Cosmology and Astronomy

At the beginning of the twentieth century, it was generally thought that the Earth's galaxy was some ten thousand light-years across and that the solar system was near the center of the galaxy. This vision of the universe was soon replaced with a revolutionary new conception. Harlow Shapley at the Mount Wilson Observatory showed that the galaxy is hundreds of thousands of light-years in diameter and the solar system is far from its center. The significance of humans and their particular planet had dwindled still further. Shapley noted a historical progression from belief in a small universe with humankind at its center to a larger universe with the earth farther from the center. The geometry had been transformed from geocentric to heliocentric to acentric. The psychological change was no less, Shapley insisted, from homocentric to acentric. Furthermore, the galaxy containing the Earth is but one of many "island universes," as Edwin Hubble soon proved. Next Hubble found that the universe is expanding. Georges Lemaître, a Belgian priest and astrophysicist, explained the expansion of the universe from an initial "cosmic egg." Einstein confirmed that Lemaître's theoretical investigations fit well into the general theory of relativity.

Advances in nuclear physics fed speculations about an expanding universe resulting from thermonuclear reactions in an early, hot, dense phase. Fred Hoyle at mid-century derisively called it the "big bang," and the term stuck. Hoyle championed instead steady-state creation, in which the universe expands but does not change in density because new matter continuously appears. Pope Pius XII announced in 1951 that big-bang cosmology affirmed the notion of a transcendental creator and was in harmony with Christian dogma. Steady-state theory, denying any beginning or end to time, was associated with atheism, though Hoyle associated it with personal freedom and anticommunism. The debate was resolved observationally with detection of a faint cosmic background radiation, a remnant of the big bang.

In 1979 an American particle physicist, Alan Guth, proposed that important cosmological features can be explained as natural and inevitable consequences of new theories of particle physics. Guth's theory of inflation states that in the first minuscule fraction of a second of the universe's evolution, a huge inflation occurred. After that, the inflationary universe theory merges with the standard big-bang theory.