Delayed Choice, Complementarity, Entanglement and Measurement

It is well known that Wheeler proposed several delayed choice experiments in order to show the impossibility to speak of the way a quantum system behaves before being detected. In a double-slit experiment, when do photons decide to travel by one way or by two ways? Delayed choice experiments seem to indicate that, strangely, it is possible to change the decision of the photons until the very last moment before they are detected. This led Wheeler to his famous sentence: No elementary quantum phenomenon is a phenomenon until it is a registered phenomenon, brought to a close by an irreversible act of amplification. Nevertheless some authors wrote that backward in time effects were needed to explain these results. I will show that in delayed choice experiments involving only one particle, a simple explanation is possible without invoking any backward in time effect. Delayed choice experiments involving entangled particles such as the so called quantum eraser can also be explained without invoking any backward in time effect but I will argue that these experiments cannot be accounted for so simply because they rise the whole problem of knowing what a measurement and a collapse are. A previously presented interpretation, Convivial Solipsism, is a natural framework for giving a simple explanation of these delayed choice experiments with entangled particles. In this paper, I show how Convivial Solipsism helps clarifying the puzzling questions raised by the collapse of the wave function of entangled systems.Comment: 3 figure

Explaining Emergence

Emergence is a pregnant property in various fields. It is the fact for a phenomenon to appear surprisingly and to be such that it seems at first sight that it is not possible to predict its apparition. That is the reason why it has often been said that emergence is a subjective property relative to the observer. Some mathematical systems having very simple and deterministic rules nevertheless show emergent behavior. Studying these systems shed a new light on the subject and allows to define a new concept, computational irreducibility, which deals with behaviors that even though they are totally deterministic cannot be predicted without simulating them. Computational irreducibility is then a key for understanding emergent phenomena from an objective point of view that does not need the mention of any observer.Comment: 13 pages, 15 figures, to appear in the forthcoming proceedings of the UM6P Science Week 2023 Complexity Summi

The measurement problem in Quantum Mechanics: Convivial Solipsism

The problem of measurement is often considered an inconsistency inside the quantum formalism. Many attempts to solve (or to dissolve) it have been made since the inception of quantum mechanics. The form of these attempts depends on the philosophical position that their authors endorse. I will review some of them and analyze their relevance. In this paper, I defend a new position, the “Convivial Solipsism”, according to which the outcome that is observed is relative to the observer, different but in close parallel to the Everett’s interpretation and sharing also some similarities with Rovelli’s relational interpretation and Quantum Bayesianism. I also show how “Convivial Solipsism” can help getting a new standpoint about the EPR paradox providing a way out of the seemingly unavoidable non-locality of quantum mechanics

Les limites de la connaissance

Analyse des apports venant des mathématiques (théorie des ensembles et logique) et de la physique (théorie des systèmes non linéaires et mécanique quantique) et de leurs conséquences quant à ce qu'il est possible de "connaître". Discussion des différentes positions philosophiques aujourd'hui acceptables sur le problème du réalisme et de la conception qu'on peut avoir de l'Univers

Abductive logics in a belief revision framework

Abduction was first introduced in the epistemological context of scientific discovery. It was more recently analyzed in artificial intelligence, especially with respect to diagnosis analysis or ordinary reasoning. These two fields share a common view of abduction as a general process of hypotheses formation. More precisely, abduction is conceived as a kind of reverse explanation where a hypothesis H can be abduced from events E if H is a "good explanation" of E. The paper surveys four known schemes for abduction that can be used in both fields. Its first contribution is a taxonomy of these schemes according to a common semantic framework based on belief revision. Its second contribution is to produce, for each non-trivial scheme, a representation theorem linking its semantic framework to a set of postulates. Its third contribution is to present semantic and axiomatic arguments in favor of one of these schemes, "ordered abduction," which has never been vindicated in the literature

The Concept of Emergence

Complex systems are omnipresent. Everywhere in the real world we can see them. First of all in biology, a living cell, the genetic system, the brain are complex systems. But there are lots of complex systems of different kind. A galaxy, a financial market, an ants colony, Internet, a supply chain are also complex systems. They are in general not easy to understand because they are made up of many components interacting not linearly. Their global behaviour is difficult to predict because it results from the many local interactions of their components. Frequently this behaviour is surprising and counter intuitive even though it is the simple consequence of these interactions: It seems that from the mere consideration of these interactions it is not possible to deduce the behaviour actually observed. This is the so called "emerging behaviour". One can also speak of the "emerging properties" of a complex system. Beyond this simple intuition, the concept of emergence is not so easy to define because, though not very recent, it can be understood in different acceptation more or less objective

Everett’s Interpretation and Convivial Solipsism

I show how the quantum paradoxes occurring when we adopt a standard realist framework (or a framework in which the collapse implies a physical change of the state of the system) vanish if we abandon the idea that a measurement is related (directly or indirectly) to a physical change of state. In Convivial Solipsism, similarly to Everett’s interpretation, there is no collapse of the wave function. However, contrary to Everett’s interpretation, there is only one world. This also allows us to get rid of any non-locality and to provide a solution to the Wigner’s friend problem and its more recent versions