Scientists examining the oldest light in the universe say they've found clear evidence that matter expanded at an almost inconceivable rate after the big bang, creating conditions that led to the formation of the first stars.
Light from the big bang's afterglow shows that the universe grew from the size of a marble to an astronomical size in just a trillionth of a second after its birth 13.7 billion years ago, researchers from Johns Hopkins and Princeton universities say.
Readings from a NASA probe also show that the earliest stars formed about 400 million years after the big bang - not 200 million years afterward, as the research team once thought.
"With this new data, theories about the early universe have just taken their first exam and they passed with flying colors," said David Spergel, a Princeton astrophysicist and co-author of the findings published yesterday.
The results are based on readings from the Wilkinson Microwave Anisotropy Probe, a robotic instrument with two telescopes that sweeps the sky every six months in an orbit 1 million miles from Earth.
Dark energy, matter
Light from the probe also has confirmed a theory that the universe is made up mostly of dark energy, a mysterious force that continues to cause the universe's expansion, said Hopkins astrophysicist Charles L. Bennett, the probe's principal investigator.
"This light is just invaluable. It's really the only fossil we have from that time," Bennett said.
Inflationary theorists argue that at the time of the big bang, the universe was at first microscopic. But three events changed things: fluctuations in temperature, bursts that transformed energy into matter and a rapid expansion of the universe that ultimately enabled stars and galaxies to form.
By polarizing and filtering out light from the earliest stars, the researchers were able to uncover evidence of those inflationary moments - fluctuations in brightness of the light scattered around the big bang's afterglow.
"It amazes me that we can say anything about the first trillionth of a second of the universe, but we can," Bennett said.
The researchers say the findings also confirm that only 4 percent of the universe is composed of the familiar atoms that make up what we see around us.
An additional 22 percent is dark matter - a gravitational force made up of cold particles - and 74 percent is dark energy, a force that appears to be causing the universe to expand.
Experts say the findings will help cosmologists and astronomers for years as they try to unravel mysteries about the early universe and the forces that still govern it.
"The observations are spectacular and the conclusions are stunning," said Brian Greene, an astronomer at Columbia University who attended the news briefing in Princeton, N.J., where the results were announced. "It shows that galaxies are nothing but quantum mechanics writ large across the sky."
Adam Reiss, an astronomer and expert on supernovae at the Space Telescope Science Institute in Baltimore, said WMAP will probably help him in his research into dark energy.
"It should help sort out some of the background noise of the universe, so you can subtract out some of what's there and get at the more subtle effects of whatever it is you're trying to measure," Reiss said.
WMAP was launched in 2001 to probe the afterglow of the big bang. It measures light and temperatures in the cosmic microwave background that is invisible to the naked eye but shows up as "snow" on TV sets in fringe reception areas.
`Snap of time'
The WMAP team plans to continue looking for clues into the forces that drove the universe's inflation.
"What happened in that instant snap of time is still a mystery. There's a lot of uncertainty about inflation in general," said Gary Hinshaw, an astrophysicist at the Goddard Space Flight Center and a WMAP researcher.
The researchers released a map yesterday of the afterglow as it appears in the cosmic microwave background, showing it in the shape of an oval. Cool spots appear blue and green; hot spots are red and yellow. White lines show the direction of the polarized light.
The map is similar to one the researchers released in 2003 based on temperature readings, but the new one is more detailed.
The cosmic microwave background, often called the afterglow of the big bang, is a spectrum of light discovered in 1965 by radio astronomers at Bell Laboratories who were searching for an explanation for the hissing noise on their radio. Arno Penzias and Robert Wilson won Nobel Prizes for their work.