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	~~{{pp-semi-vandalism\|small=yes}}~~
	~~{{Unreferenced\|date=January 2008}}~~
	'''Theoretical physics''' is a branch of [[physics]] which employs [[mathematical model]]s and [[abstraction]]s of [[physics]] in an attempt to explain natural phenomena. Its central core is [[mathematical physics]],<ref group=note>Sometimes ''mathematical physics'' and ''theoretical physics'' are used synonymously to refer to the latter.</ref> though other conceptual techniques are also used. The goal is to rationalize, explain and predict physical [[phenomenon\|phenomena]]. The advancement of [[science]] depends in general on the interplay between [[experiment]]al studies and [[theory]]. In some cases, theoretical physics adheres to standards of [[Rigour#Mathematical rigour\|mathematical rigor]] while giving little weight to experiments and observations. For example, while developing [[special relativity]], [[Albert Einstein]] was concerned with the [[Lorentz transformation]] which left [[Maxwell's equations]] invariant, but was apparently uninterested in the [[Michelson-Morley experiment]] on [[Earth\|Earth's]] drift through a [[luminiferous aether\|luminiferous ether]]. On the other hand, Einstein was awarded the [[Nobel Prize]] for explaining the [[photoelectric effect]], previously an experimental result lacking a theoretical formulation.		'''Theoretical physics''' is a branch of [[physics]] which employs [[mathematical model]]s and [[abstraction]]s of [[physics]] in an attempt to explain natural phenomena. Its central core is [[mathematical physics]],<ref group=note>Sometimes ''mathematical physics'' and ''theoretical physics'' are used synonymously to refer to the latter.</ref> though other conceptual techniques are also used. The goal is to rationalize, explain and predict physical [[phenomenon\|phenomena]]. The advancement of [[science]] depends in general on the interplay between [[experiment]]al studies and [[theory]]. In some cases, theoretical physics adheres to standards of [[Rigour#Mathematical rigour\|mathematical rigor]] while giving little weight to experiments and observations. For example, while developing [[special relativity]], [[Albert Einstein]] was concerned with the [[Lorentz transformation]] which left [[Maxwell's equations]] invariant, but was apparently uninterested in the [[Michelson-Morley experiment]] on [[Earth\|Earth's]] drift through a [[luminiferous aether\|luminiferous ether]]. On the other hand, Einstein was awarded the [[Nobel Prize]] for explaining the [[photoelectric effect]], previously an experimental result lacking a theoretical formulation.

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	*[http://www.phys.uu.nl/~thooft/theorist.html How to Become a Theoretical Physicist by a Nobel Laureate]		*[http://www.phys.uu.nl/~thooft/theorist.html How to Become a Theoretical Physicist by a Nobel Laureate]
	*[http://www.odomann.com Theory of longitudinal and transversal angular momentums]		*[http://www.odomann.com Theory of longitudinal and transversal angular momentums]

	~~{{metaphysics}}~~

	[[Category:Theoretical physics\| ]]		[[Category:Theoretical physics\| ]]
	[[Category:History of physics]]		[[Category:History of physics]]

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{{pp-semi-vandalism|small=yes}}
{{Unreferenced|date=January 2008}}
'''Theoretical physics''' is a branch of [[physics]] which employs [[mathematical model]]s and [[abstraction]]s of [[physics]] in an attempt to explain natural phenomena. Its central core is [[mathematical physics]],<ref group=note>Sometimes ''mathematical physics'' and ''theoretical physics'' are used synonymously to refer to the latter.</ref> though other conceptual techniques are also used. The goal is to rationalize, explain and predict physical [[phenomenon|phenomena]]. The advancement of [[science]] depends in general on the interplay between [[experiment]]al studies and [[theory]]. In some cases, theoretical physics adheres to standards of [[Rigour#Mathematical rigour|mathematical rigor]] while giving little weight to experiments and observations. For example, while developing [[special relativity]], [[Albert Einstein]] was concerned with the [[Lorentz transformation]] which left [[Maxwell's equations]] invariant, but was apparently uninterested in the [[Michelson-Morley experiment]] on [[Earth|Earth's]] drift through a [[luminiferous aether|luminiferous ether]]. On the other hand, Einstein was awarded the [[Nobel Prize]] for explaining the [[photoelectric effect]], previously an experimental result lacking a theoretical formulation.

==Overview==
A '''physical theory''' is a model of physical events. It is judged by the extent to which its predictions agree with empirical observations. The quality of a physical theory is also judged on its ability to make new predictions which can be verified by new observations. A physical theory differs from a [[mathematics|mathematical]] [[theorem]] in that while both are based on some form of [[axioms]], judgment of mathematical applicability is not based on agreement with any experimental results.

