It is sometimes a matter of dispute whether general relativity and cosmology should appear in undergraduate syllabuses at all. The criticism is often made that they are included simply to add glamour to physics courses, to act as a lure to attract students into ‘real hard-core’ physics. I take a much more positive view of their inclusion as an integral part of physics.

General relativity follows on rather naturally from special relativity and results in even more profound changes to our concepts of space and time than those which follow from special relativity. The idea that the geometry of space–time is influenced by the distribution of matter, which then moves along paths in curved space–time is one of the fundamental concepts of modern physics. Indeed, the bending of space–time is now regularly observed as the gravitational lens effect in deep astronomical images (Fig. VII.1). Unfortunately, general relativity is technically complex, in the sense that the necessary mathematics goes beyond what can normally be introduced at the undergraduate level, and it would be wrong to underestimate these technical difficulties. Nonetheless, a great deal can be achieved without the use of advanced techniques, provided the reader is prepared to accept a few results which will simply be made plausible, the exact results then being quoted. This seems a small price to pay for some insight into the intimate connection between space–time geometry and gravitation and for understanding some of the more remarkable phenomena which are expected to be observed in strong gravitational fields, such as those found in the vicinity of black holes.