In physics, a unified field theory is a type of field theory that allows all of the fundamental forces between elementary particles to be written in terms of a single field. There is no accepted unified field theory yet, and this remains an open line of research. The term was coined by Nikola Tesla who attempted to unify the general theory of relativity with electromagnetism into a single field theory. A Theory of Everything is closely related to unified field theory, but differs by not requiring the laws of nature to be fields, and also attempting to explain all physical constants of nature. This article needs additional references or sources for verification. ... Field theory (mathematics), the theory of the algebraic concept of field. ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... The magnitude of an electric field surrounding two equally charged (repelling) particles. ... Nikola Tesla (1856-1943)[1] was a world-renowned Serbian inventor, physicist, mechanical engineer and electrical engineer. ... An illustration of a rotating black hole at the center of a galaxy General relativity (GR) (aka general theory of relativity (GTR)) is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... Field theory (mathematics), the theory of the algebraic concept of field. ... This article or section is in need of attention from an expert on the subject. ...

There is no a priori reason why a unified field theory is the correct description of nature; however, this goal has led to a great deal of progress in modern theoretical physics and continues to motivate research. Ultimately, a unified field theory is only one approach at simplifying the underlying structure of the Standard Model of particle physics. The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ...

Introduction

In physics, the forces (e.g. the gravitational force) between objects are not transmitted directly between the two objects, but instead go through an intermediary entity called fields. All of the four fundamental forces are mediated by fields. Specifically the four forces that are attempting to be unified are (from strongest to weakest): The magnitude of an electric field surrounding two equally charged (repelling) particles. ...

• Strong nuclear force: Force responsible for holding quarks together to form neutrons and protons, and holding neutrons and protons together to form nuclei. The exchange particles that mediate this force are gluons.
• Electromagnetic force: It is the familiar force that acts on electrically charged particles. The photon is the exchange particle for this force.
• Weak nuclear force: Responsible for radioactivity, it is a repulsive short-range interaction that acts on electrons, neutrinos and quarks. It is governed by the W boson.
• Gravitational force: A long-range attractive force that acts on all particles with mass. The exchange particles have been postulated and named gravitons.

A unified field theory attempts to bring these four force-mediating fields together into a single framework. The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ... For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... This article or section does not adequately cite its references or sources. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... In particle physics, gluons are subatomic particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei. ... In physics, the electromagnetic force is the force that the electromagnetic field exerts on electrically charged particles. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... This article covers the physics of gravitation. ... In physics, the graviton is mainly still considered to be a hypothetical elementary particle that mediates the force of gravity in the framework of quantum field theory. ...

History

Historically, the first unified field theory was developed by James Clerk Maxwell. In 1820 Hans Christian Oersted discovered that electric currents exerted forces on magnets, while in 1831, Michael Faraday made the observation that time-varying magnetic fields could induce electric currents. Until then, electricity and magnetism had been thought of as unrelated phenomena. In 1864, Maxwell published his famous paper on a dynamical theory of the electromagnetic field. This was the first example of a theory that was able to encompass previous field theories (namely electricity and magnetism) to provide a unifying theory of electromagnetism. Ultimately, Albert Einstein realized the reason for the unification of electricity and magnetism was because space and time were unified into an entity called space-time in his theory of special relativity. James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and theoretical physicist. ... Hans Christian Ørsted Hans Christian Ørsted (August 14, 1777 in Rudkøbing – March 9, 1851 in Copenhagen) was a Danish physicist and chemist, influenced by the thinking of Immanuel Kant. ... Electric current is the flow (movement) of electric charge. ... Iron filings in a magnetic field generated by a bar magnet A magnet is a material or object that produces a magnetic field. ... Michael Faraday, FRS (September 22, 1791 – August 25, 1867) was an English chemist and physicist (or natural philosopher, in the terminology of that time) who contributed significantly to the fields of electromagnetism and electrochemistry. ... Magnetic field lines shown by iron filings In physics, a magnetic field is a solenoidal vector field in the space surrounding moving electric charges and magnetic dipoles, such as those in electric currents and magnets. ... “Einstein” redirects here. ... The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest...

