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[[Fitxer:Fritz Zwicky Memorial Plate - Varna.jpg|thumb|left|Placa commemorativa de Fritz Zwicky]]
[[Fitxer:Fritz Zwicky Memorial Plate - Varna.jpg|thumb|left|Placa commemorativa de Fritz Zwicky]]
'''Fritz Zwicky''' ([[14 de febrer]] de [[1898]] - [[8 de febrer]] de [[1974]]) va ser un [[astrònom]] i [[físic]] europeu emigrat als EUA.
'''Fritz Zwicky''' ([[14 de febrer]] de [[1898]] - [[8 de febrer]] de [[1974]]) va ser un [[astrònom]] i [[físic]] europeu emigrat als EUA.
Línia 6: Línia 7:


Va conduir una àmplia investigació de les [[galàxies]] veïnes mitjançant les supernoves i en va descobrir 18; només al voltant de 12 havien estat registrades prèviament en tota la història de l'astronomia. Entre els anys [[1943]] i [[1946]], al costat de [[Theodore von Kármán]] i d'altres, va ajudar a desenvolupar els primers sistemes d'enlairament assistit per reactors.
Va conduir una àmplia investigació de les [[galàxies]] veïnes mitjançant les supernoves i en va descobrir 18; només al voltant de 12 havien estat registrades prèviament en tota la història de l'astronomia. Entre els anys [[1943]] i [[1946]], al costat de [[Theodore von Kármán]] i d'altres, va ajudar a desenvolupar els primers sistemes d'enlairament assistit per reactors.

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'''Fritz Zwicky''' ({{IPAc-en|ˈ|t|s|v|ɪ|k|i}};<ref>[http://www.dictionary.com/browse/zwicky "Zwicky"]. ''[[Random House Webster's Unabridged Dictionary]]''.</ref> {{IPA-de|ˈtsvɪki|lang}}; February 14, 1898 – February 8, 1974) was a [[Swiss people|Swiss]] [[astronomer]]. He worked most of his life at the [[California Institute of Technology]] in the [[United States|United States of America]], where he made many important contributions in theoretical and observational astronomy.<ref>{{cite journal |author=Arp, Halton |authorlink=Halton Arp |title=Fritz Zwicky |journal=Physics Today |date=June 1974 |volume=27 |issue=6 |pages=70–71 |url=http://www.physicstoday.org/resource/1/phtoad/v27/i6/p70_s1?bypassSSO=1 |doi=10.1063/1.3128662 |bibcode=1974PhT....27f..70A |deadurl=yes |archiveurl=https://web.archive.org/web/20130927175046/http://www.physicstoday.org/resource/1/phtoad/v27/i6/p70_s1?bypassSSO=1 |archivedate=2013-09-27 |df=}}</ref> In 1933, Zwicky was the first to use the [[virial theorem]] to infer the existence of unseen [[dark matter]], describing it as "''{{lang|de|dunkle Materie}}''".<ref name="Zwicky 1933 110–127">{{Citation | last = Zwicky | first = F. | bibcode = 1933AcHPh...6..110Z | title = Die Rotverschiebung von extragalaktischen Nebeln | date = 1933 | journal = Helvetica Physica Acta | volume = 6 | pages = 110–127}} See also {{Citation | last = Zwicky | first = F. | bibcode = 1937ApJ....86..217Z | title = On the Masses of Nebulae and of Clusters of Nebulae | date = 1937 | journal = Astrophysical Journal | volume = 86 | pages = 217 | doi = 10.1086/143864}}</ref><ref>{{cite journal|last1=de Swart|first1=J. G.|last2=Bertone|first2=G.|last3=van Dongen|first3=J.|title=How dark matter came to matter|journal=Nature Astronomy|date=2017|volume=1|issue=59|pages=0059|arxiv=1703.00013|doi=10.1038/s41550-017-0059|url=http://www.nature.com/articles/s41550-017-0059|bibcode = 2017NatAs...1E..59D }}</ref>

== Biography ==
Fritz Zwicky was born in [[Varna]], [[Principality of Bulgaria|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).<ref name="dnes+">{{cite news|url=http://dnesplus.bg/Society.aspx?f=99&d=206709|title=Организират конференция, посветена на родения във Варна астроном Фриц Цвики|date=2008-02-13|publisher=Днес+|language=Bulgarian|accessdate=18 March 2010|deadurl=yes|archiveurl=https://web.archive.org/web/20100201093915/http://dnesplus.bg/Society.aspx?f=99|archivedate=1 February 2010|df=}}</ref> The Zwicky House in Varna was designed and built by Fridolin Zwicky. Fritz's mother, Franziska Vrček (b. 1871), was an ethnic [[Czech people|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, 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.<ref name="ivanova">{{Citation|last=Ivanova|first=Natasha|title=110th anniversary of the astrophysicist Fritz Zwicky|pages=135|volume=10|date=2008|journal=Bulgarian Astronomical Journal|language=Bulgarian|bibcode=2008BlgAJ..10..135I}}</ref>

