If you know that Planck time is the smallest time measurement possible—basically ten to the negative 44th power in seconds—and that it relates to quantum mechanics, you're ahead of many of us. If you're already perplexed, however, let this insightful and accessible guide enlighten, inform, and entertain you as you use mathematics in order to grasp the basics of physics. A Fellow of the Royal Astronomical Society who got a degree in astrophysics and more importantly, science communication, Colin Stuart provides a sequential, user-friendly tour of physics' most crucial numbers, arriving at an unimaginably large one that you may have wondered about in your idle hours: the estimated mass-energy of the universe.