On Time Order and Causal Order in the EPR Experiment

Haṡok Chang, Nancy Delaney Cartwright

Raphael Neelamkavil

Alessandra Melas

This Ph.D. thesis is about causality in Quantum Mechanics, namely about the possibility to provide a causal explanation for quantum Einstein – Podolsky – Rosen (EPR) correlations.The well-known interpretation of the Bell’s Theorem by Bastian Van Fraassen, who inferred that quantum correlations cannot be embedded in any causal model, compels us to suppose that microscopic nature cannot have a causal structure and that causality is an anthropological concept.However, this interpretation is not commonly accepted and this doctoral thesis is the first general overview of some recent works about causal explanation for EPR correlations. Particularly, it analyses the possible causal explanations for the EPR/Bohm experiments by means of the Hans Reichenbach’s model, by means of backward causation models, and by means of models that imply a direct causal link. In order to do it, it pays particular attention to the Relativistic space-time features and it considers the studies in the History of Philosophy about the link between causal arrow and temporal arrow. Moreover, this work aims to endorse the idea that the best way to explain EPR/Bohm correlations causally is to adopt an indeterministic non-Reichenbachian common cause model, particularly Cartwright’sgeneral forksmodel.My conclusion is that causal models for quantum correlations remain viable, and that there is no contrast between genuinely indeterministic interpretation of Quantum Theory and causal explanation, with the philosophical implication that the Causal Realism is still acceptable.

Raphael Neelamkavil

Michel Gondran, Alexandre Gondran

In this paper we study a two-step version of EPR-B experiment, the Bohm version of the Einstein-Podolsky-Rosen experiment. Its theoretical resolution in space and time enables us to refute the classic "impossibility" to decompose a pair of entangled atoms into two distinct states, one for each atom. We propose a new causal interpretation of the EPR-B experiment where each atom has a position and a spin while the singlet wave function verifies the two-body Pauli equation. In conclusion we suggest a physical explanation of non-local influences, compatible with Einstein's point of view on relativity.

Ognyan Oreshkov, Fabio Costa, Časlav Brukner

The idea that events obey a definite causal order is deeply rooted in our understanding of the world and at the basis of the very notion of time. But where does causal order come from, and is it a necessary property of nature? Here, we address these questions from the standpoint of quantum mechanics in a new framework for multipartite correlations that does not assume a pre-defined global causal structure but only the validity of quantum mechanics locally. All known situations that respect causal order, including space-like and time-like separated experiments, are captured by this framework in a unified way. Surprisingly, we find correlations that cannot be understood in terms of definite causal order. These correlations violate a 'causal inequality' that is satisfied by all space-like and time-like correlations. We further show that in a classical limit causal order always arises, which suggests that space-time may emerge from a more fundamental structure in a quantum-to-classical transition. Causal order is a concept that is engrained in the standard understanding of time, both in classical and quantum mechanics. Oreshkovet al.generalize the standard formalism of quantum theory to a framework with no pre-existing causal order, and find a new class of correlations that have no analogue in the classical world.