The Sciences

What Made the Bang so Big?

If the findings are verified, BICEP2 will have amassed the strongest support yet for cosmic inflation.

By Steve NadisNov 26, 2014 6:00 AM
The BICEP2 telescope in Antarctica looked for the cosmic pattern. | Steffen Richter, Harvard University


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Earlier in 2014, cosmologists thought they were finally closing in on an answer to that age-old question, “How did it all begin?” In March, Harvard astrophysicist John Kovac announced that a small telescope at the South Pole called BICEP2 (short for Background Imaging of Cosmic Extragalactic Polarization) had captured signals that apparently come from “the first trillionth of a trillionth of a trillionth of a second in the history of the universe.”

Independent confirmation was still needed, said Kovac, who heads the BICEP2 team, but if the result held up, it would mean scientists were on the verge of witnessing and understanding the moment of creation for our cosmos. Then data from the European Space Agency’s Planck space telescope rolled in six months later, casting doubt over the earlier result. The world won’t know the final verdict until the BICEP2 and Planck scientists release their joint report.

Assuming its findings are validated, BICEP2 will have amassed the strongest support yet for cosmic inflation, a theory that attempts to explain exactly what happened during the Big Bang, the universe’s explosive birth event. Inflationary theory holds that our newborn universe started as a tiny fleck of matter, less than one-billionth the size of a proton, and grew exponentially fast — expanding faster than the speed of light, in fact, while doubling in size at least 100 times.

This telltale swirling pattern of light may be evidence of cosmic inflation. | BICEP Collaboration

Inflation is the brainchild of MIT physicist Alan Guth, who came up with the idea in 1979. “I didn’t think it would be tested in my lifetime,” says Guth, because when he dreamed up the theory, no one could conceive of a practical way to verify it.

The runaway expansion lasted from about 10-36 of a second to 10-32 of a second after the Big Bang, but it would have deformed space violently enough to produce gravitational waves, just as a vibrating drumhead emits sound waves. These gravitational waves generated during inflation would be so weak by now, 13.8 billion years after the Big Bang, that they’d be undetectable. But in 1997, five physicists hit upon a possible strategy: Inflationary gravity waves could distort the light left over from the Big Bang in a discernible way.

Eons after the primordial blast, this remnant light fills all space, constituting a faint glow everywhere in the sky known as the cosmic microwave background, or CMB. The key lies in determining how that vestigial light is polarized — basically, how the light waves are oriented. Inflation-era gravity waves, which alternately stretch and compress space as they pass through, would leave a permanent mark in the cosmic radiation background, adding a twist to the CMB polarization. This distinctive, swirling pattern is called a B-mode. If astronomers could detect that, they would, in effect, see the fingerprint of inflation.

BICEP2 was specifically designed to look for this pattern. From 2010 to 2012, the telescope observed a small patch of sky visible from Antarctica. Kovac and his co-investigators — Jamie Bock of Caltech, Chao-Lin Kuo of Stanford and Clem Pryke of the University of Minnesota — then spent over a year scrutinizing the data. “We checked it 14 different ways to make sure it was consistent,” Kovac says, before announcing they had identified the telltale vortex-like pattern expected from gravitational waves generated during inflation.

The researchers believe the signal they detected was cosmic in origin and did not come from our own galaxy, although that point has come under question. The big issue is whether the BICEP2 investigators properly accounted for the effects of dust within our own galaxy, as it could also have given rise to the swirling B-mode pattern.

While that’s being straightened out, the BICEP2 team is moving ahead, poring over new data from the South Pole’s Keck Array, which is part of the series of experiments co-led by Kovac and his colleagues. BICEP3, BICEP2’s more sensitive successor, is set to begin a three-year observational run in early 2015. And several competing groups are going after the B-mode signal as well.

If the original claims are substantiated and the emerging picture of the universe’s beginning is upheld, what would that mean? First, it would tell us that gravitational waves, predicted by Einstein’s century-old theory of general relativity, really do exist. Second, it would greatly clarify our understanding of the Big Bang, telling us, as Guth puts it, “what banged and why it banged.” Third, it would build an almost ironclad case for inflation.

Some uncertainty would still persist because cosmologists don’t fully grasp the underlying physics behind inflation. But the story of our universe’s first moments would, nevertheless, come into sharper focus than ever before — far beyond what many observers had deemed possible.

Clouded by a Veil of Dust

Euphoria overtook the science world on March 17, when members of the BICEP2 team announced the discovery of gravitational waves that represented the “first tremors of the Big Bang.” A couple of months later, two independent analyses claimed the BICEP2 researchers had underestimated the effects of dust in our galaxy, as it could produce the pattern they had attributed to gravitational waves.

On Sept. 22, data from the Planck space telescope showed that the portion of the sky BICEP2 studied contained more galactic dust than previously assumed. The two teams have joined forces to determine whether the signal BICEP2 detected originated, at least in part, from gravitational waves, or if it’s entirely explained by dust.

The results should appear in late 2014. Meanwhile, astronomers are continuing the kinds of observations undertaken by BICEP2, which are still regarded as the most promising means of witnessing the birth throes of our universe.

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