Georges Lemaitre was born in 1894. He began studying engineering but, like Friedmann, his studies were interrupted by World War I. In the trenches he observed first-hand the effects of German mustard gas and won the Croix de Guerre. After the war he returned to his studies but switched to theoretical physics. He also enrolled in the seminary and was ordained a priest in 1923. For the remainder of his life he pursued two careers, physics and the priesthood, saying “There were two ways of arriving at the truth. I decided to follow them both.”
In 1923 after spending two years in Cambridge with Arthur Eddington, Lemaitre returned to Belgium and began his own cosmological quest for truth. He adopted Einstein’s general relativity but, like Friedmann, rejected the notion of the cosmological constant. Without knowing anything about Friedmann’s work, Lemaitre resurrected the expanding universe model. Unlike Friedmann who was a mathematician, interested mainly in the numbers of the theory, Lemaitre wanted to understand the reality behind the numbers. If the cosmos were expanding, Lemaitre decided to run the clock backwards. An expanding universe implied that things were closer together yesterday, closer still 100 years ago and still closer 1 million years ago. Run the clock backward enough and the inescapable conclusion was that everything was together at one point.
Perhaps influenced by his theological training, Lemaitre realized that general relativity implied a moment of creation. He concluded that the universe began in a relatively small, compact region that suddenly expanded and evolved into what we observe today. He refined his theory into what he called the primeval atom that contained all of the matter that eventually became the stars and planets. Though a moment of creation was central to his theory, Lemaitre was interested in the evolution of the universe from the primeval atom to the stars and galaxies.
Lemaitre published his theory and was met with the same deafening silence that greeted Friedmann. To make matters worse, Lemaitre also had a run-in with Einstein who rebuffed him, saying that his mathematics were correct but his “physics is abominable.” Einstein had thus been offered two chances to accept an alternative to the steady state view of the universe and rejected both. As the world authority on cosmology, Einstein’s words had the force of law. It is ironic that, having challenged authority in his early career Einstein had now become the authority behind whom virtually all scientists fell into line. It probably didn’t help Lemaitre that he was a priest and his theory smacked of a Creator. Though it had been nearly four centuries since Galileo was forced to confess, the wounds science felt from religion were still tender.
The truth is, both theories were appealing and both had flaws. The flaw in the steady state theory was the cosmological constant, which, as we have seen, is nothing but a fudge factor to make the theory conform to the accepted view of how things are. The flaw in the nascent big bang theory (it still had not been thus named) was that there was no evidence to support the theory of a sudden explosion, other than the logic behind an expanding universe. For that matter, though, there was no evidence to support a steady state model other than the belief that this is how things are. The theorists needed evidence to support their various theories so they turned to the experimental physicists, the astronomers.