Einstein's Special Theory of Relativity

EINSTEIN'S SPECIAL THEORY OF RELATIVITY

A New Idea

The German Jewish theoretical physicist Albert Einstein formulated the special theory of relativity in 1905. Relativity is that area of physics that has to do with how observers in motion with respect to the phenomenon observed can account for their observations given that two different frames of reference (that of the observer and that of what is observed) are involved. Einstein labeled his 1905 theory "special" because it dealt with a limited range of phenomena, namely uniform linear motion at constant but high velocities. The consequences of special relativity became cornerstones of twentieth-century physics and displaced some of the central tenets of Newtonian physics that had been pillars of scientific thought for two centuries.

Einstein's Discoveries

First, Einstein showed that time, space, and matter are interdependent, as expressed in the famous formula e - mc2 , where e is energy, m is mass, and c is the speed of light. The mass of material objects is determined by their energy; if they give off energy, their mass decreases. Mass increases with velocity and since the velocity of light is so great, a small mass traveling at the speed of light is equivalent to a vast amount of energy. (Atomic energy is an example of the special theory but was not based on it.) Second, time is not absolute: it depends on the circumstances of the ob-servers. Third, there are no privileged observers: what one person sees or measures may not be what another person measures, even if both think they are measuring the same phenomenon, especially if one is moving faster than the other. For example, according to the special theory, a person on a moving train and another on an adjacent embankment do not see the same light signal on the railroad station at the same time and thus cannot say that the two observations were simultaneous. Fourth, space is not absolute; it is only a conventional way of describing the relationships of objects. Fifth, as American physicist Albert Michelson had already demonstrated, the ether, an invisible substance that supposedly filled the entire universe and through which light waves were propagated, does not exist.

Fun and Games

The theory gave rise to all kinds of widely discussed paradoxes that delighted Einstein and his supporters and enraged physicists opposed to the theory. The most famous was the "twin paradox" of the space traveler. An astronaut travels through space at speeds approaching that of light for many years. When he returns to Earth, he finds his twin brother to be an old man while he has hardly aged at all. Einstein's theory explained that at very high speeds time slows down.

The American Debate

There were few theoretical physicists in the United States when Einstein published his theory. Most physicists were experimentalists and were hostile to the theory that struck many of them as hopelessly abstract and counter to intuition and common sense. Moreover, they were committed to Maxwell's principles of electrodynamics, which purported space to be filled with aether. The first Americans to comment on relativity were Gilbert N. Lewis, professor of physical chemistry at MIT, and his student, Richard C. Tolman. In a paper published in 1909 they argued that Einstein's theory was both practical and based on empirical evidence. Other American scientists, with considerably less understanding, ridiculed special relativity, attacking it as metaphysical and unrelated to observation. Many were bothered by the counterintuitive nature of the theory and asserted that if a scientific theory were true, it would be, almost by definition, comprehensible to everyone. Tolman, on the other hand, always responded to such doubts by reasserting his conviction that Einstein's hypotheses could be tested by experiment. Both Einstein's early supporters and detractors in the United States, therefore, appealed to American scientific traditions of practicality and experimental verification.

The General Theory

In 1914 Einstein broadened his concepts to include nonlinear motion in a general theory of relativity. This introduced his famous theory of curved space. When certain predictions contained in the theory were later verified (as when observations during the solar eclipse of 1919 confirmed that light rays emitted by stars bent when passing through the gravitational field of the sun), many scientists who previously had been skeptical now accepted the special theory as well. Einstein won the Nobel Prize in 1921, not for relativity—still considered too controversial—but for another of his discoveries of 1905, the photoelectric effect.

Delayed Acceptance of Relativity

The first book in English on special relativity was published by mathematician Robert D. Carmichael of Indiana University in 1912. At the same time, physicist Percy W. Bridgman began to work out the role of relativity in the philosophy of modern physics. But, perhaps because of the difficulty of the theory and its lingering aura of controversy, coverage of the theory in textbooks was sparse. Prior to World War II most American textbooks simply presented special relativity as a theory suggested by the Michelson-Morley experiment, which was understood as having proven that the speed of light was invariant. Such discussions were wrong on two counts: first, Michelson-Morley measured the speed of light but made no claims regarding its invariance; second, Einstein was in all likelihood unaware of that famous experiment when he conceived his theory.

EDISON'S CONCRETE ARCHITECTURE

In 1906, four years after he had founded the Edison Portland Cement Company at Stewartsville, New Jersey, Thomas Edison announced that his solution to the problem of the housing shortage and inner city slums was the reinforced concrete house, which, if he had his way, could be built in a week. Edison thought he might be able to pour an entire house in one operation. Houses could then roll off a production line and be sold at a low price. Such houses could be built almost entirely of fire-resistant materials, thus also saving the cost of fire insurance.

Edison identified bentonite clay as a substance that had the binding and stability requirements suitable to such monumental concrete structures and determined that more than one structure would have to be built on a single site in order to save on construction costs. All architectural and decorative features, from staircases to exterior flourishes, were included in the mold, and colors were added to the concrete mix to avoid any separate painting of the structure.

After years of hoopla Edison had failed to produce a single house. Finally two houses were cast in Montclair, New Jersey (they remain standing today), but Edison decided that the process was too grandiose and complex. He then designed a smaller, two-bedroom model with a front porch, weighing 250,000 pounds, some 200,000 less than the Montclair prototypes. This house was built in South Orange, New Jersey, in 1910. Edison's ideas for the utility of concrete extended even to house-hold furnishings. He boasted that a line of furniture made from a kind of foamy concrete would cost half as much as wood and outlast the marriages of their buyers. In 1911 he actually molded some prototypes, including cabinets, a bathtub, and even a piano! Edison's cement business was to have some great achievements, including the building of Yankee Stadium, and several successful Edison houses were built in Union, New Jersey, in 1917, but the idea never caught on. In spite of the longevity of those houses that were built, Edison, at least in the area of design, was a prophet without honor.

Source:

Michael Peterson, "Thomas Edison's Concrete Houses," The American Heritage of Invention and Technology, 11 (Winter 1996): 50-56.

Source:

Thomas F. Glick, ed., The Comparative Reception of Relativity (Dordrecht, Netherlands: D. Reidel, 1987).