Although we’re certain that we can describe the very early Universe as being hot, dense, rapidly expanding, and full of matterandradiation — i.e., by the hot Big Bang — the question of whether that was truly the beginning of the Universe or not is one that can be answered with evidence. The differences between a Universe that began with a hot Big Bang and a Universe that had an inflationary phase that precedes and sets up the hot Big Bang are subtle but tremendously important. After all, if we want to know what the very beginning of the Universe was, we need to look for evidence from the Universe itself.