Superseded scientific theories

A superseded, or obsolete, scientific theory is a scientific theory that mainstream scientific consensus once commonly accepted but now no longer considers the most complete description of reality, or considers to be simply false. This label does not cover protoscientific or fringe science theories with limited support in the scientific community. Also, it does not mean theories that were never widely accepted. Some theories that were only supported under specific political authorities, such as Lysenkoism, may also be described as obsolete or superseded.

In some cases a theory or idea is found baseless and is simply discarded. For example, the phlogiston theory was entirely replaced by the quite different concept of energy and related laws. In other cases an existing theory is replaced by a new theory that retains significant elements of the earlier theory; in these cases, the older theory is often still useful for many purposes, and may be more easily understood than the complete theory and lead to simpler calculations. An example of this is the use of Newtonian physics, which differs from the currently accepted relativistic physics by a factor that is negligibly small at velocities much lower than that of light. All of Newtonian physics is so satisfactory for most purposes that it is more widely used except at velocities that are a significant fraction of the speed of light, and simpler Newtonian but not relativistic mechanics is usually taught in schools. Another case is the theory that the earth is approximately flat; while it has for centuries been known to be wrong for long distances, considering part of the earth's surface as flat is usually sufficient for many maps covering areas that are not extremely large, and surveying.

The obsolete Geocentric model of the universe places the Earth at the centre.

Superseded theories

Biology

• Spontaneous generation - is a principle regarding the spontaneous generation of complex life from inanimate matter, which held that this process was a commonplace and everyday occurrence, as distinguished from univocal generation, or reproduction from parent(s). Falsified by an elegant experiment by Louis Pasteur—where apparently spontaneous generation of microorganisms occurred, it did not happen on repeating the process without access to unfiltered air; on then opening the apparatus to the atmosphere, bacterial growth started.
• Transmutation of species, Lamarckism, inheritance of acquired characteristics - first theories of evolution. Not supported by experiment, and rendered obsolete by Darwinian evolution, Mendelian genetics and epigenetics (although some elements of Lamarckian evolution are coming back in the area of epigenetics).
• Mendelian genetics, classical genetics, Boveri–Sutton chromosome theory - first genetical theories. Not invalidated as such, but subsumed into molecular genetics.
• Maternal impression – the theory that the mother's thoughts created birth defects. No experimental support (a notion rather than a theory), and rendered obsolete by genetic theory (see also fetal origins of adult disease, genomic imprinting)
• Miasma theory of disease – the theory that diseases are caused by "bad air". No experimental support, and rendered obsolete by the germ theory of disease.
• Preformationism – the theory that all organisms have existed since the beginning of life, and that gametes contain a miniature but complete preformed individual. No support when microscopy became available. Rendered obsolete by cytology, discovery of DNA, and atomic theory.
• Recapitulation theory – the theory that "ontogeny recapitulates phylogeny". See Baer's laws of embryology.
• Telegony – the theory that an offspring can inherit characteristics from a previous mate of its mother's as well as its actual parents, often associated with racism.
• Vitalism – the theory that living things are alive because of some "vital force" independent of nonliving matter, as opposed to because of some appropriate assembly of nonliving matter. It was gradually discredited by the rise of organic chemistry, biochemistry, and molecular biology, fields that failed to discover any "vital force". Friedrich Wöhler's synthesis of urea from ammonium cyanate was only one step in a long road, not a great refutation.
• Out of Asia theory of human origin – The majority view is of a recent African origin of modern humans, although a multiregional origin of modern humans hypothesis has much support (which incorporates past evidence of Asian origins)

Chemistry

• Caloric theory - the theory that a self-repelling fluid called "caloric" was the substance of heat. Rendered obsolete by the mechanical theory of heat.
• Classical elements - All matter was once thought to be composed of various combinations of classical elements (most famously air, earth, fire, and water). This was finally refuted by Antoine Lavoisier's publication of Elements of Chemistry, which contained the first modern list of chemical elements, in 1789.
• Phlogiston theory – The theory that combustible goods contain a substance called "phlogiston" which entered air upon combustion. Replaced by Lavoisier's work on oxidation
• Point 2 of Dalton's Atomic Theory was obsoleted by discovery of isotopes, and point 3 by discovery of subatomic particles and nuclear reactions.
• Vitalism - See section on biology.

