Jonathan Bain
Dept. of Technology, Culture and Society
Polytechnic School of Engineering, New York University


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2013f. 'Three Principles of Quantum Gravity in the Condensed Matter Approach'

Research on quantum gravity (QG) has historically relied on appeals to guiding principles.  This essay frames three such principles within the context of the condensed matter approach to QG.  I first identify two distinct versions of this approach, and then consider the extent to which the principles of asymptotic safety, relative locality, and holography are supported by these versions.  The general hope is that a focus on distinct versions of a single approach may provide insight into the conceptual and foundational significance of these principles.

2013e. 'Emergence in Effective Field Theories'
This essay considers the extent to which a concept of emergence can be associated with effective field theories (EFTs).  I suggest that such a concept can be characterized by microphysicalism and novelty underwritten by the elimination of degrees of freedom from a high-energy theory, and argue that this makes emergence in EFTs distinct from other concepts of emergence in physics that have appeared in the recent philosophical literature.
2013d. 'CPT, Spin and Statistics, and the Ontology of Relativistic Quantum Field Theories'
CPT invariance and the spin-statistics connection are typically taken to be essential properties in relativistic quantum field theories (RQFTs), insofar as the CPT and Spin-Statistics theorems entail that any state characterized by an RQFT must possess these properties.  Moreover, in the physics literature, they are typically taken to be properties of particles.  But there is a Received View among philosophers that RQFTs cannot fundamentally be about particles.  This essay considers what proofs of the CPT and Spin-Statistics theorems suggest about the ontology of RQFTs, and the extent to which this is compatible with the Received View.
2013c.
The Emergence of Spacetime in Condensed Matter Approaches to Quantum Gravity'
Condensed matter approaches to quantum gravity suggest that spacetime emerges in the low-energy sector of a fundamental condensate.  This essay investigates what could be meant by this claim.  In particular, I offer an account of low-energy emergence that is appropriate to effective field theories in general, and consider the extent to which it underwrites claims about the emergence of spacetime in effective field theories of condensed matter systems of the type that are relevant to quantum gravity.
2013b. 'Category-Theoretic Structure and Radical Ontic Structural Realism'
Radical Ontic Structural Realism (ROSR) claims that structure exists independently of objects that may instantiate it.  Critics of ROSR contend that this claim is conceptually incoherent, insofar as, (i) it entails there can be relations without relata, and (ii) there is a conceptual dependence between relations and relata.  In this essay I suggest that (ii) is motivated by a set-theoretic formulation of structure, and that adopting a category-theoretic formulation may provide ROSR with more support.  In particular, I consider how a category-theoretic formulation of structure can be developed that denies (ii), and can be made to do work in the context of formulating theories in physics.

2013a.
'Effective Field Theories'
An effective field theory (EFT) of a physical system is a theory of the dynamics of the system at energies small compared to a given cutoff.  For some systems, low-energy states with respect to this cutoff are effectively independent of ("decoupled from") states at high energies.  Hence you can study the low-energy sector of the theory without the need for a detailed description of the high-energy sector (this makes calculations easier, plus you don't have to worry about thorny issues like renormalizability).  Many physicists currently think that the Standard Model of particle physics is an example of an EFT of an, as yet, unknown high-energy theory.  This essay is a general review of EFTs; in particular, it identifies two conceptually distinct types ("Wilsonian" and "continuum"), and considers how they might be interpreted, and also what they say (and do not say) about the notion of emergence.
2011. 'Quantum Field Theories in Classical Spacetimes and Particles'
According to a Received View among philosophers, relativistic quantum field theories (RQFTs) do not admit particle interpretations.  This view requires that particles be localizable and countable, and that these characteristics be given mathematical expression in the forms of local and unique total number operators.  Various results (the
Reeh-Schlieder theorem, the Unruh Effect, Haag's Theorem) then indicate that formulations of RQFTs do not support such operators.  These mathematical results, however don't hold for non-relativistic quantum field thelories (NQFTs).  I point out that this is due to the absolute temporal structure of the classical spacetimes associated with NQFTs.  This seems to suggest that the choices that the Received View makes in mathematically representing its intuitions about the nature of particles are (implicitly) informed by non-relativistic intuitions.
2010. 'Relativity and Quantum Field Theories'
Relativistic quantum field theories (RQFTs) are invariant under the action of the symmetry group of a Lorentzian spacetime -- a spacetime that admits a Lorentzian (i.e., "relativistic") metric.  Non-relativistic quantum field theories (NQFTs) are invariant under the action of the symmetry group of a classical spacetime -- a spacetime that minimally admits separate absolute spatial and temporal metrics.  This essay is concerned with cashing out two implications of this basic difference.  First, it suggests that a Received View that claims RQFTs cannot support particle interpretations is perhaps implicitly biased with non-relativistic intuitions (this is argued for in more detail in 2011a).  Second, the relations between RQFTs and NQFTs also suggest that routes to quantum gravity are more varied than is typically acknowledged.  In particular, they suggest it should be conceptually possible to construct a quantum theory of gravity by taking the "thermodynamic limit" of a relativistic quantum "particle" (i.e., finite degrees of freedom) theory of gravity (although I have no idea how this might be made more precise).
2008.
'Condensed Matter Physics and the Nature of Spacetime'
Some condensed matter systems exhibit low-energy behavior that can be described by effective field theories that are formally similar to field theories that appear in other areas of physics.  The "acoustic" spacetime research programme, for instance, is based on modeling general relativity by the low-energy behavior of superfluid Helium 4 (and similar systems). Aspects of the Standard Model of particle physics can be modeled by the low-energy behavior of superfluid Helium 3-A, and aspects of conformal field theories (for which
twistors come in handy) can be modeled by the low-energy behavior of the edge of 4-dimensional quantum Hall liquids.  This paper evaluates such examples and considers what they have to tell us about the nature of spacetime; in particular, how they might impact the debate between substantivalists and relationalists.
2006. 'Spacetime Structuralism'
This paper goes hog-wild with a number of different mathematical formalisms (twistors, Einstein algebras, geometric algebra) that can be used to formulate classical field theories.  The point is to indicate that if you're predisposed to read ontology off of your formalism, then you'd be advised to dig deep and go for some notion of structure, seeing as how alternative formalisms can be very different beasts, indeed.
2004.
'Theories of Newtonian Gravity and Empirical Indistinguishability'
There's not just one, but many theories of Newtonian gravity.  Some are in flat spacetime, others are in curved spacetime.  Are they really different theories, or just different ways of formulating the same basic theory?  Inquiring minds want to know...
2003.
'Einstein Algebras and the Hole Argument'
Einstein algebras are abstract algebras that encode the essential structure associated with general relativity (GR).  They've been suggested, and rejected, as a way to avoid the Infamous Hole Argument against one way of interpreting GR.  This paper points out that some physicists are trying to use them to construct theories of quantum gravity, and that this gives them a bit more respectability than they've typically been afforded.
2001.
'What Should Philosophers of Science Learn from the History of the Electron?'  (with John Norton)
That it's structure that's retained across theory-change, and that structure is kinda hard to define in a precise way (although we do make an effort).
2000a.
'Against Particle/Field Duality:  Asymptotic Particle States and Interpolating Fields in Interacting QFT (or: Who's Afraid of Haag's Theorem?)'
This paper tries to indicate how the LSZ formalism that's used by practicing physicists suggests ways of interpreting fuzzy concepts like "particle" and "localization" in quantum field theory (as well as dealing with
Haag's Theorem).  And that these ways are to be preferred to the ways suggested by more abstract (and expressively incomplete) formalisms (like the algebraic formalism).
2000b.
'The Coordinate-Independent 2-component Spinor Formalism and the Conventionality of Simultaneity'
Some philosophers of spacetime have claimed that the structure associated with half-integer-spin (fermionic) fields can settle the debate over the conventionality of simultaneity.  This paper disputes this claim, in particular by calling attention to how fermionic fields can be represented in a manifestly coordinate-independent way.
1999.
'Weinberg on QFT:  Demonstrative Induction and Underdetermination'
This paper reviews an argument by Steven Weinberg that seeks to establish a particular formulation of quantum field theory as the only type of quantum theory in accord with the relevent evidence and satisfying two basic physical principles.  The paper reconstructs Weinberg's argument as a demonstrative induction and indicates it’s role as a (potential) foil to the underdetermination arugment in the debate over scientific realism.
1998.

