Talks

We introduce a new top down approach to canonical quantum gravity, called Algebraic Quantum Gravity (AQG): The quantum kinematics of AQG is determined by an abstract $*-$algebra generated by a countable set of elementary operators labelled by an algebraic graph. The quantum dynamics of AQG is governed by a single Master Constraint operator. While AQG is inspired by Loop Quantum Gravity LQG), it differs drastically from it because in AQG there is fundamentally no topology or differential structure. The missing information about the topology and differential structure of the spacetime manifold as well as about the background metric to be approximated is supplied by coherent states and is therefore only available in the semiclassical sector of the theory. Given such data, the corresponding coherent state defines a sector in the Hilbert space of AQG which can be identified with a usual QFT on the given manifold and background. Thus, AQG contains QFT on all curved spacetimes at once, possibly has something to say about topology change and provides the contact with the familiar low energy physics. We will show that AQG admits a semiclassical limit whose infinitesimal gauge symmetry generators agree with the ones of General Relativity.

I will first argue that the notion of black hole entropy extends universally to causal horizons. Then I will deduce the causal dynamics of spacetime from the equilibrium thermodynamics of causal horizons. Specifically, it will be shown how the Clausius relation dS = dQ/T between entropy change, energy flux, and acceleration temperature for all local causal horizons implies the Einstein equation, with Newton's constant determined by the universal horizon entropy density. Implications, non-equilibrium processes, and relations to AdS/CFT duality will also be discussed.