Emergent spacetime and empirical (in)coherence

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.Comment: 18 pages, 1 figure, accepted for publication in Studies in History and Philosophy of Modern Physic

Priority Monism Beyond Spacetime

“…Huggett and Wüthrich 2013). These structures can be thought of as being made of "spacetime atoms" with particular properties, and must give rise to a structure similar to general relativity in order to explain its predictive success in the domains where general relativity has been well-confirmed.…”

Incubating a future metaphysics: quantum gravity

“…Geometry in general relativity is modeled by the mathematical metric field G. 19 This field encodes all the geometric properties which we associate with the relativistic spacetime of GR. Spatial lengths, areas, volumes, and temporal duration are all encoded by the field G. Physical properties such as momentum, force, and energy are also modeled, at least in part, by the metric field.…”

“…However, as mentioned above, the quantum states of LQG are able to reproduce or mimic the geometry of GR (in special cases). In this way, spacetime-qua the geometry of GR-is an effective structure (see Huggett and Wüthrich (2013)). If one interprets effective structures as having an existence all their own, over and above fundamental reality, then one might claim spacetime to be an emergent piece of ontology.…”

The Interpretation of String-Theoretic Dualities

“…For the five superstring theories, this suspected unifying theory is known as M-theory, and was first proposed by Witten in 1995 [21]. Witten offers the following summary of the situation:…”