WHEN THE UNIVERSE WAS GIVEN A HISTORY

• BY ANDRÉ GRANDCHAMPS

At the start of the 20th century, the work of two astronomers led to a discovery that would radically alter scientists’ conception of our world: the expansion of the Universe. That discovery caused a revolution that would change astronomy forever.

Priest and astrophysicist Georges Lemaître was the first protagonist in this story. His understanding of Einstein’s theory of general relativity made him realize that the Universe cannot be static. The various objects that constitute the Universe must be moving away from one another. In conducting his analysis, he recognized that in the past, the Universe must have been far smaller, denser and hotter. For Lemaître, the primitive Universe must have been compressed in a small, extremely hot and dense “egg,” which then expanded until it reached the size we observe today.

The work Lemaître published in 1927 was theoretical, however. To be accepted by other astronomers, experimental evidence of the expansion had to be found.

This is where the second main figure in this scientific adventure intervened. At that time, American astronomer Edwin Hubble was studying galaxies using the Mount Wilson telescope in California. Through his observations, he discovered that the galaxies were moving away from us, as Lemaître had predicted. He even showed that the farther a galaxy is away from us, the faster it is moving away.

These observations constituted striking proof of Lemaître’s theories about the expansion of the Universe.

The relationship between the distance of a galaxy and the speed at which it is moving away is now called the Hubble-Lemaître law. Thanks to this discovery, astronomers recognized that the Universe as we know it is not unchanging, but has its own history that has been unfolding since the dawn of time. This realization led to the Big Bang theory.

In this theory, the original state of the Universe is referred to as the initial singularity. That singularity began expanding at a dizzying rate at the start of its history, and then proceeded to slow down. As it expanded, the Universe cooled, allowing matter to form and acquire structure. Ultimately, 10 billion years later, life emerged on a tiny planet in our solar system and gradually evolved into the huge diversity we are familiar with today.

You can discover this fascinating story—and many more like it—in the film Horizon, now showing at the Planétarium Rio Tinto Alcan.