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Fritz Zwicky

Fritz Zwicky
Born February 14, 1898
Varna, Principality of Bulgaria
Died February 8, 1974(1974-02-08) (aged 75)
Pasadena, California, US
Residence USA
Citizenship Swiss
Fields Astronomy
Institutions California Institute of Technology
Alma mater ETH Zürich
Doctoral advisor Peter Debye and Paul Scherrer
Known for Dark Matter, Supernovae, Galaxies, Neutron stars
Notable awards President's Medal of Freedom (1949)
Gold Medal of the Royal Astronomical Society (1972)

Fritz Zwicky (February 14, 1898 – February 8, 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.[1] In 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen dark matter matter, describing it as "dunkle Materie".[2]


  • Biography 1
  • Scientific work 2
    • Ionic crystals and electrolytes 2.1
    • Supernovae and neutron stars 2.2
    • Standard candles 2.3
    • Gravitational lenses 2.4
    • Dark matter 2.5
    • Tired light 2.6
    • Morphological analysis 2.7
    • Catalog of Galaxies and Clusters 2.8
    • Guns and goblins 2.9
  • Humanitarian 3
  • Honors 4
  • Publications 5
  • Notes and references 6
  • External links 7


Fritz Zwicky was born in Varna, Bulgaria, to a Swiss father. His father, Fridolin (b. 1868), was a prominent industrialist in the Bulgarian city and also served as ambassador of Norway in Varna (1908–1933).[3] The Zwicky House in Varna was designed and built by Fridolin Zwicky. Fritz's mother, Franziska Vrček (b. 1871), was an ethnic Czech of the Austro-Hungarian Empire. Fritz was the oldest of the Zwicky family's three children: he had a younger brother named Rudolf and a sister called Leonie. Fritz's mother died in Varna in 1927 and his father Fridolin remained in Bulgaria until 1945, when he returned to Switzerland. His sister Leonie married a Bulgarian from Varna and spent her entire life in the city.[4]

In 1904, at the age of six, Fritz was sent to his grandparents in the family's ancestral canton in Glarus, Switzerland, to study commerce.[5] His interests shifted to math and physics and he received an advanced education in mathematics and experimental physics at the Swiss Federal Institute of Technology, located in Zürich, Switzerland. In 1925, he emigrated to the United States to work with Robert Millikan at California Institute of Technology (Caltech) with an office down the hall from Robert Oppenheimer after receiving the "international fellowship from the Rockefeller Foundation."[5]

He was responsible for positing numerous cosmological theories that have a profound impact on the understanding of our universe today. He was the first to coin the term "supernova" during his fostering the concept of neutron stars. Zwicky was a lone wolf and did all of his own mathematical work. He intended to write an autobiography titled: "Operation Lone Wolf." It would be five years later when Oppenheimer would publish his landmark paper announcing "neutron stars". Fritz was appointed Professor of Astronomy at Caltech in 1942 and also worked as a research director/consultant for Aerojet Engineering Corporation (1943–1961) and staff member of Mount Wilson Observatory and Palomar Observatory for most of his career. He developed some of the earliest jet engines and holds over 50 patents, many in jet propulsion, and is the inventor of the Underwater Jet (TIME March 14, 1949), the Two Piece Jet Thrust Motor and Inverted Hydro Pulse.[6]

In April 1932, Fritz Zwicky married Dorothy Vernon Gates, the daughter of a prominent local family and Senator Egbert Gates. Her money was instrumental in the funding of the Palomar Observatory during the Great Depression. Nicholas Roosevelt, cousin of President Theodore Roosevelt, was his brother-in-law by marriage to Tirzah Gates. Zwicky and Dorothy divorced amicably in 1941.[7] In 1947 Zwicky was married in Switzerland to Anna Margaritha Zurcher and they had three daughters, Margrit, Franziska, and Barbarina. The Zwicky Museum at the Landesbibliothek, Glarus, houses many of his papers and scientific works, and the Fritz Zwicky Stiftung (Foundation) in Switzerland carries on his ideas relating to "Morphological analysis". Zwicky died in Pasadena on February 8, 1974, and was buried in Mollis, Switzerland.