In 1921 Theodor Kaluza extended General Relativity to five dimensions and in 1926 Oscar Klein proposed that the fourth spatial dimension be curled up (or compactified) into a small, unobserved circle. This was dubbed Kaluza-Klein theory. It was quickly noticed that this extra spatial direction gave rise to an additional force that looked similar to electricity and magnetism. This was heavily studied as the basis for Albert Einstein's later unsuccessful attempts at a unified field theory. In physics, Kaluza-Klein theory (or KK theory, for short) is a model that seeks to unify the two fundamental forces of gravitation and electromagnetism. ... “Einstein” redirects here. ...

Modern Progress

In 1963 American physicist Sheldon Glashow proposed that the weak nuclear force and electricity and magnetism could arise from a partially unified electroweak theory. In 1967, Pakistani Abdus Salam and American Steven Weinberg independently revised Glashow's theory by having the masses for the W particle and Z particle arise through spontaneous symmetry breaking with the Higgs mechanism. This unified theory was governed by the exchange of four particles: the photon for electromagnetic interactions, and a neutral Z particle and two charged W particles for weak interaction. As a result of the spontaneous symmetry breaking, the weak force becomes short range and the Z and W bosons acquire masses of 80.4 and 91.2 GeV / c², respectively. Their theory was first given experimental support by the discovery of weak neutral currents in 1973. In 1983, the Z and W bosons were first produced at CERN by Carlo Rubbia's team. For their insights, Salam, Glashow and Weinberg were awarded the Nobel Prize in Physics in 1979. Carlo Rubbia and Simon van der Meer received the Prize in 1984. Professor Sheldon Lee Glashow (born December 5, 1932) is an American physicist. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ... Abdus Salam at Nobel Prize ceremony with the King of Sweden Dr. Abdus Salam (Urdu: عبد السلام) (January 29, 1926 at Santokdas, Sahiwal in Punjab – 21 November 1996 in Oxford, England) was a Pakistani theoretical physicist who received the Nobel Prize in Physics in 1979 for his work in electroweak theory which... Steven Weinberg (born May 3, 1933) is an American physicist. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... Spontaneous symmetry breaking in physics takes place when a system that is symmetric with respect to some symmetry group goes into a vacuum state that is not symmetric. ... The Higgs mechanism or Anderson-Higgs mechanism, originally proposed by the British physicist Peter Higgs based on a suggestion by Philip Anderson, is the mechanism that gives mass to all elementary particles in particle physics. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... CERN logo The European Organization for Nuclear Research (French: ), commonly known as CERN (see Naming), pronounced (or in French), is the worlds largest particle physics laboratory, situated just northwest of Geneva on the border between France and Switzerland. ... Carlo Rubbia (born March 31, 1934) is an Italian physicist. ... Hannes Alfvén (1908–1995) accepting the Nobel Prize for his work on magnetohydrodynamics [1]. List of Nobel Prize laureates in Physics from 1901 to the present day. ... Simon van der Meer (born November 24, 1925) is a Dutch physicist. ...

