English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Quantum field theory - our basic framework for describing allnon-gravitational physics - conflicts with general relativity: the latterprecludes the standard definition of the former's essential principle oflocality, in terms of commuting local observables. We examine this conflictmore carefully, by investigating implications of gauge (diffeomorphism)invariance for observables in gravity. We prove a dressing theorem, showingthat any operator with nonzero Poincare charges, and in particular anycompactly-supported operator, in flat-spacetime quantum field theory must begravitationally dressed once coupled to gravity, i.e. it must depend on themetric at arbitrarily long distances, and we put lower bounds on this nonlocaldependence. This departure from standard locality occurs in the most severe waypossible: in perturbation theory about flat spacetime, at leading order inNewton's constant. The physical observables in a gravitational theory thereforedo not organize themselves into local commuting subalgebras: the principle oflocality must apparently be reformulated or abandoned, and in fact we lack aclear definition of the coarser and more basic notion of a quantum subsystem ofthe Universe. We discuss relational approaches to locality based ondiffeomorphism-invariant nonlocal operators, and reinforce arguments that anysuch locality is state-dependent and approximate. We also find limitations tothe utility of bilocal diffeomorphism-invariant operators that are consideredin cosmological contexts. An appendix provides a concise review of thecanonical covariant formalism for gravity, instrumental in the discussion ofPoincare charges and their associated long-range fields.

Observables, gravitational dressing, and obstructions to locality and subsystems