The decoherence puzzle

The understanding of decoherence is critical to philosophical debates on several different topics, including measurements, the ‘emergence’ of classical mechanics from quantum mechanics, and the arrows of time. This paper first reviews the basic mechanisms of decoherence in Nature, stressing recent discoveries and the crucial importance of ‘low-energy’ physics. The way in which the interpretation of some recent experiments relates to the problem is also delineated. Finally, some of the more common questions posed by philosophers about decoherence are reformulated, and partial answers are given to these. Throughout the article, the incomplete nature of our understanding is stressed, and the way it depends on several different unresolved questions in both low- and high-energy physics.