For most of the 20th century, scientiœc thought was dominated by the ideas of the uniformity of the Universe and the uniqueness of the laws of physics. Indeed, cosmological observations indicated that the Universe (on the largest possible scales) is approximately homogeneous and isotropic and that the same laws of physics operate everywhere. Uniformity of the Universe was somewhat of a mystery; but, instead of explaining it, scientists invoked the “cosmological principle,” which said, ironically, that the Universe simply must be uniform because of the cosmological principle. Of course, we know that the Universe is not quite uniform; for example, it contains many galaxies that are crucially important for the existence of life. Thus, the cosmological principle could not be entirely correct; and if it is not entirely correct, it cannot be a fundamental principle of science.