Christmas Special This chart shows every object that has ever existed, and raises a question: is the universe a black hole?Some 13.8bn years ago, the universe came into existence in the Big Bang. Its first moments were a period of pure energy with intense, possibly infinite, heat and density. As the universe expanded, it cooled and objects began to emerge, like snowflakes forming in cold air. In less than a nanosecond the elementary particles—photons, electrons, quarks and gluons—condensed from...