In 1904, at the age of six, Fritz was sent to his grandparents in the family's ancestral canton of [[Glarus]], Switzerland, to study commerce.<ref name="Panek">Richard Panek, ''The Father of Dark Matter.'' Discover. 2009. pp. 81-87.</ref> His interests shifted to math and physics and he received an advanced education in mathematics and experimental physics at the [[Swiss Federal Polytechnic]] (today known as ETH Zurich) in [[Zurich]]. In 1925, he immigrated 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."<ref name="Panek"/>

He was responsible for positing numerous cosmological theories that have a profound impact on the understanding of our universe today. He coined the term "supernova" during his fostering the concept of neutron stars. 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.<ref name="U.S. Patent # 3044252">{{Citation|title = U.S. Patent # 3044252 | url = https://www.google.com/patents/US3044252?dq=US3044252&hl=en&sa=X&ei=VIE2VMOlG8iHyASxxoKIDg&ved=0CB8Q6AEwAA}}</ref>

In April 1932, Fritz Zwicky married Dorothy Vernon Gates (1904-1991), a member of a prominent local family and a daughter of California State Senator Egbert Gates. Her money was instrumental in the funding of the [[Palomar Observatory]] during the [[Great Depression]]. [[Nicholas Roosevelt (diplomat)|Nicholas Roosevelt]], cousin of President Theodore Roosevelt, was his brother-in-law by marriage to Tirzah Gates. Zwicky and Dorothy divorced amicably in 1941.<ref>{{Citation | title = Fritz Zwicky: Leben und Werk des grossen Schweizer Astrophysikers, Raketenforschers und Morphologen (1898-1974) | first = R. | last = Muller | publisher = Verlag Baeschlin | date = 1986 | language = German }}</ref> 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 [http://www.zwicky-stiftung.ch/ Fritz Zwicky Stiftung] (Foundation) in Switzerland carries on his ideas relating to "[[Morphological analysis (problem-solving)|Morphological analysis]]". Zwicky died in Pasadena on February 8, 1974, and was buried in [[Mollis]], Switzerland.

Zwicky was an [[atheist]].<ref>{{cite book|author1=Swiss-American Historical Society|title=Newsletter, Volumes 42-43|date=2006|publisher=The Society|page=17|url=https://books.google.com/?id=2IAOAQAAMAAJ&q=%22miracle+(God)+is+unnecessary+and+not+acceptable+for+any+serious+thinker.%22&dq=%22miracle+(God)+is+unnecessary+and+not+acceptable+for+any+serious+thinker.%22|quote=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".}}</ref>

He is remembered as both a genius and a [[wikt:Special:Search/curmudgeon|curmudgeon]].<ref>{{cite web|url=http://discovermagazine.com/2009/jan/30-the-father-of-dark-matter-still-gets-no-respect|title=The Father of Dark Matter Still Gets No Respect - DiscoverMagazine.com|publisher=}}</ref> 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 one looked at them.<ref>Ken Freeman, Geoff Mcnamara, In Search of Dark Matter p22-23 {{ISBN|978-0-387-27616-8}}</ref>

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 [http://www.amg.swemorph.com/pdf/amg-1-3-2012.pdf ''Acta Morphologica Generalis''].

== Scientific work ==
[[Image:Fritz Zwicky Memorial Plate - Varna.jpg|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.|250px|right|thumb]]

