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Agency under indefinite causality: operational eternalism in higher-order quantum theory

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arxiv 2512.22879 v2 pith:ULRHPAKP submitted 2025-12-28 quant-ph

Agency under indefinite causality: operational eternalism in higher-order quantum theory

classification quant-ph
keywords operationaltheoryagencyagentscausalityeternalismglobalgroupings
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After two decades of research on indefinite causality, a conceptual lesson emerges: the tension between operational quantum theory and dynamical spacetime physics requires observers, or agents, to be defined within the theory itself. Agents arise from admissible groupings of input and output data in a global Hilbert space, and redefining these groupings may eliminate non-causality. Agency is perspectival: from Alice's perspective, Bob may fail to qualify as an observer, and vice versa. We interpret these results through an \emph{operational eternalism}, a stance analogous to the block-universe view but applied to information rather than geometry. Observers are thus well-defined in the global eternalist picture, but they are not universal across local perspectives.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Causality from the spectrum: Emergence of causal order from process-matrix mereology

    quant-ph 2026-07 conditional novelty 7.0

    A process matrix can be unitarily transformed to a fixed-causal-order process exactly when its eigenvalue multiplicities are divisible by the final output dimension; generic high-dimensional spectra are close to such spectra.

  2. Frame perspectives for process matrices: from coordinate parametrization to spacetime representation

    quant-ph 2026-04 unverdicted novelty 6.0

    Causal reference frame and time-delocalized subsystem descriptions of pure processes are coordinate parametrizations of a single neutral object, with unitary perspective transformations possible by reshuffling time or...