Research on Quantum Theories of Gravity and Spacetime (Physics)

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The program of Dr. Jacobson is primarily on quantumgravity. The research involves several facets of that subject: 1) Conceptual problems of extending the probabilisticinterpretation of quantum theory to quantum gravity will bestudied; 2) The difficulty of applying the usual framework ofquantization to a system with vanishing hamiltonian will beanalyzed with the help of a class of simple models; 3) Spacetime slicings which render the hamiltonian of general relativity positive will be studied; 4) Discrete models of spacetime will be studied from two points of view: a) Hints will be sought from all quarters as to the possible nature of discrete spacetime, including black hole thermodynamics, energy-momentum conservation requirements and interpretive requirements of quantum theory; b) The properties of specific discrete spacetime models (spin networks, causal sets,...) will be explored. Broadly speaking, this research is motivated by the belief that the problem of quantum gravity fundamentally requires a quantum theory of spacetime itself, as opposed to aquantization of classical gravity.