Fritz Zwicky

Fritz Zwicky

Fritz Zwicky (1898 – 1974) was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and observational astronomy. Zwicky was an extraordinarily original thinker, and his contemporaries frequently had no way of knowing which of his ideas would work out and which would not. In a retrospective look at Zwicky’s life and work, Stephen Maurer said:

When researchers talk about neutron stars, dark matter, and gravitational lenses, they all start the same way: “Zwicky noticed this problem in the 1930s. Back then, nobody listened . . .”

Here are few of Zwicky’s contributions:

Ionic crystals and electrolytes – His first scientific contributions pertained to ionic crystals and electrolytes.

Supernovae and neutron stars – Together with colleague Walter Baade, Zwicky pioneered and promoted the use of the first Schmidt telescopes used in a mountain-top observatory in 1935. He hand-carried the Schmidt lens from Germany, which had been polished by the optician, Bernard Schmidt. In 1934 he and Baade coined the term “supernova” and hypothesized that they were the transition of normal stars into neutron stars, as well as the origin of cosmic rays. It was a prescient insight that had tremendous impact in determining the size and age of the universe in subsequent decades.


In support of this hypothesis, Zwicky started hunting for supernovae, and found a total of 120 by himself (and one more, SN 1963J, in concert with Paul Wild) over a stretch of 52 years (SN 1921B through SN 1973K), a record which stood until 2009 when finally passed by Tom Boles

Standard candles – In 1938, Zwicky’s colleague Walter Baade proposed using supernovae as standard candles to estimate distances in deep space. Because light curves of many type-Ia supernovae show a common peak luminosity, they establish a cosmological distance scale by a well known intrinsic brightness.

Distant Type Ia supernovae show a nonlinear Hubble relationship, which scientists have explained in terms of an acceleration in the expansion rate for the universe.

Gravitational lenses – In 1937, Zwicky posited that galaxy clusters could act as gravitational lenses by the previously discovered Einstein effect. It was not until 1979 that this effect was confirmed by observation of the so-called “Twin Quasar” Q0957+561.

Dark matter – While examining the Coma galaxy cluster in 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen matter, which he referred to as dunkle Materie ‘dark matter’. He calculated the gravitational mass of the galaxies within the cluster and obtained a value at least 400 times greater than expected from their luminosity, which means that most of the matter must be dark. The same calculation today shows a smaller factor, based on greater values for the mass of luminous material; but it is still clear that the great majority of matter appears to be dark.

Tired light – When Edwin Hubble discovered a somewhat linear relationship between the distance to a galaxy and its redshift expressed as a velocity, Zwicky immediately pointed out that the correlation between the calculated distances of galaxies and their redshifts had a discrepancy too large to fit in the distance’s error margins. He proposed that the reddening effect was not due to motions of the galaxy, but to an unknown phenomenon that caused photons to lose energy as they traveled through space. He considered the most likely candidate process to be a drag effect in which photons transfer momentum to surrounding masses through gravitational interactions; and proposed that an attempt be made to put this effect on a sound theoretical footing with general relativity. He also considered and rejected explanations involving interactions with free electrons, or the expansion of space.

Zwicky was skeptical of the expansion of space in 1929, because the rates measured at that time seemed too large. It was not until 1956 that Walter Baade corrected the distance scale based on Cepheid variable stars, and ushered in the first accurate measures of the expansion rate. Cosmological redshift is now conventionally understood to be a consequence of the expansion of space; a feature of Big Bang cosmology.

Morphological analysis – Zwicky developed a generalised form of morphological analysis, which is a method for systematically structuring and investigating the total set of relationships contained in multi-dimensional, usually non-quantifiable, problem complexes. He wrote a book on the subject in 1969, and claimed that he made many of his discoveries using this method.

Catalogue of Galaxies and Clusters – Zwicky devoted considerable time to the search for galaxies and the production of catalogues. From 1961 to 1968 he and his colleagues published a comprehensive six volume Catalogue of galaxies and of clusters of galaxies. They were all published in Pasadena, by the California Institute of Technology.

Edited from Fritz Zwicky by Deskarati

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