The Day We Found the Universe - Marcia Bartusiak [129]
The rival theories of Einstein and de Sitter were, in a way, complementary rather than competitive. In de Sitter's universe there was no matter to provide a gravitational attraction, but the cosmological repulsion allowed for movement. Einstein's universe, on the other hand, included matter, which provided enough of a gravitational force to oppose the repulsion. With enough matter, all was in perfect balance. Einstein's universe remained motionless. Friedmann blended the best aspects of these universes. He brought the two extremes under one mathematical roof, providing a model that better described the universe as we observe it: containing matter and yet also moving.
What Friedmann did most of all was introduce time into the deliberations. In papers written in 1922 and 1924 Friedmann began to play, in a sense, with Einstein's cosmological model. He wanted to see how curvatures in space-time might change over time—to “demonstrate the possibility,” as he put it. To Friedmann, this was purely a mathematical enterprise, not astronomy at all. His sole goal was to try out possible solutions to Einstein's equations when applied to the entire cosmos. Like Einstein, he too filled his model universe with matter, but this time had it rapidly moving as the eons passed. Moreover, depending on the amount of matter, this movement of space-time could be an expansion, a contraction, or even an oscillation between the two states. “We shall call this universe the periodic world,” he wrote in his report to the Zeitschrift für Physik. Friedmann even computed an age for the universe, a first in the annals of astronomy. He arrived at a figure of ten billion years, not far from today's consensus of nearly fourteen billion years, although Friedmann considered his estimate more a curiosity. He made sure to note the age could also be infinite. But, all in all, his paper was predominantly an exercise in relativistic mathematics rather than cosmology, which is why it received so little attention at the time. Friedmann made no mention of nebulae, radiation, or redshifts, nor did he promote a cosmic expansion over a contraction. The journal in fact had indexed his article under relativity theory, making no reference that it dealt with cosmology, which is why it was easily overlooked.
Einstein was certainly aware of the Russian's paper, though. He promptly dismissed the solution, thinking it had no physical significance whatsoever. In a letter to the Zeitschrift, sent off right before he went on tour in Japan, he wrote that Friedmann's results “appear to me suspicious.” Friedmann, unfortunately, had little chance to either defend or champion his intriguing idea. In 1925, he became ill with typhoid, just a month after conducting a record-breaking balloon ascent (an altitude of 4.6 miles) to make meteorological and medical observations. He soon died at the age of thirty-seven. In a way, Friedmann had offered his solution too early. At this stage, most general relativists weren't terribly interested in astronomy, and astronomers who had more at stake in this quest didn't yet make the connection, believing that such models of the universe were more like mathematical toys, fun to fiddle with but hardly attached to the real world. They didn't take them seriously.
Lemaître was the exception. From the very start of his independent calculations in the mid-1920s, he kept astronomy foremost in his mind, unlike Friedmann. De Sitter's universe could explain the redshifted nebulae but required the universe be nearly empty (which it was not). Einstein's universe could be filled with matter but