In science, a defunct theory is a theory that has become obsolete, disproved, irrelevant, non-functional, superseded, and or replaced by a newer theory, generally owing to newer insights and or scientific discoveries that invalidate the former.

The following are noted defunct theories:

Superseded by
Disproved byComment

Nature abhors a vacuum
Nearly perfect vacuums can exist (although some contend that recent particle physics theories abrogate this view)
Galileo Galilei
Evangelista Torricelli
Blaise Pascal
Otto Guericke

Sulphur principle1524-c.1669Terra pinguis theoryc.1669Johann Becher
Terra pinguis theory1669-1703Phlogiston theory1697-1703Georg Stahl
Phlogiston theory1703-1787Caloric theory1768-1787Antoine Lavoisier
Matter (fermions), energy (force) (bosions), vacuum, and laws (of the universe) defining their operations.1802Pierre Laplace Comment (to Napoleon): “I had no need of that hypothesis.” See: Napoleon Laplace anecdote
Free will
Affinities, exchange force, readiness potential, induced movement, etc.1799-1809Johann Goethe Comment: “None are so hopelessly enslaved than those who believe they are free.” (c.1809); see Elective Affinities.
Caloric theory1787-c.1824Heat as motion, mechanical equivalent of heat, kinetic theory, entropy, photon, Bohr model, retinal molecule model (of movement)
1798-1865Benjamin Thompson
Humphry Davy

(life force)
(although derivatives remained)
Physical-chemical explanations (although the origin of life issue remained, i.e. "life" vs. "non-life" divide or gap).1828-early 20th centuryEmil Reymond
Ernst Brücke
Hermann Helmholtz
See: Helmholtz school and the 1842 Reymond-Brucke oath.
Space-time; relativity.1905Albert Einstein
Origin of life18th century up into 1916 (and further)There is no origin.1916William Sidis Summary: “Our theory of the origin of life is that there is no origin, but only a constant development and change in form.”
Life3100BC-2009Defunct theory of life1925-ongoing Nikola Tesla
Libb Thims

Further reading
● Bothamley, Jennifer. (2002). Dictionary of Theories: One Stop to more than 5,000 Theories. Visible Ink Press.

External links
Defunct theories (quiz) –
Superseded scientific theories – Wikipedia.
Obsolete scientific theories (category) – Wikipedia.

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