2010a. 'Relativity and Quantum Field Theories' Relativistic quantum field theories (RQFTs) are invariant under the action of the Poincaré group, the symmetry group of Minkowski spacetime. Non-relativistic quantum field theories (NQFTs) are invariant under the action of the symmetry group of a classical spacetime; i.e., a spacetime that minimally admits absolute spatial and temporal metrics. This essay is concerned with cashing out two implications of this basic difference. First, under a Received View, RQFTs do not admit particle interpretations. I argue (...) that the concept of particle that informs this view is motivated by non-relativistic intuitions associated with the structure of classical spacetimes, and hence should be abandoned. Second, the relations between RQFTs and NQFTs also suggest that routes to quantum gravity are more varied than is typically acknowledged. The second half of this essay is concerned with mapping out some of this conceptual space. (shrink)
Algebraic substantivalism, as an interpretation of general relativity formulated in the Einstein algebra formalism, avoids the hole argument against manifold substantivalism. In this essay, I argue that this claim is well-founded. I first identify the hole argument as an argument against a specific form of semantic realism with respect to spacetime. I then consider algebraic substantivalism as an alternative form of semantic realism. In between, I justify this alternative form by reviewing the Einstein algebra formalism and indicating the extent to (...) which it is expressively equivalent to the standard formalism of tensor analysis on differential manifolds. (shrink)
This essay considers the prospects of modeling spacetime as a phenomenon that emerges in the low-energy limit of a quantum liquid. It evaluates three examples of spacetime analogues in condensed matter systems that have appeared in the recent physics literature, indicating the extent to which they are viable, and considers what they suggest about the nature of spacetime.
In this essay, I consider what condensed matter physics has to say about the nature of spacetime. In particular, I consider the extent to which spacetime can be modeled as a quantum liquid, with matter and force fields described by effective field theories of the low-energy excitations of the liquid. After a brief review of effective field theories in 2-dim highly-correlated condensed matter systems, I evaluate analogies in the recent physics literature between spacetime and superfluid Helium, and proposals that suggest (...) spacetime is an emergent phenomenon arising from the edge states of a 4-dim Quantum Hall liquid. KeyworCh: spacetime, effective field theory, condensed matter, quantum gravity.. (shrink)
An effective field theory <span class='Hi'></span>(EFT)<span class='Hi'></span> is a theory of the dynamics of a physical system at energies small compared to a given cut-off.<span class='Hi'></span> Low-energy states with respect to this cut-off are effectively independent of states at high energies;<span class='Hi'></span> hence one may study the low-energy dynamics without the need for a detailed description of the high-energy dynamics.<span class='Hi'></span> Many authors have suggested that,<span class='Hi'></span> because of the essential role the cut-off plays in the standard <span class='Hi'></span>(Wilsonian)<span class='Hi'></span> (...) method of constructing an EFT,<span class='Hi'></span> an appropriate interpretation of an EFT requires a realistic interpretation of the cut-off.<span class='Hi'></span> For some,<span class='Hi'></span> this suggests an ontology of <span class='Hi'></span>"quasi-autonomous domains"<span class='Hi'></span> (Cao and Schweber 1993)<span class='Hi'></span>; for others,<span class='Hi'></span> it suggests an ontology in which space is discrete and finite <span class='Hi'></span>(Fraser 2009)<span class='Hi'></span>; and for yet others,<span class='Hi'></span> it suggests that EFTs engage in idealizations and are inherently approximate <span class='Hi'></span>(Fraser 2009,<span class='Hi'></span> Castellani 2002)<span class='Hi'></span>. I argue that these interpretations are not forced upon us,<span class='Hi'></span> in so far as there is an alternative to the Wilsonian method for constructing an EFT that does not explicitly employ a cut-off. (shrink)
Motivated by examples from general relativity and Newtonian gravitation, this essay attempts to distinguish 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 theory based on its dynamical structure, and a structural realist interpretation of spacetime, as described by a theory, based on its kinematical structure. I offer category-theoretic formulations of dynamical and kinematical structure and indicate the extent to which such (...) formulations deflect recent criticism of the radical ontic structural realist's conception of structure as "relations devoid of relata". (shrink)
In this essay, I consider the ontological status of spacetime from the points of view of the standard tensor formalism and three alternatives: twistor theory, Einstein algebras, and geometric algebra. I briefly review how classical field theories can be formulated in each of these formalisms, and indicate how this suggests a structural realist interpretation of spacetime.
