It is known that Maxwell’s electrodynamics—as usually understood at the present time—when applied to moving bodies, leads to asymmetries which do not appear to be inherent in the phenomena. Take, for example, the reciprocal electrodynamic action of a magnet and a conductor. The observable phenomenon here depends only on the relative motion of the conductor and the magnet, whereas the customary view draws a sharp distinction between the two cases in which either the one or the other of these bodies (...) is in motion. For if the magnet is in motion and the conductor at rest, there arises in the neighbourhood of the magnet an electric field with a certain definite energy, producing a current at the places where parts of the conductor are situated. But if the magnet is stationary and the conductor in motion, no electric field arises in the neighbourhood of the magnet. In the conductor, however, we find an electromotive force, to which in itself there is no corresponding energy, but which gives rise—assuming equality of relative motion in the two cases discussed—to electric currents of the same path and intensity as those produced by the electric forces in the former case. Examples of this sort, together with the unsuccessful attempts to discover any motion of the earth relatively to the “light medium,” suggest that the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of absolute rest. They suggest rather that, as has already been shown to the first order of small quantities, the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good.1 We will raise this conjecture (the purport of which will hereafter be called the “Principle of Relativity”) to the status of a postulate, and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body.. (shrink)

Abraham Pais's Subtle Is the Lord was a publishing phenomenon: a mathematically sophisticated exposition of the science and the life of Albert Einstein that reached a huge audience and won an American Book Award. Reviewers hailed the book as "a monument to sound scholarship and graceful style", "an extraordinary biography of an extraordinary man", and "a fine book". In this groundbreaking new volume, Pais undertakes a history of the physics of matter and of physical forces since the discovery of x-rays. (...) The book attempts to relate not only what has happened over the last hundred years but why it happened the way it did, what it was like for those scientists involved, and how what at the time may have seemed a series of bizarre or unrelated events, now with hindsight emerges as a logical sequence of events. Pais, a noted physicist, was personally involved in many of the developments he describes, and thus Inward Bound, like his earlier book, is filled with unique insights into the world of big and small physics. Between 1895 and 1983, the period he covers, the smallest distances explored have shrunk a hundred millionfold, Pais notes. Along this incompletely traveled "road inward," scientists have established markers that later generations will rank among the principal monuments of the twentieth century. In alternating technical and nontechnical sections, this magisterial survey richly conveys what has been discovered about the constituents of matter, the laws to which they are subject, and the forces that act on them. But the advances have certainly not come smoothly. The book shows that these have been times of progress and stagnation, of order and chaos, of clarity and confusion, of belief and incredulity, of the conventional and the bizarre; also of revolutionaries and conservatives, of science by individuals and by consortia, of little gadgets and big machines, and of modest funds and big money. About the Author: Abraham Pais is Detlev W. Bronk Professor of Physics at the Rockefeller University. The author of the prizewinning biography of Einstein now undertakes a history of modern physics. (shrink)

In this article the Dirac equation is used a guideline to see the historical emergence of the concept of quanta, associated with the quantum field. In P. Jordan’s approach, the electron as quanta results from the quantization of a classical field described by the Dirac equation. The concept of quanta becomes a central piece in the applications of the theory and is seen as fundamental in the intelegibility of the interaction between fields, being the Fock space the natural mathematical structure (...) that permits maintaining the quanta concept when considering interactions. This doesn’t seem to avoid the apparent impossibility of using the concept of quanta – and with it the common interpretation of quantum field, when interacting fields are considered together as one complete system. In this article it is defended that the type of analysis that leads itself to so drastic conclusions is avoidable if a clear distinction is made of the theoretical framework and particular models used in the empirical corroboration of the theory. When dealing with models there is really no complete interacting fields, and what we have is a description of interaction between distinct fields. In this situation the concept of quanta is central in the description of interacting fields. (shrink)