Hubble's Expanding Universe and Lemaître's Primeval Atom

It was here in Washington on New Year’s Day of 1925, at a joint meeting of the AAAS and the American Astronomical Society that Edwin Hubble (in absentia) announced that he had established the distance of the Andromeda Nebula as 930,000 light-years. Within a few more years, he established something even more remarkable, that the fainter the spiral nebula, the greater its spectral Doppler shift. In other words, the farther the spiral nebula, the faster it appeared to be receding from us.

Within a year of Hubble’s announcement what was to become the big bang cosmology was born, largely in the hands of a young Belgium priest, Georges Lemaître. He envisioned the universe as exploding out of a primeval atom into an expanding universe, but he never really described that opening moment. Instead, he mused that “Standing on a well-chilled cinder, we see the slow fading of suns, and we try to recall the vanished brilliance of the origin of the worlds.”

Perhaps the California poet Robinson Jeffers, brother of the Lick Observatory astronomer Hamilton Jeffers, came closer to the indescribable with his lines from “The Great Explosion”:

“There is no way to express that explosion... All that exists
Roars into flame, the tortured fragments rush away from
each other into all the sky, new universes 
Jewel the black breast of night; and far off the outer nebulae
like charging spearmen again
Invade emptiness.”

Whether Lemaître’s Catholic background played any role in motivating his creation cosmology is hard to guage. In 1933 he wrote, “Hundreds of professional and amateur scientists actually believe the Bible pretends to teach science. This is a good deal like assuming that there must be authentic religious dogma in the binomial theorem.” At a Solvay Conference 25 years later he declared, “As far as I can see, such a theory [of the pimeval atom] remains entirely outside any metaphysical or religious question.”

In the 1930s Hubble continued to explore the red shifts and distances of the galaxies and by 1936, in his book The Realm of the Nebulae, he was able to plot 34 points on his velocity-distance relation for these nebulae, going out to a distance of 6.5 million light-years. He determined what is today called the Hubble constant or Hubble parameter, whose reciprocal is related to the expansion age of the universe. Today it seems quite astonishing that he could get a value eight times too large, and a reciprocal value for the age of the expanding universe eight times too small. What went wrong?

Hubble himself held some suspicions that the number had problems. Writing in 1937, he stated that “the observations as they stand lead to the anomaly of a closed universe, curiously small and dense, and, it may be added, suspiciously young.” Part of the answer as to what went wrong, but only part, was an error in the calibration of the cepheid variable stars that had been used to establish the distance scale. As Walter Baade was to show in a brilliant piece of astronomical detective work in the early 1950s, and this contributed just over a factor of two in the discrepancy. Simply doubling the distances of the fainter galaxies was of course not enough to reduce the Hubble constant by a factor of eight. Using the 200-inch Hale reflector as well as red-sensitive plates, Allan Sandage recognized that many of the “stars” in the faint nebulae that Hubble had measured with the 100-inch were in fact much more luminous H II regions. This discovery had an even greater impact on the Hubble constant than Baade’s recalibration of the distance scale. By 1959 Sandage had established a Hubble constant reasonably close to the value widely accepted today.

Contributed by: Dr. Owen Gingerich