**Semaine de philosophie de la physique / Philosophy of physics week**

Atelier principal le 18 mars 2009 à l’Ecole Normale Supérieure, salle Celan

17h : Jeremy Butterfield (University of Cambridge) "Mixing physics and logic : is a quantum system an object ?"

The founding fathers of quantum theory debated whether the peculiar behaviour of quantum systems, such as their non-classical statistics, meant that they were not objects. In current philosophy of physics, the debate continues, using the tools of modern logic and metaphysics. This talk will review the state of play.

18h30 : café

19h : Miklos Rédei (LSE) "Von Neumann’s lifelong struggle with quantum mechanics"

Von Neumann started working on the mathematical foundations of quantum mechanics in 1926 in Goettingen while he was Hilbert’s assistant, and he chose the problem of quantum probability and quantum logic as the topic of his talk on open problems of mathematics delivered during the World Congress of Mathematics in 1954 in Amsterdam. In the 28 years between these dates von Neumann worked out many aspects of the mathematical foundations of quantum mechanics but was struggling with the conceptual-interpretational issues, which he never regarded as satisfactorily understood and clarified. The talk reviews some of von Neumann’s contributions to the mathematical foundations of quantum mechanics and analyzes von Neumann’s views on the interpretation of the quantum formalism. Special attention will be paid to the issue of how von Neumann’s concept of quantum logic is related to why von Neumann considered Hilbert space formalism of quantum mechanics unsuitable and why he thought that operator algebra theory is the proper mathematical framework for quantum theory.