Mystery would add excitement

Many physicists and astronomers live in a slow Euclidean world where bodies lumber along at velocities way below that of light, and the gravitational fields are weak and feeble. Others venture into the more exotic realms of four-dimensional space-time geometry, where general relativity amalgamates special relativity and gravitation. Here, we join our authors by entering the world of Einstein equations, cosmological constants, event horizons, inflation and gravitational waves.

To produce this textbook, M. P. Hobson, G. P. Efstathiou and A. N. Lasenby have used the notes from 40 lectures they give to third and fourth-year Cambridge University natural science tripos astrophysics and theoretical physics students. These notes have been polished and illustrated by typical "Cambridge" examination questions. Also the students have been tempted beyond the bare bones of the syllabus with a few extracurricular titbits such as relativistic stars, black holes, linearised gravity and variational principles.

What I enjoyed was the clarity. The text was erudite and thorough, and flowed beautifully. The reader was never left wondering how, for example, equation 16.63 follows from equations 16.61 and 16.62. It was clear that the students, with diligent application, could work their own way through the text and benefit hugely from self-discovery of this fascinating subject. What surprised me somewhat was the absence of mystery. There was little hint that anyone was doing any research in the subject. The reference section was meagre and mainly focused on listing a handful of the field's older textbooks. One was left feeling that all the discoveries had been made.

Where was the excitement of the frontier? What was still unknown and in doubt? Why should you plough through all this material if you were not being shown just how useful it will be for the progress of science?

David W. Hughes is professor of astronomy, Sheffield University.