Unification and the Limits of Knowledge

I examine the question of whether it is possible to construct a final theory of Nature in a reductionist sense. Complete unification implicitly assumes total knowledge of physical reality. Can such knowledge be obtained? I examine two fundamental limitations which indicate that the answer is in the negative. To begin, science cannot explain the problem of the first cause, even within a valid quantum mechanical formulation of gravity. Also, our knowledge of reality depends on a fundamental way on our measuring devices. These, in turn, are subject to technological and, at a deeper level, to quantum mechanical limitations. Since we cannot measure all there is, we cannot know all there is. Thus, the boundaries of measurement set the limits of physics and of our explanations of physical reality. INTRODUCTION Are there unanswerable questions? Or can scientists, through their remarkable ingenuity and inventiveness, answer all questions related to physical reality? Since Thales of Miletus wondered about the material composition of the world some twenty-five centuries ago, a sense of invincibility has characterized the rational quest for knowledge: given enough time, Nature’s secrets will all be revealed to us. And indeed, as Galileo framed his telescope on the silvery disk of the Moon in 1608, the pace of scientific ∗ Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA. [email protected]