Concerning the nature of the universe, Einstein's theory of general relativity (1915) perversely predicted that the universe would collapse inwardly due to gravitation without some countervailing force. To get a stable universe, Einstein proposed a "cosmological constant." This purely mathematical calculation would correct for the mutual pull gravitation between heavenly bodies so that the universe could persist unchanged. Einstein eventually called this his greatest mistake. Alexander Friedmann, a Russian mathematician, stated in a 1922 paper that the cosmological constant is not necessary. A sudden initial expansion, for instance, could instead counteract the pull of gravity. This theory made the universe dynamic, i.e., constantly changing, rather that static. It was a difficult concept for the time.

The next year (1922) observational astronomy began to bear on this grand theorizing. Edwin Hubble, a Missouri born astronomer working at the 100-inch telescope on Mount Wilson in California, was able to make an accurate estimate of the distance to the great nebula of Andromeda. It was almost a million light years away! Such a distance made it a great galaxy of stars similar to our own Milky Way. Other nebulae in the sky must be even further away and therefore also great galaxies containing hundreds of millions of stars. It expanded the size of the known universe by a hundred fold. Theorists went back to their calculations to make revisions.

The year Hubble published his estimate Father George Lemaître was still pursuing an education that unusually combined priesthood in the Roman Catholic Church and theoretical physics. After ordination, this Belgian cleric worked with Eddington at Cambridge University for a year and then went to Massachusetts Institute of Technology to obtain a Ph.D. In 1925 he took up an academic post at the University of Louvain in Belgium and began to develop cosmological models. Independently of Friedmann, he realized that Einstein's Theory of General Relativity worked only if the universe is expanding. If it is expanding now, it has been doing so for a long time to get to its great size. If one goes back in time long enough, it must have been compacted in a very tiny region. He called this super compact universe the "primeval atom." To find observational support for his theory, he alighted on cosmic rays, first discovered in 1912. These are highly energetic particles coming from outer space. Lemaître considered them persistent evidence of a large radioactive decay event long before and described his theory in 1927. Einstein, still favoring a stable universe, was dismissive, telling Lemaître: "Your calculations are correct, but your physics is abominable."

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The idea of an expanding universe, however, was soon rescued by observations. Edwin Hubble took up a new line at Mount Wilson involving the spectroscope. To describe his important work, we have to go back a way. Newton had first noted that a prism would break white light into a spectrum of many colors from red to violet. Later scientists deduced that this was because of the wave nature of light. The white light from the sun contains many colors because it is a mixture of different wavelengths.

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