Physics: 1907

Michelson, Albert Abraham pronounced MY kuhl suhn, (1852-1931), was the first American citizen to win a Nobel Prize in science. He received the 1907 Nobel Prize in physics for his design of precise optical instruments and for the accurate measurements he obtained with them.

Michelson was born in Strzelno, Poland (then in the domain of Prussia), near Inowroclaw. His family emigrated to the United States when he was 2. In 1873, Michelson graduated from the U.S. Naval Academy.

In 1880, while studying in Germany, Michelson designed an instrument to measure the speed of the earth through the ether. At that time, scientists believed that all space was filled with a stationary substance, which they called ether. They thought that light must travel in such a substance as ether in order to travel through space. Michelson's instrument, now known as the Michelson interferometer, compares the speed of a light beam moving in one direction with that of a beam moving at a right angle to it. By measuring the interference of the two light beams, Michelson believed he could find the velocity of the earth through the ether. He determined from the interference pattern actually produced that the speed of the earth in relation to the ether was zero. In 1887, Michelson refined this experiment with the aid of Edward Morley, an American chemist and physicist. The result was the same as before. Michelson and Morley's experiment helped destroy the ether theory.

Michelson resigned his naval commission in 1881. He taught physics at the University of Chicago for most of his career.

Ether, in physics, was once believed to be a substance that filled all space. By the late 1600's, some physicists believed that light traveled in waves. They knew that light could travel through artificially created vacuums and through the void of outer space. But they could not explain how light could travel without a medium (substance) to travel through. As a result, they assumed the presence of a luminiferous (light-carrying) ether, a substance that differed from all other matter. It could not be seen, felt, or weighed and was present in vacuums, outer space, and all matter. The ether was stationary, and the earth and other bodies in space moved through it.

In 1864, the British physicist James Clerk Maxwell correctly suggested that light waves are electromagnetic and travel as disturbances of an electromagnetic field. Therefore, they do not need a medium to travel through. But Maxwell and other physicists still believed in the existence of ether.

In 1887, two American scientists, Albert A. Michelson and Edward W. Morley, conducted an experiment to measure the speed of the earth relative to the ether. Their findings suggested that the earth did not move through ether. However, Hendrik A. Lorentz, a Dutch physicist, explained the finding by assuming that ether affected matter in a complicated way. In 1905, the German-born physicist Albert Einstein published his special theory of relativity, which shows how light behaves and does not rely on the existence of ether.

Interferometer, pronounced IHN tuhr fuh ROM uh tuhr, is an instrument that uses the interference of waves to make precise measurements. It can measure very small distances, or changes in the density and other properties of substances. Some interferometers employ sound waves or radio waves. But the most common types use waves of visible light. This article deals with light interferometers.

A simple light interferometer divides a beam of light into two beams and brings the beams back together again. The recombined beams shine on a screen or other object, forming an interference pattern (a series of bright and dark bands). For an explanation of why interference patterns appear. The pattern reveals any differences in the routes taken by the two beams. Scientists analyze these differences to make their measurements. For example, one beam might be reflected from a mirror being tested for smoothness while the other is reflected from a mirror known to be smooth. Any imperfection in the test mirror, such as a microscopic hill or valley, would produce a distortion in the interference pattern. Some interferometers can monitor the rapidly changing temperature and density inside a flame. Interferometers also can measure tiny distances, such as the amount a plant grows in a second.

In the early 1800's, the English scientist Thomas Young demonstrated the wave nature of light by using the principle of interference. In 1881, the American physicist Albert A. Michelson devised an interferometer to measure the earth's motion.