For the first time, scientists have mapped the polarization of the light lingering from the fiery birth of the universe. The new measurements show that the earliest stars emerged 400 million years after the big bang and tighten the bounds on theories of how the universe grew in less than a trillionth of a second from marble-size to nearly its present size.
Light from the big bang has cooled and stretched to longer and longer wavelengths as the universe has evolved, leaving a faint haze of microwaves that pervades all space. Tiny variations in that cosmic microwave background may reveal how the universe sprang into existence, much as fossils record the evolution of life on Earth. Three years ago, researchers working with NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite charted the minuscule variations in the temperature of the microwaves across the sky (Science Breakthrough of the Year 2003). By scrutinizing the details, they deduced that the universe is 13.7 billion years old, is "flat" (curved neither inward like a gigantic sphere nor outward like a gigantic saddle), and consists of a smattering of ordinary matter, much more unseen dark matter, and a whopping amount of space-stretching "dark energy."
Now, WMAP researchers have analyzed data collected during the second and third years of the satellite's mission, which began with its launch in 2001. The microwaves coming from different places in the sky can point in different directions, like the arrows conveying wind speeds on a weather map, and the new work maps out variations in that polarization across the sky. The data give researchers another window into the infant universe, team leader Charles Bennett, an astrophysicist at Johns Hopkins University in Baltimore, Maryland, said at a press conference at Princeton University in New Jersey.
Because the polarization is affected by the first stars, the researchers could tell that the first stars emerged about 400 million years after the big bang. The researchers also teased out how much of the observed unevenness in the cosmic microwave background was there before the stars, says David Spergel, an astrophysicist at Princeton and member of the WMAP team.
That information lets researchers rule out certain theories of inflation, the mind-boggling expansion that took place in the universe's first split second, says Brian Greene, a theoretical physicist from Columbia University: "This is a powerful step toward winnowing the field of contenders of how inflation took place."