Scientists beginning with "O"
- Obreimov, Ivan Vasilyevich — (8.03.1894—2.12.981) was a Soviet experimental physicist and an academician (1958; corresponding member 1933).
- Occhialini, Giuseppe Stanislao — (born 5.03.1907) is an Italian physicist and a member of the Accademia dei Lincei (1958).
- Ohm, Georg Simon — (16.03.1787-6.07.1854) was a German physicist, a corresponding member of the Berlin Academy of Sciences (1839).
- Okubo, Susumu — (born 22.02.1930) is a Japanese theoretical physicist.
- Okun, Lev Borisovich — (born 7.07.1929) is a Soviet theoretical physicist and a corresponding member of the USSR Academy of Sciences (1966).
- Oliphant, Marcus Laurence Elwin — (born 8.10.1901) is an Australian physicist and a member of the Australian Academy of Science, of which he was president in 1954 — 57.
- Olszewski, Karol — (29.01.1846-24.03.1915) was a Polish physicist and chemist and a member of the Polish Academy of Sciences (1888).
- Onsager, Lars — (27.02.1903-5.10.1976) was an American chemist and physicist, one of the creators of non-equilibrium thermodynamics, a member of the National Academy of Sciences (1947).
- Oppenheimer, Robert — (22.04.1904-20.02.1967) was an American theoretical physicist, a member of the National Academy of Sciences (1941).
- Ørsted, Hans Christian — (14.08.1777-9.03.1851) was a Danish physicist and, from 1815, permanent secretary of the Royal Danish Society.
- Osipyan, Yuri Andreyevich — (born 15.02.1931) is a Soviet physicist, an academician (1981, corresponding member 1972).
- Ostrogradsky, Mikhail Vasilyevich — (24.09.1801-1.01.1862) was a Russian mathematician and mechanician, a member of the St Petersburg Academy of Sciences (1830).
- Ostwald, Wilhelm Friedrich — (2.09.1853 —4.04.1932) was a German physical chemist and idealist philosopher, a corresponding member of the Berlin Academy of Sciences (1905).