In the 20th Century, there have been two periods of intense interest among physicists in unifying aspects of their science. The first began around 1919, following the astronomical confirmation of Einstein's general relativity theory. Several attempts were made by Einstein and others to combine gravity and electromagnetism into a single "unified field theory." These attempts ultimately failed, although some ideas useful to later physics emerged from them. In the second period, which began around 1960 and continues today, the emphasis is on finding a single description for various of the forces and particles of subatomic physics.
In his book, "Einstein's Dream," Barry Parker, professor of physics and astronomy at Idaho State University, tells the story of each of these attempts at unification. In simple, non-mathematical language, he discussed the principles of electromagnetism, quantum theory, general relativity and particle physics, the ideas that physicists have been trying to unite into an all-encompassing theory. "Einstein's Dream" also describes a good deal of the astronomical background needed to understand current ideas about the relation between the early universe and subatomic physics. This includes a discussion of the discoveries of the expanding universe and of the microwave radiation that pervades it. The book also contains a detailed summary of the life cycle of stars, indicating why very massive stars are thought to eventually collapse into black holes.
A book such as this must be measured by how well it achieves what it sets out to do, which is to explain complex ideas to a general audience. While there is some good writing in "Einstein's Dream," I think on the whole that it will be unsuccessful in conveying to non-physicists much real understanding of what progress physicists have recently made toward unification.
I found the most successful parts of Parker's book to be the astronomical sections. The material on stars, and on the expanding universe is presented clearly and authoritatively. Historical anecdotes abound, such as a lively description of the events leading up to the invention of the steady-state model of the universe by Hermann Bondi, Thomas Gold and Fred Hoyle. These astronomical sections are as good as or better than similar sections in other recent books that I have seen on modern physics. Also well done is Parker's discussion of the early attempts by Einstein and others to unify gravity with electromagnetism. This material is not adequately covered in other books and should be of interest to readers with a historical turn of mind.
The sections of the book that deal with particle physics and with recent attempts at unification are not so successful; they contain many errors, both of principle and detail. For example, the concept of local gauge invariance, which forms the basis of most modern unified theories, is incorrectly said by Parker to involve changes in the electric and magnetic field, whereas actually it involves changes only in unobservable potentials. The names of important physicists, such as Thomas Kibble and Oscar Greenberg, are misstated as Kimble and Greely. Some of the terminology of particle physics is misused; the word generators, for instance, is incorrectly substituted for generations. Such mistakes cannot but put off readers with some prior knowledge of the subject, and can seriously mislead those without it.
Although "Einstein's Dream" is ostensibly devoted to a discussion of attempts at unification in physics, this theme is absent for most of the book after the opening chapters. When it does reappear at the end, the treatment of recent attempts at unification, such as supergravity and superstring theories, is so abbreviated and difficult to follow that I doubt many readers will learn much from it. An effective popular treatment of unification in modern physics may have to await a definitive breakthrough in physics itself, allowing writers to know what shape the actual unification will take.