  The thermodynamics of local causal horizons has been shown to imply
gravitational dynamics. In this essay, we discuss the principles underlying
this observation, and its significance in our understanding of (quantum)
gravity. We also show why the local thermodynamic methods cannot by themselves
recover general relativity. Instead, they lead to the so-called Weyl transverse
gravity. Because of this, local thermodynamic approaches avoid huge vacuum
energy contributions to the cosmological constant. They even suggest a possible
source for its small observed value. We also outline a way in which
thermodynamics allows us to study low energy quantum gravitational effects. We
arrive at quantum corrections to the gravitational equations which are
suppressed by the Planck length squared.

General Relativity and Quantum Cosmology;High Energy Physics - Theory