# Tools, Objects, and Chimeras: Connes on the Role of Hyperreals in Mathematics

*Foundations of Science*18 (2):259-296 (2013)

**Abstract**

We examine some of Connes’ criticisms of Robinson’s infinitesimals starting in 1995. Connes sought to exploit the Solovay model S as ammunition against non-standard analysis, but the model tends to boomerang, undercutting Connes’ own earlier work in functional analysis. Connes described the hyperreals as both a “virtual theory” and a “chimera”, yet acknowledged that his argument relies on the transfer principle. We analyze Connes’ “dart-throwing” thought experiment, but reach an opposite conclusion. In S , all definable sets of reals are Lebesgue measurable, suggesting that Connes views a theory as being “virtual” if it is not definable in a suitable model of ZFC. If so, Connes’ claim that a theory of the hyperreals is “virtual” is refuted by the existence of a definable model of the hyperreal field due to Kanovei and Shelah. Free ultrafilters aren’t definable, yet Connes exploited such ultrafilters both in his own earlier work on the classification of factors in the 1970s and 80s, and in Noncommutative Geometry, raising the question whether the latter may not be vulnerable to Connes’ criticism of virtuality. We analyze the philosophical underpinnings of Connes’ argument based on Gödel’s incompleteness theorem, and detect an apparent circularity in Connes’ logic. We document the reliance on non-constructive foundational material, and specifically on the Dixmier trace −∫ (featured on the front cover of Connes’ magnum opus) and the Hahn–Banach theorem, in Connes’ own framework. We also note an inaccuracy in Machover’s critique of infinitesimal-based pedagogy.

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2013

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KANTOA-2

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Archival date: 2012-11-13

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References found in this work BETA

Real Patterns.Dennett, Daniel C.

Mathematics as a Science of Patterns.Resnik, Michael D.

Philosophy of Mathematics: Structure and Ontology.Shapiro, Stewart

Where Mathematics Comes From How the Embodied Mind Brings Mathematics Into Being.Lakoff, George & Núñez, Rafael E.

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Citations of this work BETA

Gregory’s Sixth Operation.Bascelli, Tiziana; Błaszczyk, Piotr; Kanovei, Vladimir; Katz, Karin U.; Katz, Mikhail G.; Kutateladze, Semen S.; Nowik, Tahl; Schaps, David M. & Sherry, David

The Mathematical Intelligencer Flunks the Olympics.Gutman, Alexander E.; Katz, Mikhail G.; Kudryk, Taras S. & Kutateladze, Semen S.

Controversies in the Foundations of Analysis: Comments on Schubring’s Conflicts.Błaszczyk, Piotr; Kanovei, Vladimir; Katz, Mikhail G. & Sherry, David

Proofs and Retributions, Or: Why Sarah Can’T Take Limits.Kanovei, Vladimir; Katz, Karin U.; Katz, Mikhail G. & Schaps, Mary

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