Cosmic microwave background spectral distortions

Cosmic microwave background spectral distortions are changes in the way that light from the early universe is spread out across different colors. This light comes from all directions in the sky and helps us understand what the universe was like a long time ago. It was once very, very hot and full of a lot of energy. The way it looks today is different - it is cooler and less energetic. The distortions let us know that there was a lot of energy in the early universe and that it has cooled down over time.