A poet, a physicist, and a philosopher explored the greatest enigmas in the universe—the nature of free will, the strange fabric of the cosmos, the true limits of the mind—and each in their own way uncovered a revelatory truth about our place in the world “[A] mind-expanding book. . . . Elegantly written.” —The New York Times Argentine poet Jorge Luis Borges was madly in love when his life was shattered by painful heartbreak. But the breakdown that followed illuminated an incontrovertible truth—that love is necessarily imbued with loss, that the one doesn’t exist without the other. German physicist Werner Heisenberg was fighting with the scientific establishment on the meaning of the quantum realm’s absurdity when he had his own epiphany—that there is no such thing as a complete, perfect description of reality. Prussian philosopher Immanuel Kant pushed the assumptions of human reason to their mind-bending conclusions, but emerged with an idea that crowned a towering philosophical system—that the human mind has fundamental limits, and those limits undergird both our greatest achievements as well as our missteps. Through fiction, science, and philosophy, the work of these three thinkers coalesced around the powerful, haunting fact that there is an irreconcilable difference between reality “out there” and reality as we experience it. Out of this profound truth comes a multitude of galvanizing ideas: the notion of selfhood, free will, and purpose in human life; the roots of morality, aesthetics, and reason; and the origins and nature of the cosmos itself. As each of these thinkers shows, every one of us has a fundamentally incomplete picture of the world. But this is to be expected. Only as mortal, finite beings are we able to experience the world in all its richness and breathtaking majesty. We are stranded in a gulf of vast extremes, between the astronomical and the quantum, an abyss of freedom and absolute determinism, and it is in that center where we must make our home. A soaring and lucid reflection on the lives and work of Borges, Heisenberg, and Kant, The Rigor of Angels movingly demonstrates that the mysteries of our place in the world may always loom over us—not as a threat, but as a reminder of our humble humanity.