Degeneration

In quantum mechanics they most frequently deal s v. the energy levels of the system, when system has the specific value of energy, but in this case it can be in several different states. For example, for the free particle there is infinite-to-one v. on the energy: energy of particle is determined only by the numerical value of pulse, whereas the direction of pulse can be any (i.e. it can be selected with the infinite number of methods). In this example clearly is manifested the connection between v. and phys. by the symmetry of system - here this symmetry is equality of rights of all directions in the space.

With the particle motion in the external field v. it is substantially connected with the structure of this field, with the fact, with what properties of symmetry it possesses. If field is spherically symmetrical, i.e. if in the field the equality of rights of directions remains, then the directions of the orbital moment of momentum, magnetic moment and particle spin (for example, electron in the atom) cannot influence the value of energy (atom). Consequently, and here there is v. on the energy. However, if we place this system into the magnetic field N, then the direction of magnetic moment Q begins to affect the value of energy; those coincided before the value of energy of different states (with the different directions m) prove to be now different: as a result of interaction of the magnetic moment of particle with this field of particle is derived additional energy m_nN, whose the value depends on the mutual orientation of magnetic moment and field (m_n- projection also on the direction of field N, which in quantum mechanics it can assume only an discrete number of values). Occurs "splitting" of energ. levels, i.e. with n of 4 t and e v., complete or partial (when multiplicity v. only decreases) - this depends on specific conditions. Splitting the levels (atoms, molecules, crystals) in the magnetic field NAZ. Zeeman by phenomenon. Splitting levels can occur even х vnesh. elec. field (Stark phenomenon).

Thus, the removal of v. is caused by the "start" of suitable interactions. Since the presence v. speaks about existence in the system of the some of symmetry, the removal of v. occurs with this change phys. in the conditions, in which is located the system, when the order of these of symmetry is reduced. In the example given above the system initially possessed sferich. the symmetry (in it not there were chosen directions); the switching on of external magnetostatic field isolated direction - the direction of field, the symmetry of system was lowered and it became axial (axial), i.e. by symmetry relative to the axis, directed along the field.

If the start of interaction leads to reduction in the symmetry and removal of v., then is correct the reverse assertion: with the "disconnection" of interaction will occur an increase in the symmetry of system and the appearance Of v. eto is important for the classification of elementary particles. For example, if we disregard electromagnetic (and weak) interactions ("to turn off" ikh), then the properties of neutron and proton prove to be identical and them can be considered as two different (charge, i.e. characterizing by only elec. charge) states of one particle - nucleon. Track, the state of nucleon in this case doubly degenerate.

It is cast. see with the articles quantum mechanics. Atom. V. i. Grigoryev, V. d. kukin.