Friedmann equations from nonequilibrium thermodynamics of the Universe: A unified formulation for modified gravity
Friedmann equations from nonequilibrium thermodynamics of the Universe: A unified formulation for modified gravity
Inspired by the Wald-Kodama entropy $S=A/(4{G}_{\text{eff}})$ where $A$ is the horizon area and ${G}_{\mathrm{eff}}$ is the effective gravitational coupling strength in modified gravity with field equation ${R}_{\ensuremath{\mu}\ensuremath{\nu}}\ensuremath{-}R{g}_{\ensuremath{\mu}\ensuremath{\nu}}/2=\phantom{\rule{0ex}{0ex}}8\ensuremath{\pi}{G}_{\mathrm{eff}}{T}_{\ensuremath{\mu}\ensuremath{\nu}}^{(\text{eff})}$, we develop a unified and compact formulation in which the Friedmann equations can be derived from thermodynamics of the Universe. The Hawking and …