First principle study of gravitational pressure and thermodynamics of FRW universe

A bstract We make a first principle study of gravitational pressure in cosmic thermo- dynamics. The is directly derived from the unified law, fact Einstein field equation spherically symmetric spacetime. By using this pressure, we obtain thermodynamics for FRW universe, especially presenting state spacetime itself, i.e. P = ( R , T ) time. Furthermore, Joule-Thomson expansion as an application thermodynamic to find cooling-heating property universe. demonstrate that there inversion temperature universe if its enthalpy ℋ negative. These investigations shed insights on evolution our view thermodynamics.