Zwicky was an atheist.[8]

He is remembered as both a genius and a curmudgeon.[9] One of his favorite insults was to refer to people he did not approve of as "spherical bastards", because, he explained, they were bastards no matter which way you looked at them.[10]

A recent biography in English was published by the Fritz Zwicky Foundation: Alfred Stöckli & Roland Müller: Fritz Zwicky – An Extraordinary Astrophysicist. Cambridge Scientific Publishers, Cambridge, 2011. A review of the book is available from Acta Morphologica Generalis

Scientific work

The memorial plaque on the house in Varna where Zwicky was born. His contributions to the understanding of the neutron stars and the dark matter are explicitly mentioned.

Fritz Zwicky was a prolific scientist and made important contributions in many areas of astronomy.

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.[11][12] 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),[13] 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.[14] 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.[15]

Gravitational lenses

In 1937, Zwicky posited that galaxy clusters could act as gravitational lenses by the previously discovered Einstein effect.[16] It was not until 1979 that this effect was confirmed by observation of the so-called "Twin Quasar" Q0957+561.[17]

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'.[2] 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 was correctly inferred to be dark.[18]

Tired light

When Edwin Hubble discovered a somewhat linear relationship between the distance to a galaxy and its redshift expressed as a velocity,[19] 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.[20]

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.[21] Cosmological redshift is now conventionally understood to be a consequence of the expansion of space; a feature of Big Bang cosmology.[22]

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.[23] He wrote a book on the subject in 1969,[24] and claimed that he made many of his discoveries using this method.

Catalog of Galaxies and Clusters

Zwicky devoted considerable time to the search for galaxies and the production of catalogs. 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.

  1. Zwicky, F.; Herzog, E.; Wild, P. (1961), Catalogue of Galaxies and of Clusters of Galaxies 1,  
  2. Zwicky, F.; Herzog, E.; Wild, P. (1963), Catalogue of Galaxies and of Clusters of Galaxies 2,  
  3. Zwicky, F.; Herzog, E.; Wild, P. (1966), Catalogue of Galaxies and of Clusters of Galaxies 3,  
  4. Zwicky, F.; Herzog, E., Catalogue of Galaxies and of Clusters of Galaxies 4,  
  5. Zwicky, F.; Karpowicz, M.; Kowal, C.T. (1965), Catalogue of Galaxies and of Clusters of Galaxies 5,  
  6. Zwicky, F.; Kowal, C.T. (1968), Catalogue of Galaxies and of Clusters of Galaxies 6,  

Galaxies in the original catalog are called Zwicky galaxies, and the catalog is still maintained and updated today.[25] Zwicky with his wife Margaritha also produced an important catalog of compact galaxies, sometimes called simply The Red Book.

Zwicky, F.; Zwicky, M.A. (1971), "Catalogue of selected compact galaxies and of post-eruptive galaxies", Guemligen: Zwicky,  

Guns and goblins

Zwicky was an 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:[26]

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 . . ."

He is celebrated for the discovery of neutron stars. He also went on to consider nuclear goblins, which he proposed as "a body of nuclear density ... only stable under sufficient external pressure within a massive and dense star". He considered that goblins could move within a star, and explode violently as they reach less dense regions towards the star's surface, and serve to explain eruptive phenomena, such as flare stars.[27] This idea has never caught on.

