Word: redshift
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Dates: during 1970-1979
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...distant than astronomers had previously believed. That, in turn, meant the expansion had been going on longer than anyone thought, and that the age of the universe was at least 16 billion years, or roughly 4 billion to 6 billion years older than earlier estimates. Even more important, the redshift measurements of nearby galaxies gave no indication of any significant gravitational slowdown in the outward rush of the galaxies. "It's a terrible surprise," says Sandage, who for years had been leading proponent of the idea that the universe would eventually close in on itself...
Gunn, a Caltech astronomer, made no direct observations. In collaboration with three associates, he spent six years studying a wide variety of evidence-including Sandage's redshift measurements. For one thing, he examined the galaxies' brightness and movement, which offer clues to their mass. He also estimated the probable incidence of "black holes," small but extremely massive bodies that are invisible to astronomers. From these and other clues, Gunn's group concluded that the universe has no more than a tenth of the mass-and probably less -needed to close it. "Pulling all the arguments together," says...