Quantum Theory May Twist Cause And Effect Into Loops, With Effect Causing The Cause

Science Alert  February 14, 2021
Quantum correlations violating Bell inequalities defy satisfactory causal explanations within the framework of classical causal models. The first challenge has been addressed through the recent development of intrinsically quantum causal models, allowing causal explanations of quantum processes – provided they admit a definite causal order, i.e., have an acyclic causal structure. An international team of researchers addresses causally nonseparable processes and offers a causal perspective on them through extending quantum causal models to cyclic causal structures. Among other applications of the approach, it is shown that all unitarily extendible bipartite processes are causally separable and that for unitary processes, causal nonseparability and cyclicity of their causal structure are equivalent…read more. Open Access TECHNICAL ARTICLE

Examples of cyclic directed graphs. Credit: Nature Communications volume 12, Article number: 885 (2021) 


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