Of all the eponymous discoveries that emerged from 19th-century physics—Young’s fringes, the Biot–Savart law, the Fresnel lens, the Carnot cycle, the Faraday effect, Maxwell’s equations, Michelson’s interferometer, and many more—only one is heard daily on the evening news: the Doppler effect.The effect, which describes the change in a wave’s frequency heard by an observer moving relative to the wave source, is shown in figure. You experience the effect as you wait by the roadside for a train to pass by or a jet to fly overhead. Albert Einstein may have the most famous name in physics, but Christian Doppler’s is probably the most commonly used. That’s ironic because Doppler was hounded by a pompous nemesis, ridiculed for his effect, stripped of his university position, and forced to abandon Vienna in public disgrace and declining health. He finally retreated to Venice and died a few months later.

Despite Doppler’s ignominious end, today his effect tells scientists of Earth’s motion across the universe, allows physicists to cool atoms in laser traps to a fraction of a degree Kelvin, and is used to detect alien planets orbiting distant stars. With Doppler light scattering, scientists can see the flow of blood in arteries, and they are beginning to personalize chemotherapy by measuring tiny Doppler shifts from the motion of components inside living cells.So why did his peers reject his idea, even years after his death, and how has it been rehabilitated so thoroughly that we now stake our lives on it? The answer begins with a troubled career that almost failed to launch.

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Doppler was born in 1803 in Salzburg, Austria, to a long-standing family of stonemasons. By the age of 30, he was at the end of a temporary mathematics assistantship at the Imperial and Royal Polytechnic Institute (now TU Wien) in Vienna and could not find work except as a bookkeeper at a cotton factory. The Austrian empire in the early 19th century was a sprawling bureaucratic state with layers of regulations and armies of able applicants for any position. Doppler was lost in that environment despite his advanced education. His applications for permanent technical posts were denied, and he despaired of ever finding a suitable life, so he decided to emigrate to the US. He sold most of his possessions to pay for his journey and visited the US consulate in Munich to obtain the necessary paperwork. But on his return to Austria, on the eve of leaving Europe for an uncertain future, he received an offer for a teaching position in Prague, which he took in 1835.

He began to publish scholarly papers and in 1837 was appointed supplementary professor of higher mathematics and geometry at the Prague Polytechnical Institute (now Czech Technical University); in 1841 he was promoted to full professor of applied geometry. There he met Bernard Bolzano—a political agitator and a mathematician who developed rigorous concepts of mathematical limits. He is famous today for his part in the Bolzano–Weierstrass theorem in functional analysis. Bolzano presided as chairman over a meeting of the Royal Bohemian Society of Sciences on 25 May 1842, the day Doppler read a landmark paper on the color of stars to a meager assembly of only five regular members of the society.

Doppler had become fascinated by astronomy and by the phenomenon of stellar aberration. It was discovered by James Bradley in 1727 and could be explained by Earth’s motion around the Sun combined with the finite speed of light, which causes the apparent position of a distant star to change slightly through a year. As Doppler studied Bradley’s work, he wondered how Earth’s relative motion would affect the color of the star. By making the simple analogy of a ship traveling with or against a series of ocean waves, he concluded that the frequency of the wave peaks hitting the ship’s bow was no different from the peaks of light waves impinging on the eye. He concluded that the color of light would be shifted slightly to the blue if the eye was approaching towards, and to the red if it was receding from, the light source.

Proceedings of the Royal Bohemian Society of Sciences a few months after he read it to the society, was titled “Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels” (“On the colored light of the double stars and certain other stars of the heavens”). 3 3. C. Doppler, Abh. Königl. Böhm. Ges. Wiss. 2, 465 (1842). 2 His interest in astronomy had made Doppler familiar with binary stars in which the relative motion of the light source might be large enough to cause color shifts. In fact, the star catalogs included examples of binaries that had complementary red and blue colors. Therefore, his paper, published in thea few months after he read it to the society, was titled “Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels” (“On the colored light of the double stars and certain other stars of the heavens”).Although Doppler was mistaken in his assumption that stellar motion would cause a change in the broad-spectrum color of a star, his derivation of frequency shifts was correct. Figureshows Doppler’s own drawings of his effect at high speeds.