In the 1920s, astronomical observations suggested a dynamic and evolving universe, a concept that later challenged Einsein’s assumptions of a more static origin. In May 1931, a paper was published by a Belgian Catholic priest in nature that suggested that the expansion of the universe indicates a beginning of space and time.

Brilliant Idea of Georges Lemaître’s

Imagine yourself standing on the moon holding a steel ball between your finger and thumb on the moon. If you’d let go of the ball, it’d slowly fall to the surface of the moon, because the gravity of the moon is weaker than Earth, but the ball would still fall.

If, instead of dropping it, you throw it upwards gently, it’d rise slowly but would still fall to the surface of the moon but if you’d toss the ball upwards with power, it could escape the moon’s gravity and will make its way into the depths of space forever.

Now let’s say you release the ball but don’t throw it, and surprisingly it either hangs in the air or slowly rises upwards. You quickly decide that something invisible is at work; Maybe it’s the magic of the magnet. What is true of ball bearings is also true of galaxies.

In 1917, Albert Einstein published the theory of general relativity. Mathematicians began to wonder what this new way of thinking about gravity might mean for the universe as a whole. Just like a steel ball and the moon, there is a gravitational force between any two galaxies in our universe. The distances between galaxies are very large, and the gravitational pull they exert on each other is extremely weak. But given enough time, gravity will take effect. For cosmologists who think in billions of years, time is a rich resource!

Einstein realized that in the absence of any mysterious repulsive force, as a result, each galaxy in the universe would clump together (with the speed of a steel ball falling onto the moon’s surface). Einstein said that there’s an unknown force that keeps the galaxies in their position (now referred to as ‘dark energy’, it is a technical term which means ‘we don’t know what it is’).

Enter Georges Lemaître a Belgian Catholic priest who was born in Charleroi in 1894. He was a talented mathematician who had seen military service in World War 1. Unfortunately, he could not secure a higher position due to his habit of correcting the ballistic calculations of his superior. He pursued a master’s in mathematics after the war. He quickly completed the three-year course to become a priest, and then Cardinal Mercier gave him special permission to continue his scientific studies. After being ordained in 1923, he studied at Cambridge for a year before moving to the United States and earning a doctorate from the Massachusetts Institute of Technology.

Lemaître understood that Einstein’s description of the universe wasn’t just the only way of applying General Relativity. Alternatives of throwing the steel ball were also there, some with it falling back, and others, sailing on forever. Along with Cambridge Sir Arthur Eddington, he acknowledged a universe that almost looked dynamic for a very long time (Your index finger and thumb will hold the ball for as long as you want) But over time, extension becomes important (the ball will eventually have to be thrown upwards, but the swing will start in super slow motion).

This model was released in 1927, in French, and not just a theory but Lemaître looked for observational confirmation of his ideas. A  technique to calculate cosmic scales to other galaxies was made available in 1931c but the observational results were omitted.

Edwin Hubble published his well-known paper in 1929 which caught the world’s attention to the matter that galaxies go faster, the further away they are from each other, astronomers now know it as ‘Hubble Law’As Hubble’s name got associated with the discovery, Lemaître did not protest. He was a man in poverty and still, he didn’t crave fame and physics prizes and gave away his money, yet seemed happy.

The primordial Particle

Lemaître further reasoned: If our universe is expanding now, couldn’t it have started completely compressed? If that were the case, the entire universe would be as dense as an atomic nucleus. In 1935, Lemaître proposed a “primordial atom” that collapsed to create the universe as we know it.

 In the 1940s and 1950s, most physicists still believed that the universe was expanding due to what Einstein termed ‘dark energy’, represented by the mysterious power factor, which started very similar to today. universe. Lemaître’s idea of ​​the primordial atom was a marginal alternative theory. Another idea mainly backed by British scientists suggested that the universe has always been the same, which proposed that matter was constantly being formed to match the expansion of the universe, so that the universe appeared essentially the same at all times, past and future.

In a 1949 American radio broadcast, steady-state proponent Fred Hoyle denounced Lemaître’s idea of ​​a primordial atomic explosion as nothing more than a “big bang.” and the nickname sticks! Today we no longer talk about the “primordial atom,” and Georges Lemaitre has been mercilessly given the title “Father of the Big Bang.”

Legacy of Lemaître

Lemaitre got a lot of things right. He predicted Hubble’s law before Hubble predicted it. He proposed an ultra-dense origin for the universe, followed by a rapid expansion leaving behind a faint echo of radiation. He figured the age of the universe was around 10 billion years, and recent research results show that it is 13 to 15 billion years old. So he was on the right track. But he was infallible, and he devoted much of his working life to the study of cosmic radiation, known as “cosmic rays,” which he believed were produced by the Big Bang. Now we know its origins are not that far away.

The Big Bang theory was firmly established as soon as the evidence became available. Radiation from the edge of space? check. Predictions about the mixing of elements in the early universe? yes! The ability to run computer simulations of the early universe and arrive at what we see today? totally! The Big Bang was so successful that all talk of mysterious “dark energy” permeating the universe was quietly abandoned. There was no need for that when the impact of the original Big Bang was enough to make the universe that size. today.

But in the 1990s, our ability to determine gaps to other galaxies became even better. It became clear that at greater distances from Earth, the expansion of the universe was accelerating, necessitating the presence of “dark energy.” Then we know how the universe will end. It will end not with a bang, but with a whisper that gets smaller and smaller as it expands into a darker and colder void.

Among Georges Lemaitre’s many achievements, two stand out. To be fair, his 1927 discovery of what we should now call Lemaître-Hubble’s law for the expansion of the universe, and his 1931 paper in The Big Bang Man, dared to suggest. Although God’s creative activity is well hidden behind the veil of physics, mathematics may require us to consider that the universe had a beginning in time. And the universe as we know it today was born in the commotion of cosmic fireworks.

Gareth Leyshon would like to thank the spokesperson at the April 2011 Faraday Institution conference commemorating the 80th anniversary of Lemaitre’s 1931 paper who provided much of the information above. He talked about the accomplishments of Lemaître and the Big Bang at the 2013 OISF.