In 1930 Einstein became convinced of Hubble's expansion law, and later admitted that the introduction of the cosmological constant was one of the greatest mistakes of his life. However, theory has a habit of rebounding and once Pandora's box is opened, it becomes hard to close. The first real revival came from theory. In 1981 inflationary cosmology provided the first major new insight into the big bang since the 1920s. This period of rapid expansion flattened the geometry of the universe.
Inflation predicts that the universe is at the critical density.
Dark matter could not account for the critical energy, and the cosmological constant remained the plausible culprit, if inflation did indeed occur. Precision measurements If we could directly measure the geometry of the universe, then we could bypass the dark-matter problem and test the inflationary prediction of flatness. Enter the Boomerang experiment. Boomerang results One of the key pieces of evidence for the big bang is that the cosmic microwave background has a perfect black-body spectrum with a temperature around 2.73 K in all directions. Indeed, such fluctuations were discovered in 1992 by the COBE satellite, which had an angular resolution of 7 o .