BICEP2’s cosmological conundrum

What a fascinating moment to be a cosmologist! Astrophysicists at the South Pole saw something in the sky, and it might have been the tell-tale, long-predicted, much-sought-after B-modes, a type of polarization of the Cosmic Microwave Background (CMB) radiation caused by gravitational waves emanated in a brief inflationary spasm at the beginning of the universe.

This is basically the fingerprint of the Creation if you want to get dramatic about it. It’s “quantum gravity” etched in the sky. If you wanted to detect gravitational waves like this experimentally, you’d have to build a machine that has a trillion times the energy of the Large Hadron Collider. Instead, you use the universe as your laboratory, and build a really sensitive telescope, and stare for a long time, and squint really hard, and then hope you know what you’re looking at.

But as my story Saturday reported [excerpt below], there’s a decent chance that the BICEP2 signal is just a foreground effect. The polarization of the CMB may come from dust within our own galaxy, or from something else that’s non-cosmological. If it’s galactic, that doesn’t mean inflation theory is wrong, or that the gravitational waves aren’t there. It would merely mean that everyone has to keep looking.

New data from the Planck telescope should clarify the picture in the months ahead. In the meantime, scientists are debating whether the BICEP2 scientists overstated their conclusions.

My reporting suggests that they could have been more cautious in how they framed their result, particularly in the last line of the paper: “The long search for tensor B-modes is apparently over, and a new era of B-mode cosmology has begun.”

They may yet be proved correct as the Planck data come in. But even so, there’s a lesson here: When you report huge results, it’s always best to understate. When Edwin Hubble reported the red-shifting of the galaxies in the late 1920s, he didn’t say that he had discovered that the universe was expanding (I covered that as a cub reporter, you know). [Got it right here: Hubble had detected this nice, linear relationship between the distance to a galaxy and the extent to which it was red-shifted, and this was a clear sign of an expanding universe. But he wrote that he awaited new data to provide confirmation of this distance-velocity relationship, and “it is thought premature to discuss the obvious consequences of the present result.”]

The BICEP2 results were the subject of a meeting this weekend at Caltech. The PowerPoint presentations and graphs etc. are available on the Web and are coming out via Twitter. There was a fair bit of skepticism in the air, is my impression from what I’ve seen so far.

A number of scientists have told me they are quite concerned that a retraction would be deeply embarrassing for the field of cosmology. When I attended a luncheon at the Institute for Advanced Study, one scientist mentioned “cold fusion” as an analog. Another asked if it would have been possible for The Post to have held off on publishing our initial story on the BICEP2 announcement at Harvard on grounds that the associated scientific paper had not yet been peer-reviewed or published. I replied that I could have told my cat that it had not been peer-reviewed, but that this was going to be a big story in the paper given the significance of the result and the competitive nature of the news business.

This is not actually a cold fusion scenario. These are top-notch scientists doing excellent, if difficult, work. It reminds me more of the case of the Mars rock — ALH84001. Again, first-rank NASA scientists doing innovative work on a meteorite from Mars. But they, too, may have overstated their conclusions when they said they’d found evidence of Martian microfossils. Most of their colleagues didn’t believe them and that hasn’t changed much as far as I know. A touch more modesty by the NASA scientists in their description of their conclusion would have served them well. (By the way: When NASA held the presser announcing the Mars meteorite microfossil “discovery,” the agency included a skeptic on stage: William Schopf, a combative scientist at UCLA. Schopf basically announced that the other scientists had gotten it all wrong. So from the very start, the public knew that this wasn’t a slam-dunk.)

The study of the CMB is a highly competitive field and there are something like seven teams trying to nail down that cosmological signal of gravitational waves from the initial inflationary epoch. The competition may influence some of the reactions to the BICEP2 findings. And there are theorists who disfavor inflation and the associated implication of a “Multiverse” and who are likely to give this result a skeptical eye. One of them is Paul Steinhardt of Princeton, who helped develop inflation theory and later turned against it (that’s a longer discussion and one I’d have to do my homework for).  “I’ve been upset about this paper since even before that press conference,” Steinhardt told me. He’d seen an early version of the BICEP2 paper, saw a number of things that didn’t seem right, and assumed that it would be changed before it was made public. It wasn’t, he said. Among his complaints: There is data presented by BICEP2 that matches the theoretic predictions perfectly — too perfectly.

“There’s something wrong. There’s something they don’t understand,” Steinhardt said.

He added:

“This is a very hard, challenging kind of science. It’s extremely difficult to get a very tiny signal out of the sky. And also it’s therefore possible to get it wrong.”

Excerpt from my front-page story on Saturday:

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.

[story continues…]

Joel Achenbach writes on science and politics for the Post's national desk and on the "Achenblog."

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Joel Achenbach · May 15, 2014