Albert Einstein’s theory of special relativity challenged Newtonian physics, replacing the theory of three-dimensional space and one-dimensional time with the theory of space-time.
Albert Einstein first articulated his special theory of relativity in an article in 1905 in the German journal Annalen der Physik under the title “Zur Elektrodynamik bewegter Körper” (on the electrodynamics of moving bodies), in which he did not mention the formula now so closely associated with his name: E = mc
2 (energy = mass times the speed of light squared). In this article, Einstein points out that time cannot be viewed as an absolute. He asserts, rather, that time is relative and broaches the question of simultaneity, which one must consider when one contemplates events occurring in time and space. Because it takes an infinitesimal amount of time for the light that illuminates an event that occurs near a person to travel to the perceptor, the event necessarily is perceived after it happens rather than when it happens. It was not until later in 1905 that Einstein published in the same journal the three-page article containing his famed formula: “Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?” (Does the inertia of a body depend on its energy content?)
In the normal course of earthly events, the slight discrepancy between when an event occurs and when it is perceived matters little. The discrepancy usually can be measured in milliseconds. Considering this matter in cosmic terms, however, Einstein clearly demonstrated that the discrepancy may become significant. Related to this observation is what was then a new way of viewing the correlations between time and space.
According to Einstein, the speed of light
Einstein postulated that nothing can move faster than the speed of light. He further conjectured that as objects accelerate toward the speed of light, they will become shorter in the direction they are traveling, their mass will become greater, and time will pass more slowly for them. This hypothesis has been demonstrated in various ways, notably by physicists who carried finely tuned atomic clocks with them on around-the-world commercial jet flights and then checked the clocks against other comparable clocks in their laboratories on their return. They found that the clocks they had carried with them had, indeed, lost time, totally in accordance with their predictions based on Einstein’s theory.
If it were possible physically for an object to travel in excess of the speed of light, that object would predictably move backward in time. Because objects do not move at anything approaching the speed of light, the loss of length and time and the gaining of mass that rapidly moving objects incur is barely perceptible. An object moving at the incredible speed of one-seventh the speed of light—26,614 miles, or slightly more than one circumnavigation of the globe at the equator every second—would change in mass, length, and time measurement by only 1 percent.
Drastic alterations take place, however, as the object approaches the speed of light more closely. When the velocity is six-sevenths the speed of light, the mass is twice what it is when the object is at rest, and the length and time measurements are cut in half. Were the velocity of the object to equal the speed of light, its mass would become infinite. In terms of Einstein’s theory of relativity, if a person were in a vehicle capable of coming within 99.995 percent of the speed of light, the mass of the person and the vehicle would be increased one thousand times and time would pass for them at one one-thousandth of the normal rate, so that each year of such travel would be equivalent to one thousand years of time, as scientists normally measure it.
Einstein’s findings generally have been verified by various means, ranging from carrying clocks on commercial jet flights, as mentioned above, to experiments with high-speed electrons that, under laboratory conditions, frequently achieve ten thousand times their normal mass as their speed increases.
Central to Einstein’s special theory of relativity is his shattering of the Newtonian theory that space is three-dimensional and that time is one-dimensional. Rather than thinking of time and space separately, Einstein viewed space-time as a coordinated, four-dimensional system. Time cannot be conceived of outside the spatial context; space cannot be conceived of outside the temporal context. The two exist simultaneously and interdependently as a coordinated system.
The only major physical phenomenon that Einstein could not explain using his special theory of relativity was gravity; this led him, in 1915, to the articulation of his general theory of relativity.
The flat space-time concept of the special theory of relativity, despite the curvature of space-time, is still serviceable when one is making local measurements, such as measuring the distance from one’s front door to one’s garage. If, however, one wants exact measurements of an area whose boundaries are Montreal, Tierra del Fuego, Auckland, and Seoul, the curvature of space-time must be taken into account for the calculations to be wholly accurate. The inaccuracy of the measurement increases as the size of what is being measured increases if a flat space-time methodology is used. The special theory of relativity is comparable to Euclidean geometry, whereas the general theory of relativity is comparable to the geometry of curved surfaces.
Fundamental to Einstein’s concept of relativity is the notion that energy (the E in his equation) and mass (the m) are really the same: All energy has mass; all mass, if conditions are right, can be converted to energy. Indeed, it can be converted into energy sufficient to cause the fission that, with the splitting of the atom, has resulted in the creation and harnessing of nuclear energy.
Einstein’s study of Brownian motion
When Einstein entered the Eidenössische Technische Hochschule in Zurich, Switzerland, after completing his secondary school education, he followed the advice of his elders and concentrated on mathematics rather than physics because, according to his advisers, little remained to be done in physics. Many believed that all that was significant in the field of physics had already been discovered; it was regarded as a scientific specialty in which no new worlds remained to be conquered. It is ironic, therefore, that Einstein was the person who, more than any other, brought insights to the field that were so compelling as to cause a complete restructuring of the discipline. Because all activity in the various subspecialties of physics—optics, electromagnetism, mechanics—takes place in a space-time continuum, Einstein’s postulation of a four-dimensional space-time context affected every aspect of the discipline and moved it into areas that had not only important scientific implications but also highly significant philosophical implications.
