  According to Wilson's theory of critical phenomena, critical exponents are
universal functions of $d$, the dimension of space, and $n$, the dimension of
the symmetry group. SO(5) theory of antiferromagnetism and superconductivity
predicts a bicritical point where $T_N$ and $T_c$ intersect. By measuring
critical exponents close to the bicritical point, and knowing that $d=3$, one
can experimentally measure the number 5 of the SO(5) theory.
