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Perhaps it was too good to be true. Two months ago, a team of cosmologists reported that it had spotted the first direct evidence that the newborn universe underwent a mind-boggling exponential growth spurt known as inflation. But last week a new analysis suggested the signal, a subtle pattern in the afterglow of the big bang, or cosmic microwave background (CMB), could be an artifact produced by dust within our own galaxy. "We're certainly not retracting our result," says John Kovac, a cosmologist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and co-leader of the team, which used a specialized telescope at the South Pole known as BICEP2. Others say the BICEP team has already lost its case. "At this time, I think the fair thing to say is that you cannot claim detection-period," says Paul Steinhardt, a theoretical physicist at Princeton University. From 2010 through 2012, BICEP2 peered at a small patch of the CMB to measure the polarization of the microwaves as it varies from point to point. On 17 March, BICEP researchers announced at a press conference in Cambridge that they had spotted ultrafaint pinwheel-like swirls in the sky. Those swirls, or B modes, are most likely traces of gravitational waves rippling through space and time during the 10-32 seconds that inflation lasted, the BICEP team says, and they fulfill a key prediction of the theory of inflation. Many cosmologists hailed the detection as a smoking gun for that theory.