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On gravitational-quantum systems and the emergence of spacetime

  • Guilherme Franzmann
    • Nordic Institute for Theoretical Physics


What is a physical subsystem? How classical physical subsystems localized in spacetime are identified from quantum ones? Traditionally, classical systems have been uniquely identified with quantum systems, typically represented as factors in Hilbert space for finite-dimensional systems or associated with a local algebra of operators in QFT. Both representations aim to instantiate a specific prescription of subsystems' independence, that they must be statistically independent for state preparations and measurements. Despite this prescription, it is easy to show that canonical linearized quantum gravity prevents us from obtaining a gauge-invariant local algebra, thus undermining one of the conditions needed for statistical independence of subsystems in QFT. Arguably, this precludes most of the modeling associated with early universe cosmology as well as current attempts to model gravity-induced-entanglement table-top experiments. Nonetheless, primarily it presents a major roadblock towards a theory of quantum gravity. In this talk, after reviewing the aforementioned points, I will propose that a way forward is a particular approach to spacetime emergence where locally finite Hilbert spaces are considered.

On gravitational-quantum systems and the emergence of spacetime


Higgs Centre Seminar Room, JCMB (Find us on campus maps)
The Higgs Centre for Theoretical Physics
School of Physics and Astronomy
James Clerk Maxwell Building, 4305
Peter Guthrie Tait Road



Passcode: higgs_20