After Gerardus 't Hooft showed the Glashow-Weinberg-Salam electroweak interactions was mathematically consistent, the electroweak theory became a template for further attempts at unifying forces. Sheldon Glashow and Howard Georgi proposed unifying the strong and electroweak interactions into a Grand Unified Theory in 1974, which applied to energies much above 100 GeV. Since then there have been several proposals for Grand Unified Theories, although none is currently universally accepted. A major problem for experimental tests of such theories is the energy scale involved, which is well beyond the reach of current accelerators. Grand Unified Theories make predictions for the relative strengths of the strong, weak and electromagnetic forces and in 1991, LEP determined that supersymmetric theories have the correct ratio of couplings for a Georgi-Glashow Grand Unified Theory. Many Grand Unified Theories predict that the proton can decay and if this were to be seen, details of the decay products could give hints at more aspects of the Grand Unified Theory. It is at present unknown if the proton can decay although experiments have determined a lower bound of 10³⁵ years for its lifetime. Gerard t Hooft at Harvard University Gerardus (Gerard) t Hooft [ut-hooft] (The prefix ’t is pronounced as ‘ut’ and stands for ‘het’) (born July 5, 1946) is a professor in theoretical physics at Utrecht University, The Netherlands. ... Howard Mason Georgi III, born in 1947 in San Bernardino, California, is Harvard College Professor and Mallinckrodt Professor of Physics at Harvard University, where he is also Director of Undergraduate Studies in Physics and Master of Leverett House. ... Grand unification, grand unified theory, or GUT is a theory in physics that unifies the strong interaction and electroweak interaction. ... For the DC Comics Superhero also called Atom Smasher, see Albert Rothstein. ... The Large Electron-Positron Collider (usually called LEP for short. ... A Minimal Supersymmetric Standard Model is a class of proposed supersymmetric extensions to the Standard Model. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, usually a neutral pion and a positron. ...

The Current State of Unified Field Theories

Gravity has yet to be included in a theory of everything. Due to the differing structure of General Relativity, relative to the strong and electroweak interactions, it is not possible to mimick the structure of electroweak unification to unify all of the forces. Theoretical physicists have been so far incapable of formulating a consistent theory that combines general relativity and quantum mechanics. The two theories have proved to be incompatible and the quantization of gravity remains an outstanding problem in the field of physics. It is currently believed in theoretical physics that a quantum theory of general relativity may require going beyond field theory itself with frameworks such as string theory or loop quantum gravity. One promising string theory is the heterotic string which can tie together gravity and the three other forces into a tight connection. Other candidate string theories do not have this feature of unifying the forces and gravity in a compelling manner. Similarly, loop quantum gravity does not appear to link the electroweak and strong forces to gravity and if so, this would not be a unified field theory. Ultimately, nature may not arise from a unified field theory and its conceptualization may not have been correct, though it has led to advances in physics, most notably the electroweak theory and grand unification. Gravity is a force of attraction that acts between bodies that have mass. ... An illustration of a rotating black hole at the center of a galaxy General relativity (GR) (aka general theory of relativity (GTR)) is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... Loop quantum gravity (LQG), also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the seemingly incompatible theories of quantum mechanics and general relativity. ... In physics, a heterotic string is a peculiar mixture (or hybrid) of the bosonic string and the superstring (the adjective heterotic comes from the Greek word heterosis). ...

Non-Mainstream Theories

Albert Einstein famously spent the last two decades of his life searching for a Unified Field Theory. This has led to a great deal of fascination with the subject and has drawn some people from outside the portion of the physics community that typically addresses these issues to work on a Unified Field Theory. Most of this work typically appears in non-peer reviewed sources, such as self-published books or personal websites. The work that appears outside of the standard scientific channels often are pseudo-science that do not live up to the rigors necessary to be considered a real scientific theory. Much of this work goes under the name non-mainstream theories. An example of such a theory is Heim theory. This article may be too technical for most readers to understand. ...

References

See also

• Classical unified field theories
• Electromagnetic force
• Weak nuclear force
• Grand Unification
• MSSM
• General Relativity
• String theory
• Theory of Everything

This article is in need of attention. ... In physics, the electromagnetic force is the force that the electromagnetic field exerts on electrically charged particles. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ... It has been suggested that this article or section be merged into Unified field theory. ... A Minimal Supersymmetric Standard Model is a class of proposed supersymmetric extensions to the Standard Model. ... An illustration of a rotating black hole at the center of a galaxy General relativity (GR) (aka general theory of relativity (GTR)) is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... This article or section is in need of attention from an expert on the subject. ...

External links

• PBS: NOVA
• http://arxiv.org/html/physics/9908024