Sean Carroll has challenged people to describe complex ideas in 3 Twitter Tweets. With that being said, I decided to tackle the Cosmic Microwave Background (CMB):
I encourage everyone to try do this with some complex idea as it is both fun and a useful skill to be able to boil down complex ideas to short simple explanations. And even if you don't have a Twitter account you should try it. If nothing else, you can post three 140 character descriptions of any complex topic here in the comments.