For particularly brilliant theoretical physicists such as James Clerk Maxwell, Paul Dirac, and Albert Einstein, the search for mathematical truths led to strange new understandings of the ultimate nature of reality. But what are these truths? What are the mysterious numbers that explain the universe? In Fantastic Numbers and Where to Find Them, the leading theoretical physicist and YouTube star Antonio Padilla takes us on an irreverent cosmic tour of nine of the most extraordinary numbers in physics, offering a startling picture of how the universe works. They include Graham's number, which is so large that if you thought shout it in the wrong way, your head would collapse into a singularity; TREE(3), whose finite nature can never be definitively proved because to do so would take so much time that the universe would experience a Poincaré recurrence, resetting to precisely the state it currently holds, down to the arrangement of individual atoms; and 10 120 , measuring the desperately unlikely balance of energy needed to allow the universe to exist for more than just a moment, to external beyond the size of a single atom. Fantastic Numbers and Where to Find Them is a combination of popular and cutting-edge science-and a lively, entertaining, and even funny exploration of the most fundamental units of the universe.