Points, Particles, and Structural Realism

Abstract

First dra : July ; this dra : December Even if we are able to decide on a canonical formulation of our theory, there is the further problem of metaphysical underdetermination with respect to, for example, whether the entities postulated by a theory are individuals or not. . .We need to recognise the failure of our best theories to determine even the most fundamental ontological characteristic of the purported entities they feature. . . What is required is a shi to a di erent ontological basis altogether, one for which questions of individuality simply do not arise. Perhaps we should view the individuals and nonindividuals packages, like particle and eld pictures, as di erent representations of the same structure.ere is an analogy here with the debate about substantivalism in general relativity. (Ladyman )In his paper "What is Structural Realism?" ( ) James Ladyman drew a distinction between epistemological structural realism (ESR) and metaphysical (or ontic) structural realism (OSR). In recent years this distinction has set much of the agenda for philosophers of science interested in scienti c realism. It has also led to the emergence of a related discussion in the philosophy of physics that concerns the alleged di culties of interpreting general relativity that revolve around the question of the ontological status of spacetime points. Ladyman drew a suggestive analogy between the perennial debate between substantivalist and relationalist interpretations of spacetime on the one hand, and the debate about whether quantum mechanics treats identical particles as individuals or as 'non-individuals' on A version of this paper will appear in Rickles, French and Saatsi (eds), e Structural Foundations of Quantum Gravity, Oxford University Press. Please quote from and cite the published version.

Whence Ontological Structural Realism?

“…But there is a crucial disanalogy to the case of quantum statistics: the underdetermined alternatives in the spacetime case-haecceitism and anti-haecceitism with respect to spacetime points-concern the modal identity of spacetime points, not their individuality. (Pooley, 2006) Nevertheless, the lesson generalises. We can account for the the success of quantum statistics without reference to the metaphysical nature of particles.…”

“…So, prima 2 Ladyman (1998), French & Ladyman (2003) and French & Rickles (2003) defend this premise particularly for quantum particles and quantum fields, and tentatively point towards the nature of spacetime. Pooley (2006) dissents, especially regarding the underdetermined status of spacetime points. See also Redhead & Teller (1992) and Saunders (2003b) for criticism of the underdetermination thesis, and French & Krause (2006) for further defence.…”

Quantization as a Guide to Ontic Structure

“…In particular, it remains to be seen whether or not the specification of a structural ontology is on its own sufficient to resolve a genuine case of formulation driven ontological underdetermination (Pooley 2006). As is well illustrated by the alternative notion of 'structural realism' defended by North (2009) (her position is, within our terminology, a variant of conventional realism within which a geometric simplicity criterion is invoked in order to break formalism underdetermination), it is quite possible for the structural ontological vocabulary itself to be underdetermined if it is characterized in such a way as to be particular to each formalism.…”

“…However, such a characterisation of the structural ontology is also problematic. As further noted by Pooley (2006), such interrelations between formulations offer only a very thin notion of structure that alone seems insufficient to be the fundamental furniture of the world: what is needed is a 'single, unifying framework [which we can] interpret as corresponding more faithfully to reality than do its various [conventional] realist representations' (p.7). Thus, the challenge to the ontic structural realist is to offer more than a purely set theoretic characterisation of the common underlying structure invoked to dissolve cases of underdetermination.…”

On Some Troubles with the Metaphysics of Fermionic Compositions

“…See e.g. [2,[4][5][6]12,14,15,22,26]. Caulton [4] deserves to be singled out here as containing the most technically and conceptually advanced analysis of the permutation-invariant method of individuating quantum particles.…”