{{Rquote|right|
<math>\mathrm{Ricci} = k\,g</math>

''The equations for an [[Einstein manifold]], used in [[general relativity]] to describe the curvature of [[spacetime]]''
}}

A physical theory involves one or more relationships between various measurable quantities. [[Archimedes]] realized that a ship floats by displacing its mass of water, [[Pythagoras]] understood the relation between the length of a [[oscillation|vibrating]] string and the [[music]]al tone it produces, and how to [[calculation|calculate]] the [[dimension|length]] of a [[rectangle]]'s diagonal. Other examples include [[entropy]] as a measure of the uncertainty regarding the positions and [[motion (physics)|motions]] of unseen [[molecule|particles]] and the [[quantum mechanics|quantum mechanical]] idea that ([[action (physics)|action]] and) [[energy]] are not continuously variable.

Sometimes the vision provided by pure mathematical systems can provide clues to how a physical system might be modeled; e.g., the notion, due to [[Bernhard Riemann|Riemann]] and others, that [[space]] itself might be curved.

Theoretical advances may consist in setting aside old, incorrect [[paradigm]]s (e.g., Burning consists of evolving [[phlogiston]], or [[Astronomy|Astronomical]] bodies revolve around the [[Earth]]) or may be an alternative model that provides answers that are more accurate or that can be more widely applied.

Physical theories become accepted if they are able to make correct predictions and no (or few) incorrect ones. The theory should have, at least as a secondary objective, a certain economy and elegance (compare to [[mathematical beauty]]), a notion sometimes called "[[Occam's razor]]" after the 13th-century English [[philosophy|philosopher]] [[William of Ockham|William of Occam]] (or Ockham), in which the simpler of two theories that describe the same matter just as adequately is preferred. (But conceptual simplicity may mean mathematical complexity.) They are also more likely to be accepted if they connect a wide range of phenomena. Testing the consequences of a theory is part of the [[scientific method]].

Physical theories can be grouped into three categories: ''[[theoretical physics #mainstream theories|mainstream theories]]'', ''[[theoretical physics #proposed theories|proposed theories]]'' and ''[[theoretical physics #fringe theories|fringe theories]]''.

==History==
{{details|History of physics}}

Theoretical physics began at least 2,300 years ago, under the pre-[[Socrates|Socratic]] [[Ancient Greece|Greek]] philosophers, and continued by [[Plato]]; and [[Aristotle]], whose views held sway for a millennium. In [[medieval]] times, during the rise of the [[university|universities]], the only acknowledged intellectual disciplines were [[theology]], [[mathematics]], [[medicine]], and [[law]]. As the concepts of [[matter]], energy, space, time and [[causality]] slowly began to acquire the form we know today, other sciences spun off from the rubric of [[natural philosophy]]. During the [[Middle Ages]] and [[Renaissance]], the concept of [[experiment]]al science, the [[counterpoint]] to theory, began with scholars such as [[Ibn al-Haytham]] and [[Francis Bacon]]. The modern era of theory began perhaps with the [[Nicolaus Copernicus|Copernican]] paradigm shift in [[astronomy]], soon followed by [[Johannes Kepler]]'s expressions for planetary orbits, which summarized the meticulous observations of [[Tycho Brahe]].

The great push toward the modern concept of explanation started with [[Galileo Galilei|Galileo]], one of the few [[physicist]]s who was both a consummate theoretician and a great [[experimentalist]]. The [[analytic geometry]] and mechanics of [[René Descartes|Descartes]] were incorporated into the [[calculus]] and [[classical mechanics|mechanics]] of [[Isaac Newton]], another theoretician/experimentalist of the highest order. [[Joseph-Louis Lagrange]], [[Leonhard Euler]] and [[William Rowan Hamilton]] would extend the theory of classical mechanics considerably. Each of these individuals picked up the interactive intertwining of [[mathematics]] and [[physics]] begun two millennia earlier by Pythagoras.

Among the great conceptual achievements of the 19th and 20th centuries were the consolidation of the idea of [[energy]] by the inclusion of [[heat]], then [[electricity and magnetism]] and [[light]], and finally [[mass]]. The [[laws of thermodynamics]], and especially the introduction of the singular concept of [[entropy]] began to provide a macroscopic explanation for the properties of matter.

The pillars of [[modern physics]], and perhaps the most revolutionary theories in the history of physics, have been [[theory of relativity|relativity theory]] and [[quantum mechanics]]. Newtonian mechanics was subsumed under special relativity and Newton's [[gravity]] was given a [[kinematic]] explanation by [[general relativity]]. Quantum mechanics led to an understanding of [[black body|blackbody]] [[electromagnetic radiation|radiation]] and of anomalies in the [[specific heat capacity|specific heats]] of [[solid]]s — and finally to an understanding of the internal structures of [[atom]]s and [[molecule]]s.

