Exchange Interaction and Quantum State Symmetry
As another, entirely distinct, meaning of exchange force, it is sometimes used as a synonym for the exchange interaction, between electrons which arises from a combination of the identity of particles, exchange symmetry, and the electrostatic force.
To illustrate the concept of exchange interaction, any two electrons, for example, in the universe are considered indistinguishable particles, and so according to quantum mechanics in 3 dimensions, every particle must behave as a boson or a fermion. In the former case, two (or more) particles can occupy the same quantum state and this results in a lack of exchange interaction between them; in the latter case, the particles can not occupy the same state according to the Pauli exclusion principle. From Quantum field theory, the spin-statistics theorem demands that all particles with half-integer spin behave as fermions and all particles with integer spin behave as bosons. Thus, it so happens that all electrons are fermions, since they have spin 1/2.
As a mathematical consequence, fermions exhibit strong repulsion when their wave functions overlap, but bosons do not. This repulsion is what the exchange interaction models. Fermi repulsion results in "stiffness" of fermions. That is why atomic matter, is "stiff" or "rigid" to touch. Where wave functions of electrons overlap, Pauli repulsion takes place. The same is true for protons and neutrons where due to their larger mass, the rigidity of baryons is much larger than that of electrons.
Read more about this topic: Exchange Force
Famous quotes containing the words exchange, interaction, quantum, state and/or symmetry:
“I sometimes feel a great ennui, profound emptiness, doubts which sneer in my face in the midst of the most spontaneous satisfactions. Well, I would not exchange all that for anything, because it seems to me, in my conscience, that I am doing my duty, that I am obeying a superior fatality, that I am following the Good and that I am in the Right.”
—Gustave Flaubert (1821–1880)
“UG [universal grammar] may be regarded as a characterization of the genetically determined language faculty. One may think of this faculty as a ‘language acquisition device,’ an innate component of the human mind that yields a particular language through interaction with present experience, a device that converts experience into a system of knowledge attained: knowledge of one or another language.”
—Noam Chomsky (b. 1928)
“But how is one to make a scientist understand that there is something unalterably deranged about differential calculus, quantum theory, or the obscene and so inanely liturgical ordeals of the precession of the equinoxes.”
—Antonin Artaud (1896–1948)
“Marry first, and love will come after is a shocking assertion; since a thousand things may happen to make the state but barely tolerable, when it is entered into with mutual affection.”
—Samuel Richardson (1689–1761)
“What makes a regiment of soldiers a more noble object of view than the same mass of mob? Their arms, their dresses, their banners, and the art and artificial symmetry of their position and movements.”
—George Gordon Noel Byron (1788–1824)