The special theory of relativity left unanswered many of Einstein’s salient questions. In moving beyond his early work in relativity in 1905, Einstein formulated his general theory of relativity, which, in 1915, responded to many questions regarding gravity that his earlier hypothesis had not answered to his satisfaction. The two theories corrected some of Sir Isaac Newton’s crucial scientific hypotheses that had, to that time, been sacrosanct among many physicists. It freed physicists to pursue studies that led to the splitting of the atom, to the development of nuclear energy, to space exploration, to the development of a theory of superconductivity, and to countless other accomplishments that have helped humankind explore the universe and understand it in greater depth than had previously been possible.
One can point to no area of modern science that has not been affected by Einstein’s work in relativity, the heart of which is found in his initial work on the special theory of relativity. Einstein redefined space and time, and his definition of space-time as a coordinated system has withstood the thousands of tests to which it has been put. His hypothesis has not been diminished by the extensive tests to which researchers have subjected it.
Einstein, as a scientist who continually searched and constantly questioned, certainly never foreclosed the possibility that his hypotheses might one day be disproved. Were he alive today, he would be at the forefront of testing them scrupulously and unfailingly as he did in his work, with Johann Jakob Laub, on black body radiation and in his subsequent work in the direction of evolving a unified field theory of physics. The astrophysical research into black holes, which now teeters on the brink of explaining much about the origins of the solar system and of the entire universe, is one of the direct offshoots of Einstein’s early work in relativity. The implications of such research are, perhaps, as important as those of any exploration being conducted in the field of physics.
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Bernstein, Jeremy. Einstein. New York: Viking Press, 1973. One of the most popular studies of Albert Einstein for laypersons. Chapter titled “E = mc
2” is particularly lucid in its presentation of Einstein’s theory of special relativity. Includes annotated bibliography. -
Clark, Ronald W. Einstein: The Life and Times. 1971. Reprint. New York: Avon Books, 1984. Detailed biography provides substantial information on Einstein’s role in world affairs. Accessible to lay readers. Includes many historical photographs. -
Crease, Robert P., and Charles C. Mann. The Second Creation: Makers of the Revolution in Twentieth-Century Physics. Rev. ed. New Brunswick, N.J.: Rutgers University Press, 1996. Readable volume follows the development of physics from its nineteenth century roots to the mysteries of the late twentieth century. Examines characters and personalities as well as issues of physics. Includes discussion of Einstein’s work. -
Eddington, A. S. Space, Time, and Gravitation. 1920. Reprint. Cambridge, England: Cambridge University Press, 1995. Of Eddington’s several books about Einstein and relativity, this one deals most valuably with the theory of special relativity and is especially clear in its presentation of how Einstein departed from Newtonian physics and the implications of that departure for the discipline of physics. Recommended for well-informed readers. -
Frank, Philipp. Einstein: His Life and Times. Translated by George Rosen. 1947. Reprint. New York: Da Capo Press, 2002. Biography has not been supplanted by any of the subsequent studies of Einstein that have appeared, although it was first published before Einstein’s death. Well written, with scientific explanations that are as lucid as possible, given the inherent complexity of Einstein’s work. -
Highfield, Roger, and Paul C. Carter. The Private Lives of Albert Einstein. New York: St. Martin’s Press, 1993. Presents carefully researched information on Einstein’s everyday life and the personal relationships that may have influenced his work. -
Hoffmann, Banesh, and Helen Dukas. Albert Einstein: Creator and Rebel. New York: Viking Press, 1972. Presents “the essential flavor of the man and his science.” Dukas was Einstein’s personal secretary for many years, and she offers some interesting insights. Includes many historical photographs. -
Katz, Robert. An Introduction to the Special Theory of Relativity. Princeton, N.J.: D. Van Nostrand, 1964. Excellent, exhaustive work focuses specifically on Einstein’s theory of special relativity. Intended for readers with background in physics. -
Pais, Abraham. Subtle Is the Lord: The Science and the Life of Albert Einstein. 1982. Reprint. New York: Oxford University Press, 2005. Meticulously referenced biography places Einstein’s scientific achievements within the context of the other aspects of his life. Features detailed chronology of Einstein’s life, good subject index, and exhaustive name index. -
Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon & Schuster, 1986. Comprehensive, highly detailed volume describes the physical discoveries leading up to the first nuclear weapons and Einstein’s role in the decision to develop the atomic bomb. -
Rigden, John S. Einstein 1905: The Standard of Greatness. Cambridge, Mass.: Harvard University Press, 2005. An account of the new insights and turmoil engendered among physicists by the five groundbreaking research papers that Albert Einstein published in 1905. Accessible to lay readers. Includes simple diagrams and reproductions of the front pages of the five papers.
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