Abstract
The tradition of a strict conceptual dichotomy between space(time) and matter--all entities and structures in our universe are to be categorised and conceptualized as either spacetime or matter, never both, never neither--originates with Democritus’ atomism--everything in our universe is ultimately reducible to either atoms (matter) or void (space)–and has reigned supreme ever since Newton. The framework of Newtonian mechanics typically includes a collection of point particles (representing e.g. the planets) that obey an action-reaction principle, carry energy and have mass, as well as a static, immutable space, which was often thought of as the arena or theatre in which the play performed by the planets unfolds. This picturesque way of thinking about Newtonian space is echoed by the famous container metaphor according to which space is conceived of as a container for matter, i.e. the contained (Sklar, 1974).
Although this strict conceptual dichotomy did make a lot of sense in the context of our pre-20th-century worldview, this paper contends that it is no longer tenable, and even a hindrance to further progress. More precisely, each of the main ingredients--General Relativity, inflation, dark matter and dark energy--of our highly-successful and well-established standard model of cosmology that was developed over the course of the 20th century puts pressure on the outdated Newtonian idea that the space(time) and matter concepts can and should be strictly distinguished.
This paper focuses on 1) comparing dark matter to its modified gravity alternatives, as well as 2) comparing various models of dark energy, including a cosmological constant and modified gravity alternatives. Dark energy is typically referred to as the intrinsic energy of spacetime, but ‘carrying energy’ is also a paradigmatic property of matter--some models even associate a mass with dark energy. Then again, the simplest interpretation of dark energy as a cosmological constant suggests that it has to do with the nomological structure rather than the gravitational/spacetime structure or the matter content of the universe. This paper analyses the various senses in which dark matter and dark energy and the respective modified gravity alternatives suggest a breakdown of the traditional spacetime-matter dichotomy. It furthermore investigates the consequences of these breakdowns for the philosophical debate between substantivalism and relationalism about spacetime. To the extent that dark matter and dark energy are not pure spacetime or pure matter but a mixture of both, the container metaphor clearly makes no sense anymore--what would it even mean for these entities to be both the container and contained in itself--and hence the traditional substantivalist and relationalist positions do not straightforwardly apply to theories including these entities (contra Baker, 2005).