All of these achievements depended on the theoretical physics as a moving force both to suggest experiments and to consolidate results — often by ingenious application of existing mathematics, or, as in the case of Descartes and Newton (with [[Gottfried Leibniz|Leibniz]]), by inventing new mathematics. [[Joseph Fourier|Fourier's]] studies of heat conduction led to a new branch of mathematics: [[Fourier series|infinite, orthogonal series]].

Modern theoretical physics attempts to unify theories and explain phenomena in further attempts to understand the [[Universe]], from the [[physical cosmology|cosmological]] to the [[elementary particle]] scale. Where experimentation cannot be done, theoretical physics still tries to advance through the use of mathematical models. Some of their most prominent and well thought out advancements in this field include:

===Prominent theoretical physicists===
Famous ''theoretical physicists'' include<br />
<div class="references-small" style="-moz-column-count:4; column-count:4;">
*[[Christiaan Huyghens]] (1629–1695)
*[[Isaac Newton]] (1643–1727)
*[[Leonhard Euler]] (1707–1783)
*[[Joseph Louis Lagrange]] (1736–1813)
*[[Pierre-Simon Laplace]] (1749–1827)
*[[Joseph Fourier]] (1768–1830)
*[[Nicolas Léonard Sadi Carnot]] (1796–1842)
*[[William Rowan Hamilton]] (1805–1865)
*[[Rudolf Clausius]] (1822–1888)
*[[James Clerk Maxwell]] (1831–1879)
*[[J. Willard Gibbs]] (1839–1903)
*[[Ludwig Boltzmann]] (1844–1906)
*[[Hendrik A. Lorentz]] (1853–1928)
*[[Henri Poincare]] (1854–1912)
*[[Nikola Tesla]] (1856–1943)
*[[Max Planck]] (1858–1947)
*[[Albert Einstein]] (1879–1955)
*[[Emmy Noether]] (1882-1935)
*[[Max Born]] (1882–1970)
*[[Niels Bohr]] (1885–1962)
*[[Erwin Schrödinger]] (1887–1961)
*[[Louis de Broglie]] (1892–1987)
*[[Satyendra Nath Bose]] (1894–1974)
*[[Wolfgang Pauli]] (1900–1958)
*[[Enrico Fermi]] (1901–1954)
*[[Werner Heisenberg]] (1901–1976)
*[[Paul Dirac]] (1902–1984)
*[[Eugene Wigner]] (1902–1995)
*[[Robert Oppenheimer]] (1904–1967)
*[[Sin-Itiro Tomonaga]] (1906–1979)
*[[Hideki Yukawa]] (1907–1981)
*[[John Bardeen]] (1908–1991)
*[[Lev Landau]] (1908–1967)
*[[Anatoly Vlasov]] (1908–1975)
*[[Nikolay Bogolyubov]] (1909–1992)
*[[Subrahmanyan Chandrasekhar]] (1910–1995)
*[[Richard Feynman]] (1918–1988)
*[[Julian Schwinger]] (1918–1994)
*[[Feza Gursey]] (1921–1992)
*[[Chen Ning Yang]] (1922– )
*[[Freeman Dyson]] (1923– )
*[[Gunnar Källén]] (1926–1968)
*[[Abdus Salam]] (1926–1996)
*[[Murray Gell-Mann]] (1929– )
*[[Riazuddin]] (1930– )
*[[Roger Penrose]] (1931– )
*[[George Sudarshan]] (1931– )
*[[Sheldon Glashow]] (1932– )
*[[Steven Weinberg]] (1933– )
*[[C. R. Hagen]] (1936–)
*[[Michael Berry]] (1941– )
*[[Stephen Hawking]] (1942– )
*[[Alexander Markovich Polyakov|Alexander Polyakov]] (1945–)
*[[Gerardus 't Hooft]] (1946– )
*[[Jacob Bekenstein]] (1947–)
*[[Bertrand Halperin]] (1950–)
*[[Robert Laughlin]] (1950–)
*[[Edward Witten]] (1951– )

</div>

==Mainstream theories==
'''Mainstream theories''' (sometimes referred to as ''central theories'') are the body of knowledge of both factual and scientific views and possess a usual scientific quality of the tests of repeatability, consistency with existing well-established science and experimentation. There do exist mainstream theories that are generally accepted theories based solely upon their effects explaining a wide variety of data, although the detection, explanation and possible composition are subjects of debate.

