In this book Einstein discusses his motive and philosophical guidance in forming relativity theory and some other topics. It is not a good book to learn about the relativity theories themselves. It could be said to be concerned with the philosophy of relativity, which of course fits the fact that it was published as part of the Philosophical Library.

The primary motivation for Einstein was a belief in the simplicity and unity of nature and natural laws. He searched for the simplicist explanation of the reality that we see around us. Simplicity in this context does not mean easy to calculate, but means the logical scheme with the least axioms. This view is expressed very clearly in this book. For Einstein the distinguishing advantage of the theories of relativity is their logical completeness, not the accuracy of their predictions or the ease of calculation of the predictions. One of his motivations for the general theory of relativity was to explain by one axiom the identity of gravitational and inertial mass.

In one essay, the nature of reality is discussed. In view of Mermin's article in the May 2010 issue of Physics Today, questioning the reality of fields, this essay is of special interest. If he were still alive, Einstein would surely have joined in the chorus of critical letters, since in this book (probably written early in the 20th century) he affirms his firm belief in the reality of electromagnetic fields even though the ether played no role in forming the fields. His expectation of the developement of physics was that all observed phenomena would be expressed as fields, ie., solutions of partial differential equations without singularities, with particles being clumps of high intensity fields. Said in this way, Einstein's goal is presently being approached with fields being the Lagrangian fields of QED, but Einstein went further than this and expected that only the values of metric field and another field describing the property of parellel direcrtions would be needed. This attempt to explain fields and particles in term of just these two fields as an clearly an example of the search for logical simplicity.

The need for the parallel field has been obviated by modern relativity theory since this characteristic has been supplied by the concept of parallel transport which in turn comes from the covariant deravitive and this in turn comes from the derivatives of the metric field. Although it seems that we are very close to realizing "Einstein's dream" with just one basic field, it has been found too difficult to close the gap in a mathematically consistent way, but this story may not be over.

Einstein gives a good description of his thought processes in coming to the general theory. The first step was the equivalence principle: that the phenomena of gravitation was equivalent to an acceleration of the coordinate system. This brought in the idea of a nonlinear transformation of coordinates, a problem, since this was in conflict with the conept of a coordinate as a physical entity. The equivalence principle also brought in another problem since according to special relativity the mass of a body depends on its energy and if gravity was a force proportional to mass, bodies of different energy content could not fall at the same rate.
The common solution was Riemann geometry where the metric was also changed by a transformation of coordinates with physical reality being only the combination of a coordinate system with a metric, and where the path of a freely moving body could be given by a geodesic in the Riemann space with that metric, thus giving up the idea of a force of gravity. The concept of massive body being the origin of a force was replaced by showing that the paths of bodies responding to gravitation were determined by properties of space (curvature as expressed by the metric) through which they passed which in turn were determined by the surrounding distribution of matter and/or energy (Einstein field equations).

The belief in fundamental logical simplicity was almost surely the fundamental reason why Einstein was upset by quantum mechanics (which has no logical connection to relativity theory). This situation is best described by assuming the relation between relativity theory and quantum theory as their being connected by a black box. Some say we have no need to know what is in the box because the two theories together describe reality as we know it. From this book it is clear that Einstein would say we need to know what is in that box. ( )

Who says you can't judge a book by its cover? I haven't read this one yet, but it looks really interesting. Some of Einstein's speeches and papers, given on various topics, were gathered together in 1934 and published in book form as "The World As I See It." This little volume is a reprint of just the science topics from that book. According to the dust jacket, the central core of the Theory of Relativity is explained in clear language accessible to any interested reader. Einstein also holds forth on the principles of research, the nature of scientific truth, and the method of theoretical physicsHe also offers acute analyses and appreciation of the work of such giants as Johannes Kepler, Isaac Newton, Clerk Maxwell, and Niels Bohr. In short, the book offers a rare look into one of the greatest minds of the 20th century. I'm looking forward to reading it. ( )