Occasionally, physicists have postulated the existence of a fifth force in addition to the four known fundamental forces. The force is generally believed to have roughly the strength of gravity (i.e. it is much weaker than electromagnetism or the nuclear forces) and to have a range of anywhere from less than a millimeter to cosmological scales. Beyond the range, the force is assumed to rapidly become insignificant. A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... It has been suggested that Law of universal gravitation be merged into this article or section. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... 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. ...

The idea is difficult to test, because gravity is such a weak force: the gravitational interaction between two objects is only significant when one is very heavy. Therefore, it takes very precise equipment to measure gravitational interactions between objects that are small compared to the Earth. Nonetheless, in the late 1980s a fifth force, operating on municipal scales (i.e. with a range of about 100 meters), was reported by researchers (Fishbach et al.) who were reanalyzing results of Roland Eötvös from earlier in the century. The force was believed to be linked with hypercharge. Over a number of years, other experiments have failed to duplicate this result, and physicists now believe that there is no evidence for a fifth force. Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third most distant planet from the Sun. ... // Events and trends The 1980s marked an abrupt shift towards more conservative lifestyles after the momentous cultural revolutions which took place in the 60s and 70s and the definition of the AIDS virus in 1981. ... Roland Eötvös Vásárosnaményi Báró Eötvös Loránd, better known as Roland Eötvös (July 27, 1848 - April 8, 1919) was a Hungarian physicist. ... In particle physics, the hypercharge (represented by Y) is the sum of the baryon number B and the flavor charges: strangeness S, charm C, bottomness and topness T, although the last one can be omitted given the extremely short life of the top quark (it decays to other quarks before...

Theory and Experiment

There are at least three kinds of searches that can be undertaken, which depend on the kind of force being considered, and its range.

One way is to search for a fifth force with tests of the strong equivalence principle: this is one of the most powerful tests of Einstein's theory of gravity, general relativity. Alternative theories of gravity, such as Brans-Dicke theory, have a fifth force -- possibly with infinite range. This is because gravitational interactions, in theories other than general relativity, have degrees of freedom other than the "metric," which dictates the curvature of space, and different kinds of degrees of freedom produce different effects. For example, a scalar field cannot produce the bending of light rays. The fifth force would manifest itself in an effect on solar system orbits, called the Nordvedt effect. This is tested with Lunar Laser Ranging Experiment and very long baseline interferometry. In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... Two-dimensional visualization of space-time distortion. ... In mathematical physics, the Brans-Dicke theory of gravitation (sometimes called the Jordan/Brans/Dicke theory) is a well-known competitor of Einsteins theory of general relativity. ... The phrase degrees of freedom is used in three different branches of science: in physics and physical chemistry, in mechanical and aerospace engineering, and in statistics. ... In mathematics, in Riemannian geometry, the metric tensor is a tensor of rank 2 that is used to measure distance and angle in a space. ... Curvature is the amount by which a geometric object deviates from being flat. ... In mathematics and physics, a scalar field associates a single number (or scalar) to every point in space. ... The three principal experimental tests of general relativity are the perihelion shift of the planet Mercurys orbit, the bending of starlight by a massive object and the existence of gravitational waves. ... Categories: Physics stubs | Measuring instruments | Astronomy | General relativity | Apollo program ... Very Long Baseline Interferometry (VLBI) is a type of interferometry in which the data received at each antenna in the array is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk. ...

A likely kind of fifth force, which arises in Kaluza-Klein theory, where the universe has extra dimensions, or in supergravity or string theory is the Yukawa force, which is transmitted by a light scalar field (i.e. a scalar field with a long Compton wavelength, which determines the range). This has prompted a lot of recent interest, as a theory of supersymmetric large extra dimensions -- dimensions with size slightly less than a millimeter -- has prompted an experimental effort to test gravity on these very small scales. This requires extremely sensitive experiments which search for a deviation from the inverse square law of gravity over a range of distances. Essentially, they are looking for signs that the Yukawa interaction is kicking in at a certain length. Kaluza-Klein theory (or KK theory, for short) is a model which sought to unify classical gravity and electromagnetism. ... Kaluza-Klein theory (or KK theory, for short) is a model which sought to unify classical gravity and electromagnetism. ... A supergravity theory is a field theory combining supersymmetry and general relativity. ... String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics. ... A Yukawa potential (also called a screened Coulomb potential) is a potential of the form Hideki Yukawa showed in the 1930s that such a potential arises from the exchange of a massive scalar field such as the field of the pion whose mass is . ... The Compton wavelength of a particle is given by , where is the Planck constant, is the particles mass and is the speed of light. ... In particle physics, supersymmetry is a hypothetical symmetry that relates bosons and fermions. ... In physics, an inverse-square law is any physical law stating that some quantity is inversely proportional to the square of the distance from a point. ...

