Today the cosmology community is full of chatter about an impending announcement – I heard the story from people on three continents. Moreover, the Center for Astrophysics at Harvard has scheduled a media conference on Monday with the promise of a major discovery, so there is some substance to the stories.

As always though, rumours run beyond the available facts, starting with the claim that the discovery was made by BICEP2, a telescope at the South Pole. BICEP2 is one of a number of instruments around the world that are dedicated to observations of the microwave background, the afterglow of the Big Bang. The word is that the BICEP team will announce evidence for a primordial B-mode – a delicate twist in the polarisation-pattern of the microwave sky,

Unlike the dark matter and dark energy that dominate the cosmos today, a B-mode would be a tiny pinch of spice that adds an oh-so-subtle flavour to the recipe of the universe. What makes a B-mode interesting (at least to a theorist) is how it gets there. Most realistic cosmological models rely on inflation, a hypothetical period of accelerated growth, to solve "initial conditions problems" that plague simple models of the Big Bang. During inflation, quantum ripples in spacetime are stretched until they span the visible universe. It is these ripples, or gravitational waves, that would induce a B-mode in the microwave sky. Conversely, the B-mode predicted by competing solutions to the initial conditions problems is unobservably small, making the B-mode a "smoking gun" for inflation. So if the rumours hold up, BICEP could have detected a "signal" that confirms a key tenet of modern cosmology and which was written into the sky a trillion, trillion trillionth of a second after the Big Bang. And that would be a very big deal indeed.

When it comes to the details, the stories diverge. Some claim a (relatively) large B-mode that could be hard to square with other datasets, or would imply that the early universe is weirder than we imagine. Other rumours tell of a signal that is consistent with everything else we know, but might permit only a more tentative detection. (And not all possible B-modes match the predictions of simple inflationary models: a big B-mode that was not an inflationary B-mode might be the most astonishing outcome of all.)

This is a blog about a rumour and what it would mean if the rumours are correct (and the results then stand the test of time). It may be that rumours are wrong and the announcement is about something entirely different but at Noon, Eastern Daylight Time on March 17th we will know.