===Examples===
<div class="references-small" style="-moz-column-count:4; column-count:4;">
* [[Black hole thermodynamics]]
* [[Classical mechanics]]
* [[Condensed matter physics]]
* [[Conservation of energy]]
* [[Dark Energy]]
* [[Dark matter]]
* [[Dynamics (mechanics)|Dynamics]]
* [[Electromagnetism]]
* [[Field theory (physics)|Field theory]]
* [[Fluid dynamics]]
* [[General relativity]]
* [[Molecular modeling]]
* [[Particle physics]]
* [[Physical cosmology]]
* [[Quantum chromodynamics]]
* [[Quantum computers]]
* [[Quantum electrochemistry]]
* [[Quantum electrodynamics]]
* [[Quantum field theory]]
* [[Quantum information theory]]
* [[Quantum mechanics]]
* [[Solid mechanics]]
* [[Solid state physics]] or [[Condensed Matter Physics]] and the [[Semiconductor|electronic structure of materials]]
* [[Special relativity]]
* [[Standard Model]]
* [[Statistical mechanics]]


* [[Thermodynamics]]
</div>

==Proposed theories==
The '''proposed theories''' of physics are usually relatively new theories which deal with the study of physics which include scientific approaches, means for determining the validity of models and new types of reasoning used to arrive at the theory. However, some proposed theories include theories that have been around for decades and have eluded methods of discovery and testing. Proposed theories can include fringe theories in the process of becoming established (and, sometimes, gaining wider acceptance). Proposed theories usually have not been tested.

===Examples===
<div style="-moz-column-count:2; column-count:2;">
* [[Causal Sets]]
* [[Dark energy]] or [[Cosmological Constant|Einstein's Cosmological Constant]]
* [[Einstein-Rosen Bridge]]
* [[Emergence]]
* [[Grand unification theory]]
* [[Loop quantum gravity]]
* [[M-theory]]
* [[String theory]]
* [[Supersymmetry]]
* [[Theory of everything]]

</div>

==Fringe theories==
'''Fringe theories''' include any new area of scientific endeavor in the process of becoming established and some proposed theories. It can include speculative sciences. This includes physics fields and physical theories presented in accordance with known evidence, and a body of associated predictions have been made according to that theory.

Some fringe theories go on to become a widely accepted part of physics. Other fringe theories end up being disproven. Some fringe theories are a form of [[protoscience]] and others are a form of [[pseudoscience]]. The falsification of the original theory sometimes leads to reformulation of the theory.

===Examples===
* [[Dynamic theory of gravity]]
* [[Grand unification theory]]
* [[Luminiferous aether]]
* [[Scalar field theory (pseudoscience)]]
* [[Orgone]]
* [[Biefeld-Brown effect#Electrogravity|Biefeld Brown Electrogravity]]

== Thought experiments vs real experiments ==
{{Main|Thought experiment}}

"Thought" experiments are situations created in ones mind, asking a question akin to "Suppose you are in this situation. Assuming such is true, what would follow?". They are usually created to investigate phenomena that are not readily experienced in every-day situations. Famous examples of such thought experiments are [[Schrodinger's cat]], the [[EPR paradox|EPR thought experiment]], [[Time_dilation#Simple inference of time dilation|simple illustrations of time dilation]], and so on. These usually lead to real experiments designed to verify that the conclusion (and therefore the assumptions) of the thought experiments are correct. The EPR thought experiment lead to the [[Bell inequalities]], which were then [[Bell test experiments|tested to various degrees of rigor]], leading to the acceptance of the current formulation of [[quantum mechanics]] and [[Quantum indeterminacy|probabilism]] as a [[working hypothesis|working hypotheses]].

==See also==
{{wikibooks|Introduction to Theoretical Physics}}
* [[Experimental physics]]
* [[List of theoretical physicists]]

== Notes ==
{{reflist|group=note}}

==References==
{{reflist}}

==Further reading==
* {{cite book | author=Landau, L. D.; Lifshitz, E. M. | title=Course of Theoretical Physics | publisher=Butterworth-Heinemann | year=1976 | id=ISBN 0-7506-2896-0}}
* {{cite book | author=Morse, Philip; Feshbach, Herman | title=Methods of Theoretical Physics | publisher=Feshbach Publishing | year=2005 | id=ISBN 0-9762021-2-3}}

==External links==
*[http://superstringtheory.com/history/history3.html Timeline of Theoretical Physics]
*[http://ctp.lns.mit.edu/index.html MIT Center for Theoretical Physics]
*[http://www.ejtp.com Electronic Journal of Theoretical Physics (EJTP)]
*[http://www.phys.uu.nl/~thooft/theorist.html How to Become a Theoretical Physicist by a Nobel Laureate]
*[http://www.odomann.com Theory of longitudinal and transversal angular momentums]

{{metaphysics}}

[[Category:Theoretical physics| ]]
[[Category:History of physics]]

About theoretical physics - Revision history

wikademia>Eme at 16:18, 7 December 2009

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