# Decoherence and Reality *The Cushing Memorial Lecture*

Jos Uffink Institute for History and Foundations of Science, University of Utrecht (Netherlands)

This talk will review the implications of the program of "environment-induced decoherence" for the foundations of quantum mechanics, in particular for the so-called "measurement problem". In the first part of the talk I will try to explain how environment-induced decoherence is supposed to address this problem, or at least part of it. As is well known, decoherence cannot solve the part known as the "problem of outcomes" in quantum measurements, but it is generally believed to solve the so-called "preferred basis problem".

In the second part I will analyse the claim that decoherence solves the preferred basis problem. It will be argued that the proposed solution is fairly straightforward - although it requires a tacit non-standard assumption - and does not invoke most of the machinery of the decoherence program. In particular, the definition of a preferred basis does not require a principle that states that the environment is "irrelevant" to the observer and should therefore be traced out. I will argue that this principle is interpretationally superfluous.

The talk will conclude with some remarks concerning the meaning of the decoherence program for the foundations of quantum mechanics, and formulate a number of open problems for this approach.

*******************

This year's Cushing Memorial Lecture honor's the memory of Professor Uffink's student, Hanneke Janssen, who was posthumously awarded the 2009 Cushing Memorial Prize for her Master's Thesis, "Reconstructing Reality: Environment-Induced Decoherence, the Measurement Problem, and the Emergence of Definiteness in Quantum Mechanics," which was presented at the University of Nijmegen in the Netherlands in 2008. For more on the award see: http://www.nd.edu/~cushpriz/2009%20Award.htm