Big bang: Scientists study light from a softball-sized universe

In the big bang's microwave afterglow is an odd light polarization pattern from when the universe was one millionth of a trillion trillionths of a second old. Scientists hope it illuminates a faster-than-light expansion.

By , Staff writer

The afterglow from the big bang, the primordial release of energy that gave rise to the universe, has revealed a great deal about the composition of the universe and how it evolved the structure astronomers see today.

This afterglow, known as the cosmic microwave background, corresponds to a time when the universe was about 380,000 years old.

Now, astrophysicists have detected a rare phenomenon in this background radiation that they say eventually could open a window on a fleeting period when the universe was only one millionth of a trillion trillionths of a second old.

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At that time, theorists say, the universe mushroomed at a faster-than-light pace. In the space of a few thousandths of a trillion trillionths of a second, it would have grown from far smaller than the size of a proton to about the size of a softball. This is known as the inflationary period.

But the cosmic microwave background represents a curtain to the observable universe, beyond which direct evidence of earlier processes, such as inflation, are undetectable.

That's where the newly spotted phenomenon – a peculiar twist in the polarization pattern in this early light – is expected to help.

This twist "can really only be generated, we think, very early in the universe, during inflation" or later when gravity from massive structures such as galaxies or galaxy clusters bends the microwave radiation as it travels through space, says Duncan Hanson, an astrophysicist at McGill University in Montreal. He's the lead author of a paper describing the results in the latest issue of the journal Physical Review Letters.

Thus, he says, the twist not only can help devise more-accurate maps of the distribution of matter in the universe, it also can provide indirect evidence for the inflationary period itself.

The twist, known as the B-mode, is one of two polarization modes that radiation from the cosmic microwave background exhibit. It's by far the rarer of the two, so it's fiendishly hard to detect.

Researchers relied on the South Pole Telescope, a 10-meter dish that detects microwave radiation from space and the European Space Agency's Herschel Space Observatory, which operates at comparable wavelengths to make the measurements.

The most immediate help the B-mode measurements can provide is in building maps of the distribution of matter in the universe, Dr. Hanson says.

Some 5 percent of the matter and energy in the universe is visible matter. Another 25 percent of the cosmos consists of so-called dark matter. Researchers infer its presence by its gravitational effects on the matter they can see.

Current techniques for estimating the amount of matter in the universe relies on measurements in which gravity's ability to bend light – gravitational lensing – magnifies the fainter, more distant objects along an astronomer's line of sight. The approach provides the distribution of mass between the background objects and the observer.

But those background objects get smaller and fainter with distance and only correspond to a time when stars and galaxies were forming. Using the microwave background radiation's B-mode polarization pattern as a probe, researchers will be able to gauge the distribution of matter all the way back to a universe that was 380,000 years old – long before the first stars formed in galaxy wannabes some 100 million to 250 million years after the big bang.

The measurements Hanson and his colleagues made agreed quite well with theoretical predictions of what the B-mode should look like if it's induced by gravitational lensing, the international research team reports. 

Sorting out the difference between signatures resulting from lensing and from the inflationary period is more challenging, Hanson acknowledges. Different theoretical models suggest different looks. Some models predict that because so much energy was involved in driving inflation, triggering a lot of turbulence, the B-mode polarization pattern from that period should be intense enough to reflect the turbulence of the times.

He adds that given trends in technology and improvements in the sensitivity needed to make the measurements, the first indirect detection of inflation could come in about 10 years.

And if nothing primordial shows up? "We might just live in a universe where there isn't a primordial B mode at all, and that's interesting in its own right," he says.

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