# Otto Wiener (physicist)

Otto Heinrich Wiener (15 June 1862 – 18 January 1927) was a German physicist.

## Life and work

Otto Wiener was a son of Christian Wiener and Pauline Hausrath. Orphan of mother at the age of 3, he married Lina Fenner at 32.
He was a pupil of August Kundt at the University of Strasbourg, where he received his doctorate in 1887 with a thesis on the phase change of light upon reflection, and methods to determine the thickness of thin films.
Wiener is known for the experimental proof of standing light waves in 1890. In the same experiment series he demonstrated that it is the electrical and not magnetic component of light wave responsible for its action on photographic film, as well as proved that the wave is tangential. These experiments made him skeptical about the luminiferous aether theory.
He was professor at the University of Giessen from 1895.
In 1899 he became professor at the Physics Institute of the University of Leipzig, where he succeeded Gustav Wiedemann. Together with Theodor des Coudres, he built an excellent physical institute there, and appointed Peter Debye and Gregor Wentzel.
In his academic inaugural lecture at Leipzig of 1900 on The Extension of our Senses, he presented the theory of physical education in the context of evolutionary theory. He took up Heinrich Hertz's theory that separates internal images —a conceptualization of reality— from descriptions of experiment (Principles of Mechanics, 1894). It was the dawn of media technology. Wiener added to Hertz's work, and theorized cinematography as an extension of our senses (1900).

## The Standing Lightwaves Experiment

Otto Wiener's fame is mostly due to the experiment where he visualized light waves in steady conditions. Although it could be considered equivalent to Hertz's detection of radio waves, their intent differed. Hertz aimed at validating Maxwell's theory, while Wiener's purpose was to determine the plane of vibration of light waves, as they were conceived in mechanical theory. Note that both scientists, like most of their contemporaries, assumed the existence of aether. With the rise of quantum mechanics, the concept of luminous field changed dramatically. Nowadays, quantum optics replaced the problem of visualizing light waves with that of simultaneously measuring their phase and amplitude.

### Experimental setup

The light was obtained from a carbon arc light, entering the darkroom through a slit. Then it was filtered through a prism, discarding most of the red side of the spectrum. An achromatic lens focused an 8mm-wide, slightly converging light beam. 220mm after the lens, the light hit a polished silver mirror perpendicularly. Monochromatic light would result in a uniform wavelength, hence a regular standing waves pattern, parallel to the mirror's surface. Wiener's orthochromatic film was transparently thin, about 20 nm, measured by interference, which is much less than the wavelength (the sodium doublet is at about 589 nm). It was laid on the mirror, over an equally thin slice of gel. That way, by applying pressure on one side of the film only, Wiener could slightly tilt it so as to make it traverse several standing waves. The standing waves were revealed by exposing the film for 20~35 minutes, after development and printing.

### Drude's critique

Wiener added benzene to the wedge after having been criticized for not considering the possibility of having photographed thin-film interference fringes rather than standing waves. His interpretation validated Fresnel's interpretation rather than Neumann's. Paul Drude criticized Wiener for this. With Nernst, he repeated Wiener's experiment using a fluorescent film as detector, in order to prove that the effect was due to electric fields.

### Relationship with interferential photography

A photographic experiment for validating Fresnel's theory had already been suggested by Wilhelm Zenker (1829-1899), after a call by the French Academy of Sciences in 1865. Zenker's proposal didn't delve into the thickness of the film, though. By exposing a thicker film, to be observed by reflection rather than by transparency, Gabriel Lippmann discovered interferential color photography, which he was awarded the Nobel prize for. Wiener contributed to Lippmann's theory thereafter.

### Further repetitions of the experiment

Repetition of the experiment under different conditions was carried out by Leistner, a Wiener's student, to better characterize the radiation. Leistner modified a Mach–Zehnder interferometer so as to insert the film between the mirrors. Another repetition was the thesis of Ernst Schult, commissioned by Nernst and Max von Laue for comparing light intensity with the energy as measured with a micropyrometer, along the verification of the energy quantization hypothesis with respect to the simple wave theory. A further notable repetition, aimed at evaluating the dependence of a cesium film's photoelectric emission upon illumination conditions. Ives and Fry controlled bands formation using a thicker film to be dissected upon development. More recent repetitions avail of laser technology.