ABSTRACT
In a three-dimensional simple cubic lattice, each spin that points up is surrounded by six nearest neighbor spins which point down. In an antiferromagnet, therefore, things look like two interpenetrating sublattices, the spins in each of which are aligned as in a ferromagnet, but in opposite directions for the two sublattices. It is always tempting to speculate on the applicability of models of ferromagnets to the decision behavior of social groups. It is illustrative to compare the transverse hydrodynamic fluctuations in the isotropic antiferromagnet with those found in the corresponding ferromagnet, and in the paramagnetic temperature range for either system. For the many systems, for which anisotropic contributions to the spin interaction energy are large, terms which violate spin conservation, very little can be said about the spectrum of spin fluctuations even at long wavelength, except by explicit microscopic calculation.
