Theoretical physics employs mathematical models and abstractions, as opposed to experimental processes, in an attempt to understand Nature. Central to it is mathematical physics ¹, though other conceptual techniques are also used. The goal is to rationalize, explain and predict physical phenomena. The advancement of science depends in general on the interplay between experimental studies and theory. In some cases, theoretical physics adheres to standards of mathematical rigor while giving little weight to experiments and observations. For example, while developing special relativity, Einstein was concerned with the Lorentz transformation which left Maxwell's equations invariant, but was apparently uninterested in the Michelson-Morley experiment on Earth's drift through a 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.

Contents [hide] 1 Overview 2 History 2.1 Prominent theoretical physicists 3 Mainstream theories 3.1 Examples 4 Proposed theories 4.1 Examples 5 Fringe theories 5.1 Examples 6 Notes 7 See also 8 External links

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Overview

A physical theory is a model of physical events and cannot be proven from basic axioms. A physical theory is different from a mathematical theorem; physical theories model reality and are a statement of what has been observed, and provide predictions of new observations.

Hence, more is involved than the application, or even invention, of mathematics — to wit: concept formation. Archimedes realized that one could determine the volume of an irregularly-shaped object by immersing it in a liquid, and that a ship floats by displacing its weight of water. Pythagoras understood the relation between the length of a vibrating string and the musical tone it produces, and how to calculate the length of a rectangle's diagonal. Other examples include entropy as a measure of the uncertainty regarding the positions and motions of unseen particles and the quantum mechanical idea that (action and) energy are not continuously variable. Sometimes it is the vision of mathematicians which provides the clue; e.g., the notion, due to Riemann and others, that space itself might be curved.

Theoretical advances often consist in setting aside old paradigms

• Heat is a fluid called caloric.
• Burning consists of evolving phlogiston.
• Astronomical bodies revolve around the Earth.

often replacing them with new ones

• Physical objects are made up of molecules and atoms.
• Diseases can be caused by unseen microbes.
• Energy is exchanged in discrete packets called quanta.

Physical theories become accepted if they are able to make correct predictions and avoid incorrect ones. All else being equal, simple theories tend to be accepted over theories which are complex. (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: mainstream theories, proposed theories and fringe theories.

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History

For more details on this topic, see History of physics.

Theoretical physics began, at least 2,300 years ago under the pre-Socratic Greek philosophers, and continued by Plato; and Aristotle, whose views held sway for a millennium. In medieval times, during the rise of the 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 Renaissance, the modern concept of experimental science, the counterpoint to theory, began with Francis Bacon. The modern era of theory began perhaps with the Copernican paradigm shift in astronomy, soon followed by the actual planetary orbits due to Kepler, based on the meticulous observations of Tycho.

The great push toward the modern concept of explanation started with Galileo, one of the few physicists who was both a consummate theoretician and a great experimentalist. The analytic geometry and mechanics of Descartes was incorporated into the calculus and 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, filled in a great missing link in the attempt to explain why things happen.

The most pivotal theories of modern physics, and perhaps the most revolutionary in the history of physics, have been 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 blackbody radiation and of anomalies in the specific heats of solids — and finally to an understanding of the internal structures of atoms and molecules.

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 Leibniz), by inventing new mathematics. Fourier's studies of heat conduction lead to a new branch of mathematics: infinite, orthogonal series.

Modern theoretical physics attempts to unify theories and explain phenomena in further attempts to understand the Universe, from the cosmologic to the elementary particle scale. Where experimentation cannot be done, theoretical physics still tries to advance through the use of mathematical models.

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Prominent theoretical physicists

Famous theoretical physicists include Isaac Newton, Albert Einstein, Stephen Hawking, Niels Henrik Bohr, Werner Heisenberg, Max Born, Hendrik A. Lorentz, Max Planck, Erwin Schrödinger, Paul Dirac, Richard Feynman, Gordon Freeman, Lev Landau, Abdus Salam, Enrico Fermi, Louis Victor Broglie and Wolfgang Pauli.

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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.