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 camera|Schmidt telescope]]s 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]],<ref name="baas33_1330">
{{cite journal
|last1=Osterbrock |first1=D. E.
|year=2001
|title=Who Really Coined the Word Supernova? Who First Predicted Neutron Stars?
|journal=[[Bulletin of the American Astronomical Society]]
|volume=33 |pages=1330
|bibcode=2001AAS...199.1501O
}}</ref> as well as the origin of [[cosmic ray]]s.<ref>{{Citation | first = W. | last = Baade | first2 = F. | last2 = Zwicky | title = On Super-Novae | journal = Proceedings of the National Academy of Sciences | volume = 20 | issue = 5 | date = 1934 | pages = 254–259 | doi = 10.1073/pnas.20.5.254 | pmc = 1076395 | pmid=16587881 | bibcode=1934PNAS...20..254B}}</ref><ref>{{Citation | title = Cosmic Rays from Super-novae
|last1=Baade | first1 = W. | first2 = F. | last2 = Zwicky | journal = Proceedings of the National Academy of Sciences | volume = 20 | issue = 5 | date = 1934 | pages = 259–263 | bibcode = 1934PNAS...20..259B | doi = 10.1073/pnas.20.5.259 }}</ref> 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<!--- must discount 1956C, which turned out to be minor planet (9574) Taku, and 1954J, now thought to have been a pre-SN outburst of an eta-Carinae-like star ---> by himself (and one more, [[SN 1963J]], in concert with [[Paul Wild (Swiss astronomer)|Paul Wild]]) over 52 years ([[SN 1921B]] through [[SN 1973K]]),<ref>{{Citation | url = http://cbat.eps.harvard.edu//lists/Supernovae.html | accessdate = 2007-07-10 | title = List of Supernovae }} (provided by [http://cbat.eps.harvard.edu/ CBAT])</ref> 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 lens]]es by the previously discovered Einstein effect.<ref>{{Citation | last = Zwicky | first = F. | title = Nebulae as Gravitational Lenses |date=February 1937 | journal = [[Physical Review]] | volume = 51 | issue = 4 | pages = 290 | doi = 10.1103/PhysRev.51.290|bibcode = 1937PhRv...51..290Z | url= http://authors.library.caltech.edu/5611/}}</ref> It was not until 1979 that this effect was confirmed by observation of the so-called [[Twin Quasar|"Twin Quasar" Q0957+561]].<ref>{{Citation | last = Walsh | first = D. | last2 = Carswell | first2 = R.F. | last3 = Weymann | first3 = R.J. | bibcode = 1979Natur.279..381W | title = 0957 + 561 A, B - Twin quasistellar objects or gravitational lens | journal = Nature | date = May 31, 1979 | volume = 279 | issue = 5712 | pages = 381&ndash;384 | doi = 10.1038/279381a0 | pmid = 16068158 | url= http://www.nature.com/physics/looking-back/walsh/index.html}}</ref>

=== 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]]'.<ref name="Zwicky 1933 110–127"/> 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.<ref>Some details of Zwicky's calculation and of more modern values are given in {{Citation | first = M. | last = Richmond | title = Using the virial theorem: the mass of a cluster of galaxies | url = http://spiff.rit.edu/classes/phys440/lectures/gal_clus/gal_clus.html | accessdate = 2007-07-10}}.</ref>

=== 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,<ref>{{Citation | first = E. | last = Hubble | bibcode = 1929PNAS...15..168H | title = A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae | journal = Proceedings of the National Academy of Sciences | volume = 15 | issue = 3 | date = 1929 | pages = 168–173 | doi = 10.1073/pnas.15.3.168 | pmc = 522427 | pmid=16577160}}</ref> 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 [[Margin of Error|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.<ref>{{Citation | last = Zwicky | first = F. | bibcode = 1929PNAS...15..773Z | title = On the Red Shift of Spectral Lines through Interstellar Space | date = 1929 | journal = Proceedings of the National Academy of Sciences | volume = 15 | issue = 10 | pages = 773–779 | doi = 10.1073/pnas.15.10.773 | pmc = 522555 | pmid=16577237}} ([http://www.pnas.org/cgi/reprint/15/10/773.pdf full article])</ref>

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.<ref>{{Citation | first = W. | last = Baade | title = The Period-Luminosity Relation of the Cepheids | bibcode = 1956PASP...68....5B | date = 1956 | journal = Publications of the Astronomical Society of the Pacific | volume = 68 | issue = 400 | pages = 5–16 | doi = 10.1086/126870 }}</ref> Cosmological redshift is now conventionally understood to be a consequence of the [[expansion of space]]; a feature of [[Big Bang|Big Bang cosmology]].<ref>{{Citation | first = S. | last = Singh | title = Big Bang | publisher = Fourth Estate | date = 2004 | url = http://www.simonsingh.net/Big_Bang.html | deadurl = yes | archiveurl = https://web.archive.org/web/20070630195328/http://www.simonsingh.net/Big_Bang.html | archivedate = 2007-06-30 | df = }}</ref>

