[fluctuation and specific heat] near the critical point we know (fi) for sorne positive exponent α (a critical exponent). this divergence should be understood as a large (internal) energy (density) fluctuation of the system (1) using the canonical partition function, compute the second moment of the internal energy fluctuation: ( (f2) where h is the system hamiltonian (for simplicity we consider a large but finite syste (2) relate cv to the energy fluctuation this is an almost obvious question