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

by Richard Panek

the value of omega depended on the measure of matter, and whatever matter the universe had then, it would have now and forever. But for Big Bang theorists like Dicke and Peebles, a flat universe posed a problem similar to the one Newton and Einstein faced: Why would a universe that was full of matter not be collapsing through the effects of gravity? Newton had to invoke a universe of evenly spaced stars—plus God. Einstein had to invoke a universe of randomly spaced stars—plus lambda. Evidence for an expanding universe had allowed Einstein to abandon lambda and prompted future generations to try to figure out how to measure the rate at which the expansion was slowing. But now Dicke and Peebles were arguing that in a Big Bang universe, omega had to equal 1. The expansion had to slow to a virtual stop and stay there forever. All the matter in the universe had to reach a state of gravitational equilibrium—an eventuality with the same likelihood as a pencil standing on its point forever. Not impossible, according to the laws of classical physics, but not likely either.