ABSTRACT
As we set o, I undertook to oer a guided tour of those aspects of theoretical physics that are central to our current understanding of the ways of nature. Arguably, the greatest challenge to that understanding is the way in which nature has contrived a reality to which both quantum mechanics and general relativity provide useful approximations. If string theory is correct, then it may well have the potential to describe such an underlying reality. However, we have no evidence that even the rst step in that theory, the study of relativistic strings, is a step in the right direction. The main substance of this nal chapter is to explore a more conservative approach, whose point of departure consists in nothing more than the established theories of general relativity and quantum mechanics, for whose approximately validity we have a great deal of solid evidence.
