Adiabatic halving: T_f/T_i = 2^(2/3) for γ=5/3 monatomic

Sympy-exact witness of the monatomic adiabatic halving temperature ratio. Setup: T_f/T_i = (V_i/V_f)^(γ-1) (rearranged Poisson adiabat). Identity: at V_f = V_i/2 and γ = 5/3, T_f/T_i = 2^(5/3 - 1) = 2^(2/3) — the canonical monatomic…