In the first article of this series, you learned of Vesto Slipher’s discovery that galaxies were speeding away from us at astonishing speeds.
In the second, you learned of Edwin Hubble’s epic discovery, first reported in 1929, of an expanding universe where the speed at which galaxies receded from our point of view was directly proportional to their distance, a relationship we now call Hubble’s Law.
Now let’s turn to the explanation of why the universe expands, and the implications of its expansion for its beginning…
To the astronomers of the day, Hubble’s discovery was unexpected and, in his own words, “rather startling”. Most believed the universe was static and unchanging, if only because that’s how it appeared upon observing the random and ponderous motions of stars within our own galaxy. Hubble had no idea why galaxies were flying apart, and he was not inclined to speculate carelessly. Nor did he know this exact phenomenon was predicted by a powerful new theory developed in 1915 by a Swiss physicist named Albert Einstein.
Ten years in the making, Einstein’s General Theory of Relativity was the great man’s masterpiece. Its mathematics are complex, but its basic idea is simple. The theory replaces the Newtonian idea of gravity with the idea of space as a pliable geometrical framework that bends and curves in the presence of massive objects. Planets follow their orbits, Einstein showed, because they follow a curve in space created by their sun (see video below). This theory made many astonishing predictions, some of which were verified with observation by the early 1920’s, making Einstein world famous. Yet his ideas were so complex that few understood their implications, including Hubble. George Ellery Hale, Hubble’s boss, said of general relativity, “I fear it will always remain beyond my grasp”.
Which is too bad, because Einstein’s theory made another prediction: the space within the universe itself should be either expanding or contracting. Yet even Einstein, years before Hubble’s discovery, considered the notion of an expanding universe so preposterous that he fudged his theory to ensure it predicted a static universe. So when Hubble announced that galaxies are flying apart, no one could reconcile his measurements with the view of the universe based on Einstein’s theory of general relativity. By 1930, cosmologists were perplexed.
It turns out the connection between Hubble’s observations and Einstein’s theory had already been made in 1927 by an obscure Belgian scientist-priest named Georges Lemaitre. Lemaitre, the son of a glassmaker, was a jovial and unassuming man who had decided at the age of nine to become a clergyman and a scientist. (“There is no conflict between religion and science”, he declared). In the mid-1920’s Lemaitre had toured America, attended many scientific conferences, and learned of Vesto Slipher’s discovery of receding galaxies. Struck by Slipher’s results, Lemaitre returned to Brussels and wrote a paper that established a mathematical framework connecting Slipher’s receding galaxies to Einstein’s theory. Lemaitre essentially built on Einstein’s theory to predict Hubble’s Law two full years before Hubble’s observations were published.
But the humble Lemaitre published his work in an obscure journal where it remained completely unnoticed. In 1930, Lemaitre pointed out his paper to the great British cosmologist Arthur Eddington. This time the world did notice, and Lemaitre and his work became widely known. Even Einstein, who initially dismissed Lemaitre as a crank, by 1933 came to respect the ideas of the young priest, declaring his work as “very beautiful”. Einstein later cursed himself for fudging his theory to explain away the expanding universe, an action he later called his “biggest blunder”.
Of course an expanding universe meant things must have looked very different in the past. Galaxies must have been closer together, for example, and matter was packed tighter into a smaller space. Go far enough back in time and the universe must have been very small indeed, perhaps smaller than a single atom, yet incredibly dense. Lemaitre, enchanted by this idea, called this the “primordial atom”, and he called its explosion as our universe the “Big Noise”. Eddington abhorred this notion, as did the cosmologist Fred Hoyle, who came up with his own derisive name for this event. He called it the “Big Bang”.
Until next time…