Australian researchers, attempting to measure the gravitational constant deep in a mine shaft, found a discrepancy between the predicted and measured value, with the measured value being two percent too small. They concluded that the results may be explained by a repulsive fifth force with a range from a few centimetres to a kilometre. Similar experiments have been carried out onboard a submarine (USS Dolphin (AGSS-555)) while deeply submerged. According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... USS Dolphin (AGSS-555) is the United States Navys only operational diesel-electric, deep-diving, research and development submarine. ...

The above experiments search for a fifth force that is, like gravity, independent of the composition of an object, so all objects experience the force in proportion to their masses. Forces that depend on the composition of an object can be very sensitively tested by torsion balance experiments of a type invented by Roland Eötvös. Such forces may depend, for example, on the ratio of protons to neutrons in an atomic nucleus, or the relative amount of different kinds of binding energy in a nucleus (see the semi-empirical mass formula). Searches have been done from very short ranges, to municipal scales, to the scale of the Earth, the sun, and dark matter at the center of the galaxy. A torsion spring is a ribbon, bar, or coil that reacts against twisting motion. ... Roland Eötvös Vásárosnaményi Báró Eötvös Loránd, better known as Roland Eötvös (July 27, 1848 - April 8, 1919) was a Hungarian physicist. ... Properties In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Binding energy is the energy required to disassemble a whole into separate parts. ... In nuclear physics, the semi-empirical mass formula (SEMF) is a formula used to approximate the mass and various other properties of an atomic nucleus. ... Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third most distant planet from the Sun. ... By ancient tradition, the Sun is the light in the heavens whose presence is day and whose absence is night. ... In cosmology, dark matter consists of matter particles that cannot be detected by their emitted radiation but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. ...

Other interactions

A few physicists think that Einstein's theory of gravity will have to be modified, not at small scales, but at large distances, or, equivalently, small accelerations. They point out that dark matter, dark energy and even the Pioneer anomaly are unexplained by the Standard Model of particle physics and suggest that some modification of gravity, possibly arising from Modified Newtonian Dynamics or the holographic principle. This is fundamentally different from conventional ideas of a fifth force, as it grows stronger relative to gravity at longer distances. Most physicists, however, think that dark matter and dark energy are not ad hoc, but are supported by a large number of complementary observations and described by a very simple model. In cosmology, dark matter consists of matter particles that cannot be detected by their emitted radiation but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. ... In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure. ... The Pioneer anomaly or Pioneer effect refers to the observed deviation from expectations of the trajectories of various unmanned spacecraft visiting the outer Solar system, notably Pioneer 10 and 11. ... The Standard Model of Fundamental Particles and Interactions The Standard Model of particle physics is a theory which describes the strong, weak, and electromagnetic fundamental forces, as well as the fundamental particles that make up all matter. ... Particles erupt from the collision point of two relativistic (100 GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... The modified Newtonian dynamics (MOND) is a physical theory which attempts to explain the galaxy rotation problem by changing Newtons law of motion. ... The holographic principle is a speculative conjecture about quantum gravity theories, proposed by Gerard t Hooft and improved and promoted by Leonard Susskind, claiming that all of the information contained in a volume of space can be represented by a theory that lives in the boundary of that region. ... In physics, two experimental techniques are often called complementary if they investigate the same subject in two different ways such that two different (ideally non-overlapping) properties or aspects can be investigated. ...

References

• Ephraim Fischbach, Daniel Sudarsky, Aaron Szafer, Carrick Talmadge, and S. H. Aronson, "Reanalysis of the Eötvös experiment", Physical Review Letters 56 3 (1986).
• University of Washington Eöt-Wash group, the leading group searching for a fifth force.
• Lunar Laser Ranging [1]
• Satellite Energy Exchange (SEE) [2], which is set to test for a fifth force in space, where it is possible to achieve greater sensitivity.