commented that the new conception of the physical Universe put him "in the position status of defending religion against a certain accusation: that of being incompatible with physical science". However, he rejected "the idea that the faith characteristic of religion [could] be demonstrated on the basis of data or the methods of physical science".

For his part, Lemaître recalled that since he was a child he had dreamed of becoming a scientist and a priest: he was "as interested in truth from the point of view of scientific certainty as he was in truth from the point of view of salvation". That is why he considered that "the Christian scientist goes forward freely, with the assurance that his research cannot conflict with his faith". However, he was against the idea of "reducing God to a scientific hypothesis".

But Lemaître's thinking had not always been the same. During the war, he had been pondering the idea that the "Let there be light" of Genesis could be used to explain scientifically the beginning of the world. It was at seminar that an elderly priest pointed out to him that there was no point in looking for scientific arguments in the Holy Scriptures: "If this were to happen, I would consider it unfortunate, for it would only serve to push more unthinking people to believe that the Bible teaches infallible science." Arriving at Cambridge reinforced his conviction that "the scientist must keep an equal distance from two extreme attitudes. One, which would cause him to regard the two aspects of his life as two carefully isolated compartments from which he would draw, according to circumstances, either his science or his faith. The other, which would lead him to mix and confuse inconsiderately and irreverently what should remain separate". The following academic year was spent between Harvard University and the Massachusetts Institute of Technology (MIT), where he set to work on the topic of the doctoral thesis that Eddington had suggested to him.

In the United States, he had the opportunity to catch up with the latest astronomical discoveries. Until then it was thought that the Universe consisted of what we know today as the Milky Way, including those diffuse patches of light, then called "nebulae". It was then that Edwin Hubble broadened the horizons by pointing out that these "nebulae" were actually galaxies other than our own. On the other hand, Vesto Slipher had discovered that the spectrum of light he had collected from most galaxies was redshifted. It was not clear what this might mean, but Harlow Shapley, based on the Doppler effect, believed that this redshift was a consequence of galaxies moving away from each other.

An expanding universe

At the end of his stays at research, Lemaître returned to Belgium to become a professor at UCL, thanks to the letter of reference that Eddington had sent them. In his first years at teaching he compiled all the knowledge he had acquired and, in April 1927, he published a work in which he compiled a catalogue of forty-two galaxies, of which he knew the distances to a certain approximation, as well as the velocities at which they were moving away. He also established the proportionality between the two: the further away a galaxy was, the faster it moved away. In other words, he associated this separation with the expansion of the Universe.

When he wrote this article he was not aware of Friedmann's previous work, as it was written in Russian or German, and the Einstein and De Sitter models did not convince him. Lemaître proposed an intermediate solution between Einstein's and De Sitter's by adjusting the cosmological constant: a spherically symmetric, eternal and evolving Universe. With this model he was not only looking for a mathematically correct solution, but one that was compatible with physics by explaining astronomical observations.

As Lemaître's work went unnoticed, he felt obliged to publicise it. The first opportunity arose at the 5th Solvay Physics congress , held in Brussels in 1927. He attended the lectures and, at the end of one of them, he met Einstein, who told him: "I have read your article. Your calculations are correct, but your physics is abominable". Despite this refusal, Lemaître waited for another opportunity. This came in 1930, on the occasion of the regular meeting of the Royal Astronomical Society. In it, De Sitter expressed his doubts about Einstein's static model , a view shared by Eddington. When Lemaître read the conference proceedings of the meeting he wrote back to his former Cambridge professor to remind him that he had long ago proposed a solution to the problem. Eddington realised that he had "forgotten" and rectified this by giving a lecture entitled "The Instability of Einstein's Spherical Universe", in which he explained the solution that Lemaître had proposed.

Eddington had overlooked this model because of his reluctance to accept an evolving world. As he would comment years later, "the theory of the expanding Universe is in some respects so absurd that we naturally hesitate to surrender to it. It contains such apparently incredible elements that I am almost indignant that anyone should have 'faith' in it except myself".

Eventually, he recognised his prejudices and became Lemaître's great supporter. He had a conversation with Einstein at Cambridge, in which he defended the expansion of the Universe, and mailed a copy of his work to De Sitter and Shapley.

The origin of the cosmos

Lemaître had no objection to positing an eternal Universe. This did not contradict his belief in a world-making God, since a created Universe does not need a beginning in time. We know the temporal origin of the Cosmos through supernatural Revelation, but in theory nothing would prevent God from having created the Universe from all eternity. When it is affirmed that God is eternal, something different is said from a simple indefinite duration. Divine eternity is the possession of Being, unchanging, without before or after, totally self-sufficient. And this can never occur in a limited being, such as the universe.

However, proposal of 1927 would not be his definitive cosmological model . In January 1931, Eddington gave a lecture in London, lecture , on the end of the world from the point of view of mathematical physics. Relying on the thermodynamic concept of entropy, he concluded that the Universe would in the future reach a state of complete dispersion of the subject. Going into the past, on the contrary, the order would tend to be complete, inviting to think of a beginning for the world, a matter that Eddington strongly rejected.

