Relativity - (Full Translation with Color Illustrations and Detailed Explanations)

Author: Albert Einstein
Publisher:
Publish Date: 2006-11-01
Features: This is a groundbreaking book that completely overturns the concepts of classical physics. It denies Newton's absolute space and time, proposing that space is not a flat Euclidean space but a curved Riemannian space in a gravitational field, and that time is not an independent dimension separate from space, but is always intertwined with space, forming a unified four-dimensional spacetime continuum. This is a book that reveals the new order of the universe not through the eyes but through wisdom. It uncovers the extraordinary secrets of the universe: the relativity of simultaneity; the time dilation and length contraction effects in motion; the perihelion precession of Mercury; the redshift of the spectrum; the slowing of clocks in gravitational fields, and more—this is Einstein's "Theory of Relativity"! It completely overturns classical physics, opening up a brand new world of physics for humanity. This is not only one of the few revolutionary leaps in the history of science but also the beginning of a myth in an era! The discovery of quantum mechanics, therefore, as a revolution sparked by the introduction of the "field," has not ended. At the turn of the century, a fundamental crisis occurred unrelated to what we just discussed, which became apparent due to Max Planck's research on thermal radiation (1900). This event is historically noteworthy because, at least in the early stages, it was not influenced by any remarkable experimental discoveries. Based on thermodynamics, Kirchhoff concluded that the energy density and spectral composition of radiation in an opaque container with wall temperature T are independent of the properties of the walls. That is to say, the density of monochromatic radiation is a universal function of frequency and absolute temperature. This raises an interesting question: How to determine this function. What can we theoretically determine about this function? According to Maxwell's theory, radiation must exert pressure on the cavity walls, and this pressure is determined by the total energy density. From this point, Boltzmann deduced, using purely thermodynamic methods, that the total energy density of radiation is proportional to T. Thus, he provided theoretical justification for the law previously discovered empirically by Stefan—he linked this empirical law to the foundation of Maxwell's theory. Subsequently, Wien applied Maxwell's theory, conducted creative thinking from a thermodynamic perspective, and also discovered the elegant form of a universal function containing two variables. One of the universal constants led to quantum theory. A constant in Planck's formula accurately gave the true size of the atom. Planck clearly recognized this as a great success. However, there was a serious flaw, fortunately, which Planck did not notice at the time. For the same reason, the Planck formula should also apply to low-temperature states. However, if that were the case, the formula would be ruined. Therefore, from the existing theory, the correct conclusion should be: the average kinetic energy of oscillators given by the gas theory is wrong. This would mean denying (statistical) mechanics, or that the average kinetic energy of oscillators derived from Maxwell's theory is wrong, which would mean abandoning Maxwell's theory. In such a situation, it is possible that both theories are only correct within a limited range and not otherwise. This is indeed the case. If Planck had reached such a conclusion, he would not have made his great discovery, because it would have stripped away the foundation of his pure thinking. Now, let's return to Planck's reasoning. According to the kinetic theory of gases, Boltzmann had already discovered that, apart from a constant factor, entropy is equal to the logarithm of the "probability" of the state under consideration. Through this perspective, he recognized that processes are "irreversible" in a thermodynamic sense. However, from the perspective of molecular mechanics, all processes are reversible. If one calls the state defined by molecular theory the "microscopic state" (or simply "microstate") and the state described by thermodynamics the "macrostate," then there are countless states that belong to the macrostate. This idea is particularly important because its applicability is not limited to mechanics as