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- Jill North (2009). The “Structure” of Physics. The Journal of Philosophy 106 (2):57-88.We are used to talking about the “structure” posited by a given theory of physics. We say that relativity is a theory about spacetime structure. Special relativity posits one spacetime structure; different models of general relativity posit different spacetime structures. We also talk of the “existence” of these structures. Special relativity says the world’s spacetime structure is Minkowskian: it posits that this spacetime structure exists. Understanding structure in this sense seems important for understanding what physics is telling us about the world. But it is not immediately obvious just what this structure is, or what we mean by the existence of one structure, rather than another. The idea of mathematical structure is relatively straightforward. There is geometric structure, topological structure, algebraic structure, and so forth. Mathematical structure tells us how abstract mathematical objects t together to form different types of mathematical spaces. Insofar as we understand mathematical objects, we can understand mathematical structure. Of course, what to say about the nature of mathematical objects isn’t easy. But there seems to be no further problem for understanding mathematical structure. Modern theories of physics are formulated in terms of these mathematical structures. In order to understand “structure” as used in physics, then, it seems we must simply look at the structure of the mathematics that is used to state the physics. But it is not that simple. Physics is supposed to be telling us about the nature of the world. If our physical theories are formulated in mathematical language, using mathematical objects, then this mathematics is somehow telling us about the physical make-up of the world. What is..Reading list | Discuss | Edit | Categorize |My bibliography
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To what extent can constructive mathematics based on intuitionistc logic recover the mathematics needed for spacetime physics? Certain aspects of this important question are examined, both technical and philosophical. On the technical side, order, connectivity, and extremization properties of the continuum are reviewed, and attention is called to certain striking results concerning causal structure in General Relativity Theory, in particular the singularity theorems of Hawking and Penrose. As they stand, these results appear to elude constructivization. On the philosophical side, it is argued that any mentalist-based radical constructivism suffers from a kind of neo-Kantian apriorism. It would be at best a lucky accident if objective spacetime structure mirrored mentalist mathematics. the latter would seem implicitly committed to a Leibnizian relationist view of spacetime, but is it doubtful if implementation of such a view would overcome the objection. As a result, an anti-realist view of physics seems forced on the radical constructivist.
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| | Other links: bjps.oxfordjournals.org jstor.org bjps.oupjournals.org dx.doi.org | Scholar | At my library | More options ... 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".
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| | Other links: philsci-archive.pitt.edu | Scholar | More options ... In Mathematical Thought and Its Objects, Charles Parsons examines the notion of object, with the aim to navigate between nominalism, denying that distinctively mathematical objects exist, and forms of Platonism that postulate a transcendent realm of such objects. He introduces the central mathematical notion of structure and defends a version of the structuralist view of mathematical objects, according to which their existence is relative to a structure and they have no more of a “nature” than that confers on them.
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| | Scholar | At my library | More options ... This survey article is divided into two parts. In the first (section 2), I give a brief account of the structure of classical relativity theory. In the second (section 3), I discuss three special topics: (i) the status of the relative simultaneity relation in the context of Minkowski spacetime; (ii) the ``geometrized" version of Newtonian gravitation theory (also known as Newton-Cartan theory); and (iii) the possibility of recovering the global geometric structure of spacetime from its ``causal structure".
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| | Other links: philsci-archive.pitt.edu lps.uci.edu socsci.uci.edu | Scholar | At my library | More options ... This paper takes issue with Ontic Structural Realism (OSR). It is structured around the three elements of the title. Section 2 highlights a substantive non-structural assumption that needs to be in place before we can talk about the structure. Then, by drawing on some relevant issues concerning mathematical structuralism, it claims that (a) structures need objects and (b) scientific structuralism should focus on in re structures. But then pure structuralism is undermined. Section 3 discusses whether the world has ‘excess structure’ over the structure of appearances. The main point is: the claim that only structure can be known is false. Finally, section 4 argues directly against ORS that it lacks the resources to accommodate causation within the structuralist slogan that “all that there is, is structure”.
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| | Other links: journals.uchicago.edu dx.doi.org | Scholar | At my library | More options ... How do we figure out the fundamental nature of the world from a mathematically formulated physical theory? To figure out the nature of a world’s spacetime, we follow this rule: posit the least spacetime structure to the world that’s required by the fundamental dynamical laws. Applied to special relativity, for example, this rule tells us to not posit an absolute simultaneity structure.
I suggest that we use this rule for more than just spacetime structure. We should also posit the least statespace structure required by the fundamental dynamical laws. This rule yields surprising conclusions. Applied to classical mechanics, it suggests that a world governed by the theory has less fundamental structure than we ordinarily think. For the theory’s statespace imparts less structure to a world’s physical space than we ordinarily think.
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| | Scholar | More options ... This paper compares the statement ‘Mathematics is the study of structure’ with the actual practice of mathematics. We present two examples from contemporary mathematical practice where the notion of structure plays different roles. In the first case a structure is defined over a certain set. It is argued firstly that this set may not be regarded as a structure and secondly that what is important to mathematical practice is the relation that exists between the structure and the set. In the second case, from algebraic topology, one point is that an object can be a place in different structures. Which structure one chooses to place the object in depends on what one wishes to do with it. Overall the paper argues that mathematics certainly deals with structures, but that structures may not be all there is to mathematics.
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| | Other links: jstor.org | Scholar | At my library | More options ... The article considers structuralism as a philosophy of mathematics, as based on the commonly accepted explicit mathematical concept of a structure. Such a structure consists of a set with specified functions and relations satisfying specified axioms, which describe the type of the structure. Examples of such structures such as groups and spaces, are described. The viewpoint is now dominant in organizing much of mathematics, but does not cover all mathematics, in particular most applications. It does not explain why certain structures are dominant, not why the same mathematical structure can have so many different and protean realizations. ‘structure’ is just one part of the full situation, which must somehow connect the ideal structures with their varied examples.
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| | Scholar | At my library | More options ... How do we learn about the nature of the world from the mathematical formulation of a physical theory? One rule we follow, familiar from spacetime theorizing: posit the least amount of spacetime structure required by the fundamental dynamical laws. I think that we should extend this rule beyond spacetime structure. We should extend the rule to statespace structure. Using this rule, I argue that a classical mechanical world has a surprisingly spare amount of structure.
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| | Scholar | More options ... How do we learn about the fundamental nature of the world from a mathematically formulated physical theory? To learn about spacetime, we follow this rule: posit the least spacetime structure to the world required by a theory’s dynamical laws. Applied to special relativity, for example, this rule tells us to not posit an absolute simultaneity structure. I suggest that we should use this rule for more than just spacetime structure. We should use the rule for statespace, positing the least statespace structure required by a theory’s dynamical laws. Using this rule, I argue that a classical mechanical world has surprisingly little fundamental structure. Fundamentally, such a world does not have a Euclidean distance structure. This bears on more general questions: what physics tells us about the world; what possibilities are distinguished by a theory; what is in a theory’s fundamental ontology (which I suggest includes the statespace structure); and when two formulations of a theory are mere notational variants.
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| | Scholar | More options ... Discussion of Jill North, The “Structure” of Physics
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