JACQUES PIENAAR: What is so quantum about quantum reference frames?

The concept of a "quantum reference frame" has been explored by physicists and philosophers working together as a way to make sense of the idea of quantum superpositions of space-times. At the center of this activity is what I consider to be one of quantum gravity's deepest puzzles: how to identify space-time points between different "possible worlds"? I will argue that many of the puzzling and counter-intuitive features exhibited by quantum reference frames can already be found in the simpler problem of constructing a classical probabilistic theory of gravity.