BICEP2 claims the first direct evidence for gravitational waves
Around 35 years ago, some physicists came up with the theory of inflation to explain why opposite sides of an expanding Universe were so alike. The theory of inflation says that the very early Universe (when it was only 0.00000000000000000000000000000000001 of a second old) expanded at an incredible rate - even faster than the speed of light. It grew from something so small that we cannot begin to imagine what it looked like, into something the size of a marble in just a tiny fraction of a second. Einstein’s theory of General Relativity predicts that this violent period of expansion would create gravitational waves, compressing space in one direction and stretching it in another, thereby creating ripples. These first, or primordial, gravitational waves may be too weak for us to detect directly, but they will have left a distinctive swirly pattern in the CMB, something scientists call the primordial B-mode polarization.
Quick aside: Polarisation can be quite a difficult concept to understand, but it essentially refers to light that has a certain orientation. Whilst most light is un-polarised, certain physical conditions can cause light to become polarised - i.e. be given an orientation. With the correct instruments, we can detect the polarisation of light, and use it to understand the physical processes that are taking place in the region from which the light was emitted or travelled through.
Now when the BICEP2 team looked at the CMB, they found the expected swirly pattern (see above image) and they are confident that this confirms the theory of inflation. The B-mode polarization, which twists and curls the direction of the light to create the swirly pattern, could show us what happened in the tiny fraction of a second when inflation occurred and this is very important. There are many theories about how inflation might have worked but now we can compare patterns produced by theoretical simulations with the patterns that have actually been observed. This will help us understand how the Universe has evolved since just after its birth into the Universe we see today.
In order to be accepted by the scientific community, the BICEP2 results will have to be checked by other groups in the field, to see if they can get the same result in their observations. There is another group working on data from the Planck mission that should be reporting on a similar experiment later in the year.