World of Scientific Discovery on Werner Karl Heisenberg
The son of a humanities professor at the University of Munich, Heisenberg was born in Duisberg, Germany on December 5, 1901. Following his early education at the Maximillian Gymnasium, in 1920 Heisenberg entered the University of Munich, where he studied under the great physicist Arnold Sommerfeld. Heisenberg demonstrated an unusual talent for theoretical physics and earned his doctorate in only three years. After graduation, he was invited to work as an assistant to Max Born at the University of Göttingen. Nine years later Heisenberg worked under Niels Bohr at the University of Copenhagen, and in 1927 he returned to Germany as professor of physics at the University of Leipzig.
Heisenberg's primary research interests reflected those of his mentors--Sommerfeld, Born, and Bohr. In 1913, Bohr had proposed a new model for the atom based on quantum theory. Although in most instances the model worked reasonably well for the hydrogen atom, it failed to explain a number of observations. Over the next decade scientists strived to deal with these shortcomings in Bohr's model.
Heisenberg abandoned efforts to develop a physical model of the atom. Too much attention had already been given, he said, to phenomena that had not been--and perhaps could not be--observed. Instead Heisenberg attempted to develop a mathematical model to describe an observable phenomenon, specifically, the spectral lines of hydrogen. The first product of this effort was a new system of mathematics called matrix mechanics, which employs columns of numbers that describe all possible transitions within an atom. The solutions to the matrix correspond to the wavelengths of the hydrogen spectral lines.
Matrix mechanics was one of the two earliest forms of quantum mechanics. The second form was the system of wave mechanics developed at about the same time by Erwin Schrödinger. In 1944, Hungarian mathematician John von Neumann showed that the Heisenberg and Schrödinger formulations were mathematically equivalent to each other.
One of the first applications of matrix mechanics concerned the spectrum of molecular hydrogen. That spectrum consists of alternative dark and light bands, an observation that had yet to be explained. Heisenberg suggested that the bands could be explained by assuming that the two hydrogen nuclei ( protons) were spinning on their axes. In some molecules (ortho-hydrogen), the nuclei spin in the same direction. In others (para-hydrogen), they spin in opposite directions. For his development of matrix mechanics and its application to molecular hydrogen, Heisenberg was awarded the 1932 Nobel Prize for physics.
By 1927, Heisenberg had arrived at a discovery for which he is probably best known, the uncertainty principle. Suppose we wish to measure the properties of some particle, Heisenberg said. To do so, we have to interact with that particle in some way. For example, in order to know where an electron is, we might choose to shine a light beam on it. But the very act of measuring the particle alters its behavior. The light beam shined on an electron would deflect the electron from its position. The measurement we would make, therefore, tells not where the electron is, but to what location the light deflected it.
On the scale of everyday events, this effect can be ignored, but the same is not true for atom-sized particles. The very act of measuring such particles significantly affects the results obtained.
Heisenberg concluded that it was impossible to know both the position (x) and the momentum (p; the product of mass, m, and velocity, v) at the same time. If the uncertainty in measuring either quantity is expressed by the Greek letter delta, , then, Heisenberg said, p /4. What this equation suggests is that one can measure either a particle's momentum or its position with great accuracy. But the more accurately one quantity is measured, the less accurately the other is known.
A number of scientists, among them Albert Einstein, were troubled by the uncertainty principle, also known as the principle of indeterminacy, because for nearly 2,000 years philosophers and scientists had put their faith in a more-or-less straightforward cause-and-effect view of nature. In the early 1800s, the great French philosopher Pierre Laplace had said that if he could know the position and velocity of every particle in the universe at one instant of time, he could theoretically predict the entire future of the universe. Heisenberg 's principle, now an accepted fundamental tenet in physics, showed that it was impossible to attain Laplace's basic premise.
During World War II, Heisenberg was one of the few first-class German scientists to remain in his homeland and work for the Nazi government. He is said to have hated the Nazis, but loved Germany, and to have remained only to make sure that German science would survive the war.
After the war, Heisenberg returned to Göttingen as director of the Max Planck Institute for Physics. He died in Munich on February 1, 1976.
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