This book displays some of the best and worst aspects of Anderson's writing. The basic story idea and many aspects of the background are very good. An imaginative use of what were then relatively new discoveries and ideas in cosmology, very clever constuction of alternative species, and a relatively interesting future history. Unfortunately, there is also a good deal of stilted prose, clumsy attempts at eroticism, and a rather strange combination of simpleminded libertarianism and new-agish pantheism. All of these defects occur in some of Anderson's other books, but not in such concentrated form. Aspects of this book were recycled from an earlier and better Anderson novel - Tau Zero.