Emergent spacetime and empirical (in)coherence

TL;DR

This paper explores how theories of quantum gravity without fundamental spacetime can still account for observable localized entities, addressing the challenge of empirical coherence.

Contribution

It provides a survey of quantum gravity theories and discusses how localized entities can emerge and be empirically accessible despite the absence of fundamental spacetime.

Findings

Emergent spacetime can support localized entities.

Theories can be empirically coherent despite lacking fundamental spacetime.

Formal derivations can show the reality of localized entities.

Abstract

Numerous approaches to a quantum theory of gravity posit fundamental ontologies that exclude spacetime, either partially or wholly. This situation raises deep questions about how such theories could relate to the empirical realm, since arguably only entities localized in spacetime can ever be observed. Are such entities even possible in a theory without fundamental spacetime? How might they be derived, formally speaking? Moreover, since by assumption the fundamental entities can't be smaller than the derived (since relative size is a spatiotemporal notion) and so can't 'compose' them in any ordinary sense, would a formal derivation actually show the physical reality of localized entities? We address these questions via a survey of a range of theories of quantum gravity, and generally sketch how they may be answered positively.