Fritz Zwicky
Zwicky in 1947
BornFebruary 14, 1898
Varna, Bulgaria
DiedFebruary 8, 1974(1974-02-08) (aged 75)
Pasadena, California, US
Alma materSwiss Federal Polytechnic
Known forDark matter, supernovae, galaxies as gravitational lenses, neutron stars
AwardsPresident's Medal of Freedom (1949)
Gold Medal of the Royal Astronomical Society (1972)
Scientific career
InstitutionsCalifornia Institute of Technology
Doctoral advisorPeter Debye and Paul Scherrer

Fritz Zwicky (/ˈtsvɪki/;[1] German: [ˈtsvɪki]; 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.[2] In 1933, Zwicky was the first to use the virial theorem to postulate the existence of unseen dark matter, describing it as "dunkle Materie".[3][4]


Fritz Zwicky was born in Varna, Bulgaria, to a Swiss father (citizenship in Mollis, Glarus[5]) and Czech mother. His father, Fridolin (b. 1868), was a prominent industrialist in the Bulgarian city and also served as ambassador of Norway in Varna (1908–1933).[6] Fridolin Zwicky designed and built his family's Zwicky House in Varna. Fritz's mother, Franziska Vrček (b. 1871), was an ethnic Czech of the Austro-Hungarian Empire. Fritz was the oldest of three children: he had a younger brother named Rudolf and a sister, Leonie. Fritz's mother died in Varna in 1927. His father lived and worked in Bulgaria until 1945, and returned to Switzerland after World War II. Fritz's sister Leonie married a Bulgarian from Varna and spent her entire life in the city.[7]

In 1904, at the age of six, Fritz was sent to his paternal grandparents to Glarus, Switzerland, to study commerce.[8] His interests shifted to math and physics. He received an advanced education in mathematics and experimental physics at the Swiss Federal Polytechnic (today known as ETH Zurich) in Zürich. He finished his studies there in 1922 with a Dr. sc. nat. degree (PhD equivalent) with a thesis entitled Zur Theorie der heteropolaren Kristalle (On the theory of heteropolar crystals).[5]

In 1925, Zwicky emigrated to the United States to work with Robert Millikan at California Institute of Technology (Caltech) after receiving the Rockefeller Foundation fellowship.[8] He had an office down the hall from Robert Oppenheimer.[8]

Zwicky developed numerous cosmological theories that have had a profound influence on the understanding of our universe in the early 21st century. He coined the term "supernova" while fostering the concept of neutron stars. Five years passed before Oppenheimer published his landmark paper announcing "neutron stars".

Zwicky was appointed Professor of Astronomy at Caltech in 1942. He also worked as a research director/consultant for Aerojet Engineering Corporation (1943–1961), and as a staff member of Mount Wilson Observatory and Palomar Observatory for most of his career. He developed some of the earliest jet engines and holds more than 50 patents, many in jet propulsion. He invented the Underwater Jet.[9][10] An example of his WWII rocket propulsion work would be a patent on a nitromethane engine filed by a collective of Zwicky and three other Aerojet employees in March 1944,[11] and he also published an article on chemical kinetics in rocket engines and motors in 1950.[12]

Personal life

On 25 March 1932, Fritz Zwicky married Dorothy Vernon Gates (1904-1991), a member of a prominent local family and a daughter of California State Senator Egbert James 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.[13]

On 18 October 1947 Zwicky married in Switzerland to Anna Margaritha Zürcher. They had three daughters together, Margrit, Franziska, and Barbarina. The Zwicky Museum at the Landesbibliothek, Glarus, houses many of his papers and scientific works. Zwicky died in Pasadena, California on February 8, 1974, and was buried in Mollis, Switzerland.

Zwicky was critical of religion and considered it unacceptable to attribute natural phenomena to God.[14]

He is remembered as both a genius and a curmudgeon.[15] One of his favorite insults was to refer to people whom he did not like as "spherical bastards", because, as he explained, they were bastards no matter which way one looked at them.[16]


The Fritz Zwicky Stiftung (Foundation) was established in Switzerland to carry on his ideas relating to "Morphological analysis". The foundation published a biography of Zwicky in English: Alfred Stöckli & Roland Müller: Fritz Zwicky – An Extraordinary Astrophysicist. Cambridge: Cambridge Scientific Publishers, 2011. A review of the book is available from Acta Morphologica Generalis Archived March 4, 2016, at the Wayback Machine.

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. In 1934 he and Baade coined the term "supernova" and hypothesized that supernovae were the transition of normal stars into neutron stars,[17] as well as the origin of cosmic rays.[18][19] This was an opinion which contributed to determining the size and age of the universe subsequently.