'Whitehead's Theory of Gravity'
Everything you ever wanted to know about Whitehead's theory of gravity...

Drafts
1. 'Pragmatists and Purists on CPT Invariance in Relativistic Quantum Field Theories'
Philosophers of physics are split on whether foundational issues in relativistic quantum field theory (RQFT) should be framed within pragmatist approaches, which trade mathematical rigor for the ability to formulate non-trivial interacting models, or purist approaches, which trade the ability to formulate non-trivial interacting models for mathematical rigor.  This essay addresses this debate by viewing it through the lens of the CPT theorem.  I first consider two formulations of the CPT theorem, one purist and the other pragmatist, and extract from them a set of problems that clarifies the distinction between pragmatism and purity.  I then apply this distinction to Greenberg's (2002) influential claim that the violation of CPT invariance in an interacting RQFT entails the violation of (restricted) Lorentz invariance.  I show how this claim rests on an unsuccessful attempt to mediate between pragmatism and purity.  I then evaluate another attempt at such mediation in the form of causal perturbation theory.  This approach suggests that a focus on renormalized perturbation theory as a way of distinguishing pragmatists from purists may be misleading.
2. 'Interpreting Effective Field Theories'
A condensed version of (2013a).

3. 'Motivating Structural Realist Interpretations of Spacetime'
Our best theory of spacetime, general relativity (GR), admits different mathematical formulations which, if read literally, disagree at the level of individuals-based ontology.  This suggests a structural realist interpretation of GR that commits to the structure that all such alternative formulations have in common.  However, some authors have observed that different formulations of the same theory not only underdetermine individuals-based interpretations, but also the structure these individuals instantiate; hence appeals to alternative formalisms cannot motivate structural realism.  This essay offers a response by distinguishing between the dynamical structure associated with a theory in physics, and its kinematical structure.  This enables a distinction to be made between a structural realist interpretation of a given theory, and a structural realist interpretation of spacetime, as described by a given theory.  I claim that structural realist interpretations of different formulations of GR do not suffer from underdetermination of dynamical structure; and while different formulations of GR admit different structural realist interpretations of spacetime, the underdetermination involved is less severe than that associated with individuals.  Whereas the individuals-based ontologies associated with alternative formulations of spacetime are in-principle underdetermined, the structures they instantiate are open to empirical investigation in the form of extensions of GR.  Finally, I offer a category-theoretic formulation of kinematical structure and indicate how this formulation deflects recent criticism of the ontic structural realist concept of structure as "relations without relata".
4. 'Condensed Matter Physics and the Nature of Spacetime, Version 1'
The bloated companion to (2008) above. Includes reviews of some 2-dim EFTs in condensed matter systems.
5.
'Algebraic Substantivalism and the Hole Argument'
The bloated companion to (2003) above.

6.
'Towards Structural Realism'
A paper that's been stewing in its own juices for a while.  It suggests an epistemological leg for structural realism to stand on, based on formal learning theory.