The most detailed portrait ever taken of the radiation left over from the Big Bang provides fresh evidence that the universe began with a tremendous growth spurt, expanding from subatomic scales to the size of a grapefruit in less than a trillionth of a second.
In that instant, according to the theory known as inflation, microscopic fluctuations in the density of the cosmos were greatly amplified. That blueprint ultimately developed into the rich tapestry of stars and galaxies that fill the universe today. Although inflation has explained a multitude of features about the universe, before the new evidence, many details had yet to be scrutinized.
With the new information, “our basic cosmological model has been put to its most rigorous test, and it’s thriving,” says David N. Spergel of Princeton University. His team used the first 3 years of data gathered by NASA’s Wilkinson Microwave Anisotropy Probe, which is examining the cosmic microwave background, the latent glow left over from the first moments of the universe. The probe and other telescopes see the radiation generated during the Big Bang as it appeared when it first streamed into space, a few hundred thousand years later.
At press time, the team planned to announce the findings in a telephone briefing.
Previous results from the satellite focused on the variations in the temperature of the microwave-background radiation, which has cooled over billions of years to a frigid 2.72 kelvins. Tiny variations in that temperature, less than a millionth of a kelvin hotter or colder, revealed details of the primordial density fluctuations that gave rise to stars and galaxies (SN: 2/15/03, p. 99: Cosmic Revelations: Satellite homes in on the infant universe). The new results focus on the polarization of the microwave-background radiation, the tendency of the radiation’s waves to vibrate in a specific direction.
The polarization signal reveals that the first stars formed 300 to 400 million years after the Big Bang. That’s slightly later than estimates that were based on earlier data from the same satellite, notes cosmologist Michael Turner of the University of Chicago.
Accounting for the polarization was like “removing a fog,” says Spergel. It enabled the team to scrutinize more closely than ever before the primordial fluctuations imprinted on the microwave background.
According to the simplest model of inflation, the universe didn’t balloon at a constant rate during the early growth spurt. As a consequence, variations in density of matter in the universe ought to be slightly larger on the largest scales—10 billion light-years—than on smaller scales—roughly 100 million light-years. The satellite has now found exactly that pattern, the team reports.
“This is not simply another test of inflation but something that examines the universe during its first trillionth of a trillionth of a second,” says Turner. “The entire cosmology community has been waiting for this, excited and worried.” The findings “are beginning to shed light on the mechanism [that drove] inflation,” he adds.
The new data also confirm with unprecedented accuracy the ingredients of the universe: 4.4 percent ordinary matter, or atoms, 22 percent invisible material known as dark matter, and 74 percent a mysterious entity called dark energy. The satellite also pegs the age of the universe at 13.7 billion years.