In support of this hypothesis, Zwicky started looking for supernovae, and found a total of 120 by himself (and one more, SN 1963J, in concert with Paul Wild) over 52 years (SN 1921B through SN 1973K),[20] a record which stood until 2009 when passed by Tom Boles. Zwicky did his laborious work, comparing photographic plates with the human eye, which is far more challenging and difficult than Boles accomplished using modern technology for his record.

Gravitational lenses

In 1937, Zwicky posited that galaxies could act as gravitational lenses by the previously discovered Einstein effect.[21] It was not until 1979 that this effect was confirmed by observation of the so-called "Twin Quasar" Q0957+561.[22]

Dark matter

While examining the Coma galaxy cluster in 1933, Zwicky was the first to use the virial theorem to discover the existence of a gravitational anomaly, which he termed dunkle Materie 'dark matter'.[3] The gravitational anomaly surfaced due to the excessive rotational velocity of luminous matter compared to the calculated gravitational attraction within the cluster. He calculated the gravitational mass of the galaxies within the cluster from the observed rotational velocities and obtained a value at least 400 times greater than expected from their luminosity. The same calculation today shows a smaller factor, based on greater values for the mass of luminous material.[23]

Tired light

Main article: Tired light

When Edwin Hubble discovered a somewhat linear relationship between the distance to a galaxy and its redshift expressed as a velocity,[24] 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.[25]

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.[26] Cosmological redshift is now conventionally understood to be a consequence of the expansion of space; a feature of Big Bang cosmology.[27]

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.[28] He wrote books on the subject in 1957 and 1969,[29][30] and claimed that he made many of his discoveries using this method.

Catalog of Galaxies and Clusters

Main article: Catalogue of Galaxies and of Clusters of Galaxies

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, vol. 1, California Institute of Technology,
  2. Zwicky, F.; Herzog, E.; Wild, P. (1963), Catalogue of Galaxies and of Clusters of Galaxies, vol. 2, California Institute of Technology,
  3. Zwicky, F.; Herzog, E.; Wild, P. (1966), Catalogue of Galaxies and of Clusters of Galaxies, vol. 3, California Institute of Technology,
  4. Zwicky, F.; Herzog, E., Catalogue of Galaxies and of Clusters of Galaxies, vol. 4, California Institute of Technology
  5. Zwicky, F.; Karpowicz, M.; Kowal, C.T. (1965), Catalogue of Galaxies and of Clusters of Galaxies, vol. 5, California Institute of Technology,
  6. Zwicky, F.; Kowal, C.T. (1968), Catalogue of Galaxies and of Clusters of Galaxies, vol. 6, California Institute of Technology, Bibcode:1968cgcg.bookR....Z

Galaxies in the original catalog are called Zwicky galaxies, and the catalog is still maintained and updated today.[31] 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,

Original thinker

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:[32]

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 proposed a concept he called nuclear goblins, which he described as "a body of nuclear density ... only stable under sufficient external pressure within a massive and dense star". He considered that these 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.[33] 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 smooth out the turbulence. No effect was noticed, but the event shows the kind of lateral thinking for which Zwicky was famous.[34]

In a talk to a Caltech PhD student Frank Malina, who experienced some difficulties working on a dissertation regarding characteristics of oxygen-gasoline rocket engine, Fritz Zwicky claimed the engineer "must realize that a rocket could not operate in space as it required the atmosphere to push against to provide thrust".[35] Zwicky later admitted that he had been mistaken.

He was also very proud of his work in producing the first artificial meteors.[36] 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.[32]

Zwicky also considered the possibility of rearranging the universe to our own liking. In a lecture in 1948[37] 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.[38]


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.[39][40]

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.[39]

Zwicky loved the mountains, and was an accomplished alpine climber.[32]

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.[41][42]

Media persona

Zwicky's ideas captured the imagination of the public. He was widely quoted by reporters.[43]

The New York Times published updates of Zwicky's supernova search on a regular basis. In 1934 he was featured in Literary Digest's "They Stand Out from the Crowd" column, ... and in 1935 he gave a Science Service Radio Talk titled "Stellar Guests". ...[44]

In January 1934, Los Angeles Times published the cartoon "Be Scientific with Ol' Doc Dabble", which had a caption describing Zwicky's research and which implicitly caricatured him as "Doc Dabble".[45]

Some scenes of the 13th episode of Cosmos: A Spacetime Odyssey depicts an actor playing Fritz Zwicky, at the same time that Neil DeGrasse Tyson talks about the importance of Zwicky's studies on supernovae.



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.