=== Morphological analysis ===
Zwicky developed a generalised form of [[Morphological analysis (problem-solving)|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.<ref>{{Citation | format = [[PDF]] | last = Ritchey | first = T. | date = 2002 | url = http://www.swemorph.com/pdf/gma.pdf | title= General Morphological Analysis: A General Method for Non-Quantified Modelling | accessdate = 2007-07-10}}</ref> He wrote a book on the subject in 1969,<ref>{{Citation | last = Zwicky | first = F. | date = 1969 | title = Discovery, Invention, Research Through the Morphological Approach | place = Toronto | publisher = The Macmillan Company | url = https://www.amazon.com/Discovery-invention-research-morphological-approach/dp/B0006BYL8U}}</ref> 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.
#{{Citation
| title = Catalogue of Galaxies and of Clusters of Galaxies
| first1 = F. | last1 = Zwicky
| first2 = E. | last2 = Herzog
| first3 = P. | last3 = Wild
| date = 1961
| volume=1
| publisher= [[California Institute of Technology]]
| bibcode = 1961cgcg.book.....Z
}}
#{{Citation
| title = Catalogue of Galaxies and of Clusters of Galaxies
| first1 = F. | last1 = Zwicky
| first2 = E. | last2 = Herzog
| first3 = P. | last3 = Wild
| date = 1963
| volume=2
| publisher= [[California Institute of Technology]]
| bibcode = 1963cgcg.book.....Z
}}
#{{Citation
| title = Catalogue of Galaxies and of Clusters of Galaxies
| first1 = F. | last1 = Zwicky
| first2 = E. | last2 = Herzog
| first3 = P. | last3 = Wild
| date = 1966
| volume=3
| publisher= [[California Institute of Technology]]
| bibcode = 1966cgcg.book.....Z
}}
#{{Citation
| title = Catalogue of Galaxies and of Clusters of Galaxies
| first1 = F. | last1 = Zwicky
| first2 = E. | last2 = Herzog
| date =
| volume=4
| publisher= [[California Institute of Technology]]
}}
#{{Citation
| title = Catalogue of Galaxies and of Clusters of Galaxies
| first1 = F. | last1 = Zwicky
| first2 = M. | last2 = Karpowicz
| first3 = C.T. | last3 = Kowal
| date = 1965
| volume=5
| publisher= [[California Institute of Technology]]
| bibcode = 1965cgcg.book.....Z
}}
#{{Citation
| title = Catalogue of Galaxies and of Clusters of Galaxies
| first1 = F. | last1 = Zwicky
| first2 = C.T. | last2 = Kowal
| date = 1968
| volume=6
| publisher= [[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.<ref>{{Citation | url = http://tdc-www.harvard.edu/uzc/ | accessdate = 2007-07-10 | title = The Updated Zwicky Catalog of Galaxies (UZC) }} at [http://www.cfa.harvard.edu/ the Harvard-Smithsonian Center for Astrophysics].</ref> Zwicky with his wife Margaritha also produced an important catalog of compact galaxies, sometimes called simply ''The Red Book''.
:{{Citation | last = Zwicky | first = F. | last2 = Zwicky | first2 = M.A. | title = Catalogue of selected compact galaxies and of post-eruptive galaxies | journal = Guemligen: Zwicky | date = 1971 | bibcode = 1971cscg.book.....Z }}

=== 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:<ref name ="IdeaMan">{{Citation | url = http://www.slac.stanford.edu/pubs/beamline/31/1/31-1-maurer.pdf |format=PDF| title = Idea Man | first = S.M. | last = Maurer | journal = Beamline | date = 2001 | volume = 31 | issue = 1 | accessdate = 2007-07-10}}</ref>
:<blockquote>''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..."''
</blockquote>

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.<ref>{{Citation | type = journal
| title = Nuclear Goblins and Flare Stars
| first = F. | last = Zwicky
| journal = Publications of the Astronomical Society of the Pacific
| volume = 70
|date=October 1958
| pages = 506–508
| bibcode = 1958PASP...70..506Z
| doi = 10.1086/127284
}}</ref> 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.<ref>{{Citation | url = http://www.dynamical-systems.org/zwicky/Zwicky-e.html | accessdate = 2007-07-10 | title = Supernovae, an alpine climb and space travel (biographical notes) | last = Knill | first = O. | date = 1998 }}</ref>

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|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".<ref>{{cite web|url=http://www.olats.org/pionniers/malina/aeronautique/memoir2.php|title=Pionniers & Précurseurs - FRANK J. MALINA - AERONAUTIQUE - MEMOIRES SCIENTIFIQUES - 2E TOME|publisher=olats.org}}</ref> Zwicky later admitted that he had been mistaken.

He was also very proud of his work in producing the first artificial meteors.<ref>{{Citation | type = journal
| title = On the Possibility of Earth-Launched Meteors
| first = F. | last = Zwicky
| journal = Publications of the Astronomical Society of the Pacific
| volume = 58
|date=August 1946
| pages = 260–261
| bibcode = 1946PASP...58..260Z
| doi = 10.1086/125840
}}</ref> 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.<ref name="IdeaMan"/>

Zwicky also considered the possibility of rearranging the universe to our own liking. In a lecture in 1948<ref>{{Citation | type = journal
| title = Morphological astronomy
| first = F. | last = Zwicky
| journal = The Observatory
| volume = 68
|date=August 1948
| pages = 121–143
| bibcode = 1948Obs....68..121Z
}}
</ref> 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.<ref>{{Citation | type = book
| title = Entdecken, Erfinden, Forschen im morphologischen Weltbild
| first = F. | journal = Muenchen: Droemer | last = Zwicky
| place = Muenchen
| date = 1966
| bibcode = 1966eefi.book.....Z
}} (page 237). This reference was identified from a footnote provided in an online essay: {{Citation | url = http://www.dynamical-systems.org/zwicky/Essay.html | title = Moving the Solar System | first = Oliver | last = Knill |date=November 1997 | accessdate = 2007-07-17 }}.</ref>

