Known primarily for his theories on the behavior of sound waves, Doppler was one of the first major Austrian physicists, and his research on the Doppler effect led to tremendous advances in scientific thinking, especially in the field of astronomy.
Born in Salzburg, Doppler intended to follow his father into the stonemason's trade. However, chronic health problems eliminated the possibility of so physically taxing a career, and he soon redirected his efforts toward the business field. His natural talent for mathematics placed him at the head of his classes and, at the advice of one instructor, Doppler enrolled at the Polytechnic Institute in Vienna. Unsatisfied with the curriculum, he returned to Salzburg to complete his education privately. After graduation he worked as a tutor and mathematical assistant, but he longed desperately for a professorship--so much, in fact, that he was on the brink of emigrating to America, where opportunities were less scarce, when he received an offer from the State Secondary School in Prague.
While teaching in Prague, Doppler became fascinated with the nature of sound and particularly with finding an explanation for a rather common but perplexing phenomenon. It had been observed for years that the pitch of a sound varies as the source moves toward or away from the listener. The most familiar example of this phenomenon is the train whistle: when the train is approaching, the whistle is high pitched; when it recedes, the whistle sounds deeper. Doppler knew of the existence of sound waves, and he also knew that the pitch of a sound is dependent on how far apart those waves are. If a source is moving toward the listener, he supposed, the waves in front of the source would be squeezed together, creating a higher frequency, while the waves behind would be stretched out, creating a lower frequency. He soon worked out the mathematical formula that governed this shift, presenting his theories to the scientific community in 1842.
In 1845, to substantiate his theory, Doppler arranged for his colleague C. H. D. Buys Ballot (1817-1890) to conduct what would be one of the most unusual experiments in history. Buys Ballot arranged for a locomotive to pull an open car full of trumpeters while, to the track's side, a group of musicians with perfect pitch listened. For two days the trumpeters were towed back and forth while the listeners recorded the changing pitches of their instruments. Fortunately for the reputations of Doppler and Buys Ballot, the findings provided absolute confirmation of the theory.
The Doppler effect has had two important applications in modern science. The distance and bearing of a target can be found by measuring the acoustical shift of a reflected signal. This effect forms the basis for both sonar and radar, as well as for speed-guns used by traffic police. Although his theory was never proven during his lifetime, Doppler also predicted that it should apply to light waves. In 1901, the first experiment was completed showing a Doppler shift in starlight; light that was receding from the observer was shifted toward the red end of the visible spectrum, while light approaching the observer was shifted toward the blue end. This shift, which showed that many stars (including our own) were moving away from some central point in the universe, became the foundation for the Big Bang theory of creation.