ATELIERS 2010-2011
Sauf mention explicite, les journées ont lieu dans les locaux du CREA à l'ENSTA
32, boulevard Victor - 75015 Paris.
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« STRUCTURALISME EN PHILOSOPHIE DE LA PHYSIQUE CONTEMPORAINE : ALTERNATIVES AU RÉALISME »
« Structuralism in Contemporary Philosophy of Physics : Alternatives to Realism »
(organisation : Stefano Osnaghi, CREA et Thomas Ryckman, Stanford University)
6-8 octobre 2011
Stanford University (California), USA
Presentation : |
In philosophy of physics, structuralism is often expressed either as an epistemological imitation – all we can know of nature is structure – or as an ontological thesis: according to our most fundamental physical theories, the primitive constituents of nature are relational structures, not object-like individuals extrinsically related to other individuals by laws of dynamical interaction. Importantly, these structuralist claims are a posteriori, supposedly informed by developments in physics since the late 19th century.
They are also usually realist in character: the structures are present in nature, whether known to physics or unknown. But realism and structuralism have not always been conjoined, and certainly not at the inception of structuralism.
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For more generally, structuralism draws upon three antecedent developments or traditions. The first is a central trend of early 20th century philosophy of science that emphasized the primary significance of the notion of theories as relational structures. Responding to two late 19th century and early 20th century developments in physics and foundations of geometry. thinkers as diverse as Poincaré, Hilbert, Russell, Carnap, Schlick, Cassirer, Eddington, and Weyl sought to characterize the nature of physical knowledge in structural, not necessarily realist, terms. On the one hand, in the Erlangen program of Felix Klein (1872) a geometry is characterized by the invariance of geometric configurations under transformations of a particular group. On the other hand, the use of symmetry principles in physics originated with Einstein’s theory of special relativity in 1905. From these two developments grew the view that a physical theory is structurally characterized by the group of transformations leaving its dynamical condition (lagrangian) invariant. Einstein’s theory of general relativity (1915) represents the crowning synthesis of these two trends, since the invariance group (the group of space-time diffeomorphisms) determines not only the geometry, but also at least that part of physics related to gravitation. As mentioned below, the group of general relativity places a fundamental condition on the form of the gravitational interaction. |
For realists about scientific theories, both in physics and in philosophy, symmetry principles have acquired the character of a priori principles of universal validity, capturing the simplicity of nature at the most fundamental levels. For non-realists, symmetry principles may also be regarded as a priori, but rather express in the sense of a regulative projection of universality upon the phenomena of nature. A second influence stems from specific problems with the notion of individuals within both quantum mechanics and general relativity. In quantummechanics the non-classical statistics of particles is rooted in an apparent failure of Leibniz’s principle of identity of indiscernibles, stating that no two things share all their properties. The fact that quantum states are the same – according to the quantum formalism – under interchange of particles of the same type (fermions for fermions, bosons for bosons), leads to the conclusion that quantum particles are individuals, though indistinguishable, or are not individuals at all. This result is widely viewed as grist for the mill of structuralism. |
A similar problem of individuation arises in general relativity concerning the failure of individuality of points of the space-time manifold. Because it is always possible to locally transform away the gravitational field, i.e., to choose an inertial coordinate system at each space-time point in an arbitrary gravitational field, Einstein’s field equations must satisfy the symmetry principle of general covariance. But this means that particular general relativistic models are determined only up to what has been called “Leibniz equivalence”, i.e., an equivalence class of diffeomorphically related solutions. |
Any attempt to retain a substantial identity for space-time points results in a glaring failure of determinism: that given sources of the gravitational field yield multiple space-time metrics. Again, the conclusion is favorable to structuralism: space-time points have no physical identity in the absence of the metric field. Finally, structuralism in contemporary philosophy of physics draws upon the success of the Yang-Mills quantum field theories that comprise the Standard Model of elementary interactions, the reigning view of the nature of matter since the mid-1970s. Yang-Mills theories are gauge theories, theories that, similarly to the general covariance of general relativity, stipulate invariance under transformation of local ‘gauge’ degrees of freedom. |
The purpose of the workshop is to bring together the leading representatives of non-realist perspectives on each of the above-mentioned traditions and developments in physical theory motivating the structuralist program. In this regard philosophers at Stanford, and in the Bay Area, find their natural counterparts at various institutions in France. All the participants consider themselves structuralists regarding the epistemology of physics, but our non-realist viewpoints range from varieties of transcendental idealism, both phenomenological and neo-Kantian, to pragmatic Kantianism and neo-Carnapianism, and to constructive empiricism. The aim of the workshop is to highlight our differences in emphasis, while identifying a common core. |
| Speakers : |
Jean Petitot (CREA, École polytechnique)
Michel Bitbol (CREA, École polytechnique)
Stefano Osnaghi (CREA, École polytechnique)
Alexei Grinbaum (CEA, Saclay)
Gerard Heinzmann (Université Nancy 2)
Thomas Ryckman (Stanford University)
Michael Friedman (Stanford University)
Katherine Brading (University of Indiana)
Isabelle Peschard (San Francisco State University)
Bas van Fraassen (San Francisco State University)
Johanna Wolff (University of Michigan)
Patricia Kauark (Universidade Federal de Belo Horizonte) |
The access to the Workshop is free.
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For any information, please send a message to Stefano Osnaghi.
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