Big Bang backlash: BICEP2 discovery of gravity waves questioned by cosmologists

Captured From http://www.washingtonpost.com

 

Video: In March, scientists from the Harvard-Smithsonian Center for Astrophysics announced their discovery of gravitational waves created at the dawn of the universe. These waves were created in a period of rapid expansion called cosmic inflation. This new evidence could prove the definitive confirmation of the inflation theory. But other researchers are not convinced.

By Joel Achenbach, Published: May 16 E-mail the writer

It was the science story of the year: Astrophysicists held a news conference at Harvard on March 17 announcing that their South Pole telescope had found evidence of gravity waves from the dawn of time.

Cosmology doesn’t get any bigger than this. The discovery was hailed as confirmation of a mind-boggling addendum to the big-bang theory, something called “cosmic inflation” that describes the universe beginning not in a stately expansion but with a brief, exponentially rapid, inflationary spasm.

Science is a demanding and unforgiving business, and great discoveries are greeted not with parades and champagne but rather with questions, doubts and demands for more data. So it is that, in recent days, scientists in the astrophysics community have been vocalizing their concern that the South Pole experiment, known as BICEP2, may have detected only the signature of dust in our own galaxy.

These doubters say, in effect, that rather than seeing the aftershock of the birth of the universe the scientists may have seen only some schmutz in the foreground, as if they needed to clean their eyeglasses.

This is a delicate issue. Careers and prizes are potentially at stake. So too is the credibility of a field that dares to probe the deepest secrets of the universe no matter where that search may lead.

No one is alleging an outright scientific error. It’s more of a debate about how scientists should communicate their uncertainties when presenting blockbuster findings. This is a case of “extraordinary claims demand extraordinary evidence,” to use the formulation made famous by astronomer Carl Sagan.

The South Pole telescope saw something in the sky — of that there is little doubt, because the team took great care to eliminate systematic errors that could have come from the instruments. But what the telescope saw — polarization of ancient radiation from the early universe — could have been produced by either primordial gravity waves or by foreground dust, or by some combination of both.

“They have very nice measurements of something. We don’t know what that something is,” said Uros Seljak, a professor of physics and astronomy at the University of California at Berkeley. “We can’t tell if BICEP2 has measured dust or has measured gravity waves.”

John Kovac, a Harvard astrophysicist and the principal investigator for BICEP2 — part of a larger collaboration among institutions from coast to coast — stands firmly behind his team’s findings. But he acknowledges that there are lingering uncertainties that will remain until new data is presented, likely this fall, by the European Space Agency’s Planck Space Telescope.

“We are very confident that we have measured B-modes” — polarization of light that can be caused by gravity waves — “with high statistical significance in the sky, and we have looked at them in multiple ways. And the data suggest they are unlikely to be dominated by galactic foregrounds. That is not to say that there is not uncertainty about that,” Kovac said.

Now everyone is waiting for the Planck results. The Planck telescope is scrutinizing the cosmic microwave background (CMB) radiation, a remnant of the moment when the young cosmos became transparent to light. BICEP2 looked at the radiation in a small patch of sky, but Planck is doing an all-sky survey in multiple frequencies and should produce excellent estimates of foreground effects such as dust.

The big announcement March 17 thrilled the cosmology community. People stopped what they were doing to examine the results. Cosmic inflation had been discussed for more than three decades, but this would be the first strong evidence for it.

“What inflation does is pull apart the fabric of space-time much faster than the speed of light,” said Princeton professor of physics Suzanne Staggs, part of a team studying the cosmic background radiation with a telescope in Chile.

“It’s an amazing thing that quantum processes a moment after creation may have been stretched out by inflationary expansion and literally etched across space itself — stretched across the sky,” said Brian Greene, a Columbia University theorist who is not involved in the experiments. “If we are seeing that, it is an monumental moment.”

All the more reason, he said, to ask the hard questions about the discovery, and “hit it with a sledgehammer and see if it survives.”

The BICEP2 dust-up is being played out on, among other places, a Facebook page started by people who couldn’t access the live-streamed Internet feed of the March 17 announcement at the Harvard-Smithsonian Center for Astrophysics. The controversy has popped up in recent days on physics blogs and in several science-oriented publications, including the online news sites of the journals Nature and Science, as well as New Scientist and National Geographic.

Thursday morning, theoretical physicist Raphael Flauger, who has a dual appointment at New York University and the Institute for Advanced Study in Princeton, N.J., gave a presentation at Princeton University outlining his concerns about the BICEP2 conclusions.

“I think foregrounds are maybe larger than they thought, but I’m still hopeful that there’s a signal there,” Flauger said in an interview later. “It will be the biggest discovery maybe in my lifetime. It would be a measurement of the conditions, if you want, when the universe was 10 to the minus-30 seconds old” — a millionth of a trillionth of a trillionth of a second.

Flauger noted that the BICEP2 team estimated the amount of foreground dust by relying, in part, on a slide presented at a conference. The slide gave a visual representation of observations by the Planck spacecraft but did not contain the actual data. Critics say this is not a robust way to make an estimate.

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