== Humanitarian ==
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.<ref name="Greenstein1974"/><ref>{{Citation | title = Fritz Zwicky's Extraordinary Vision | accessdate = 2007-07-16 | url = http://www.amnh.org/education/resources//rfl/web/essaybooks/cosmic/p_zwicky.html | publisher = [[American Museum of Natural History]] | deadurl = yes | archiveurl = https://web.archive.org/web/20070714004428/http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p_zwicky.html | archivedate = 2007-07-14 | df = }}, an extract from {{ Citation | title = Cosmic Horizons: Astronomy at the Cutting Edge | date = 2000 | publisher = New Press | first1 = S. | last1 = Soter | first2 = N.D. | last2 = Tyson | isbn = 978-1565846029 }}</ref>

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.<ref name="Greenstein1974"/>

Zwicky loved the mountains, and was an accomplished alpine climber.<ref name="IdeaMan"/>

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.<ref>{{Citation | title = Free World Agents of Democracy | first = F. | last = Zwicky |date=November 1949 | journal = Engineering and Science | volume = 13 | issue = 2 | url = http://calteches.library.caltech.edu/306/01/zwicky.pdf |format=PDF}}</ref><ref>{{Citation | title = Fritz Zwicky (obituary) | first = A. | last = Wilson | journal = Quarterly Journal of the Royal Astronomical Society | bibcode = 1975QJRAS..16..106. | volume = 16 | date = 1975 | pages = 106–108 }}</ref>

== Honors ==
*In 1949, Truman awarded Zwicky the [[Presidential Medal of Freedom]], for work on rocket propulsion during World War II.<ref name="Greenstein1974">{{Citation | title = Fritz Zwicky – Scientific Eagle (obituary) | url = http://www.swemorph.com/pdf/greenstein.pdf |format=PDF| accessdate = 2007-07-14 | journal = Engineering and Science |date=March–April 1974 | pages = 15–19 | first = J.L. | last = Greenstein }}</ref> In 1968, Zwicky was made professor emeritus at [[California Institute of Technology]].
*In 1972, Zwicky was awarded the [[Gold Medal of the Royal Astronomical Society]], their most prestigious award, for ''"distinguished contributions to astronomy and cosmology"''.<ref>{{Citation | title = Meeting of the Royal Astronomical Society |date=February 1972 | url = http://www.zwicky-stiftung.ch/Publikationen/Award.pdf |format=PDF| accessdate = 2007-07-14 }}</ref> This award noted in particular his work on neutron stars, dark matter, and cataloging of galaxies.
*The [[asteroid]] [[1803 Zwicky]] and the lunar crater [[Zwicky (crater)|Zwicky]] are both named in his honor.
*The [[Zwicky Transient Facility]] is named in his honor.<ref>{{Cite web|url=http://www.ztf.caltech.edu/news/zwicky-transient-facility-opens-its-eyes-to-the-volatile-cosmos|title=Zwicky Transient Facility Opens Its Eyes to the Volatile cosmos|last=|first=|date=November 14, 2017|website=Zwicky Transient Facility|archive-url=|archive-date=|dead-url=|access-date=}}</ref>