An anecdote often told of Zwicky concerns an informal experiment to see if he could reduce problems with turbulence hindering an observation session one night at Mount Wilson observatory. He told his assistant to fire a gun out through the telescope slit, in the hope it would help to smooth out the turbulence. No effect was noticed, but the event shows the kind of lateral thinking for which Zwicky was famous.[28]

He was also very proud of his work in producing the first artificial meteors.[29] He placed explosive charges in the nose cone of a V2 rocket, to be detonated at high altitude and fire high velocity pellets of metal through the atmosphere. The first attempts appeared to be failures, and Zwicky sought to try again with the Aerobee rocket. His requests were denied, until the Soviet Union launched Sputnik 1. Twelve days later, on October 16, 1957, Zwicky launched his experiment on the Aerobee, and successfully fired pellets visible from the Mount Palomar observatory. It is thought that one of these pellets may have escaped the gravitational pull of the Earth and become the first object launched into a solar orbit.[26]

Zwicky also considered the possibility of rearranging the universe to our own liking. In a lecture in 1948[30] he spoke of changing planets, or relocating them within the solar system. In the 1960s he even considered how the whole solar system might be moved like a giant spaceship to travel to other stars. He considered this might be achieved by firing pellets into the Sun to produce asymmetrical fusion explosions, and by this means he thought that the star Alpha Centauri might be reached within 2500 years.[31]


Zwicky was a generous humanitarian with a great concern for wider society. These two sides of his nature came together in the aftermath of the Second World War, when Zwicky worked hard to collect tons of books on astronomy and other topics, and shipped them to war-ravaged scientific libraries in Europe and Asia.[32][33]

He also had a longstanding involvement with the charitable Pestalozzi Foundation of America, supporting orphanages. Zwicky received their gold medal in 1955, in recognition of his services.[32]

Zwicky loved the mountains, and was an accomplished alpine climber.[26]

He was critical of political posturing by all sides in the Middle East, and of the use of nuclear weapons in World War II. He considered that hope for the world lay with free people of good will who work together as needed, without institutions or permanent organizations.[34][35]



Zwicky produced hundreds of publications over a long career, covering a great breadth of topics. This brief selection, with comments, gives a taste of his work.