In the debate over scientific realism, attention has been given recently to a realist position referred to as structural realism. In this essay, I offer a version of this position and indicate how it addresses two standard forms of underdetermination argument posed by the anti-realist.
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 one may study the low-energy sector of the theory without the need for a detailed description of the high-energy sector. Systems that admit EFTs appear in both relativistic quantum field theory (RQFT) and condensed (...) matter physics. In some cases, the high-energy theory is known and the effective theory may be obtained by a process in which high-energy effects are systematically eliminated. In other cases, the high-energy theory may not be known, and the effective theory may then be obtained by imposing symmetry and "naturalness" constraints on candidate Langrangians. Many physicists currently believe that the Standard Model of particle physics is an example of such a bottom-up EFT. In both cases, the nature of the intertheoretic relation between an EFT and its (possibly hypothetical) high-energy theory is complex and arguably cannot be described in terms of standard accounts of reduction. This essay provides a review of this relation and what it suggests about the ontological status of EFTs and the extent to which the notion of emergence can be associated with them. Keywords: effective field theory, quantum field theory, renormalization, emergence.. (shrink)
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 of a physical system 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. I will argue that such proofs suggest the Received View’s approach to ontology is flawed. (shrink)
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. Keywords: structural realism, category theory, general relativity.. (shrink)
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.
According to a Received View, 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 results, however, do not hold for nonrelativistic QFTs. I argue that this is due to the absolute (...) structure of the classical spacetimes associated with such theories. This suggests that the intuitions that underlie the Received View are non-relativistic. Thus, to the extent that such intuitions are inappropriate in the relativistic context, they should be abandoned when it comes to interpreting RQFTs. (shrink)
Relativistic quantum field theories (RQFTs) are invariant under the action of the Poincaré group, the symmetry group of Minkowski spacetime. Non-relativistic quantum field theories (NQFTs) are invariant under the action of the symmetry group of a classical spacetime; i.e., a spacetime that minimally admits absolute spatial and temporal metrics. This essay is concerned with cashing out two implications of this basic difference. First, under a Received View, RQFTs do not admit particle interpretations. I will argue that the concept of particle (...) that informs this view is motivated by nonrelativistic intuitions associated with the structure of classical spacetimes, and hence should be abandoned. Second, the relations between RQFTs and NQFTs also suggest that routes to quantum gravity are more varied than is typically acknowledged. The second half of this essay is concerned with mapping out some of this conceptual space. (shrink)
In this essay, I examine the curved spacetime formulation of Newtonian gravity known as Newton–Cartan gravity and compare it with flat spacetime formulations. Two versions of Newton–Cartan gravity can be identified in the physics literature—a ‘‘weak’’ version and a ‘‘strong’’ version. The strong version has a constrained Hamiltonian formulation and consequently a well-defined gauge structure, whereas the weak version does not (with some qualifications). Moreover, the strong version is best compared with the structure of what Earman (World enough and spacetime. (...) Cambridge: MIT Press) has dubbed Maxwellian spacetime. This suggests that there are also two versions of Newtonian gravity in flat spacetime—a ‘‘weak’’ version in Maxwellian spacetime, and a ‘‘strong’’ version in Neo-Newtonian spacetime. I conclude by indicating how these alternative formulations of Newtonian gravity impact the notion of empirical indistinguishability and the debate over scientific realism. r 2004 Elsevier Ltd. All rights reserved. (shrink)
Einstein algebras have been suggested (Earman 1989) and rejected (Rynasiewicz 1992) as a way to avoid the hole argument against spacetime substantivalism. In this article, I debate their merits and faults. In particular, I suggest that a gauge‐invariant interpretation of Einstein algebras that avoids the hole argument can be associated with one approach to quantizing gravity, and, for this reason, is at least as well motivated as sophisticated substantivalist and relationalist interpretations of the standard tensor formalism.
