Justin Roberts, University of Edinburgh
6j-symbols and the tetrahedron
A classical 6j-symbol is a real number associated to a labelling of
the six edges of a tetrahedron by natural numbers (or equivalently by
irreducible representations of SU(2)). The tetrahedral picture is
traditionally used merely to indicate the symmetry of the 6j-symbol,
but it turns out that there is a striking formula expressing the
large-label asymptotics of the symbol in terms of the geometry of a
tetrahedron in Euclidean or Minkowskian 3-space.
I will try to explain how 6j-symbols arise in physics and algebra,
why they have such a geometric interpretation, and what they are good
for in topology.