A theory of the universe has yet to be uncovered because nature is not merely mechanical. We thus promote Einstein’s cosmos and principle theory, which we believe will lead the scientific community to the elusive pinnacle of science: a final theory of the universe. We first discuss the two scientific methods of Einstein’s principle theory and Newton’s mechanical universe and how they overcome the antithesis between empiricism and rationalism. We then apply these two methods to solve the problem of the universe as a (unified) whole. We demonstrate why Einstein’s principle theory subsumes the mechanical universe and, subsequently, how Einstein’s method can address this problem while Newton’s method cannot. The goals of this paper are not only to promote Einstein’s science, but also to begin to resolve the mysteries of the universe as a whole. We sincerely invite the scientific community to pursue principle theory and Einstein’s cosmos collectively.