Causality and Entanglement in the Quantum World

Martin Ringbauer

Časlav Brukner

Jacques Pienaar

Luis de la Peña, Ana Marı́a Cetto, Andrea Valdés Hernández

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.

Guolin Wu

The classical world, governed by classical physics, might have felt more intuitive and certain. However, the 20th century’s revolutionary birth of quantum mechanics opened a way to the “quantum world”. This chapter investigates the evolving concept of “world”, especially exploring the special and general theories of relativity, with Wittgenstein’s philosophical view that the world is composed of facts, or the existence of states of things. Quantum mechanics has two essential principles: The Heisenberg uncertainty principle and the new Heisenberg uncertainty principle, where the former indicates the inherent uncertainty within the quantum world and the latter uncovers the certainty under some circumstances such as quantum entanglement. Quantum mechanics, while having multiple interpretations, is considered a relatively complete framework; however, its “counterfactuals”—scientific facts that defy classical expectations—can be challenging for the classical understanding. Additionally, the potential for “backward causality” under time symmetry conditions adds another level of complexity. These counterfactuals and the possibility of backward causality don’t contradict existing facts, but rather signal the expansion of our scientific scope and, potentially, a new scientific paradigm.