BICEP detection of gravitational waves

After some friends seemed interested, having seen it in the news, I posted a short explanation of the recent announcement from the BICEP team on facebook. They have seen B-mode polarisation of the CMB, and hence found evidence for gravitational waves being present in the early universe. I don’t think all the explanations out there in the news are that helpful, so I thought I’d reproduce my short one here in case anyone stumbles on it and is interested. Here’s what was discovered:

The BICEP team released analysis of the data they have been taking over the past few years. They observe the Cosmic Microwave Background (CMB) (wikipedia it for more info) — radiation that has propagated to us since the time of “last scattering” not long (in cosmological terms ~400,000 years) after the big bang and is now microwave radiation. In particular they can look at how this radiation is polarised. The CMB looks almost the same in every direction we look, reflecting the fact that the early universe was extremely smooth. The small differences are mainly the result of there being small differences in the distribution of matter in the early universe. Crucially, however, part of the difference could also be the result of waves in the gravitational field itself being present at the time of last scattering. Polarisation data helps scientists separate out the effects of the matter density fluctuations from the effects of the gravitational waves. The BICEP team are the first to present strong evidence that gravitational waves were indeed present in the early universe at the time of last scattering. Such waves are an important prediction of Einstein’s theory that have not yet been directly detected (by a gravitational wave telescope for example). Moreover, such waves are thought to be produced (along with the density fluctuations), during a much earlier more speculative phase of the universe’s evolution called “inflation” (this would have taken place when the universe was only a fraction of a second old). So yesterday’s discovery is also further evidence for inflation. I work on inflation so I’m pretty happy about that! Go BICEP!

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