Abstract
New universality classes in two-dimensional critical phenomena have recently been discovered using methods of quantum field theory and conformal invariance. These can equally well describe classical two-dimensional systems at their critical temperature or one-dimensional gapless quantum systems at (or near) zero temperature. (The two types of systems are related by the transfer matrix or Feynman path integral.) It is argued that isotropic one-dimensional antiferromagnets are realizations of these new universality classes. Exact predictions for the low temperature specific heat, susceptibility, correlation length, and other critical properties are made. These agree exactly with exactly solveable models and well with experimental results on CuCl2⋅2(NC5H5).