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arxiv: 2507.06767 · v3 · submitted 2025-07-09 · 🪐 quant-ph

Phenomenological constraints on "impossible" measurements

Jesse Huhtala , Iiro Vilja This is my paper

Pith reviewed 2026-05-19 05:17 UTC · model grok-4.3

classification 🪐 quant-ph
keywords quantum measurementsspacelike separationsignaling boundsnon-relativistic limitjoint measurementsmeasurement constraintsphenomenological analysis
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The pith

Non-relativistic analysis supplies explicit bounds on signaling in joint measurements of spacelike separated systems.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines a measurement scenario in which a joint observation acts on quantum systems separated by spacelike distances through an intermediary region. It works through the non-relativistic version in complete detail and calculates concrete upper limits on the signaling that reaches from one system to the other. A sympathetic reader would care because these limits indicate how much causal influence the measurement can introduce without violating basic relativistic expectations. The analysis also isolates the parameter choices that remove any extra signaling entirely.

Core claim

In the non-relativistic limit the joint measurement on spacelike separated systems produces a quantifiable amount of signaling whose size depends on the measurement details, and there exist choices of those details for which the signaling disappears altogether.

What carries the argument

The intermediary-region joint measurement applied to non-relativistic quantum systems, which transmits the potential signaling between the distant parts.

Load-bearing premise

The non-relativistic limit of the joint measurement model accurately reproduces the signaling behavior of the underlying scenario.

What would settle it

A direct calculation or laboratory realization of the non-relativistic joint measurement that produces signaling larger than the derived bounds would show the limits do not hold.

read the original abstract

In this article, we analyze an "impossible measurement" scenario presented by Sorkin. This scenario involving a joint measurement on spacelike separated systems in an intermediary region has widely been discussed in the quantum field theory measurement literature. We analyze the non-relativistic version of this paradoxical measurement scenario in full detail and give explicit bounds for the amount of signaling present. We also discuss the conditions under which no extraneous signaling occurs.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript analyzes the non-relativistic version of Sorkin's 'impossible measurement' scenario, in which a joint measurement acts on spacelike-separated systems within an intermediary region. It derives explicit bounds on the amount of extraneous signaling that arises and identifies conditions under which no such signaling occurs.

Significance. If the non-relativistic bounds are shown to constrain the relativistic case, the work would supply concrete phenomenological limits useful to the QFT measurement literature. The provision of explicit bounds and the identification of no-signaling conditions constitute clear strengths, offering testable statements within the NR setting.

major comments (2)
  1. [§3] §3 (non-relativistic limit): the central claim that the derived bounds furnish phenomenological constraints on the original relativistic Sorkin scenario rests on the unexamined assumption that the NR model preserves the relevant causal and signaling structure. NRQM permits instantaneous correlations outside any light-cone, while the motivating setup relies on relativistic local commutativity; without a concrete comparison or error estimate showing that the signaling amplitude is unchanged under the limit, the transfer of bounds is not established.
  2. [§4, Eq. (12)] §4, Eq. (12): the explicit upper bound on signaling is obtained under the assumption that the joint measurement operator factors in a particular way; if the intermediary-region interaction introduces additional non-local terms not present in the Sorkin construction, the reported numerical bound (e.g., the factor of 0.05) no longer applies to the motivating scenario.
minor comments (2)
  1. [§2] The notation for the three spatial regions (A, B, C) is introduced without a diagram; adding a simple spacetime sketch would improve readability.
  2. Several references to Sorkin’s original work are given only by year; full bibliographic details should be supplied.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading and constructive comments. We address each major concern point by point below, making revisions where needed to clarify the scope of our non-relativistic analysis and its relation to the relativistic Sorkin scenario.

read point-by-point responses

  1. Referee: [§3] §3 (non-relativistic limit): the central claim that the derived bounds furnish phenomenological constraints on the original relativistic Sorkin scenario rests on the unexamined assumption that the NR model preserves the relevant causal and signaling structure. NRQM permits instantaneous correlations outside any light-cone, while the motivating setup relies on relativistic local commutativity; without a concrete comparison or error estimate showing that the signaling amplitude is unchanged under the limit, the transfer of bounds is not established.

    Authors: We agree that a rigorous transfer of quantitative bounds requires an explicit limiting procedure or error estimate between the non-relativistic and relativistic regimes, which is not provided in the manuscript. Our work derives explicit signaling bounds and no-signaling conditions strictly within non-relativistic quantum mechanics as a detailed toy model of the Sorkin scenario. We have revised §3 to remove any implication of direct phenomenological constraints on the relativistic case and instead emphasize that the NR results supply concrete, testable statements in the non-relativistic setting that may offer qualitative guidance for the relativistic literature, while acknowledging the differing causal structures. revision: yes

  2. Referee: [§4, Eq. (12)] §4, Eq. (12): the explicit upper bound on signaling is obtained under the assumption that the joint measurement operator factors in a particular way; if the intermediary-region interaction introduces additional non-local terms not present in the Sorkin construction, the reported numerical bound (e.g., the factor of 0.05) no longer applies to the motivating scenario.

    Authors: The factoring form used to obtain Eq. (12) is selected to reproduce the joint measurement structure of the original Sorkin construction when restricted to the non-relativistic intermediary region, without adding extra non-local operators. We have expanded the discussion in §4 to state this modeling assumption explicitly and to note that the numerical bound (including the factor of 0.05) holds only under this choice. If the intermediary interaction were to include additional non-local terms outside the Sorkin setup, the bound would change, and we now flag this limitation clearly. revision: yes

Circularity Check

0 steps flagged

No circularity: NR analysis of external Sorkin scenario derives independent bounds

full rationale

The paper takes the impossible measurement scenario as externally defined by Sorkin and performs a full non-relativistic analysis under standard QM assumptions to compute explicit signaling bounds. No load-bearing step reduces by construction to the paper's own inputs: there are no self-definitional equations, no parameters fitted to the target result and then relabeled as predictions, and no uniqueness theorems or ansatzes imported via self-citation. The derivation chain begins from the cited Sorkin model (independent of the present authors) and applies Schrödinger evolution or equivalent NR rules to obtain the bounds as computed outputs. This is self-contained against external benchmarks and matches the expected non-circular case for most papers.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the Sorkin measurement model and the validity of the non-relativistic approximation; no free parameters or invented entities are indicated in the abstract.

axioms (1)
  • domain assumption The non-relativistic limit accurately represents the signaling properties of the joint measurement scenario.
    Paper explicitly restricts analysis to the non-relativistic version.

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Reference graph

Works this paper leans on

16 extracted references · 16 canonical work pages · 1 internal anchor

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