== Publicacions ==
Zwicky va produir centenars de publicacions durant una llarga carrera, cobrint un ampli ventall de temes. Aquesta breu selecció, amb comentaris, dóna una idea del seu treball.
* {{Citation
| title = On the Red Shift of Spectral Lines through Interstellar Space
| first = F. | last = Zwicky
| journal = Proceedings of the National Academy of Sciences
| volume = 15
|date=October 1929
| issue = 10
| pages = 773–779
| bibcode = 1929PNAS...15..773Z
| doi = 10.1073/pnas.15.10.773
| pmc = 522555
| pmid=16577237
}}. Aquest és l'article que proposa un model de [[llum lleugera]] per explicar la [[llei de Hubble]]. ([http://www.pnas.org/cgi/reprint/15/10/773.pdf full article])
* {{Citation
| title = On Super-novae
| first1 = W. | last1 = Baade
| first2 = F. | last2 = Zwicky
| journal = Proceedings of the National Academy of Sciences
| volume = 20
| issue = 5
| date = 1934
| pages = 254–259
| bibcode = 1934PNAS...20..254B
| doi = 10.1073/pnas.20.5.254
| pmc = 1076395
| pmid=16587881
}}, i {{Citation
| title = Cosmic Rays from Super-novae
| first1 = W. | last1 = Baade
| first2 = F. | last2 = Zwicky
| journal = Proceedings of the National Academy of Sciences
| volume = 20
| issue = 5
| date = 1934
| pages = 259–263
| bibcode = 1934PNAS...20..259B
| doi = 10.1073/pnas.20.5.259
}}. Aquests articles consecutius introdueixen la noció d'una [[supernova]] i d'una [[estrella de neutrons]] respectivament.
* {{Citation
| title = On Collapsed Neutron Stars
| first = F. | last = Zwicky
| journal = Astrophysical Journal
| volume = 88
|date=November 1938
| pages = 522–525
| bibcode = 1938ApJ....88..522Z
| doi = 10.1086/144003
}}. La idea d'una [[estrella de neutrons]], introduïda anteriorment en el paper de la supernova, s'explica juntament amb la idea de la massa estel·lar crítica i dels forats negres.
* {{Citation
| title = On the Formation of Clusters of Nebulae and the Cosmological Time Scale
| first = F. | last = Zwicky
| journal = Proceedings of the National Academy of Sciences
| volume = 25
|date=December 1939
| issue = 12
| pages = 604–609
| bibcode = 1939PNAS...25..604Z
| doi = 10.1073/pnas.25.12.604
| pmid = 16588306 | pmc = 1077981
}}. Zwicky sosté que la forma de les nebuloses indica un univers molt més antic del que es pot explicar per un model d'univers en expansió.

* {{Citation
| title = A Mosaic Objective Grating for the 18-inch Schmidt Telescope on Palomar Mountain
| first = F. | last = Zwicky
| journal = Publications of the Astronomical Society of the Pacific
| volume = 53
|date=August 1941
| pages = 242–244
| bibcode = 1941PASP...53..242Z
| doi = 10.1086/125331
}}. Zwicky was a great advocate for the use of the wide angle Schmidt telescope, which he used to great effect to make many discoveries.
*{{Citation | last = Zwicky | first = F. | title = Report on certain phases of war research in Germany | publisher = Aerojet Engineering Corp | date = 1945 | url = https://www.amazon.com/Report-certain-phases-research-Germany/dp/B0007FJ1YY/ref=sr_1_13/103-8097003-4392634?ie=UTF8&s=books&qid=1184050104&sr=1-13 }}. Zwicky did work on jet propulsion and other matters with Aerojet corporation during and after the war.
*{{Citation | last = Zwicky | first = F. | title = Morphological astronomy | publisher = Springer-Verlag | date = 1957 | url = https://www.amazon.com/Morphological-astronomy-F-Zwicky/dp/B0006AVA3K/ref=sr_1_10/103-8097003-4392634?ie=UTF8&s=books&qid=1184050104&sr=1-10 }}. In this book Zwicky gives free rein to his ideas on morphological research as a tool for making discoveries in astronomy.
* {{Citation
| title = Nuclear Goblins and Flare Stars
| first = F. | last = Zwicky
| journal = Publications of the Astronomical Society of the Pacific
| volume = 70
|date=October 1958
| pages = 506–508
| bibcode = 1958PASP...70..506Z
| doi = 10.1086/127284
}}. As well as proposing neutron stars, Zwicky also proposed unstable aggregations of neutron density matter within larger stars.
*{{Citation | last = Zwicky | first = F. | title = Entdecken, Erfinden, Forschen im Morphologischen Weltbild | publisher = Droemer Knaur | date = 1966 }}
*{{Citation | last = Zwicky | first = F. | title = Discovery, invention, research through the morphological approach | publisher = MacMillan | date = 1969 | url = https://www.amazon.com/Discovery-invention-research-morphological-approach/dp/B0006BYL8U/ref=sr_1_5/103-8097003-4392634?ie=UTF8&s=books&qid=1184050104&sr=1-5 }}. Zwicky also proposed that the morphological approach could be applied to all kinds of issues in disciplines going far beyond basic science.


-->
==Referències==
{{Referències|30em}}


== Vegeu també ==
== Vegeu també ==
Línia 11: Línia 288:
* [[I Zwicky 18]]
* [[I Zwicky 18]]


== Enllaços externs ==
{{Commonscat}}
{{Commonscat}}
{{Wikiquote}}
* {{Citation | title = Fritz Zwicky | first = T. | last = Ritchey | url = http://www.swemorph.com/zwicky.html | accessdate = 2007-07-10}}
* {{Citation | url = http://www.slac.stanford.edu/pubs/beamline/31/1/31-1-maurer.pdf |format=PDF| title = Idea Man | first = S.M. | last = Maurer | journal = Beamline | date = 2001 | volume = 31 | issue = 1 | accessdate = 2007-07-10}}
* {{Citation | url = http://www.dynamical-systems.org/zwicky/Zwicky-e.html | accessdate = 2007-07-10 | title = Supernovae, an alpine climb and space travel (biographical notes) | last = Knill | first = O. | date = 1998 }}
* [http://www.zwicky-stiftung.ch/index.php?p=15|27|28|28&url=/Publikationen/Liste.htm Fritz Zwicky foundation (in German)]
* [http://www.pnas.org/content/12/2.toc Proc Natl Acad Sci]
* [http://www.learner.org/courses/physics/unit/text.html?unit=10&secNum=2 Initial Evidence of Dark Matter — Annenberg Learner]


