Lecture by ICE Fellow Philipp Höhn

Wilder Hall, Room 202, Dartmouth College
Reference frames provide the vantage points from which to describe the remaining physics. General covariance essentially posits that “all the laws of physics are the same in every reference frame.” While this is an established pillar of general relativity and usually interpreted in terms of coordinate invariance, its fate in the quantum realm remains an open question. This is a challenge because treating frames fundamentally as quantum systems themselves is inevitable in quantum gravity, where coordinates are a priori unavailable, but also in quantum foundations once accepting that all frames are physical systems. Both fields thus face the question of how to describe physics from the perspective of quantum frames and how the descriptions relative to different such choices are related. Philipp Höhn summarizes a recent “perspective-neutral” approach to such quantum frame perspective changes, which works in analogy to coordinate changes on a manifold, except that these “quantum coordinate changes” proceed between different Hilbert spaces. He then focuses on temporal reference frames, i.e., quantum clocks, and uses this approach to argue for a new perspective on the infamous problem of time in quantum gravity and the “wave function of the universe.”