Title: 'Concepts of fundamentality: the case of information'
A familiar – perhaps traditional - conception of fundamental physics is as follows: physics presents the world as being populated at the basic level (or the pro tem basic level) by various fields or/and particles, and it furnishes equations describing how these items evolve and interact with one another over time, equations couched primarily in terms of such properties as energy, mass, and various species of charge. This evolution may be conceived to take place against a fixed background spatiotemporal arena of some kind, or in one alternative, it may well be conceived that the arena has a metrical structure which should also be treated as particular kind of field, itself subject to dynamical equations (as in General Relativity). But in recent years, stemming primarily from developments in quantum information theory and related thinking in quantum theory itself, an alternative conception has been gaining momentum, one which sees the concept of information playing a much more fundamental role in physics than this traditional picture would allow. This alternative conception urges that information must be recognised as a fundamental physical quantity, a quantity which in some sense should be conceived as being on a par with energy, mass, or charge. Perhaps even, according to strong versions of the conception, information should be seen as the new subject-matter for physics, displacing the traditional conception of material particles and fields as being the fundamental subject matter.
These are bold and interesting claims on the part of information, and regarding what is said to follow from the successes of quantum information theory. Are they well-motivated? Are they true? I will explore these issues by attempting, first of all, to delineate various ways in which something (object, structure, property, or concept) might be thought to be physically fundamental. On at least one prima facie plausible carving of the notion of fundamentality, one should distinguish between the logically independent notions of ontological fundamentality, nomological fundamentality, and explanatory fundamentality. Something is ontologically fundamental if it is posited by the most fundamental description of the world; it is nomologically fundamental if reference to it is necessary to state the physical laws in some domain; and it is explanatorily fundamental if positing it is necessary in explanation and understanding. It is straightforward to show that the concept of information is not ontologically fundamental (or more cagily put: that there is nothing at all about the successes of quantum information theory that would warrant thinking it to be ontologically fundamental), but the questions of nomological and explanatory fundamentality of information are harder to settle so succinctly.