Relativity (Barnes & Noble Library of Essential Reading): The Special and the General Theory (The Barnes & Noble Library of Essential Reading) - Softcover

Albert Einsteins Relativity: The Special and the General Theory (1920) is a cornerstone in the edifice of modern physics. With it the great scientist and humanist took his place beside other great teachers of science. Among the greatest achievements of human thinking, the theories of relativity are commonly regarded as the exclusive domain of highly trained physicists and mathematicians. Disapproving of this segregation as he was, Einstein took it upon himself to explain in this book both theories in their simplest and most down-to-earth form, intending it for "those readers who, from a general scientific and philosophical point of view, are interested in the theory, but who are not conversant with the mathematical apparatus." Indeed, within the vast literature on the philosophy of space and time, Einsteins Relativity shall remain an illuminable and intelligible exposition, highly quotable as one of the most lucid presentations of the subject matter, and a launching pad for any further inquiry on the fascinating features of our universe.

Albert Einstein (1879-1955) is one of the icons of our times, requiring almost no introduction. A Nobel laureate, the author of the special and the general theories of relativity, and a key figure in the birth of quantum mechanics, he is widely acclaimed as one of the most creative intellects of human history. The German-Jewish-born "technical-expert-third-class" in the Swiss patent office in Bern originally intended to become a secondary-school teacher - a profession for which he had a natural talent, as readers of Relativity would surely appreciate - but in 1909, having completed an astonishing range of theoreticalphysics publications, written in his spare time without the benefit of close contact with scientific literature or colleagues, he was recognized as a leading scientific thinker and two years later was appointed a full professor at the Karl-Ferdinand University in Prague. A year later he returned to Zurich to begin his work on the general theory of relativity and in 1914 accepted a distinguished research position in the Prussian Academy of Sciences together with a chair (but no teaching duties) at the University of Berlin. He was also offered the directorship of the Kaiser Wilhelm Institute of Physics in Berlin, which was about to be established. After a number of false starts, Einstein published, late in 1915, the definitive version of the general theory of relativity, and in so doing forever changed our views of the cosmos.

Einstein was first idolized by the popular press when British eclipse expeditions in 1919 confirmed his predictions on the bending of light rays near the sun. The London Times ran the headline on 7 November 1919: Revolution in science - New theory of the Universe - Newtonian ideas overthrown, and three weeks later printed Einsteins popular exposition on relativity. The exposition became a classic, and Einstein became an overnight sensation, the worlds first and greatest scientific superstar. Two years later he received the Nobel Prize for his 1905 work on the photoelectric effect. By then Einstein was internationally known, and when he was offered a post in Princeton in 1932 he moved to the United States, never to return to Germany. His late career was marked by unsuccessful attempts to unify the laws of physics, and by a strong distaste for the fashionable so-called "Copenhagen interpretation" of quantum mechanics. A week before his death, Einstein signed his last letter, written to Bertrand Russell, in which he agreed that his name should go on a manifesto urging all nations to give up nuclear weapons. It is only appropriate that one of his last acts was to argue, as he had done all his life, for international peace. With Einsteins death in 1955 the world had not only lost one of its foremost thinkers but also a humanist fighter for peace and freedom.

1905 was a remarkable year for Einstein. Among his articles published that year, the paper "On the Electrodynamics of Moving Bodies" delineated the principles of the special theory of relativity. Shortly thereafter his paper "Does the Inertia of a Body Depend upon its Energy Content?" was published; this paper contained the famous equation E = mc2 stating the equivalence of energy and mass. Both papers propounded a revolutionary operational interpretation of a certain mathematical machinery, devised originally by the Dutch physicist H. Lorentz in order to square Maxwells theory of electrodynamics with apparently contradictory experimental results. Relying as they did on the postulate of relativity and on the postulate of the constancy of the speed of light in a vacuum, they resulted in a new conception of space and time, the radical features of which were best captured in the dramatic words of Einsteins teacher, the mathematician H. Minkowski (1908): "…space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality."

The best way to understand the special theory of relativity (STR) is, according to Einstein himself, to see it as a theory of principle, its two famous principles being the relativity principle (that the laws of nature co-vary with uniformly moving reference frames, or as Bondi (1980) puts it, "that velocity does not matter"), and the light principle (that the speed of light in a vacuum is constant, independent of the speed of the source). Another famous theory of principle is thermodynamics; Einstein used to point to this theory as one of his favorites that inspired his conception of STR. In theories of principle such as thermodynamics or STR one starts from empirically observed general properties of phenomena such as the non-existence of perpetual motion machines, in order to infer general applicable results without making any assumptions on hypothetical constituents of the system at hand. Since the building blocks of these theories are "not hypothetically constructed but empirically discovered," in so doing, says Einstein, one employs "the analytic, not the synthetic method." Lorentzs contraction and dilation theory, along with statistical mechanics and its predecessor the kinetic theory of gases, are, on the other hand, examples of constructive theories. They begin, according to Einstein, with certain hypothetical elements and use these as building blocks in an attempt to construct models of more complex processes.

Einsteins "principle" approach to physics in STR differs from the "constructive" approach of Lorentz in two major ways. As the late eminent CERN physicist John S. Bell (1987) notes, there is a difference in style, and a difference in philosophy. The difference in style is that theories of principle, as Relativity: The Special and the General Theory nicely demonstrates, are generally more elegant and concise, while constructive theories are usually complicated and cumbersome. The difference in philosophy is that since the question of which uniformly moving reference frame is really at rest is experimentally undeterminable, Einstein - later to be joined happily by logical positivists such as Schlick and Reichenbach - declares the notions "real rest" and "real motion" as meaningless. For him only the relative motion of the two or more uniformly moving objects is real, hence no reference frame is "specially marked out" (Part II, Chapter XVIII). Lorentz, on the other hand, along with Fitzgerald, Larmor, and Poincaré, preferred the view that there is indeed a state of real rest, defined by the "aether," even though the laws of physics conspire to prevent us from detecting it experimentally. And although Einsteins STR is commonly favored today over Lorentzs conspiracy theory, it is important to note that (1) the facts of physics do not oblige us to accept one philosophy rather than the other, and (2)...