QuantAlpsAn ecosystem for quantum science & technologies :
From the philosopher to the industrial

The aim of the talk is to clarify some conceptual aspects of decoherence that seem largely overlooked in the recent literature. In particular, we will see that decoherence theory, in the standard framework, is rather silent with respect to the description of (sub)systems and associated dynamics. Also, the selection of position basis for classical objects is more problematic than usually thought: while, on the one hand, decoherence offers a pragmatic-oriented solution to this problem, on the other hand, this can hardly be seen as a genuine explanation of why the classical world is position-based. This is not to say that decoherence is not useful to the foundations of quantum mechanics; on the contrary, it is a formidable weapon, as it accounts for a realistic description of quantum systems. That powerful description, however, becomes manifest when decoherence theory itself is interpreted in a realist framework of quantum mechanics.

In the field of the foundations of quantum mechanics, the physical meaning of the wave function has been the subject of intense debates over the last decade. One of the quantum theories defended in this field is Bohmian mechanics. Within the Bohmian community, the dominant viewpoint is the nomological interpretation of the wave function. It consists in the idea that the wave function does not represent a material object or a physical field, but is part of the law of nature governing the behavior of material entities. The primitive ontology approach sums this up by categorizing the wave function as a nomological entity. To give a more concrete meaning to this abstract notion, the wave function is often compared to the classical Hamiltonian, which, like the wave function, is a high-dimensional field whose gradient generates the motion of particles. However, unlike the wave function, the classical Hamiltonian is not the solution of a differential equation. In this article, we are going to argue that the action function, or Hamilton’s principal function, constitutes a better classical analogue to the wave function, as it provides us with an example of a dynamic nomological entity. Based on a clear distinction between laws of nature and nomological entities, this analogy can help to address some of the common criticisms levelled at the nomological interpretation, without resorting to the interesting, yet hypothetical, Wheeler-de Witt equation.

Louis de Broglie was the brilliant discoverer of wave (and quantum) mechanics, whose centenary we are now celebrating. However, like Albert Einstein, he was also a rebel, a “realist” who never really accepted the “orthodox” interpretation of quantum mechanics (as defended by Niels Bohr and Werner Heisenberg). We'll see that Louis de Broglie's position is rooted in his work from 1923-1925, which gave rise to the hidden-variable theories of the de Broglie-Bohm pilot wave theory and the double solution. We seek to show that his early work, often overlooked, may well hold the very future of quantum physics within it.