BICEP2 paper published—with big caveat

What was supposedly the biggest discovery in cosmology in a decade has finally been published, even as a cloud of doubt enshrouds the result. In March, researchers working with BICEP2, a specialized telescope at the South Pole, reported at a press conference that they had seen pinwheel-like swirls in the polarization of the afterglow of the big bang—the cosmic microwave background (CMB)—that came from gravitational waves rippling through the infant universe. Those B modes were “the first direct evidence” that the newborn universe underwent a bizarre exponential growth spurt called inflation, at least according to a press release issued by the BICEP2 team. However, other researchers soon pointed out that the signal might emanate instead from dust within our galaxy. Now, the BICEP2 paper has been published in Physical Review Letters. And in the abstract to the final version, the team writes that its models of galactic dust “are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal.” Although stark, that statement isn’t entirely surprising. Previously, the BICEP team had acknowledged that they couldn’t quantify how much of the signal was really from the CMB.

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