Causality in a quantum world

Martin Ringbauer

Jacques Pienaar

Jürgen Audretsch

Alastair Wilson

Abstract Scientific explanations should have a character that matches their subject matter: if a fact is not apt for causal explanation, it should not be explained causally. In this chapter, the author first reviews some cases where causal explanation has been extended beyond its proper limits, identifying a pattern of error termed the problem of causal overreach. The discussion then relates these considerations to the debate over causal locality in Everettian (many-worlds) quantum mechanics (EQM), in the context of three metaphysical distinctions central to recent discussions of locality: event causation vs. worldshaping causation, local branching vs. global branching, and overlapping worlds vs. diverging worlds. The author argues that worlds in EQM are not properly regarded as themselves subject to causal explanation; instead, causation should be understood as a wholly in-world matter. This approach avoids any nonlocal causal explanation; quantum entanglement instead supports a new category of noncausal worldshaping explanations. The chapter concludes by considering the implications of worldbound causation for principles of causal inference, in particular for the Causal Markov condition, and recommends the use of quantum causal models as a foundation for in-world causal inference.

Kelvin J. McQueen, Lev Vaidman A

The many worlds interpretation of quantum mechanics (MWI) states that the world we live in is just one among many parallel worlds. It is widely believed that because of this commitment to parallel worlds, the MWI violates common sense. Some go so far as to reject the MWI on this basis. This is despite its myriad of advantages to physics (e.g. consistency with relativity theory, mathematical simplicity, realism, determinism, etc.). Here, we make the case that common sense in fact favors the MWI. We argue that causal explanations are commonsensical only when they are local causal explanations. We present several quantum mechanical experiments that seem to exhibit nonlocal "action at a distance". Under the assumption that only one world exists, these experiments seem immune to local causal explanation. However, we show that the MWI, by taking all worlds together, can provide local causal explanations of the experiments. The MWI therefore restores common sense to physical explanation.

Hamidreza Simchi

Theories such as causal sets and causal dynamic triangulation teach us that, the world we live in, composed by the causal sets. It is shown that, an information probability type can be attributed to born probability of the timid children in the causal set, but, due to the causal structure of the theory, the probability can be replaced by the topos truth values, and in consequence, the probability will be appeared as an emergent and non-fundamental concept. Accordingly, we introduce three generalized principles, called contextuality, equivalence, and absolute cause and probable effects. Based on the generalized contextuality principle, an eternal non-causal universe exists. The creation of observer-dependent causal (worlds) sets (called collapse of events) is the result of the interaction between the concisions observers and the universe which can be explained mathematically through introducing a pyramidal operator. Using the metric of conscious observers and the Green function of causal sets, we show how one can define the pyramidal operator. Based on this vision, time and time evolution are emergent and non-fundamental concepts. Also, the transition between the eternal universe and non-eternal worlds or between parallel worlds only occurs when the observer's consciousness changes. It can be assumed that the essence of observers (or facts) is enteral and preserved under the transition between the universe and the born worlds or between parallel born worlds, and as a result, it provided an appropriate answer to some philosophical ambiguities.