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Revisió del 16:55, 22 març 2019

Infotaula de personaFritz Zwicky

Modifica el valor a Wikidata
Biografia
Naixement14 febrer 1898 Modifica el valor a Wikidata
Varna (Bulgària) Modifica el valor a Wikidata
Mort8 febrer 1974 Modifica el valor a Wikidata (75 anys)
Pasadena (Califòrnia) Modifica el valor a Wikidata
SepulturaMollis, Friedhof Glarus 47° 02′ 22″ N, 9° 03′ 51″ E / 47.039388°N,9.064287°E / 47.039388; 9.064287 Modifica el valor a Wikidata
Dades personals
ReligióAteisme Modifica el valor a Wikidata
FormacióETH Zürich (1916–1922) Modifica el valor a Wikidata
Director de tesiPeter Debye i Paul Scherrer Modifica el valor a Wikidata
Activitat
Camp de treballAstrofísica Modifica el valor a Wikidata
Ocupacióastrònom, professor d'universitat, físic, astrofísic Modifica el valor a Wikidata
OcupadorInstitut Tecnològic de Califòrnia (1927–1968) Modifica el valor a Wikidata
Membre de
Obra
Localització dels arxius
Premis
Find a Grave: 70298529 Modifica el valor a Wikidata
Placa commemorativa de Fritz Zwicky

Fritz Zwicky (14 de febrer de 1898 - 8 de febrer de 1974) va ser un astrònom i físic europeu emigrat als EUA.

Va néixer a Varna, Bulgària, el 1898. Estudià a Zuric on va rebre el seu doctorat per part de l'Escola Politècnica Federal de Zuric; posteriorment, el 1925, es traslladà als Estats Units per treballar al Caltech (California Institute of Technology), on va romandre fins a 1972. El 1934 al costat de Walter Baade, va proposar que les supernoves són una classe d'explosions estel·lars completament diferents a les noves. Va morir a Pasadena, Califòrnia (EUA), el 8 de febrer de 1974.

Va conduir una àmplia investigació de les galàxies veïnes mitjançant les supernoves i en va descobrir 18; només al voltant de 12 havien estat registrades prèviament en tota la història de l'astronomia. Entre els anys 1943 i 1946, al costat de Theodore von Kármán i d'altres, va ajudar a desenvolupar els primers sistemes d'enlairament assistit per reactors. 

by himself (and one more, SN 1963J, in concert with Paul Wild) over 52 years (SN 1921B through SN 1973K),[1] 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.[2] It was not until 1979 that this effect was confirmed by observation of the so-called "Twin Quasar" Q0957+561.[3]

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'.[4] 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.[5]

Tired light

Plantilla:Main article

When Edwin Hubble discovered a somewhat linear relationship between the distance to a galaxy and its redshift expressed as a velocity,[6] 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.[7]

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.[8] Cosmological redshift is now conventionally understood to be a consequence of the expansion of space; a feature of Big Bang cosmology.[9]

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.[10] He wrote a book on the subject in 1969,[11] and claimed that he made many of his discoveries using this method.

Catalog of Galaxies and Clusters

Plantilla:Main article 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

Galaxies in the original catalog are called Zwicky galaxies, and the catalog is still maintained and updated today.[12] 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:[13]

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.[14] 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.[15]

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".[16] Zwicky later admitted that he had been mistaken.

He was also very proud of his work in producing the first artificial meteors.[17] 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.[13]

Zwicky also considered the possibility of rearranging the universe to our own liking. In a lecture in 1948[18] 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.[19]

Humanitarian

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.[20][21]

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.[20]

Zwicky loved the mountains, and was an accomplished alpine climber.[13]

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.[22][23]

Honors

Publicacions

Zwicky va produir centenars de publicacions durant una llarga carrera, cobrint un ampli ventall de temes. Aquesta breu selecció, amb comentaris, dóna una idea del seu treball.


