1923 in science

Aeronautics

• January 17 – First stable flight of the first rotorcraft, Juan de la Cierva's Cierva C.4 autogyro, in Spain.

Astronomy and space science

• June – Hermann Oberth publishes Die Rakete zu den Planetenräumen.
• October 21 – First official public showing of a planetarium projector, a Zeiss model at the Deutsches Museum in Munich.

Biology

• March 23 – The governor of Oklahoma signs House Bill 197 with the Montgomery amendment outlawing the theory of evolution in public school textbooks purchased by the state, the first anti-Darwinian legislation passed in the United States.
• Karl von Frisch publishes "Über die 'Sprache' der Bienen. Eine tierpsychologische Untersuchung".

Chemistry

• Dirk Coster and George de Hevesy publish their discovery of the transition metal element hafnium in zirconium ore, working in Copenhagen.
• Niels Bohr and Dirk Coster, working in Copenhagen, produce a paper on X-ray spectroscopy and the periodic system of the elements.
• Gilbert N. Lewis and Merle Randall's textbook Thermodynamics and the Free Energy of Chemical Reactions is influential in the replacement of the concept of chemical affinity by free energy.

Cryptography

• Enigma machine first produced commercially.

Electronics

• Otto Julius Zobel of Bell Labs describes the type of signal processing filter sections based on the image impedance design principle which will become known as Zobel networks.
• December 29 – Vladimir K. Zworykin files his first patent for "television systems".

Exploration

• Tanager Expedition.

Medicine

• February – The Maudsley Hospital, established jointly by the London County Council and Henry Maudsley, admits its first psychiatric patients.
• Capgras delusion, a delusional misidentification syndrome, is first described by Joseph Capgras.
• First diphtheria vaccine by Gaston Ramon, Emil von Behring and Kitasato Shibasaburō.

Paleontology

• July 13 – An American Museum of Natural History expedition to Mongolia under Roy Chapman Andrews is the first in the world to discover fossil dinosaur eggs. Initially thought to belong to the ceratopsian Protoceratops, they are determined in 1995 actually to belong to the theropod Oviraptor. On August 11 Peter Kaisen recovers the first Velociraptor fossil known.

Physics

• Arthur Eddington publishes the textbook The Mathematical Theory of Relativity in Cambridge.

Technology

• Herbert Grove Dorsey invents the first practical fathometer.

Awards

• Nobel Prizes
• * Physics: Robert Andrews Millikan
• * Chemistry: Fritz Pregl
• * Medicine: Frederick Banting and John Macleod
• Copley Medal: Horace Lamb
• Wollaston Medal for Geology: William Whitaker

Births

• January 1 – Daniel Gorenstein, American mathematician.
• January 11 – Robert J. Gorlin, American pathologist.
• February 13 – Chuck Yeager, American pilot.
• February 14 – Doris Calloway, née Howes, American nutritionist.
• February 20 – Helen Murray Free, American medical chemist.
• March 4 – Patrick Moore, English astronomer.
• March 9 – Walter Kohn, Viennese-born physicist.
• March 10 – Val Logsdon Fitch, American nuclear physicist, recipient of the Nobel Prize in Physics.
• April 1 – Brigitte Askonas, Viennese-born British immunologist.
• April 2 – G. Spencer-Brown, English mathematician.
• April 16 – Stewart Adams, English pharmaceutical chemist.
• April 21 – Albert C. Perdeck, Dutch ornithologist.
• April 23 – Walter Pitts, American logician and cognitive psychologist.
• July 5 – Ivo Pitanguy, Brazilian plastic surgeon.
• July 12 – René Favaloro, Argentine cardiac surgeon.
• July 23 – Ulf Grenander, Swedish-born mathematician.
• July 28 – Xia Peisu, Chinese computer scientist.
• July 31 – Stephanie Kwolek, American polymer chemist.
• August 19 – Edgar F. Codd, English-born computer scientist.
• September 9 – Daniel Carleton Gajdusek, American virologist.
• September 13 – Miroslav Holub, Czech immunologist and poet.
• September 26 – John Ertle Oliver, American geophysicist.
• October 29 – Carl Djerassi, Viennese-born chemist.
• November 8 – Jack Kilby, American electrical engineer, recipient of the Nobel Prize in Physics.
• November 18 – Alan Shepard, American astronaut.
• December 13 – Philip Warren Anderson, American physicist, recipient of the Nobel Prize in Physics.
• December 15 – Freeman Dyson, English-born theoretical physicist.

Deaths

• February 10 – Wilhelm Röntgen, German physicist, discoverer of X-rays, Nobel laureate.
• February 24 – Edward Morley, American chemist.
• March 8 – Johannes Diderik van der Waals, Dutch physicist.
• March 27 – James Dewar, Scottish-born chemist.
• April 11 – Mary Treat, American naturalist.
• July 16 – Sydney Mary Thompson, Irish-born geologist and botanist.
• August 23 – Hertha Ayrton, English electrical engineer.
• October 3 – Kadambini Ganguly, Indian physician.
• December 2 – Henry Haversham Godwin-Austen, English surveyor, geologist and naturalist.
• December 7 – Sir Frederick Treves, English-born surgeon.
• December 27 – Gustave Eiffel, French structural engineer.