BICEP2 scientists publish cosmic inflation paper hedging claim of gravitational waves


The sun sets behind BICEP2 (in the foreground) and the South Pole Telescope (in the background). (Steffen Richter/VagabondPix.co)

The esoteric field of cosmology exploded into front-page news in March when scientists announced at a news conference at Harvard that they had seen signs of gravitational waves emanated at the dawn of time. Then came the peer-review process, and now it’s all up in the air. The same scientists have published a revised and updated version of their original paper, acknowledging that it’s possible they detected only an effect created by dust in our own galaxy.

The scientists behind the BICEP2 experiment had noted, all along, that galactic dust could contaminate their observations to some degree. But they originally said the signal of these gravitational waves was far too strong to be explained by anything in the foreground.

Now, though, in its peer-reviewed paper published in the journal Physical Review Letters, the BICEP2 team states that it cannot “exclude the possibility of dust emission bright enough to explain the entire excess signal.”

This is not a retraction but rather an acknowledgment of the controversy that has been building for months, ever since the much-publicized March 17 news conference at the Harvard-Smithsonian Center for Astrophysics. The scientists continue to believe that they’ve seen the signal of “cosmic inflation,” a sudden, exponential enlargement of the baby universe in the first moments after the big bang.

But other scientists have pointed out that the BICEP2 team may have seriously underestimated the amount of foreground dust that could mimic the effects of dawn-of-time gravitational waves.

John Kovac, the leader of the BICEP2 team, has been traveling in Russia and said via e-mail: “I don’t think there are major new developments here, just the usual peer review revision process with typical additional detail and clarifications added. But we’ll see what others make of it.”

The peer-reviewed paper modifies the bold conclusion of the original, non-peer-reviewed version that went online at the time of the news conference in March. The news conference electrified the science community, and there was much talk of a possible Nobel Prize. The theorists who came up with the theory of cosmic inflation were thrilled.

The original paper concluded, “The long search for tensor B-modes is apparently over, and a new era of B-mode cosmology has begun.”

The peer-reviewed, published paper hedges that statement significantly and elaborates on the uncertainties: “If the origin is in tensors, as favored by the evidence presented above, it heralds a new era of B-mode cosmology. However, if these B modes represent evidence of high-dust foreground, it reveals the scale of the challenges that lie ahead.”

Many teams of astrophysicists are searching for the gravitational waves predicted by inflation theory. Some are using South Pole telescopes and others are operating high in the Andes. This quest is extraordinarily significant for theorists, because it speaks to the essential question of how the universe came into existence and why it has certain properties, such as the fact that it looks strikingly the same in all directions.

Moreover, if correct, the observation of primordial gravitational waves would reveal much about gravity itself. Familiar though it may be, gravity remains an elusive phenomenon, and this result would seemingly demonstrate that gravity emerges from quantum mechanics.

“The overarching theme here is that, out there at the frontier of discovery, it’s very foggy,” said University of Chicago cosmologist Michael Turner. “Maybe they got a little enthusiastic in their [original] paper, but none of the results have changed, maybe a few words in the presentation. Everybody knew that this would require a lot of follow up and skepticism. We’ll get it right.”

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