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Referències

  1. ↑ List of Supernovae, <http://cbat.eps.harvard.edu//lists/Supernovae.html>. Consulta: 10 juliol 2007 (provided by CBAT)
  2. ↑ Zwicky, F. (February 1937), "Nebulae as Gravitational Lenses", Physical Review 51 (4): 290, doi:10.1103/PhysRev.51.290, <http://authors.library.caltech.edu/5611/>
  3. ↑ 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, doi:10.1038/279381a0, <http://www.nature.com/physics/looking-back/walsh/index.html>
  4. ↑ Error de citació: Etiqueta <ref> no vàlida; no s'ha proporcionat text per les refs nomenades Zwicky 1933 110–127
  5. ↑ 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, <http://spiff.rit.edu/classes/phys440/lectures/gal_clus/gal_clus.html>. Consulta: 10 juliol 2007.
  6. ↑ 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, DOI 10.1073/pnas.15.3.168
  7. ↑ Zwicky, F. (1929), "On the Red Shift of Spectral Lines through Interstellar Space", Proceedings of the National Academy of Sciences 15 (10): 773–779, DOI 10.1073/pnas.15.10.773 (full article)
  8. ↑ Baade, W. (1956), "The Period-Luminosity Relation of the Cepheids", Publications of the Astronomical Society of the Pacific 68 (400): 5–16, DOI 10.1086/126870
  9. ↑ Singh, S. (2004), Big Bang, Fourth Estate, <http://www.simonsingh.net/Big_Bang.html>
  10. ↑ Ritchey, T. (2002), General Morphological Analysis: A General Method for Non-Quantified Modelling, <http://www.swemorph.com/pdf/gma.pdf>. Consulta: 10 juliol 2007
  11. ↑ Zwicky, F. (1969), Discovery, Invention, Research Through the Morphological Approach, Toronto: The Macmillan Company, <https://www.amazon.com/Discovery-invention-research-morphological-approach/dp/B0006BYL8U>
  12. ↑ The Updated Zwicky Catalog of Galaxies (UZC), <http://tdc-www.harvard.edu/uzc/>. Consulta: 10 juliol 2007 at the Harvard-Smithsonian Center for Astrophysics.
  13. ↑ 13,0 13,1 13,2 Maurer, S.M. (2001), "Idea Man", Beamline 31 (1), <http://www.slac.stanford.edu/pubs/beamline/31/1/31-1-maurer.pdf>. Consulta: 10 juliol 2007
  14. ↑ Zwicky, F. (October 1958), "Nuclear Goblins and Flare Stars", Publications of the Astronomical Society of the Pacific 70: 506–508, DOI 10.1086/127284
  15. ↑ Knill, O. (1998), Supernovae, an alpine climb and space travel (biographical notes), <http://www.dynamical-systems.org/zwicky/Zwicky-e.html>. Consulta: 10 juliol 2007
  16. ↑ «Pionniers & Précurseurs - FRANK J. MALINA - AERONAUTIQUE - MEMOIRES SCIENTIFIQUES - 2E TOME». olats.org.
  17. ↑ Zwicky, F. (August 1946), "On the Possibility of Earth-Launched Meteors", Publications of the Astronomical Society of the Pacific 58: 260–261, DOI 10.1086/125840
  18. ↑ Zwicky, F. (August 1948), "Morphological astronomy", The Observatory 68: 121–143
  19. ↑ Zwicky, F. (1966), "Entdecken, Erfinden, Forschen im morphologischen Weltbild", Muenchen: Droemer (Muenchen) (page 237). This reference was identified from a footnote provided in an online essay: Knill, Oliver (November 1997), Moving the Solar System, <http://www.dynamical-systems.org/zwicky/Essay.html>. Consulta: 17 juliol 2007.
  20. ↑ 20,0 20,1 20,2 Greenstein, J.L. (March–April 1974), "Fritz Zwicky – Scientific Eagle (obituary)", Engineering and Science: 15–19, <http://www.swemorph.com/pdf/greenstein.pdf>. Consulta: 14 juliol 2007
  21. ↑ Fritz Zwicky's Extraordinary Vision, American Museum of Natural History, <http://www.amnh.org/education/resources//rfl/web/essaybooks/cosmic/p_zwicky.html>. Consulta: 16 juliol 2007, an extract from Soter, S. & Tyson, N.D. (2000), Cosmic Horizons: Astronomy at the Cutting Edge, New Press, ISBN 978-1565846029
  22. ↑ Zwicky, F. (November 1949), "Free World Agents of Democracy", Engineering and Science 13 (2), <http://calteches.library.caltech.edu/306/01/zwicky.pdf>
  23. ↑ Wilson, A. (1975), "Fritz Zwicky (obituary)", Quarterly Journal of the Royal Astronomical Society 16: 106–108
  24. ↑ Meeting of the Royal Astronomical Society, February 1972, <http://www.zwicky-stiftung.ch/Publikationen/Award.pdf>. Consulta: 14 juliol 2007
  25. ↑ «Zwicky Transient Facility Opens Its Eyes to the Volatile cosmos». Zwicky Transient Facility, November 14, 2017.

Vegeu també

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