Fundamental interaction
A fundamental interaction is one of the fundamentally different ways in which physical objects can affect ( bodies, fields, particles, systems) are mutually exclusive. There are four fundamental interactions of gravitation, electromagnetism, weak interaction, strong interaction. They are also referred to as the four fundamental forces of physics.
Individually or in combination, the four fundamental interactions are responsible for all known physical processes, be they processes between elementary particles or between matter and fields in macroscopic dimensions, whether on earth or in stars in space. Other types of interactions do not seem necessary for the description of nature; occasionally established hypotheses about a "fifth force " that would be needed to explain certain observations could not be confirmed. On the other hand, it is also not yet been able to explain the variety of observed events with less than four fundamental interactions.
However, it should be noted that this simple picture, which was worked out around the middle of the 20th century, is to be modified according to recent developments: Two of the four interactions ( electromagnetic and weak interactions ) are the current standard model of elementary particle physics from a common basis derived which bears the name of electroweak interactions. Therefore, it is sometimes spoken of only three fundamental interactions. On the other hand, the standard model contains the novel Higgs field that gives through a particular kind of interaction the initially recognized as massless fermions, such as electrons, their mass. This interaction is not usually referred to as the fifth fundamental interaction.
The four fundamental forces
Gravity
Gravitation, also called gravity, was identified as a natural force in the 17th century by Isaac Newton and described mathematically. She goes by every body with mass and attracts all other masses. She takes with distance, can not be shielded and has an infinite range. The radiation emanating from the earth, gravity is the force of gravity, which affects the world we live noticeably. Gravity is the dominant interaction between the planets and the sun and thus the cause of the shape of the solar system. It has significant influence on the state and evolution of stars, but also dominates the large-scale structure of the universe. The gravitational force acts between any two objects of the size with which we deal with every day, but is then so weak that it is practically negligible in everyday life and at the end of the 18th century by Henry Cavendish has been demonstrated experimentally. In further development of the Newtonian law of gravitation todays valid theory of gravity, the general theory of relativity, which was erected in the early 20th century by Albert Einstein. An associated quantum field theory has not yet been found.
Electromagnetic interaction
The electromagnetic interaction was identified in the mid- 19th century as a fundamental force of nature, after James Clerk Maxwell had set up the eponymous Maxwell equations, with which the phenomena of electricity, magnetism and optics can be described equally. The electromagnetic interaction is based on electric charges, magnetic dipoles and electromagnetic fields. The forces that it exerts on magnetic or charged bodies may be perceived directly by the people. As gravity has an infinite range, but is attractive or repulsive depending on the sign of the charge and can therefore shield or even eliminate (positive and negative charges usually compensate almost exactly ). The electromagnetic interaction is responsible for everyday phenomena such as light, electricity, magnetism, chemical bonding, ie also for the chemical reactions and for different material properties in nature, home and technology. The quantum field theoretical development of the classical Maxwell equations led mid-20th century to quantum electrodynamics. This is the photon, responsible for all electromagnetic effects exchange particles.
Weak interaction
The, also called weak nuclear force weak interaction was discovered in 1934 and described that causes the beta radioactivity of Enrico Fermi as the new fundamental interaction. It has the extremely short range of about 10-18 m and therefore appears extremely weak compared to the electromagnetic interaction. It acts between all particles of type lepton and quarks, it can cause only one of the interactions transformations from one particle to another ( eg electron is neutrino, up quark is down quark, but not between leptons and quarks ). The weak interaction is the only one that the symmetry of natural processes over a reflection of the room, a reversal of the charges or the time direction is violated ( see parity violation, charge conjugation, time-reversal invariance ). The weak interaction can not be perceived directly by the people, but causes eg essential intermediate steps in the nuclear fusion of hydrogen to helium, from which the sun draws its radiant energy. ( The energy itself is released by the strong interactions. ) The quantum field theoretical description of weak interactions based on the abstract with the electromagnetic to the electroweak interaction, which is a cornerstone of the Standard Model of elementary particle physics. Your exchange particles are the Z0, W and W - which, by their large mass, the short range. In connection with the explanation of the mass of these exchange particles, theory predicts an additional particle, the Higgs boson. In July 2012, CERN announced the detection of a particle at the Large Hadron Collider, in which it is highly probable that the Higgs boson.
Strong interaction
The strong interaction, also called strong nuclear force that binds quarks together. So that it causes the internal cohesion of hadrons, such as the proton and neutron. She is also a cause of the mutual attraction of short-range forces acting between the hadrons. These are referred to in the narrower sense than nuclear forces, because they are responsible for the development of atomic nuclei from protons and neutrons. Thus, the strong interaction determines the binding energy of atomic nuclei and the energy turnover in nuclear reactions. These are typically millions of times greater than in chemistry, where they originate from the electromagnetic interaction between the atomic shells.
The strongest fundamental force of nature, the strong interaction has been postulated since the 1920s, but was only in the 1970s after the discovery that all hadrons are composed of two or three quarks, are correctly described. The quantum field theory of the strong interaction is quantum chromodynamics ( QCD). It represents the interaction between two quarks through the exchange of a gluon represents the particles carry a charge its own type, which occurs in contrast to the electric charge in three variants and is called color charge. It is characteristic of the strong interaction that the elementary particles in which it operates, can not occur in isolation. If one tries, for example, quarks to separate them, so much energy has to be expended, that by virtue of the equivalence of mass and energy incur additional quarks and connect to the other to complete hadrons. This as a confinement ( enclosure ) described phenomenon with the result that the range of the strong interaction effectively not the radius of a hadron ( about 10-15 m) beyond. The exact mechanisms of the strong interaction are the subject of current research.
Tabulated list
Note: The typical relative strength is so specified, as is observed in processes in the energy range up to a few GeV. Since the values strongly depend on the energy, the weak interaction is indicated in some sources also with the relative strength of 10-13, 10-38 or 10-39 with gravity. The main finding is the minuteness of the strength of gravity and the small value of the weak interaction at low energies.
Hypothetical more forces
Although there is yet no evidence could be supplied, is widely speculated in theoretical physics over other possible forces. This includes for example technicolor theories, theories of supersymmetry or string theories. New macroscopic forces are sometimes grouped under the term "fifth force ". All these forces represent hypothetical extensions of the Standard Model of elementary particle physics dar.
Unifying theories
One of the goals of physics is to find out whether all fundamental forces or interactions are described in a unified concept. Thus it might be possible to reduce all known forces to a single fundamental force. This is called unified theories. For example, the electromagnetic interaction is a unification of the electric and the magnetic interaction. Furthermore, the electromagnetic interaction and the weak interaction at energies above about 102 GeV have approximately the same strength and can be described as a unified electroweak interaction. However, in the current standard model of elementary particle physics, the strong interaction is next unconnected. A theory that would unify these three fundamental forces of the current standard model of particle physics, grand unified theory called ( Grand Unification Theory GUT). As the central part applies the approach of the coupling constants of the three interactions to a common value, when the processes are evaluated in still higher energy. Current theories assume such an approach at about 1016 GeV, which is an unattainable factor 1012 the current highest achieved in an experiment particle energy.
A theory that combines all four fundamental forces, world formula or Theory of Everything ( TOE) is called. So you must include a previously unknown also quantum theory of gravity over the still hypothetical GUT addition. String theory or superstring theories are considered as promising candidates, even if they so far have no verifiable by experiment result.
The following table describes each schematically the relationship of various fundamental forces and the corresponding hierarchy of theories of physics: