These gravitational swirls, called B-modes, are supposed confirmation of a theory known as inflation, which says that the universe expanded exponentially in the first trillionth of a trillionth of a trillionth of a second after the big bang.

But in the intervening months, scientists have begun to cast doubt on the finding, calling into question the discovery team's analysis of its data. Chiefly, concerns have centered on swirls produced by galactic dust in the sky—contamination the team may not have properly accounted for.

Now, the BICEP2 collaboration has published a report of its discovery in Physical Review Letters. Although the collaboration has stood by its results for a few months, it's now dialing back on its original claim.

We "cannot empirically