Erwin Schrödinger

Austrian physicist

• Born: August 12, 1887; Vienna, Austria-Hungary (now Austria)
• Died: January 4, 1961; Alpbach, Austria

Erwin Schrödinger invented wave mechanics in 1926, for which he received the Nobel Prize in Physics in 1933, and he helped develop the formal equations that are central to quantum mechanics. His pioneering work on the relationship between physics and living systems influenced the growth of molecular biology.

Primary fields: Physics; mathematics

Specialties: Theoretical physics; quantum mechanics

Early Life

Erwin Schrödinger was the only child of a well-to-do and highly intellectual Viennese family. With the exception of a brief stay at a public elementary school in Innsbruck, he was educated by a tutor. At the age of eleven, he commenced a program of studies in the classics and in mathematics and physics at a Viennese Gymnasium, a liberal arts high school.

Schrödinger entered the University of Vienna in 1906. The following year, he began to attend lectures in theoretical physics. In 1910, he received his doctorate and assumed a position as assistant to Franz Exner at the university’s Second Physics Institute, where he remained until the outbreak of World War I. During this period, Schrödinger published papers on a range of subjects, including magnetism, radioactivity, X-rays, and Brownian motion.

Following an undistinguished service in the military, brief appointments at Jena, Stuttgart, and Breslau culminated with Schrödinger’s appointment in 1921 to the chair of theoretical physics in Zurich, a position formerly held by Albert Einstein. Prior to his stay in Jena, he had married Annemarie Bertel on June 6, 1920. During this period, his papers touched on a number of subjects, including general relativity, probability theory, dielectric phenomena, three- and four-color theories of vision, and atomic theory in particular. The papers that secured his reputation were composed in a half-year’s flourish of creativity before he left Zurich. It was there in 1926 that Schrödinger invented wave mechanics and published what is known as the Schrödinger wave equation, laying the foundation of modern quantum mechanics.

Life’s Work

Schrödinger’s invention of wave mechanics represented an attempt to overcome some difficulties generated by Niels Bohr’s theory of the hydrogen atom. In particular, attempts to construct a theory of a stable system of more than two particles (such as the helium atom, with a nucleus and two electrons) had failed. Drawing inspiration from Louis de Broglie’s suggestion that a particle is merely a wave crest on a background of waves, Schrödinger used the mathematics of waves in a way that attempted to eliminate quantum jumps, or the notion that electrons move instantaneously from one level to another. He sought to represent this quantum transition as the passage of energy from one vibrational form into another, instead. The transition of an electron from one energy state to another, Schrödinger believed, was akin to the change in the vibration of a violin string from one note to another. These results were announced by Schrödinger in four seminal papers published in the journal Annalen der Physik (Annals of physics) in 1926, the first of which contains his famous wave equation.

Schrödinger’s wave mechanics was eagerly embraced by numerous scientists who had been puzzled by the emerging atomic theory and regarded the model of a wave as furnishing a realistic account of microprocesses. It was also criticized on a number of counts: It was not clear how a wave could make a Geiger counter click as though a single particle were being recorded or how blackbody radiation was to be explained in terms of Schrödinger’s waves. A further wrinkle arose when Carl Eckart and Paul A. M. Dirac showed that Werner Heisenberg’s equations (which were based on the supposition that electrons are particles) were equivalent to Schrödinger’s theory that electrons are waves.

Bohr suggested that both models, particle and wave physics, are valid and complementary descriptions of the world—that in some cases, it is appropriate to utilize the particle concept and, in others, it is better to use the wave concept. Max Born’s suggestion that Schrödinger’s wave function expressed the probability of finding a particle at a given point in space supported Bohr’s resolution to the controversy. The location of a particle cannot be ascertained with certainty, but the wave function enables one to work out the probability that the particle will be found in a certain place. Finally, Heisenberg suggested in 1926 that scientists cannot measure both the position and the momentum of an electron at the same time. The more one knows about its position, the less one knows about its momentum, and vice versa.

These developments were largely accepted by the time Schrödinger succeeded Max Planck in 1927 as the renowned chair of theoretical physics at the University of Berlin. There, Schrödinger enjoyed a fruitful period amid the intellectual companionship of other prominent physicists until Nazi leader Adolf Hitler assumed power in 1933, the same year that Schrödinger and Dirac received the Nobel Prize in Physics. Schrödinger’s background ensured that his position was secure. His opposition to the Nazi regime, however, induced him to give up his post. Schrödinger settled in Oxford for a brief, unproductive period, but in 1936, he succumbed to homesickness and accepted a position in Graz, Austria. He was abruptly dismissed in 1938, and he fled Austria when Hitler’s forces invaded later the same year.

