Guilherme Franzmann

Some proposed tabletop experiments aim to test whether gravity is quantum by placing two small masses in superpositions of different locations and looking for entanglement between them. This paper examines a usually implicit premise: that the masses and their measurements can be treated as independent subsystems. In perturbative quantum gravity, gauge constraints and each mass’s gravitational field make that separation less exact. The paper explains why this matters for how such experiments are modelled and interpreted, while estimating the effect to be negligible at current experimental sensitivities.

Quantum theory normally lets us divide a larger system into parts and ask what belongs to each part. This invited talk considered why that familiar move becomes difficult in quantum gravity: gravity links matter, location, and the surrounding field, so a subsystem may not have a perfectly sharp, self-contained boundary. The central issue is how to describe quantum-gravitational subsystems without assuming from the outset the independent pieces that the theory is meant to explain.

There are several distinct meanings of “independent” in quantum physics: systems may have separately measurable observables, allow separately chosen states, or combine through a simple product structure. This talk compared those meanings in quantum mechanics and quantum field theory using a common mathematical language for states and observables. It then considered how quantum gravity challenges them and what kinds of revised or approximate subsystem descriptions might be needed.

Instead of assuming spacetime as a fixed stage, some approaches ask whether its geometry could arise from quantum degrees of freedom. This talk presented that possibility through questions about distance, locality, and causal relations. The challenge is not only to recover something that behaves like spacetime, but also to identify consequences that could eventually distinguish the idea through cosmological observations or laboratory experiments.

This art–science project translated a research question into a physical encounter: a printed paper sits inside a black box on a mirror. Opening the box to identify what is ‘inside’ also places the viewer in the scene, echoing the paper’s question of how a physical system’s boundary and location depend on relations rather than simply being given in advance.

The collaboration also prompted a reflection on the economics of making work. Academics are usually paid through a salary, while artists may need the sale of an individual work to cover both materials and the time needed to make it.