Dark Matter = Modified Gravity? Scrutinising the spacetime-matter distinction through the modified gravity/ dark matter lens

TL;DR

This paper critically examines the conceptual boundary between matter and spacetime through the lens of modified gravity and dark matter theories, using superfluid dark matter as a case study to challenge traditional distinctions.

Contribution

It introduces criteria for matter and spacetime, and applies them to superfluid dark matter, revealing it embodies both properties simultaneously, questioning the clear-cut distinction.

Findings

The scalar field in SFDM meets criteria for both matter and spacetime.

SFDM's properties blur the traditional boundary between matter and spacetime.

The results challenge the conceptual separation of matter and spacetime in physics.

Abstract

This paper scrutinises the tenability of a strict conceptual distinction between space(time) and matter via the lens of the debate between modified gravity and dark matter. In particular, we consider Berezhiani and Khoury's novel 'superfluid dark matter theory' (SFDM) as a case study. Two families of criteria for being matter and being spacetime, respectively, are extracted from the literature. Evaluation of the new scalar field postulated by SFDM according to these criteria reveals that it is as much (dark) matter as anything could possibly be, but also$-$below the critical temperature for superfluidity$-$as much (of a modification of) spacetime as anything could possibly be. A sequel paper examines possible interpretations of SFDM in light of this result, as well as the consequences for our understanding of (the importance of) the modified gravity/ dark matter distinction and the broader spacetime-matter distinction.