Proof of Big Bang Seen by Space Probe, Scientists Say

Davide Castelvecchi
for National Geographic News
March 17, 2006
New NASA space-probe observations of the oldest light in the cosmos are the most direct evidence yet that the universe expanded extremely quickly immediately after the big bang, physicists say.

Charles Bennett of Johns Hopkins University in Baltimore, Maryland, led the team overseeing NASA's Wilkinson Microwave Anisotropy Probe (WMAP). He and colleagues announced the new results Thursday in a teleconference.

Previous experiments—including WMAP results released in 2003—had provided strong evidence for the rapid-expansion theory, called inflation, that was first proposed by physicist Alan Guth in 1980.

In the trillion-trillionth of a second after the big bang, the universe expanded from the size of a gumball to astronomical proportions, according to the inflation theory. The universe then settled into a more leisurely pace of expansion over the past 13.7 billion years or so.

Smoking Gun

WMAP now has the most convincing evidence yet for inflation: a reading of the light released just after the big bang. This cosmic afterglow, known as microwave background, is made of a similar type of radiation to that which carries signals to a TV antenna.

The afterglow is as valuable to a cosmologist as the earliest fossils are to a paleontologist. It is the oldest radiation ever detected, still traveling almost 14 billion years after it was emitted.

The microwaves bathe the entire universe in a perpetual buzz, reaching Earth from all directions. The buzz is virtually uniform, but not quite.

Tiny variations at different points in space allow scientists to draw maps of the early universe, as the WMAP team has done with unprecedented detail.

These cosmic baby pictures show us a time when the universe was a smooth, fiery broth, when stars and galaxies had yet to form under the pull of gravity (photo: another view of the early universe).

Finer Points

The team said cosmologists will now be able to delve into the finer details of how inflation happened.

"I think we now have crossed a threshold," said team member David Spergel of Princeton University in New Jersey. "We can now start to say something quite interesting about the physics of inflation."

Andrei Linde, a cosmologist at California's Stanford University and one of the founders of inflation theory, agrees.

"Theorists sometimes believe we are so smart—[that] nobody can be compared to us," he said in a telephone interview from Moscow. "But these experimentalists [such as the WMAP team], they can sometimes do things that look like science fiction to us."

WMAP has also for the first time mapped the big bang afterglow's polarization. "That's our big step forward," Spergel said.

Polarization is when light—which normally radiates out randomly from its source—encounters something, such as a shiny surface or fog, that causes it to assume a particular orientation.

The patterns of polarization in the newborn universe—shown as white bars on this map—provide clues that dramatically improve scientists' ability to determine the dates of key events, the team said.

Riddles Remain

The probe's high-definition data also reaffirm some long-standing riddles.

Certain features in the microwave "sky" look to some experts like statistical anomalies, and WMAP's new data make them even more conspicuous.

Some of the anomalies seem to "very oddly line up with the geometry of the solar system," said Glenn Starkman of Case Western Reserve University in Ohio.

For example, some groups of anomalies seem to be pointing in one direction. But this idea runs counter to the accepted principle that the cosmos has no preferred orientation (whereas Earth, for example, is governed by its magnetic field, which gives rise to the directions of the compass).

Joao Magueijo of Imperial College London said, "We expect everything to be more or less the same in every direction."

Still others believe that the statistical anomalies are in the eye of the beholder.

"Are those features telling you something physical and important, or are those features just random? That, I think, remains an open question that will be a subject of debate," Spergel said.

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