We have now celebrated the centenary of J. J. Thomson’s famous paper (1897) on the electron and have examined one hundred years of the history of our first fundamental particle. What should philosophers of science learn from this history? To some, the fundamental moral is already suggested by the rapid pace of this history. Thomson’s concern in 1897 was to demonstrate that cathode rays are electrified particles and not aetherial vibrations, the latter being the “almost unanimous opinion of German physicists” (...) (p. 293) But were these German physicists so easily vanquished? De Broglie proposed in 1923 that electrons are a wave phenomenon after all and his proposal was soon multiply vindicated, even by the detection of the diffraction of the electron waves. Should we not learn from such a reversal? Should we not dispense with the simple-minded idea that Thomson discovered our first fundamental particle and admit that the very notion of discovery might well be ill-suited to science? (shrink)
This essay touches on a number of topics in philosophy of quantum field theory from the point of view of the LSZ asymptotic approach to scattering theory. First, particle/field duality is seen to be a property of free field theory and not of interacting QFT. Second, it is demonstrated how LSZ side-steps the implications of Haag's theorem. Finally, a recent argument due to Redhead (1995), Malament (1996) and Arageorgis (1995) against the concept of localized particle states is addressed. Briefly, the (...) argument observes that the Reeh-Schlieder theorem entails that correlations between spacelike separated vacuum expectation values of local field operators are always present, and this, according to the above authors, dictates against the notion of a localized particle state. I claim that this moral is excessive and that a coherent notion of localized particles is given by the LSZ approach. The underlying moral to be drawn from this analysis is that questions concerning the ontology of interacting QFT cannot be appropriately addressed if one restricts oneself to the free theory. (shrink)
In recent articles, Zangari (1994) and Karakostas (1997) observe that while an &unknown;-extended version of the proper orthochronous Lorentz group O + (1,3) exists for values of &unknown; not equal to zero, no similar &unknown;-extended version of its double covering group SL(2, C) exists (where &unknown;=1-2&unknown; R , with &unknown; R the non-standard simultaneity parameter of Reichenbach). Thus, they maintain, since SL(2, C) is essential in describing the rotational behaviour of half-integer spin fields, and since there is empirical evidence for (...) such behaviour, &unknown;-coordinate transformations for any value of &unknown;<>0 are ruled out empirically. In this article, I make two observations:(a)There is an isomorphism between even-indexed 2-spinor fields and Minkowski world-tensors which can be exploited to obtain generally covariant expressions of such spinor fields.(b)There is a 2-1 isomorphism between odd-indexed 2-spinor fields and Minkowski world-tensors which can be exploited to obtain generally covariant expressions for such spinor fields up to a sign. Evidence that the components of such fields do take unique values is not decisive in favour of the realist in the debate over the conventionality of simultaneity in so far as such fields do not play a role in clock synchrony experiments in general, and determinations of the one-way speed of light in particular.I claim that these observations are made clear when one considers the coordinate-independent 2-spinor formalism. They are less evident if one restricts oneself to earlier coordinate-dependent formalisms. I end by distinguishing these conclusions from those drawn by the critique of Zangari given by Gunn and Vetharaniam (1995). (shrink)
In this essay I examine a recent argument by Steven Weinberg that seeks to establish local quantum field theory as the only type of quantum theory in accord with the relevent evidence and satisfying two basic physical principles. I reconstruct the argument as a demonstrative induction and indicate it's role as a foil to the underdetermination argument in the debate over scientific realism.
In 1922 in The Principle of Relativity, Whitehead presented an alternative theory of gravitation in response to Einstein’s general relativity. To the latter, he objected on philosophical grounds—specifically, that Einstein’s notion of a variable spacetime geometry contingent on the presence of matter (a) confounds theories of measurement, and, more generally, (b) is unacceptable within the bounds of a reasonable epistemology. Whitehead offered instead a theory based within a comprehensive philosophy of nature. The formulal Whitehead adopted for the gravitational field has (...) been described as involving both the flat metric nu, of Minkowski spacetime and a dynamic metric gu, dependent on the presence of source masses. The ontological relationship between the two must be fleshed out in the context of Whitehead’s philosophy of nature. The relationship is of some importance, not only in casting Whitehead’s theory within its proper metaphysical context vis-d—vis Einstein, but also in judging how the theory has faired empirically with respect to general relativity (GR hereafter). It makes the same predictions as GR with respect to the perihelion advance, the deflection of light rays and the gravitational red-shift; indeed, Eddington (1924) has shown that it is equivalent to the Schwarzschild solution of Einstein’s held equations for the one-body problem. However, it also appears to predict an anisotropy in the locally measured gravitational constant y that is in conflict.. (shrink)