(credit: Lawrence Berkeley Lab)
Everyone has been pretty excited by the recent observation of gravitational waves. I know that I am prone to exaggeration, but gravitational waves really do open up a new way to observe the Universe.
At the moment, when we observe the night sky, the farther into the distance we look, the further back in time we see. But relationship is based on an assumption: the light we see has not bounced off anything in between us and its origin. Normally, this is a pretty safe assumption, because space is pretty big, and most of the material in it (like dust, etc) doesn't do much.
But in the very early Universe, before atoms had formed, things were very dense, so light scattered a lot. The scattering means that the information that a photon carried about its origin was lost. As a result, we can't really see much beyond the time when all the charged particles all agreed to stick together and create the first three elements of the periodic table.
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