Why does mathematics explain the universe so well? From the big bang to the distant future via parallel worlds, Max Tegmark proposes a radical idea: that our reality is not only described by mathematics: it is mathematics. 'Daring, Radical. Innovative. A game changer.' Michio Kaku, author of Physics of the Future 'An amazing ride through the rich landscape of contemporary cosmology.' Clive Cookson, Financial Times 'An intellectual adventure . . . enlivened by the author's personal touch.' John Gribbin, Times Higher Education 'Lively . . . wonderfully accessible.' Brian Greene, author of The Elegant Universe 'Exhilarating . . . the nearest we have to a successor to Richard Feynman . . . His insights and conclusions are staggering.' Robert Matthews, Focus