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. (See “Clouded by
a Veil of Dust,” opposite page.) 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.
holds that our newborn
universe started as a tiny fleck of matter, less than onebillionth
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.
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
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.
What Made the Bang so Big?
Earlier in 2014, cosmologists