Today the latest results from the BICEP2 telescope in Antarctica are out. And boy, are they exciting! They provide stark evidence for two widely believed theoretical predictions, namely inflation and gravitational waves. The authors are already being tipped for a Nobel prize.
So what’s the science behind this magnificent discovery? It’s easiest to start with the name of the telescope. BICEP stands for “Background Imaging of Cosmic Extragalactic Polarization”. That means looking for signals from the Big Bang. Cool, huh?
After the Big Bang the universe was a hot dense soup of particles. Eventually (380,000 years later) things were cool enough for the universe to become transparent. Particles could bind together to form hydrogen atoms, emitting light in the process. Nowadays we see this ancient light as microwave radiation covering space.
This cosmic microwave background (CMB) has a particularly puzzling feature. It’s much more uniform than we should expect from a generic Big Bang explosion. Intuitively most explosions don’t generate exactly symmetrical outcomes!
What’s needed is some mechanism to smooth out the differences between different parts of space. Here’s where the idea of inflation comes in. A fraction of a second after the Big Bang we think that the universe blew up at an astonishing rate. This happened so fast that there was no time for inconsistencies to creep in. The result – a uniform cosmos.
It’s certainly an appealing explanation, but the problem is that there’s been little direct evidence. Until now, that is. Cosmologists on the BICEP project were looking for a particular signature from inflation, and it seems like they’ve found it!
To understand their method we need to know something about light. A wave of light can oscillate in different directions perpendicular to its path. A light wave coming into your eyes from your screen will oscillate somewhat up-down and somewhat left-right. These two options are known as polarizations of light.
It turns out that you can measure exactly how light in the CMB is polarized. This is useful because inflation produces a particular polarization pattern called a B mode. It’s taken decades to locate this smoking gun, but now the BICEP team have done it.
Hang on, couldn’t these B modes come about some other way? Probably not. The B mode pattern we observe seems to arise from the interaction of light with gravitational waves. And to get enough of these we need inflation. Or perhaps this effect is an observational fluke? According to the paper, we’re 99.999999% sure it isn’t.
It’s worth pointing out that this result is a double whammy. It confirms theories of inflation and gravity. Nobody has yet detected a gravitational wave, despite the fact they’re theoretically an easy consequence of Einstein’s general relativity. This latest development is further indirect evidence of their existence.