Fundamental forces are those forces of the Universe that cannot be explained in terms of more basic ones.
The fundamental forces or interactions known so far are four: gravitational, electromagnetic, strong nuclear and weak nuclear.
The gravitational It is the force of attraction that a piece of matter exerts on another, and affects all bodies. Gravity is a very weak and one-way force, but of infinite reach.
The force electromagnetic It affects electrically charged bodies, and is the force involved in the physical and chemical transformations of atoms and molecules. It is much more intense than the gravitational force, it has two senses (positive and negative) and its range is infinite.
Force or interaction strong nuclear it is the one that holds together the components of the atomic nuclei, and acts interchangeably between any two nucleons, protons or neutrons. Its scope is of the order of nuclear dimensions, but it is more intense than electromagnetic force.
Force or interaction weak nuclear is responsible for the beta decay of neutrons; Neutrinos are sensitive only to this type of interaction. Its intensity is less than that of the electromagnetic force and its range is even less than that of strong nuclear interaction.
Everything that happens in the Universe is due to the action of one or several of these forces that differ from each other because each one implies the exchange of a different type of particle, called an exchange or intermediary particle. All exchange particles are bosons, while the particles origin of the interaction are fermions.
At present, scientists are trying to demonstrate that all these fundamental forces, apparently different, are manifestations, in different circumstances, of a unique mode of interaction. The term "unified field theory" encompasses the new theories in which two or more of the four fundamental forces appear as if they were basically identical.
The theory of the great unification tries to unite in a single theoretical framework the strong nuclear interactions and weak nuclear, and the electromagnetic force. This unified field theory is still in the process of being tested. The theory of everything is another unified field theory that aims to provide a unified description of the four fundamental forces.
Today, the best candidate to become a theory at all is superstring theory. This physical theory considers the fundamental components of matter not as mathematical points, but as one-dimensional entities called "strings." It incorporates the mathematical theory of supersymmetry, which suggests that all known particle types must have a "supersymmetric companion," the majority not yet discovered.
This does not mean that there is a companion for each individual particle (for example, for each electron), but a type of particle associated with each known type of particle. The hypothetical particle corresponding to the electron would be the selectron, for example, and the one corresponding to the photon would be the fotino.
This combination of the string theory and supersymmetry is the origin of the name "superstrings".
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