But there's more.
The detection of gravitational waves in the CMB would hint at a Big Bang origin. Any ‘signal' embedded in the slight ripples of varying temperature of the CMB (features known as ‘anisotropies'), suggests that its origin would be just after the Big Bang occurred. One model of the Big Bang, and the moments just after, suggests the universe went through a rapid period of expansion known as ‘inflation.' The detection of gravitational waves in this way provided the "smoking gun" for the theory of inflation. Yet another historic discovery.
VIDEO: Big Bang Theorist Told of Gravitational Wave Discovery
Finally, for the gravitational waves to be embedded in the CMB at all, if we wind back time to the inflationary period when the universe was a fraction of the size it is now, the gravitational waves would have had to have been very tiny when they were created. In fact, they would have been created on the tiniest scales possible hinting at a quantum origin.
One of the biggest conundrums in physics is how gravity fits with the Standard Model. The Standard Model, which is a recipe book of sorts for the quantum world, ignores gravity, hinting that the Standard Model is not a complete theory or that there is some more exotic physics beyond the Standard Model. If this B-mode polarization is real, it would suggest that quantum gravity - transmitted in the form of hypothetical gravitons - left its imprint on the CMB when the universe was very young.