These ideas of his former professor led Lemaître to rethink the question of the origin of the Cosmos, and to ask himself whether it was compatible with physics that the Universe had a beginning. Finding no contradiction, he set about reformulating his cosmological model , supplementing it with what he knew of quantum physics in what he called the "early atom hypothesis", now known as the Big Bang. Essentially, he added an initial phase to the two previous proposals to give the Universe a finite age. It all began at a point, where the laws of physics lost all meaning, where the Universe would expand and space would "fill" with the products of the decay of an early atom, radioactive-like decays, which would give rise to subject, space and time as we know them today. Gravitational attraction would gradually slow down this expansion until it reached a stage of near equilibrium. At that time galaxies and their clusters would emerge from local accumulations of subject. At the end of the training of these Structures, expansion resumed in a hurry.

No prejudices, please

If the expansion of the Universe was initially unpopular with his colleagues, the idea that the world might have a beginning provoked a worse reaction. Whether the Big Bang was a physical intuition or rather a rigorously elaborated theory was not disputed, but rejected outright. Scientists, especially Einstein, found it too bold, even tendentious. There was a reverse status to the one Galileo suffered: just as Galileo Galilei was accused by some ecclesiastics of meddling in theological matters by arguing that heliocentrism was not contrary to Scripture, so Lemaître became suspect to scientists, who thought he was trying to introduce divine creation into science.

Lemaître did not intend to exploit science for the benefit of religion, for he was "firmly convinced that the two have different paths to the truth". The autonomy of science from faith was proven when he wrote that, "from a physical point of view, everything happened as if theoretical zero were really a beginning; whether it was really a beginning or rather a creation, something that starts from nothing, is a philosophical question that cannot be resolved by physical or astronomical considerations". In 1932, Lemaître returned to the USA with another scholarship from research to be able to justify his Big Bang theory with astronomical data . At Harvard he attended a lecture by his former Cambridge professor. Eddington discussed the expanding Universe hypothesis and proclaimed his final adherence to it. The audience turned their gaze to Lemaître and gave him a standing ovation that moved him.

He also visited the Mount Wilson Observatory to exchange views with Hubble on the relationship between the distance to galaxies and their velocity of departure. Finally, he came to Pasadena to give a lecture on his cosmological theory at seminar . At its conclusion, Einstein -who was present- commented that it had been "the most beautiful explanation of Creation that I have ever heard". He then had to admit the expansion of the Universe, although he did not give in to the Big Bang. It is not easy to let go of prejudices. Deep down, it is impossible not to have them. The problem lies in not recognizing them.

The bequest of Lemaître

Lemaître never lost the youthful coolness of asking nature for its secrets. For the rest of his life, he tried to confirm his cosmological theory through the study of cosmic rays, which he believed represented the echo of the great explosion that would have given rise to our world. The love of truth, of the resolution of the great enigma of the Universe, was for him an ideal that he should not abandon. But Georges Lemaître has not only left us an example of confidence in human intelligence, he has also opened the way to a slightly better understanding of our world: an immensely large Universe that we access through the knowledge of the extremely small, which leads us to overcome the paradox of the existence of an initial physical instant that breaks with the static vision of the Cosmos that existed until then.

A man of faith who loved the Cosmos

Georges Lemaître was born on 17 July 1894 in Charleroi, a mining town in Belgium, into a well-to-do family. He was a child with many plans, who loved mathematics and riding his bicycle. He achieved his first dream in 1923 when he was ordained a priest, and his second when he went to England and then to the United States to study astronomy. In those countries he had the opportunity to meet the world's leading scientists and learn about their discoveries. He returned to Belgium in 1925 to teach at the Catholic University of Louvain, at the same time as he was chaplain to a student chaplaincy residency program . He had a reputation among his students as an absent-minded scholar, as he was often late for classroom and most of his students were not able to follow him, as he explained his own research in his lectures. During the first years of teaching, he finished his doctoral dissertation and gave a solution to the equations of Einstein's theory of General Relativity, establishing his first cosmological model (1927). But in 1931, as a result of a lecture that Eddington gave in London, he arrived at the Big Bang theory. Lemaître returned to the United States on many occasions to find some test to support his theory. Together with the Mexican Manuel Sandoval, he began to study cosmic rays, hoping to find in them the echo of the Big Bang. At the outbreak of the Second World War, Lemaître tried to flee to England, but failed, and returned to his battered university, where he was isolated from the rest of the astrophysicists. During this time he devoted himself to his priestly ministry, to teaching and to caring for his widowed mother. After the war, he created a calculating machine laboratory to obtain the trajectories of cosmic rays numerically. Gradually, he acquired more and more sophisticated machines until he reached the first computers. In one of the BBC radio programmes, Fred Hoyle, the leading proponent of the steady-state theory, disparagingly called Lemaître's model "the big bang". Both theories were compatible with the astronomical data of the time, but Hoyle's theory had emerged to drive God out of science. George Gamow took up the baton of the Big Bang theory, approaching the matter from a thermodynamic perspective. In the beginning, besides being very dense, the universe must have been very hot and during the expansion it cooled down. Lemaître had no interest in talking to Gamow, as he thought that everything would become clearer when quantum theory was further developed. The pace of Lemaître's work was very intense. In addition to his scientific and priestly occupations, he was a member of the Pontifical Academy of Sciences from its foundation and second president after the Franciscan Agostino Gemelli.

Lemaître suffered several heart attacks as a result of too much work and not following his strict diet. In 1966 he was admitted to hospital with heart failure. A few days before his death, his friend Odon Godart told him that his theory had been confirmed: Penzias and Wilson had discovered a cosmic microwave background radiation, a fossil trace of the great explosion that started our world.