  Spin relaxation close to the glass temperature of CuMn and AuFe spin glasses
is shown, by neutron spin echo, to follow a generalised exponential function
which explicitly introduces hierarchically constrained dynamics and macroscopic
interactions. The interaction parameter is directly related to the normalised
Tsallis non-extensive entropy parameter, q, and exhibits universal scaling with
reduced temperature. At the glass temperature q=5/3 corresponding, within
Tsallis' q-statistics, to a mathematically defined critical value for the onset
of strong disorder and non-linear dynamics.
