Statistical Physics from Quantum Envariance Principles

We build on the foundational work of Deffner and Zurek [S. Deffner and W. H. Zurek, {New J. Phys.18, 063013 (2016)}] to demonstrate how the principles of statistical mechanics can be derived from quantum mechanics using the concept of envariance (environment-assisted invariance). In particular, we show how the Binomial, Poisson, and Gaussian distributions naturally emerge from entangled system--environment states. Furthermore, we resolve the Gibbs paradox using entanglement entropy, obtaining the Sackur--Tetrode equation with quantum corrections. Extending this framework, we derive a modified Saha equation for ionization equilibrium and recover Bose--Einstein and Fermi--Dirac statistics from quantum symmetries. Our results reinforce and extend the view that statistical mechanics arises as a direct consequence of quantum information dynamics, rather than being founded on phenomenological postulates.