INTRODUCTION

Physics and metaphysics are two distinct occupations of human beings, and not long ago a lot of effort was invested into keeping them strictly apart. Nowadays, however, the situation seems to be changing. A couple of years ago, an international conference was organised at Cambridge, UK, the proceedings of which bear the title ‘Physics Meets Philosophy at the Planck Scale’. What is special about the Planck Scale that physics and philosophy (of which metaphysics is an essential part) seem to have something to tell to each other?

In physicists' jargon the ‘Planck Scale’ or the ‘Planck era’ means either the most fundamental level of the physical Universe, or an edge at which our present theories of physics break down (this is why the Planck era is also called the Planck threshold). Currently, these two meanings are almost synonymous since the fundamental theory of physics lies beyond the reach of our well-founded physical theories and models.

There are two directions along which we could approach the Planck era. We can either adopt the path followed by cosmologists, or that followed by elementary particle physicists. In cosmology, one tries to reconstruct the history of the Universe starting from our present era as far backward in time as possible. As one moves in this direction, the Universe contracts and becomes denser and denser, till one reaches a density of the order of 1095 g/cm3, and then one finds oneself at the Planck era.