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Examples

• Big Bang Theory
• Classical mechanics
• Condensed matter physics
• Dynamics
• Dark matter
• Electromagnetism
• Field theory
• Fluid dynamics
• General relativity
• Particle physics
• Quantum mechanics
• Quantum field theory
• Quantum electrochemistry
• Solid state physics and the electronic structure of materials
• Special relativity
• Standard Model
• Statistical mechanics
• String Theory
• Thermodynamics
• Particle Cosmology

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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.

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Examples

• Dark energy
• Einstein's Cosmological Constant
• Einstein-Rosen Bridge
• Emergence
• Grand unification theory*
• Loop quantum gravity*
• M-theory
• Plasma Universe
• String theory
• Supersymmetry
• Theory of everything*

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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.

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Examples

• Dynamic theory of gravity
• Grand unification theory*
• Loop quantum gravity*
• Luminiferous aether
• Steady state theory
• Theory of everything*
• Metatheory

* These theories are both proposed and fringe theories.

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Notes

• Note 1: Sometimes mathematical physics and theoretical physics are used synonymously to refer to the latter.

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See also

List of theoretical physicists

Wikibooks has more about this subject:

Theoretical physics

• Wikibooks Theoretical Physics (Introduction)

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External links

• Timeline of Theoretical Physics

Retrieved from "http://en.wikipedia.org/wiki/Theoretical_physics"

Categories: Theoretical physics | Physics | Mathematics | History of physics

 

 

 

 

 

 

 

 

Teoretisk fysik är den del av fysiken som använder matematiska eller datorbaserade modeller för att försöka förstå och beskriva naturen. Teoretiska fysiker formulerar modeller av verkligheten som används för att förklara, organisera och förutsäga fysikaliska fenomen. Dessa modeller kallas för fysikaliska teorier.

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Typer av teoretisk fysik

Det finns olika "nivåer" av teoretisk fysik. En del av den teoretiska fysiken ligger närmare experimentell fysik och arbetar med att tolka resultat från experiment och att utveckla nya modeller, teorier och beräkningsmetoder utifrån detta. Denna typ av teoretisk fysik kallas ibland för fenomenologi, och den mer beräkningsinriktade teoretiska fysiken kallas ibland för beräkningsfysik. Matematisk fysik å andra sidan har stora krav på matematisk bevisföring och matematiska fysiker arbetar till exempel med att utveckla nya matematiska metoder och formuleringar och att göra existerande teorier mer matematiskt rigorösa. Matematiska fysiker ägnar sig i allmänhet inte åt att studera experimentella data eller åt numeriska beräkningar.

Mellan dessa områden finns en flytande skala av olika typer av aktiviteter, och ibland särskiljs dessa så att man med teoretisk fysik varken menar matematisk fysik eller fenomenologi och beräkningsfysik utan det som finns emellan. Det kan röra sig om sådant som kvantfältteori, allmän relativitetsteori, strängteori och så vidare.

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Fysikaliska teorier

En fysikalisk teori är en matematisk formulering av fysikaliska lagar, som ska innefatta observerade fenomen och förutsäga nya. Exempel på fysikaliska teorier är den elektromagnetiska fältteorin och kvantmekaniken. De flesta teorier som dagens teoretiska fysiker arbetar med har sina grunder i den allmänna relativitetsteorin och/eller kvantmekaniken.

En teoris "kvalitet" är till stor grad kopplad till dess förmåga att göra förutsägelser (av resultat från nya experiment) och dess omfattning. Förutsägelserna måste i sin tur kunna prövas mot nya observationer och avgör om hypotesen-teorin kan godtas, måste modifieras eller förkastas. En annan viktig bedömningsgrund är teoretisk enkelhet (Occams rakkniv) och elegans.

Historiskt sett har man ofta haft en fysikalisk observation som utgångspunkt för att skapa en ny teoretisk beskrivning. Detta är dock inte alltid fallet; i vissa fall har dock en hel teori kunna byggas upp utan att någon specifik observation förelegat. I så fall måste teorins förutsägelser prövas genom observationer i efterhand för att kunna godtas. Detta var fallet för Einsteins allmänna relativitetsteori, vars tillkomst var helt genom teoretiskt arbete. Den har därefter verifierats experimentellt.

Ett aktuellt exempel är strängteorin, som ännu inte kunnat testas experimentellt men som har stort stöd bland teoretiska fysiker på grund av dess teoretiska egenskaper.

 

Artikelkategori: Fysik