Summary: Scientists at the BICEP2 collaboration at the South Pole have detected signal that confirm theories of the rapid expansion of the universe immediately after the big bang. If validated by other experiments (which is likely to happen as the signal found is actually stronger than predicted) this confirms a super-rapid expansion within the first instants of the universe before "slowing down" to rapid expansion. What they found were twists in Cosmic Radiation Background that could have only been produced by gravitational waves.
So what does this mean? These signals tell astronomers that gravity was present during this time in which quantum effects dominated the, then very tiny, universe. This gives us greater hope that the Four Fundamental Forces can be one day combined into a unified Theory of Everything which could better describe conditions at the big bang.
Minute Physics video explaining the discovery
Discussion on background and implications
Video of the founding scientists hearing the news