Philosophy of Physics Seminar (Thursday - Week 5, TT22)

The characteristic – Planck – energy scale of quantum gravity is utterly beyond current technology, making experimental access to the relevant physics apparently impossible. Nevertheless, low energy experiments linking gravity and the quantum have been undertaken: the Page and Geilker quantum Cavendish experiment, and the Colella-Overhauser-Werner neutron interferometry experiment, for instance. However, neither probes states in which gravity remains in a coherent quantum superposition, unlike — it is claimed — recent proposals that have created considerable interest among physicists. In essence, if two initially unentangled subsystems interacting solely via gravity become entangled, then a simple theorem of quantum mechanics shows that gravity cannot be a classical subsystem. There are formidable challenges to creating such a system, but remarkably, tabletop technology into the gravitational fields of very small bodies has advanced to the point that such an experiment might be feasible in the next several years. In this talk I will explain the proposal and what it aims to show, highlighting the important ways in which its interpretation is theory-laden. (Drawn from joint work with Niels Linnemann and Mike Schneider.)