  1. ^ "Zwicky". Random House Webster's Unabridged Dictionary.
  2. ^ Arp, Halton (June 1974). "Fritz Zwicky". Physics Today. 27 (6): 70–71. Bibcode:1974PhT....27f..70A. doi:10.1063/1.3128662. Archived from the original on September 27, 2013.
  3. ^ a b Zwicky, F. (1933), "Die Rotverschiebung von extragalaktischen Nebeln" [The red shift of extragalactic neubulae], Helvetica Physica Acta (in German), 6: 110–127, Bibcode:1933AcHPh...6..110Z From p 125: "Um, wie beobachtet, einen mittleren Dopplereffekt von 1000 km/sek oder mehr zu erhalten, müsste also die mittlere Dichte im Comasystem mindestens 400 mal grösser sein als die auf Grund von Beobachtungen an leuchtender Materie abgeleitete. Falls sich dies bewahrheiten sollte, würde sich also das überraschende Resultat ergeben, dass dunkle Materie in sehr viel grösserer Dichte vorhanden ist als leuchtende Materie." (In order to obtain an average Doppler effect of 1000 km/s or more, as observed, the average density in the Coma system would thus have to be at least 400 times greater than that derived on the basis of observations of luminous matter. If this were to be verified, the surprising result would then follow that dark matter is present in very much greater density than luminous matter.)
  4. ^ de Swart, J. G.; Bertone, G.; van Dongen, J. (2017). "How dark matter came to matter". Nature Astronomy. 1 (59): 0059. arXiv:1703.00013. Bibcode:2017NatAs...1E..59D. doi:10.1038/s41550-017-0059. S2CID 119092226.
  5. ^ a b Fritz Zwicky: Zur Theorie der heteropolaren Kristalle. Promotionsarbeit. ETH Zurich, 1922. Retrieved 16 November 2022.
  6. ^ "Организират конференция, посветена на родения във Варна астроном Фриц Цвики" (in Bulgarian). Днес+. February 13, 2008. Archived from the original on February 1, 2010. Retrieved March 18, 2010.
  7. ^ Ivanova, Natasha (2008), "110th anniversary of the astrophysicist Fritz Zwicky", Bulgarian Astronomical Journal (in Bulgarian), 10: 135, Bibcode:2008BlgAJ..10..135I
  8. ^ a b c Richard Panek, The Father of Dark Matter. Discover. 2009. pp. 81-87.
  9. ^ "The Two Piece Jet Thrust Motor and Inverted Hydro Pulse", TIME, March 14, 1949).
  10. ^ U.S. Patent # 3044252
  11. ^ U.S. patent 2433943A
  12. ^ Zwicky, Fritz (January 16, 1950). "Chemical Kinetics and Jet Propulsion". Chemical & Engineering News Archive. 28 (3): 156–158. doi:10.1021/cen-v028n003.p156. ISSN 0009-2347.
  13. ^ Muller, R. (1986), Fritz Zwicky: Leben und Werk des grossen Schweizer Astrophysikers, Raketenforschers und Morphologen (1898-1974) (in German), Verlag Baeschlin,
  14. ^ 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".
  15. ^ "The Father of Dark Matter Still Gets No Respect - Discover".
  16. ^ Ken Freeman, Geoff Mcnamara, In Search of Dark Matter, p22-23 ISBN 978-0-387-27616-8
  17. ^ Osterbrock, D. E. (2001). "Who Really Coined the Word Supernova? Who First Predicted Neutron Stars?". Bulletin of the American Astronomical Society. 33: 1330. Bibcode:2001AAS...199.1501O.
  18. ^ Baade, W.; Zwicky, F. (1934), "On Super-Novae", Proceedings of the National Academy of Sciences, 20 (5): 254–259, Bibcode:1934PNAS...20..254B, doi:10.1073/pnas.20.5.254, PMC 1076395, PMID 16587881
  19. ^ Baade, W.; Zwicky, F. (1934), "Cosmic Rays from Super-novae", Proceedings of the National Academy of Sciences, 20 (5): 259–263, Bibcode:1934PNAS...20..259B, doi:10.1073/pnas.20.5.259, PMC 1076396, PMID 16587882
  20. ^ List of Supernovae, retrieved July 10, 2007 (provided by CBAT)
  21. ^ Zwicky, F. (February 1937), "Nebulae as Gravitational Lenses", Physical Review, 51 (4): 290, Bibcode:1937PhRv...51..290Z, doi:10.1103/PhysRev.51.290, archived from the original on December 25, 2013, retrieved December 24, 2013
  22. ^ 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, Bibcode:1979Natur.279..381W, doi:10.1038/279381a0, PMID 16068158, S2CID 2142707
  23. ^ 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 July 10, 2007.
