Speaker
Description
In classical general relativity, we measure the gravitational field indirectly by probing it with test particles and fields. In this talk, I want to address to what extent we can do the same in the quantum theory, focusing on the low-energy regime of quantum gravity, which has seen much recent progress through the use of tools from quantum information theory. There are two challenges when trying to model a test particle probing the quantum state of the gravitational field: one technical, the other more fundamental. On the technical side, one needs to find the appropriate approximation to obtain a tractable problem. After discussing briefly some of the possible strategies, we will focus on a Born-Oppenheimer approximation, treating the linearised quantum gravitational field as a slow background degree of freedom, compared to a light test particle. More fundamentally, probing the quantum state of the gravitational field indirectly, i.e. without direct access to the gravitational field itself, means that we have to trace out the gravitational degrees of freedom, generally leading to a loss of coherence also in the test particles’ state. The question thus arises to what extent we can make inferences about the quantum properties of the gravitational field by measurements on the test particle alone.
