Light is a wave, and as it travels it does its "waving" along a certain direction - its
polarization.
Polarization, among other things, heavily influences the way light bounces and scatters
- that's why horizontally polarized light reflects off of a lake or car windshield,
which in turn is why sunglasses with a vertical polarizing filter can block that light.
And in the hot plasma of the baby universe, light was bouncing off of electrons left and
right - until the plasma cooled enough to become transparent so the light could start
traveling through space.
But before heading out on its 13+ billion year journey, this light bounced one last
time off of the plasma, and the direction each photon went was influenced by how its
polarization interacted with the precise temperature, density and motion of the plasma.
So if we measure the polarization of light coming from this cosmic background radiation,
it can tell us about the big bang.
The details are complicated, but roughly speaking, clumps in the plasma of the early universe
created polarization aligned along or across the direction from hot to cold, while jiggles
created polarization at 45° angles to the hot-cold direction.
And by jiggles I mean the stretching and squeezing of space due to gravitational waves passing
through.
Anyway, starting with the results from the BICEP telescope at the South Pole, we see
that while a majority of the polarization came from clumps in the early universe, about
15% of it seems to come from jiggles.
And these jiggles are a big deal - they were caused just fractions of fractions of a second
into the life of the universe by quantum fluctuations of the gravitational field, so not only does
their discovery mark the first confirmation that gravity is indeed a quantum mechanical
phenomenon, but it also opens the door for us to look 380,000 years farther back than
ever before, into the very birth of our cosmos.
Congrats to the BICEP collaboration!
- assuming of course, that their results are confirmed by other experiments.