vol 2: Synopsis
part III: Modern physics
page 1`6: Albert Einstein
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Albert Einstein
(1879-1955)
At the turn of the twentieth century, even the existence of atoms was moot. Einstein not only produced a new vision of physical space through the special and general theories of relativity, but made great contributions to the new idea that the physical world is both discrete and continuous. In particular he suggested that light, even though it has wave properties, is emitted and moves as a particle, the photon. The problem of 'particle-wave duality' remained until quantum mechanics was fully developed.
Einstein announced his 'new kinematics', now known as the special theory of relativity in 1905. He was motivated by difficulties in reconciling the behaviour of electromagnetic radiation, like light, with other physical objects. He wondered what one would see if one travelled alongside a particle of light.
In particular, he was faced by the apparent contradiction that (representing the velocity of light by c) c + c = c. His answer revealed that 'ordinary space' has a rather extraordinary structure. This structure arises essentially from the fact that the finite maximum velocity of any physical signal delays communication between two points in space. The time delay inherent in movement between two points means that space and time are coupled to one another.
Newtonian physics works in a space that comprises the three dimensions of 'ordinary' space, plus the fourth time dimension. Newtonian space and time are independent. In real life we can move in any direction in physical space, but we are restricted to one direction in time which we usually see as a movement from past to future. Newtonian physics still works if we reverse the direction of time. In Newtonian physics, signals travel at infinite velocity, so that cause and effect are simultaneous, no matter how far apart.
Einstein reexamined the notion of simultaneity in an environment where signals travelled at finite speed. It is easy to understand two events occurring simultaneously at one point in space. But what if events occur some distance apart? Then the question of simultaneity involves the distance between them. Time and distance are related by the velocity of light. The distance between two events is a function of both time and space.
An interesting result of Einstein's new metric (measure of distance) is that the spacetime distance between two events may be zero, even though they are far apart in space and time. Time behaves in a way as the opposite of space, so that we can observe here and now (ie at a spacetime distance of 0) supernovae that took place a billion years ago and a billion light years away.
A further consequence of special relativity is that mass and energy are equivalent. This allows the creation of particles out of energy and the annihilation of particles into energy that lies at the heart of quantum field theory.
The metric imposed on physical space by the finite velocity of light has an analogue in all other situations where communications take a finite time to cover a finite distance. The evolution of email to replace snail mail, for instance, changes the spacetime metric of written communication in a manner analogous to increasing the velocity of light in physics.
From the special theory, which describes local phenomena, Einstein extrapolated to the general theory of relativity, which has the capacity to represent the whole of spacetime. The structure of the universe is constrained by the time delay in communication, so we will not be surprised to find that much of the structure of the universe is constrained by the structure of communication
Books
| Einstein, Albert, The Principle of Relativity, Dover 1924 Amazon.com reader review: 'This book is a collection of the most important lectures given by Einstein, Lorentz, Minkowski and Weyl that led to the formulation of the theory of relativity in its two parts. The first part is the special theory, which studies the inertial and moving reference frames without considering the effects of gravity. The second part, the general theory, explains the nature of gravity.' Reinaldo Olivares Amazon back |
| Hawking, Steven W, and G F R Ellis, The Large Scale Structure of Space-Time , Cambridge UP 1975 Preface: Einstein's General Theory of Relativity ... leads to two remarkable predictions about the universe: first that the final fate of massive stars is to collapse behind an event horizon to form a 'black hole' which will contain a singularity; and secondly that there is a singularity in our past which constitutes, in some sense, a beginning to our universe. Our discussion is principally aimed at developing these two results.' Amazon back |
| Misner, Charles W, and Kip S Thorne, John Archibald Wheeler, Gravitation, Freeman 1973 Jacket: 'Einstein's description of gravitation as curvature of spacetime led directly to that greatest of all predictions of his theory, that the universe itself is dynamic. Physics still has far to go to come to terms with this amazing fact and what it means for man and his relation to the universe. John Archibald Wheeler. ... this is a book on Einstein's theory of gravity (general relativity).' Amazon back |
| Nathan, Otto, and Heinz Norden (eds), Einstein on Peace, Avenel 1981 Bertrand Russell, Preface: "It is a very good thing that Einstein's letters and writings on other than scientific subjects are being collected and printed. Einstein was not only the ablest man of science of his generation, he was also a wise man, which is something different. If statesmen had listened to him, the course of human events would have been less disastrous than it has been.' http://www.amazon.com/exec/obidos/ASIN/0517345803/tnrp">Amazon back |
| Pais, Abraham, 'Subtle is the Lord...': The Science and Life of Albert Einstein, Oxford UP 1982 Jacket: In this ... major work Abraham Pais, himself an eminent physicist who worked alongside Einstein in the post-war years, traces the development of Einstein's entire ouvre. ... Running through the book is a completely non-scientific biography ... including many letters which appear in English for the first time, as well as other information not published before.' Amazon back |
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