Abstract
The conventional explanation of delayed-choice experiments appears to violate our causal intuition at the quantum level. I reanalyze these experiments using time-reversed and time-symmetric formulations of quantum mechanics. The time-reversed formulation does not give the same experimental predictions. The time-symmetric formulation gives the same experimental predictions but actually violates our causal intuition at the quantum level. I explore the reasons why our causal intuition may be wrong at the quantum level, suggest how conventional causation might be recovered in the classical limit, propose a quantum analog to the classical block universe viewpoint, and speculate on implications of the time-symmetric formulation for cosmological boundary conditions.
Highlights
The original Conventional Formulation (CF) explanations of the delayed-choice experiment by Lewis, Weizsäcker, and Wheeler only appeared to violate our causal intuition at the quantum level
The Time-Symmetric Formulation (TSF) explanation of the same experiment says the effects of an intervention can occur before the intervention, violating our causal intuition at the quantum level
Some may see this as reason to discard the TSF, but other aspects of quantum mechanics violate our causal intuition
Summary
In 1926 Lewis proposed a delayed-choice thought experiment which appeared to show retrocausation in the Conventional Formulation of quantum mechanics [2,3]. Retrocausation, known as future input dependence [4], is when a model parameter associated with time t depends on model inputs associated with times greater than t He considered a double-slit interference experiment using a single photon from a distant star. Our intervention appears to cause the photon to change its route before the intervention happens, in violation of our causal intuition that effects never happen before interventions
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