The Meaning Of Relativity

BY W. H. MCCREA, F. R. S. 'THE only justification for our concepts and system of concepts is that they serve to represent the complex of our experiences; beyond this they have no legitimacy. ' So Einstein writes on page 2 of this book. Most present-day physicists would agree, and many before Einstein must have held the same opinion. Einstein, however, put the opinion into practice to better purpose than any physicist before him. And for Einstein it evidently meant what it means for most of us today: a theory is the construction of a theoretical model of the world of physics; all the mathematical discussion applies to the model; the model embodies the 'system of concepts', and it serves 'to represent the complex of our experiences' if the experience of the theoretical observer in the theoretical model can be put into satisfactory correspondence with the experi- ence of the actual observer in the actual physical world. Classical mechanics and classical electromagnetism pro- vide models that are good representations of two sets of actual experiences. As Einstein was the first fully to appreciate, however, it is not possible to combine these into a single self-consistent model. The construction of the simplest possible self-consistent model is the achieve- ment of Einstein's theory of special relativity. The theory is found, in particular, to give a satisfactory representation of the electromagnetic interaction between charged particles through its use of the concept of the electromagnetic field.

In 1921, a young Albert Einstein traveled to America to give four lectures at Princeton University, paving the way for a more complete acceptance of his theory of general relativity. These lectures are published together as The Meaning of Relativity, and were revised with each new edition until Einstein's death. Despite Einstein's profession that he thought without using words, his examples and descriptions of the relativistic world he perceived are clear and easy to follow. Unfortunately for nontechnical readers, his presentation requires deep diversions into mathematics often enough to break up the flow of his narrative, and they may find this rough terrain. But for the mathematically sophisticated or the devoted scientific historian, these lectures are profoundly illuminating--Einstein's bright, quiet genius shines through in the simplicity and economy of his writing. Two appendices follow the lectures: the first covers advances and experimental verifications after 1921; the second, "Relativistic Theory of the Non-Symmetric Field," was Einstein's last scientific paper. The Meaning of Relativity documents a revolution in progress and yields to the careful student deeper truths than those found in physics textbooks. --Rob Lightner