Review of 'Quantum Information Theory and the Foundations of Quantum Mechanics', by Christopher G. Timpson
Laura Felline
Information is on everyone's lips.It seems that nowadays there is no philosophical or scientific inquiry that cannot benefit from a reformulation in terms of information theory (IT).Quantum theory (QT) is no exception.Indeed, one of the liveliest debates in the foundations of QT concerns the role that information may play in the solution of the well-known problems in the foundations of QT.For instance, one of the hottest discussions concerns quantum non-locality.On the one hand, IT folks stress how, rather than approaching non-local entanglement as an 'embarrassment', IT invites us to see it as a resource for new information-processing protocols.On the other hand, it is unclear how this invitation can contribute to the solution of the problem of accounting for the apparent nonlocality involved in quantum correlations.Christopher G. Timpson's beautiful book is a welcome contribution to this dialectic.It provides an admirable mix of conceptual and technical analysis of the notion of information and critically analyses the most prominent proposals on the table in the debate over the role of IT in the foundations of QT.Although the focus of Timpson's book is quantum information theory (QIT) and the foundations of QT, a considerable component of its basic precepts will be found extremely useful in any branch (be it more philosophical or more scientific) of applied IT.It is because of this additional value that in this review, sometimes to detriment of exhaustiveness, I prefer to concentrate on providing some samples of Timpson's main argumentative line.This should give a better idea of how this volume can represent valuable reading for both specialists in QIT and non-specialists.First things first.In chapter 2, Timpson provides a sharp analysis of the concepts of information.The plural is due to the necessary distinction between information in the everyday sense and information in the technical sense (informationt).Both are abstract mass nouns, but while the former refers to a semantic and epistemic notion, informationt is a physically defined quantity, measured classically by Shannon information.Informationt is usually described as an undefined notion.Contrary to this claim, at the roots of Timpson's analysis is a neat definition: 'Informationt is what is produced by an informationt source that is required to be reproducible at the destination if the transmission is to be counted a success' (22).Although avowedly deflationary, this definition provides a fertile background to dissipate much of the fog around the nature of informationt and its behaviour.It actually turns out that the majority of the results of this book pivots on this very simple definition.Here is a straightforward example.According to the definition above, a successful transmission requires that the message be reproducible at destination.However, what it is said to be repeatable is not the token of a message, but the type.When we talk about something that is transmitted in communication protocols (the so-called pieces of information) we refer to types, i.e. abstracta, rather than to concrete objects.The operation of conceptual cleansing continues when we pass from classical to quantum informationt (chapter 3).An especially noteworthy result is the rejection of the common view that quantum informationt is different in nature from classical informationt.Timpson's methodology allows instead to account for it as an extension of Shannon informationt.In fact, with the template of classical informationt at hand, Timpson reconstructs the notions of quantum informationt source, measure of quantum informationt and piece of quantum informationt, the latter being a sequence of Hilbert space states.
•Jan 1, 2014•0 citations