The 4% Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality

by Richard Panek

The following year, Peebles wrote a paper, “Tests of Cosmological Models Constrained by Inflation,” that offered his theoretical interpretation of that data. Maybe omega was indeed 0.2 and lambda equaled 0, he wrote, but in that case “we lose the attractive inflationary explanation for the observed large-scale homogeneity of the universe.” He didn’t want a cosmological constant. “It’s ugly,” he often said. “It’s an addition.” If he were building a universe, he thought, he wouldn’t put in a cosmological constant: “No bells and whistles.” But perhaps because inflation solved the flatness problem he’d articulated with Dicke, or perhaps because he constitutionally distrusted a simple universe, he accepted the possibility with equanimity. “Considering the observations,” he said, “I think the universe might have put in bells and whistles—a cosmological constant.”