Physics

• Emission theory of vision – discredited by Ibn al-Haytham (Alhacen)
• Aristotelian physics – superseded by Newtonian physics
• Ptolemy's law of refraction, replaced by Snell's law
• Luminiferous aether – failed to be detected by the sufficiently sensitive Michelson-Morley experiment, made obsolete by Einstein's work.
• Caloric theory – Lavoisier's successor to phlogiston, discredited by Rumford's and Joule's work
• Contact tension - a theory on the source of electricity
• Vis viva – Gottfried Leibniz's elementary and limited early formulation of the principle of conservation of energy
• "Purely electrostatic" theories of the generation of voltage differences.
• Emitter theory – another now-obsolete theory of light propagation.
• Progression of atomic theory

• Democritus, the originator of atomic theory, held that everything is composed of atoms, which are indestructible
• John Dalton's model of the atom, which held that atoms are indivisible and indestructible (superseded by nuclear physics) and that all atoms of a given element are identical in mass (superseded by discovery of atomic isotopes).
• Plum pudding model of the atom—assuming the protons and electrons were mixed together in a single mass
• Rutherford model of the atom with an impenetrable nucleus orbited by electrons
• Bohr model with quantized orbits
• Electron cloud model following the development of quantum mechanics in 1925 and the eventual atomic orbital models derived from the quantum mechanical solution to the hydrogen atom

• All of classical physics, including Newtonian physics, superseded by relativistic physics and quantum physics. However, classical physics is a limiting case of the latter two theories, and it is often a very good approximation.

Astronomy and cosmology

• Ptolemaic system – replaced by Nicolaus Copernicus' Heliocentric model.
• Geocentric universe – made obsolete by Copernicus
• Heliocentric universe – made obsolete by discovery of the structure of the Milky Way. Heliocentrism only applies to the Solar System, and only approximately, since the Sun's center is not at the Solar System's center of mass.
• Copernican system – made obsolete by Johannes Kepler and Isaac Newton
• Newtonian gravity – superseded by general relativity, to which it is an excellent approximation unless typical speeds approach that of light in a vacuum (c). The anomalous perihelion precession of Mercury was the first observational evidence that Newtonian gravity was not totally accurate.
• Luminiferous aether theory
• Steady State Theory, a model developed by Hermann Bondi, Thomas Gold, and Fred Hoyle whereby the expanding universe was in a steady state, and had no beginning. It was a competitor of the Big Bang model until evidence supporting the Big Bang and falsifying the steady state was found.

Geography and climate

• Flat Earth theory. On length scales much smaller than the radius of the Earth, a flat map projection gives a quite accurate and practically useful approximation to true distances and sizes, but departures from flatness become increasingly significant over larger distances.
• Terra Australis
• Hollow Earth theory
• The Open Polar Sea, an ice-free sea once supposed to surround the North Pole
• Rain follows the plow – the theory that human settlement increases rainfall in arid regions (only true to the extent that crop fields evapotranspirate more than barren wilderness)
• Island of California – the theory that California was not part of mainland North America but rather a large island

Geology

• Abiogenic petroleum origin
• Catastrophism was largely replaced by uniformitarianism
• Flood geology replaced by modern geology and stratigraphy
• Neptunism replaced by plutonism
• The following were superseded by plate tectonics:
  • Expanding Earth theory (superseded by subduction)
  • Geosyncline theory
  • The theory of continental drift was incorporated into and improved upon by plate tectonics

Psychology

• Pure behaviorist explanations for language acquisition in infancy, falsified by the study of cognitive adaptations for language.

Medicine

• Theory of the four bodily humours (see also Four temperaments)
• Eclectic Medicine – Transformed into alternative medicine, and is no longer considered a scientific theory.
• Physiognomy, related to phrenology, held that inner character was strongly correlated with physical appearance.

Obsolete branches of enquiry

• Alchemy, which led to the development of chemistry
• Astrology, which led to the development of astronomy
• Phrenology, a pseudoscience
• Numerology, a pseudoscience

Theories now considered incomplete

Here are theories that are no longer considered the most complete representation of reality, but are still useful in particular domains or under certain conditions. For some theories a more complete model is known, but in practical use the coarser approximation provides good results with much less calculation.

• Atomic nuclei disintegrate at high energy.
• Newtonian mechanics was extended by the theory of relativity and by quantum mechanics. Relativistic corrections to Newtonian mechanics are unmeasurably small at velocities not approaching the speed of light, and quantum corrections are usually negligible at atomic or larger scales; Newtonian mechanics is totally satisfactory in engineering and physics under most circumstances.
• Classical electrodynamics is a very close approximation to quantum electrodynamics except at very small scales and low field strengths.
• Bohr model of the atom was extended by the quantum mechanical model of the atom.
• The formula known as Newton's sine-square law of air resistance for the force of a fluid on a body, though not actually formulated by Newton but by others using a method of calculation used by Newton, has been found incorrect and not useful except for high-speed hypersonic flow.

See also

• Scientific theory
• Philosophy of science
• Protoscience
• Fringe science
• Pathological science
• Paradigm shift
• History of evolutionary thought
• Creation–evolution controversy

Lists

• List of discredited substances
• List of famous discoveries
• List of famous experiments
• List of topics characterized as pseudoscience