  24. ^ 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, Bibcode:1929PNAS...15..168H, doi:10.1073/pnas.15.3.168, PMC 522427, PMID 16577160
  25. ^ Zwicky, F. (1929), "On the Red Shift of Spectral Lines through Interstellar Space", Proceedings of the National Academy of Sciences, 15 (10): 773–779, Bibcode:1929PNAS...15..773Z, doi:10.1073/pnas.15.10.773, PMC 522555, PMID 16577237 (full article)
  26. ^ Baade, W. (1956), "The Period-Luminosity Relation of the Cepheids", Publications of the Astronomical Society of the Pacific, 68 (400): 5–16, Bibcode:1956PASP...68....5B, doi:10.1086/126870
  27. ^ Singh, S. (2004), Big Bang, Fourth Estate, archived from the original on June 30, 2007
  28. ^ Ritchey, T. (2002), General Morphological Analysis: A General Method for Non-Quantified Modelling (PDF), retrieved July 10, 2007
  29. ^ Zwicky, Fritz (1957). Morphological Astronomy. Germany: Springer.
  30. ^ Zwicky, F. (1969), Discovery, Invention, Research Through the Morphological Approach, Toronto: The Macmillan Company, ISBN 978-1114243064
  31. ^ The Updated Zwicky Catalog of Galaxies (UZC), retrieved July 10, 2007 at the Harvard-Smithsonian Center for Astrophysics.
  32. ^ a b c Maurer, S.M. (2001), "Idea Man" (PDF), Beamline, 31 (1), retrieved July 10, 2007
  33. ^ Zwicky, F. (October 1958), "Nuclear Goblins and Flare Stars", Publications of the Astronomical Society of the Pacific (journal), 70 (416): 506–508, Bibcode:1958PASP...70..506Z, doi:10.1086/127284
  34. ^ Knill, O. (1998), Supernovae, an alpine climb and space travel (biographical notes), retrieved July 10, 2007
  35. ^ "Pionniers & Précurseurs - FRANK J. MALINA - AERONAUTIQUE - MEMOIRES SCIENTIFIQUES - 2E TOME". Archived from the original on March 22, 2019. Retrieved February 15, 2016.
  36. ^ Zwicky, F. (August 1946), "On the Possibility of Earth-Launched Meteors", Publications of the Astronomical Society of the Pacific (journal), 58 (343): 260–261, Bibcode:1946PASP...58..260Z, doi:10.1086/125840
  37. ^ Zwicky, F. (August 1948), "Morphological astronomy", The Observatory (journal), 68: 121–143, Bibcode:1948Obs....68..121Z
  38. ^ Zwicky, F. (1966), "Entdecken, Erfinden, Forschen im morphologischen Weltbild", Muenchen: Droemer (book), Muenchen, (page 237). This reference was identified from a footnote provided in an online essay: Knill, Oliver (November 1997), Moving the Solar System, retrieved July 17, 2007.
  39. ^ a b c Greenstein, J.L. (March–April 1974), "Fritz Zwicky – Scientific Eagle (obituary)" (PDF), Engineering and Science: 15–19, retrieved July 14, 2007
  40. ^ Fritz Zwicky's Extraordinary Vision, American Museum of Natural History, archived from the original on July 14, 2007, retrieved July 16, 2007, an extract from Soter, S.; Tyson, N.D. (2000), Cosmic Horizons: Astronomy at the Cutting Edge, New Press, ISBN 978-1565846029
  41. ^ Zwicky, F. (November 1949), "Free World Agents of Democracy" (PDF), Engineering and Science, 13 (2)
  42. ^ Wilson, A. (1975), "Fritz Zwicky (obituary)", Quarterly Journal of the Royal Astronomical Society, 16: 106–108
  43. ^ Johnson Jr., John (2019). Zwicky: The Outcast Genius Who Unmasked the Universe. Harvard University Press. p. 12. ISBN 9780674979673.
  44. ^ Turatto, Massimo; Benetti, Stefano; Zampieri, Luca (2005). 1604-2204: Supernovae as Cosmological Lighthouses. Astronomical Society of the Pacific. p. 58. ISBN 9781583812099.
  45. ^ Longair, Malcolm S. (2006). The Cosmic Century: A History of Astrophysics and Cosmology. Cambridge University Press. ISBN 9780521474368.
  46. ^ "Dr. Fritz Zwicky, Astronomer, Jet Propulsion Expert, 74, Dies". The New York Times. February 11, 1974.
  47. ^ Meeting of the Royal Astronomical Society (PDF), February 1972, retrieved July 14, 2007
  48. ^ "Zwicky Transient Facility Opens Its Eyes to the Volatile cosmos". Zwicky Transient Facility. November 14, 2017. Archived from the original on November 11, 2021. Retrieved February 8, 2019.


Further reading