A Common Fallacy in Quantum Mechanics: Why Delayed Choice Experiments do NOT imply Retrocausality

David Ellerman

S. Malin

David Ellerman

There is a very common fallacy, here called the separation fallacy, that is involved in the interpretation of quantum experiments involving a certain type of separation such as the: double-slit experiments, which-way interferometer experiments, polarization analyzer experiments, Stern-Gerlach experiments, and quantum eraser experiments. It is the separation fallacy that leads not only to flawed textbook accounts of these experiments but to flawed inferences about retrocausality in the context of "delayed choice" versions of separation experiments.

Fedor Herbut

Colm P. Bracken, Jonte R. Hance, Sabine Hossenfelder

The Delayed-Choice Quantum Eraser experiment is commonly interpreted as implying that in quantum mechanics a choice made at one time can influence an earlier event. We here suggest an extension of the experiment that results in a paradox when analysed in a local realist interpretation combined with backward causation (``dynamical retrocausality''). We argue that resolving the paradox requires giving up the idea that, in quantum mechanics, a choice can influence the past in this way, and that it instead requires a violation of Statistical Independence without (what most people think of as) retrocausality. Finally, we propose an implementation of the experiment that we believe to be possible with existing technology. This new experiment can distinguish between different types of hidden-variables theories in a way that Bell-type tests cannot: unlike in a Bell test, the measurement setting here is set by an earlier outcome, which makes the consistency of the backwards influence itself testable. We classify the fixed-point (consistency-enforcing) hidden-variables models of the experiment, which can reproduce quantum mechanics only if the backwards influence has no observable effect.

Greco, Giuseppe Junior

Delayed-choice and quantum eraser experiments are frequently interpreted as implying retrocausal effects, in which present measurement decisions influence past physical events. This paper develops an Observer-First Interpretation (OFI) in which quantum states are treated as observer-relative informational constructs constrained by evidence accessibility and record availability. Within this framework, delayed-choice phenomena do not involve backward-in-time physical influence, but instead arise from conditional informational updates applied to measurement records that were never globally fixed. Temporal paradoxes emerge only when observer-relative state assignments are illegitimately promoted to observer-independent histories. The proposed interpretation preserves causal ordering, respects relativistic constraints, and reproduces all standard quantum predictions without modifying the formalism of quantum mechanics.