ABSTRACT
In this chapter, I shall discuss an area of investigation that illustrates many of the theoretical ideas developed in the rest of the book, namely cosmology and the early history of the universe. Only in the last 70 years or so has it been possible to treat cosmology as a matter for serious scientic enquiry rather than philosophical speculation. Since we cannot (presumably) create a new universe in the laboratory, any theory concerning the history of our own universe must remain to some extent speculative. If, however, it is accepted that our knowledge of physics as established in the laboratory and by astronomical observations continues to be valid in the distant past, then a remarkable amount can be said with a fair degree of condence. For example, if the standard cosmological model (roughly speaking, what is known as the CDM model) is correct, the present age of the universe can be estimated as 13.7 billion years (1 billion = 109) with a precision of about 1%. Our established knowledge of physics can, of course, be applied with condence only when conditions in the universe were such that a condent extrapolation can be made from conditions which can be created in the laboratory. This has been true ever since the universe was about one millisecond old. In the rst millisecond, however, events moved extremely rapidly.
