1900 in science
- Richard Dixon Oldham distinguishes between primary, secondary and tertiary waveforms as recorded by seismometers.
- American explorer Robert Peary first sights Kaffeklubben Island, the northernmost point of land on Earth.
- Max Dehn introduces two examples of Dehn plane and the Dehn invariant.
- David Hilbert states his list of 23 problems which show where some further mathematical work is needed.
- Russell's paradox is first discovered by Ernst Zermelo but he does not publish it, and it is known only to Hilbert, Husserl and other members of the University of Göttingen.
- Gaston Tarry confirms Euler's conjecture that no 6×6 orthogonal Graeco-Latin square is possible.
- Alfred Young introduces the Young tableau.
- Hermann Johannes Pfannenstiel, best remembered for the eponymous "Pfannenstiel's incision", a transverse incision used in genitourinary surgery that is still widely used today, published his paper in 1900 when he described "Pfannenstiel incision".
- Barnum Brown finds the first partial skeleton of Tyrannosaurus rex in eastern Wyoming.
- Dr. James K. Hampson identifies the Island 35 Mastodon skeleton in the Mississippi River.
- April 26 – Guglielmo Marconi patents the tuned circuit.
- October 19 – Max Planck produces Planck's law of black-body radiation and Planck constant, marking the birth of quantum physics.
- December 7 – Max Planck states his quantum hypothesis.
- December 23 – Reginald Fessenden, experimenting with a high-frequency spark transmitter, successfully transmits speech over a distance of about 1.6 kilometers (one mile), from Cobb Island, Maryland, which appears to have been the first audio radio transmission.
- Gamma rays discovered by Paul Villard while studying uranium decay.
- Karl Landsteiner makes the first discovery of blood types, identifying the ABO blood group system.
- Carl Rasch coins the term 'polymorphous light eruption'.
- Jokichi Takamine and Keizo Uenaka discover adrenaline.
- March 9 – Howard H. Aiken (died 1973), American computing pioneer.
- March 19 – Frédéric Joliot (died 1958), French physicist.
- April 25 – Wolfgang Pauli (died 1958), Austrian-born physicist.
- April 26 – Charles Richter (died 1985), American geophysicist and inventor.
- April 28 – Jan Oort (died 1992), Dutch astronomer.
- May 22 – Honor Fell (died 1986), English biologist.
- June 24 – Wilhelm Cauer (killed 1945), German mathematician and electronic engineer.
- July 9 – Frances McConnell-Mills, born Frances Mary McConnell (died 1975), American toxicologist.
- August 25 – Hans Adolf Krebs (died 1981), German-born medical doctor and biochemist.
- August 26 – Hellmuth Walter (died 1980), German-born engineer and inventor.
- December 9 – Joseph Needham (died 1995), English biochemist and writer on the history of science and technology in China.
- December 12 – Mária Telkes (died 1995), Hungarian-American scientist and inventor
- Ernest Gibbins (killed 1942), English entomologist.
- January 13 – Peter Waage (born 1833), Norwegian chemist.
- January 22 – David E. Hughes (born 1831), British-American inventor.
- March 6 – Gottlieb Daimler (born 1834), German engineer, automotive pioneer.
- March 10 – George James Symons (died 1838), English meteorologist.
- April 1 – George Jackson Mivart (born 1827), English biologist.
- August 4 – Étienne Lenoir (born 1822), Belgian mechanical engineer.
- August 31 – John Bennet Lawes (born 1814), English agricultural scientist.
- October 16 – Henry Acland (born 1815), English physician.
- October 29 – Bruno Abakanowicz (born 1852), Polish mathematician, inventor and electrical engineer.
- Grout, Andrew (2004). "Oldham, Richard Dixon (1858–1936)". Oxford Dictionary of National Biography. Oxford University Press. doi:10.1093/ref:odnb/37820. Retrieved 2011-10-20. (subscription or UK public library membership required)
- De Vries, H. (1900). "Sur la loi de disjonction des hybrides". Comptes rendus de l'Académie des sciences. Paris. 130: 845–847.
- "From Latin Squares to Sudoku:A History of Magic Numbers". Archived from the original on 2008-10-01.
- "36 Officer Problem". Archived from the original on 2008-08-28.
- Tarry, Gaston (1900). "Le Probléme de 36 Officiers". Compte Rendu de l'Association Française pour l'Avancement des Sciences. Secrétariat de l'Association. 1: 122–123.
- Tarry, Gaston (1901). "Le Probléme de 36 Officiers". Compte Rendu de l'Association Française pour l'Avancement des Sciences. Secrétariat de l'Association. 2: 170–203.
- Planck, M. (1900). "Über eine Verbesserung der Wien'schen Spectralgleichung". Verhandlungen der Deutschen Physikalischen Gesellschaft. 2: 202–204. Translated in ter Haar, D. (1967). "On an Improvement of Wien's Equation for the Spectrum". The Old Quantum Theory (PDF). Pergamon Press. pp. 79–81. LCCN 66029628.
- Planck, M. (1900). "Zur Theorie des Gesetzes der Energieverteilung im Normalspectrum". Verhandlungen der Deutschen Physikalischen Gesellschaft. 2: 237–245. Translated in ter Haar, D. (1967). The Old Quantum Theory (PDF). Pergamon Press. p. 82. LCCN 66029628.
- Landsteiner, K. (1900). "Zur Kenntnis der antifermentativen, lytischen und agglutinierenden Wirkungen des Blutserums und der Lymphe". Zentralblatt für Bakteriologie. 27: 357–62.
- Yamashima, T. (2003). "Jokichi Takamine (1854–1922), the samurai chemist, and his work on adrenalin". Journal of Medical Biography. 11 (2): 95–102. PMID 12717538.
- Bennett, M. (1999). "One hundred years of adrenaline: the discovery of autoreceptors". Clinical Autonomic Research. 9 (3): 145–59. doi:10.1007/BF02281628. PMID 10454061.
- "Richard J. Ussher and "The Birds of Ireland"". Ask about Ireland. Retrieved 2012-10-04.