Notes and references

  1. ^  
  2. ^ a b Zwicky, F. (1933), "Die Rotverschiebung von extragalaktischen Nebeln", Helvetica Physica Acta 6: 110–127,  
  3. ^ "Организират конференция, посветена на родения във Варна астроном Фриц Цвики" (in Bulgarian). Днес+. 2008-02-13. Retrieved 18 March 2010. 
  4. ^ Ivanova, Natasha (2008), "110th anniversary of the astrophysicist Fritz Zwicky", Bulgarian Astronomical Journal (in Bulgarian) (Astronomical Observatory and Planetarium of Varna) 10: 135,  
  5. ^ a b Richard Panek, The Father of Dark Matter. Discover. pp.81-87. January 2009.
  6. ^ U.S. Patent # 3044252 
  7. ^ Muller, R. (1986), Fritz Zwicky: Leben und Werk des grossen Schweizer Astrophysikers, Raketenforschers und Morphologen (1898-1974) (in German), Verlag Baeschlin 
  8. ^ Swiss-American Historical Society (2006). Newsletter, Volumes 42-43. The Society. p. 17. Zwicky has dealt critically with religion during his whole life. A 1971 diary entry states: "To base the inexplainabilty and the immense wonder of nature upon another miracle, God, is unnecessary and not acceptable for any serious thinker." According to one story, Zwicky once discussed the beginning of the universe with a priest. The priest, quoting Scriptures, stated that the universe had started with "and there is light." Zwicky replied that he would buy this, if instead God had said "and there is electromagnetism". 
  9. ^ [2]
  10. ^ Ken Freeman, Geoff Mcnamara, In Search of Dark Matter p22-23 ISBN 978-0-387-27616-8
  11. ^ Baade, W.; Zwicky, F. (1934), "On Super-Novae", Proceedings of the National Academy of Sciences 20 (5): 254–259,  
  12. ^ Baade, W.; Zwicky, F. (1934), "Cosmic Rays from Super-novae", Proceedings of the National Academy of Sciences 20 (5): 259–263,  
  13. ^ List of Supernovae, retrieved 2007-07-10  (provided by CBAT)
  14. ^ Baade, W. (1938), "The Absolute Photographic Magnitude of Supernovae", Astrophysical Journal 88: 285–304,  
  15. ^ Perlmutter, S. (April 2003), "Supernovae, Dark Energy, and the Accelerating Universe" ( 
  16. ^ Zwicky, F. (February 1937), "Nebulae as Gravitational Lenses",  
  17. ^ Walsh, D.; Carswell, R.F.; Weymann, R.J. (May 31, 1979), "0957 + 561 A, B - Twin quasistellar objects or gravitational lens", Nature 279 (5712): 381–384,  
  18. ^ Some details of Zwicky's calculation and of more modern values are given in Richmond, M., Using the virial theorem: the mass of a cluster of galaxies, retrieved 2007-07-10 .
  19. ^ Hubble, E. (1929), "A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae", Proceedings of the National Academy of Sciences 15 (3): 168–173,  
  20. ^ Zwicky, F. (1929), "On the Red Shift of Spectral Lines through Interstellar Space", Proceedings of the National Academy of Sciences 15 (10): 773–779,   (full article)
  21. ^ Baade, W. (1956), "The Period-Luminosity Relation of the Cepheids", Publications of the Astronomical Society of the Pacific 68 (400): 5–16,  
  22. ^ Singh, S. (2004), Big Bang, Fourth Estate 
  23. ^ Ritchey, T. (2002), General Morphological Analysis: A General Method for Non-Quantified Modelling ( 
  24. ^ Zwicky, F. (1969), Discovery, Invention, Research Through the Morphological Approach, Toronto: The Macmillan Company 
  25. ^ The Updated Zwicky Catalog of Galaxies (UZC), retrieved 2007-07-10  at the Harvard-Smithsonian Center for Astrophysics.
  26. ^ a b c Maurer, S.M. (2001), "Idea Man" (PDF), Beamline (SLAC) 31 (1), retrieved 2007-07-10 
  27. ^ Zwicky, F. (October 1958), "Nuclear Goblins and Flare Stars", Publications of the Astronomical Society of the Pacific (journal) 70: 506–508,  
  28. ^ Knill, O. (1998), Supernovae, an alpine climb and space travel (biographical notes), retrieved 2007-07-10 
  29. ^ Zwicky, F. (August 1946), "On the Possibility of Earth-Launched Meteors", Publications of the Astronomical Society of the Pacific (journal) 58: 260–261,  
  30. ^ Zwicky, F. (August 1948), "Morphological astronomy", The Observatory (journal) 68: 121–143,  
  31. ^ Zwicky, F. (1966), "Entdecken, Erfinden, Forschen im morphologischen Weltbild", Muenchen: Droemer (book) (Muenchen: Droemer),  .
  32. ^ a b c Greenstein, J.L. (March–April 1974), "Fritz Zwicky - Scientific Eagle (obituary)" (PDF), Engineering and Science (CalTech): 15–19, retrieved 2007-07-14 
  33. ^ Fritz Zwicky's Extraordinary Vision,  
  34. ^ Zwicky, F. (November 1949), "Free World Agents of Democracy" (PDF), Engineering and Science (California Institute of Technology) 13 (2) 
  35. ^ Wilson, A. (1975), "Fritz Zwicky (obituary)", Quarterly Journal of the Royal Astronomical Society 16: 106–108,  
  36. ^ Meeting of the Royal Astronomical Society (PDF), February 1972, retrieved 2007-07-14 

External links

  • Ritchey, T., Fritz Zwicky, retrieved 2007-07-10 
  • Maurer, S.M. (2001), "Idea Man" (PDF), Beamline (SLAC) 31 (1), retrieved 2007-07-10 
  • Knill, O. (1998), Supernovae, an alpine climb and space travel (biographical notes), retrieved 2007-07-10 
  • Fritz Zwicky foundation (in German)
  • Proc Nat Acad Sci
  • Initial Evidence of Dark Matter — Annenberg Learner
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