Multipolära

Multipolära, or multipolar, is a term used to describe systems that have several centers of influence or sources contributing to a field. The concept appears in physics to describe the spatial distribution of quantities such as electric charge or mass, and in international relations to describe how power is distributed among states or blocs. In both contexts the idea is to move beyond a single dominant source and to account for more complex patterns of influence.

In physics, a multipole expansion expresses the potential of a distributed source as a sum of terms with increasing angular structure: monopole, dipole, quadrupole, and higher-order moments. The monopole term corresponds to the total charge or mass, the dipole to the separation of charges, and the quadrupole and higher terms to more intricate arrangements. This expansion is especially useful in the far field, where contributions from higher-order moments diminish with distance. Mathematically, multipoles arise in solving Laplace’s equation and are closely related to angular functions such as Legendre polynomials and spherical harmonics.

Applications of multipole analysis span electromagnetism, gravitation, chemistry, and antenna theory. It helps describe electric and magnetic fields around molecules, predict transition probabilities in nuclear and atomic processes, and simplify the design of radiation patterns in antennas and sensors. The same framing is used in gravitational physics to approximate the field of extended bodies.

In international relations, multipolarity describes a world in which several powers or blocs exercise substantial influence, rather than a single dominant actor (unipolar) or two competing powers (bipolar). It implies overlapping interests, shifting alignments, and potential regional hubs of power, with debates about stability, balance, and cooperation in a complex global system. See also multipole expansion and concepts of unipolar and bipolarity.