Einstein Gravity as an emergent phenomenon?

TL;DR

This paper argues that Einstein gravity may be an emergent phenomenon arising from more fundamental theories, with effective spacetime geometry and dynamics emerging at low energies and long distances.

Contribution

It provides a conceptual framework linking emergent spacetime geometry with classical and quantum field theories, explaining the universality of Einstein gravity as an effective low-energy theory.

Findings

Emergent curved spacetime from linearized scalar fields.

One-loop quantum corrections produce Einstein-Hilbert action.

Effective gravity is insensitive to high-energy details.

Abstract

In this essay we marshal evidence suggesting that Einstein gravity may be an emergent phenomenon, one that is not ``fundamental'' but rather is an almost automatic low-energy long-distance consequence of a wide class of theories. Specifically, the emergence of a curved spacetime ``effective Lorentzian geometry'' is a common generic result of linearizing a classical scalar field theory around some non-trivial background. This explains why so many different ``analog models'' of general relativity have recently been developed based on condensed matter physics; there is something more fundamental going on. Upon quantizing the linearized fluctuations around this background geometry, the one-loop effective action is guaranteed to contain a term proportional to the Einstein--Hilbert action of general relativity, suggesting that while classical physics is responsible for generating an ``effective geometry'', quantum physics can be argued to induce an ``effective dynamics''. This physical picture suggests that Einstein gravity is an emergent low-energy long-distance phenomenon that is insensitive to the details of the high-energy short-distance physics.