Kavli Affiliate: Yasunori Nomura
| First 5 Authors: Yasunori Nomura, Tomonori Ugajin, , ,
| Summary:
We study how meaningful physical predictions can arise in nonperturbative
quantum gravity in a closed Lorentzian universe. In such settings, recent
developments suggest that the quantum gravitational Hilbert space is
one-dimensional and real for each $alpha$-sector, as induced by spacetime
wormholes. This appears to obstruct the conventional quantum-mechanical
prescription of assigning probabilities via projection onto a basis of states.
While previous approaches have introduced external observers or augmented the
theory to resolve this issue, we argue that quantum gravity itself contains all
the necessary ingredients to make physical predictions. We demonstrate that the
emergence of classical observables and probabilistic outcomes can be understood
as a consequence of partial observability: physical observers access only a
subsystem of the universe. Tracing out the inaccessible degrees of freedom
yields reduced density matrices that encode classical information, with
uncertainties exponentially suppressed by the environment’s entropy. We develop
this perspective using both the Lorentzian path integral and operator
formalisms and support it with a simple microscopic model. Our results show
that quantum gravity in a closed universe naturally gives rise to meaningful,
robust predictions without recourse to external constructs.
| Search Query: ArXiv Query: search_query=au:”Yasunori Nomura”&id_list=&start=0&max_results=3