Unified field theory

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.

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.

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):

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.

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.

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.

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 $GeV/c^{2}$ , 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.

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 $10^{35}$ years for its lifetime.

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.

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.

There are also some "non-mainstream" theories that have been demonstrated successful, either through technology applications or through ability to derive constants in the standard model. Or for example, the Aether Physics Model by David Thomson and Jim Bourassa, which has been able to derive the electron binding equation.

Here is a list of demonstrated theories not currently in the "main-stream."

Aether Physics Model by David Thomson and Jim Bourassa which successfully derives the electron binding equation http://www.16pi2.com/

The Grand Unified Theory of Classical Quantum Mechanics by Randell Mills who invented the Blacklight Process of moving the electron in the Hydrogen atom to a less than ground state, thus liberating massive amounts of energy. http://www.blacklightpower.com/theory/theory.shtml

The Science of Actuality by Mel Winfield who predicted the Hutchison Effect, named after John Hutchison who later "borrowed" the idea and received credit. http://www.spacetelescopes.com/gravitation.html

The Final Quantum revelation by Kiril Chukanov who invented the ball lightning generator which produces "quantum free energy" (more energy out than in) http://www.chukanovenergy.com/index.php?section=34

4D unified math by Warren York who, with Mike Windell, has conducted research with resonating cold plasma beams resulting in effects such as free energy manifestations, materials transformations, and time distortions. http://webpages.charter.net/pubmaster/

This is only a short list. Many of these non-mainstream theories are being rejected by the Peer Review Journals simply because they violate classic laws of physics such as the 2nd law of thermodynamics, even though they have been demonstrated. It is common historical knowledge that new discoveries which change the paradigm of belief are often met with oppositions, and that is what is currently happening to these demonstrated theories. On the contrary, accepted and well published theories such as string theory, or m theory, or whatever new name it now has, have never been demonstrated either by technological applications or predictive abilities.

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