During 1935, Schrödinger had published a paper that criticized the probabilistic laws of quantum theory. In quantum mechanics, a radioactive atom might decay and emit an electron, or it might not. Schrödinger was upset by the absurdity of this implication and framed a famous thought experiment designed to expose it. In this experiment, he envisioned a box that contains a radioactive source, a device for detecting radioactive particles, a live cat, and a container of poison. The detector is switched on long enough that there is a fifty-fifty chance that one of the atoms in the radioactive material will decay and that the detector will record the presence of a particle. If the detector does record such an event, the poison container is broken and the cat dies. If not, the cat lives.

In the world of ordinary experience, there is a fifty-fifty chance that the cat will be killed. Without examining the contents of the box, it is safe to assert that the cat is either dead or alive. In the world of quantum physics, neither possibility is real unless it is first observed. The atomic decay has neither occurred nor not occurred. Since the fate of the feline is tied to the state of the radioactive material, one cannot say that the cat is dead or alive until the inside of the box is examined. This implication, Schrödinger declared, reveals the absurdity of quantum mechanics. It is one thing to conceive of an elementary particle such as an electron being neither here nor there, but quite another to conceive of a concrete thing such as a cat in this indeterminate state.

In 1939, Eamon de Valera arranged for Schrödinger to serve as the first director of the school of theoretical physics at the Dublin Institute for Advanced Studies. During this fruitful period of his career, Schrödinger published many works on the application and statistical interpretation of wave mechanics and on problems concerning the relationship between general relativity and wave mechanics. As a senior professor, Schrödinger gave lectures from time to time. Four of his books, What Is Life? (1944), Science and Humanism: Physics in Our Time (1951), Nature and the Greeks (1954), and Mind and Matter (1958), were written for these lecture series. The most famous of these lectures was “What Is Life?” presented in 1944 to a large and enthusiastic audience. The thesis of these lectures is that quantum physics is required for understanding biological replication. Although his theme was controversial, it aroused much interest among many promising young physicists, including Francis Crick, and encouraged them to turn to biology.

In 1956, illness curtailed Schrödinger’s productivity. His friend Hans Thirring arranged for him to become professor emeritus of theoretical physics at the University of Vienna. He died in 1961 after a prolonged illness.

Impact

Schrödinger is primarily known for inventing wave mechanics and the equation that bears his name, but his legacy is much greater. His collected papers include important contributions to virtually every branch of physics, and he constantly encouraged physicists to examine the foundations of their discipline and its relationship to other scientific endeavors. As a philosopher, he was worried about the problems of knowers in a world governed by probabilistic laws.

While his interests knew no bounds, Schrödinger was somewhat narrow in his outlook on questions of physics. His conservativeness was not surprising, given that he was already a senior member of the scientific community steeped in traditional concepts and theories when he made his most important contributions during the mid-1920s. Indeed, Schrödinger resisted the innovations of indeterminacy and the instantaneous jumping of electrons from one state to another. His most important contribution, the articulation of wave mechanics, attempted to describe atomic structures in terms of waves, an established model in the scientific community. Schrödinger furnished scientists with invaluable tools for problem solving, but his wave mechanics represented a return to nineteenth-century ideas.

Bibliography

Gribbon, John. In Search of Schrödinger’s Cat: Quantum Physics and Reality. 1984. London: Transworld, 2012. Print. Argues that Schrödinger’s wave mechanics attempted to restore nineteenth-century concepts, an assessment first made by some of Schrödinger’s contemporaries, such as Born. Provides a historical backdrop for the development of the central concepts of quantum mechanics.

Schrödinger, Erwin. What Is Life? The Physical Aspect of the Living Cell. 1944. Cambridge: Cambridge UP, 2003. Print. Influenced an entire generation of scientists, including Francis Crick, who helped to unravel the structure of the living molecule.

Wallace, Dorothy, and Joseph J. BelBruno. The Bell That Rings Light: A Primer in Quantum Mechanics and Chemical Bonding. Hackensack: World Scientific, 2006. Print. Investigates the intersections of quantum mechanics and chemistry, with discussion of Schrödinger’s scientific discoveries.