What Happens in a Measurement?

2016/03/18 by Steven Weinberg · 2 voices
#quant-ph #hep-th

paper · pdf · doi:10.1103/physreva.93.032124

Abstract

It is assumed that in a measurement the system under study interacts with a macroscopic measuring apparatus, in such a way that the density matrix of the measured system evolves according to the Lindblad equation. Under an assumption of non-decreasing von Neumann entropy, conditions on the operators appearing in this equation are given that are necessary and sufficient for the late-time limit of the density matrix to take the form appropriate for a measurement. Where these conditions are satisfied, the Lindblad equation can be solved explicitly. The probabilities appearing in the late-time limit of this general solution are found to agree with the Born rule, and are independent of the details of the operators in the Lindblad equation.

Discussions

• What Happens in a Measurement? [hn, 15 points, 7 comments]
• Both. Each interpretation has unattractive elements and, more deeply, still fail to explain what 'measurement' really is. In his later years Weinberg reluctantly conceded that measurement was not well [bsky, 2 points, 1 comments]

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