Emergent/Quantum Gravity: Macro/Micro Structures of Spacetime

TL;DR

This paper discusses the emergent nature of spacetime and gravity, emphasizing the need for a microscopic theory beyond quantization of classical variables, and explores pathways to understand the micro-macro transition in spacetime structure.

Contribution

It provides a conceptual framework for understanding how macroscopic spacetime emerges from microscopic constituents and suggests methods to infer micro-structure clues from low-energy phenomena.

Findings

Identifies conditions for spacetime emergence from microscopic theories.

Proposes pathways to connect classical gravity with quantum micro-structures.

Highlights potential low-energy signatures of spacetime micro-structure.

Abstract

Emergent gravity views spacetime as an entity emergent from a more complete theory of interacting fundamental constituents valid at much finer resolution or higher energies, usually assumed to be above the Planck energy. In this view general relativity is an effective theory valid only at long wavelengths and low energies. For any presumed known theory for the microscopic structure of spacetime, we describe common tasks of emergent gravity (`top-down'), namely, identifying the conditions and processes or mechanisms whereby the familiar macroscopic spacetime emerges with high probability and reasonable robustness. Going in the opposite direction (`bottom-up') is the task of quantum gravity, i.e., finding a theory for the microscopic structure of spacetime, which, in this new view, cannot come from quantizing the metric or connection forms because they are the collective variables which are meaningful only for the macroscopic theory, i.e., general relativity. We suggest pathways to move `up' (in energy) from the given macroscopic conditions of classical gravity and quantum field theory to the domain closer to the micro-macro interface where spacetime emerged and places to look for clues or tell-tale signs at low energy where one could infer indirectly some salient features of the micro-structure of spacetime.