OBSERVERS IN QUANTUM GRAVITY


Markus Mueller

University of Vienna


Title

Quantum theory and the structure of spacetime in the light of operationalism


Abstract

Quantum theory and the structure of spacetime in the light of operationalism Some approaches to quantum gravity, e.g. the AdS/CFT correspondence or Sean Carroll’s approach, promote the idea that spacetime can ultimately be reconstructed from the structure of (some underlying) quantum theory. In this talk, I sketch a research program that aims at studying aspects of this idea without committing to a particular model or ansatz. Namely, simple thought experiments of communicating observers, based only on what we currently know about physics, can shed light on the structural relation between quantum theory and spacetime — in both directions. I will first present a simple thought experiment that shows how relativity of simultaneity constrains the structure of the quantum bit, without assuming the validity of quantum theory from the outset [1]. Then I will show that this kind of reasoning can be extended and reversed: if we assume the validity of quantum theory and the existence of certain types of “universal measurement procedures” (but make no assumptions about spacetime), then observers will automatically relate their descriptions of local laboratory physics by elements of the Lorentz group SO(3,1) [2]. Thus, taking the question of “how observers operate in a quantum world” seriously can help illuminate the relation between two seemingly separate aspects of physics.

[1] A.J.P. Garner, M.P. Mueller, and O. C. O. Dahlsten, The complex and quaternionic quantum bits from relativity of simultaneity on an interferometer, Proc. R. Soc. A 473, 20170596 (2017); arXiv:1412.7112
[2] P.A. Hoehn and M.P. Mueller, An operational approach to spacetime symmetries: Lorentz transformations from quantum communication, New J. Phys. 18, 063026 (2016); arXiv:1412.8462


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