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.