Flaminia Giacomini, ETH Zurich
Quantum reference frames
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It is generally accepted that the energies at which full quantum gravity effects will be relevant are so high that there is no chance of generating them in the laboratory. Full quantum gravity is only expected to be relevant in extreme environments like deep inside black holes or near the origin of the universe.
Nevertheless, there is interest is studying situations in which both quantum effects and gravity are important. Experiments can currently probe gravitational effects of masses as small as 90 milligrams, or quantum superpositions at scales of half a meter. These types of situations, though short of fully quantum gravitational in essence, can offer experimental guidance in a field that is notoriously short of it.
The talk focused on the issue of quantum reference frames. Reference frames are commonly used in physics and are treated as idealizations. In reality, any reference frame is a physical system and is subject to the laws of quantum mechanics like any other. Taking that into account leads to modifications in the form of the laws of physics from the one they take in idealized frames. In particular several important quantum properties like the "entanglement" that physical systems exhibit is a frame dependent phenomenon. Also the equivalence principle, the statement that all masses fall at the same acceleration in gravity, can be extended to be valid in quantum reference frames and in situations such as a massive object in a spatial quantum superposition.
The summary is that we do not currently know which experiments will prove definitively that gravity has quantum features, and probing regimes involving quantum mechanics and gravity can offer guidance on how to quantize gravity.
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