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A photo of the BICEP2 telescope

Using a telescope in Antarctica, the BICEP2 team searched for evidence supporting the theory of inflation, which says that the universe expanded exponentially in the first moments after the big bang.

PHOTOGRAPH BY KEITH VANDERLINDE

Nadia Drake

For National Geographic

Published June 20, 2014

One of the grandest claims in cosmology could be crumbling. The detection of gravitational wave imprints in the universe's background radiation, announced amid much fanfare in March, was originally described as a discovery "as big as it gets."

These gravitational swirls, called B-modes, are supposed confirmation of a theory known as inflation, which says that the universe expanded exponentially in the first trillionth of a trillionth of a trillionth of a second after the big bang.

But in the intervening months, scientists have begun to cast doubt on the finding, calling into question the discovery team's analysis of its data. Chiefly, concerns have centered on swirls produced by galactic dust in the sky—contamination the team may not have properly accounted for.

Now, the BICEP2 collaboration has published a report of its discovery in Physical Review Letters. Although the collaboration has stood by its results for a few months, it's now dialing back on its original claim.

We "cannot empirically exclude dust emission bright enough to explain the entire excess signal," the authors write, noting that they still think the evidence suggests they're seeing a real signal from gravitational waves.

Cosmic Swirls

When the BICEP2 team announced its discovery in March, talk of future Nobel Prizes immediately began swirling. But the tide turned quickly as scientists started scrutinizing the then-unpublished results.

First, Internet bloggers began questioning whether the team had properly estimated the amount of polarization resulting from foreground galactic dust, which can also produce B-modes. To determine how much of the detected swirly signals are the result of gravitational waves, scientists needed to first find out how much this dust contributed to the overall signal. Then they needed to subtract the dust contribution.

The team based one of these analyses on a digitized version of a foreground dust map—pulled from a Powerpoint presentation by a member of the Planck collaboration, which is looking for similar signals.

"This is not sound methodology," said Princeton University physicist Lyman Page at a May 15 seminar at Princeton. "You can't do science by digitizing other people's images."

Then, physicist Raphael Flauger, who splits his time between Princeton University and New York University, attempted to retrace the BICEP2 team's march through the data. He suspected that the team had misunderstood that crucial Planck map, and he concluded that there was too much uncertainty in the measurements to point to a signal from gravitational waves. "I'm hopeful that there is still a contribution to the signal from inflation, but one needs more data," Flauger says.

An illustration of a graph showing data from the BICEP2 telescope potentially confirming the Big Bang.
These swirly B-mode signals are imprints in the fabric of the universe. If they're the result of primordial gravitational waves, the signals are evidence for the theory of cosmic inflation.
ILLUSTRATION BY BICEP2 COLLABORATION

Waiting for Planck

In the paper formally detailing their gravitational wave finding that was just published, the BICEP2 team has excluded one of the analyses based on the Planck map, noting "the large uncertainties on this and the other dust models presented." But the team continues to stand by its claims—although perhaps with a bit more reservation.

"Has my confidence gone down? Yes," team leader Clement Pryke, of the University of Minnesota, told New Scientist.

Flauger and others suggest waiting for data from the Planck collaboration and from other experiments attempting to replicate the BICEP team's analysis.

"We will soon know whether what BICEP2 is seeing is in fact—at least in part—the signal from an early inflationary period," he says. "Or if what they see is emission from polarized dust in our own galaxy."

Follow Nadia Drake on Twitter.

2 comments
M. Omerbashich
M. Omerbashich

Fact: the only certain conclusion is the one coming from Puget at Zeldovich 100 cosmologist conference in Moscow: the Planck team now admit that, due to too complex statistics, polarized CMB, BICEP2, etc. are too hard for the Planck to assess.  Multi-channel-turned-no-channel; much adust about nothing.

Fact: "As Big Bang gets downgraded to a bang in a snap, the first scientific proof of Multiverse claimed": http://www.mynewsdesk.com/ba/pressreleases/as-big-bang-gets-downgraded-to-a-bang-the-first-scientific-proof-of-the-multiverse-claimed-97549

Fact: "A mathematical equation stands forever" - A.Einstein

Reid Barnes
Reid Barnes

Are the measurements of the tiny tiny variations in what was originally predicted to be uniform cosmic microwave background radiation truly reliable enough to support a gravitational model of cosmology based on the general theory of relativity?  Stephen Hawking said the tiny tiny variations are from tiny tiny beginnings of the formations produced eventually after the big bang, he said, by gravitational attraction.  What this doesn't really explain is how the force of gravity, tiny tiny compared to electric and magnetic force, could form galaxies out of matter that was in a plasma state (plasma being a state of matter in which its atomic parts are not in stable form–like inside a lightning bolt) said to be prevalent at the very beginning. See the Facebook Note,"How far must they go to keep a gravitational model based on general relativity?" https://www.facebook.com/notes/reid-barnes/how-far-must-they-go-to-keep-a-gravitational-model-based-on-general-relativity/748137345238842


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