The Kinematics of Quantum Gravity

Abstract

While quantum field theories are relatively unrestrictive, the consistency of quantum gravity places enormous constraints on the allowed degrees of freedom and dynamics, leading to a growing web of swampland conjectures. In this thesis, we focus solely on the kinematic swampland conjectures, and outline a unified description. Starting from the basics of black hole physics and the holographic principle, we review the basic kinematic swampland conjectures, including the absence of global symmetries and the completeness of the charge spectrum. We then argue formally that these two conjectures are not independent, but are in fact one and the same, provided that one adopts a suitably broadened notion of symmetry. However, by including fluctuations of the topology of spacetime in the form of gravitational solitons, we find that the situation simplifies. The endpoint of this line of thought is the swampland cobordism conjecture, which we introduce, motivate from various perspectives, and test in string theory. The net result of the ideas presented in this thesis is to unify the kinematic swampland to a single physical principle: the topological triviality of quantum gravity.