Intertheory Relations (III)

Nahuel Sznajderhaus

Today there is no agreement on which, if any, of the several known realist interpretations of quantum mechanics is the correct one, and disagreement on this matter is not merely verbal, but substantial. However, I will show that the interpretations share a common aim: to recover the classical world given that it is quantum. This aim responds to implicit and well-entrenched philosophical intuitions that can be phrased in terms of intertheory relations, traditionally involving theory reduction, in philosophy, and the quantum-classical limit, in the foundations of physics. However, not one of those notions is free from controversies, and many contest that there is a smooth transition from the quantum to the classical. Hence, the account of the relationship between quantum mechanics and classical mechanics is an unresolved problem, and the philosophical character of the underlying framework can be contested. This thesis will offer a critical analysis of current well-known realist interpretations and will also put forward an alternative framework. I will critically examine traditional views on intertheory relations and the recent view of interstructuralism. My main claim will be that the role of intertheory relations is overrated, because a more basic question has to be answered first: 'what is a quantum system?'. That will motivate my novel view. I will critically evaluate and defend an alternative view based on the philosophy of Werner Heisenberg. The view proposes that physical theories should be regarded as "closed" systems. This has immediate implications for how we should understand intertheory relations in general, as well as scientific realism in particular. My view will appear radical in comparison to traditional views of quantum mechanics. Yet, I will examine fruitful comparison with forms of realism such as perspectivism and metaphysical pluralism. I shall conclude with indications for future work.

Malcolm R. Forster, Alexey A. Kryukov

Classical mechanics is empirically successful because the probabilistic mean values of quantum mechanical observables follow the classical equations of motion to a good approximation (Messiah 1970, 215). We examine this claim for the one-dimensional motion of a particle in a box, and extend the idea by deriving a special case of the ideal gas law in terms of the mean value of a generalized force used to define “pressure.” The examples illustrate the importance of probabilistic averaging as a method of abstracting away from the messy details of microphenomena, not only in physics, but in other sciences as well.

Alisa Bokulich

Classical mechanics and quantum mechanics are two of the most successful scientific theories ever discovered, and yet how they can describe the same world is far from clear: one theory is deterministic, the other indeterministic; one theory describes a world in which chaos is pervasive, the other a world in which chaos is absent. Focusing on the exciting field of 'quantum chaos', this book reveals that there is a subtle and complex relation between classical and quantum mechanics. It challenges the received view that classical and quantum mechanics are incommensurable, and revives another, largely forgotten tradition due to Niels Bohr and Paul Dirac. By artfully weaving together considerations from the history of science, philosophy of science, and contemporary physics, this book offers a new way of thinking about intertheory relations and scientific explanation. It will be of particular interest to historians and philosophers of science, philosophically-inclined physicists, and interested non-specialists.

Kaspar Sakmann