Near-Critical Sensing

A project on the epistemology and physics of boundary-sensitive measurement

This project examines sensing and measurement systems that operate near regime boundaries — from 19th-century weather glasses to quantum systems near exceptional points. It asks what kind of knowledge each device produces, and why some sensing modes persist while others are displaced.

The central finding is a distinction between calibrated state instruments (invertible: from the reading, one recovers the measured quantity) and sentinel instruments (non-invertible: the output amplifies proximity to a transition but cannot be read backwards to recover any single variable). That distinction, first developed historically, turns out to connect directly to modern physics: bifurcation theory, critical slowing down, early warning signals, and non-Hermitian quantum sensing near exceptional points.

Documents

Historical Dossier: From Natural Signs to Measurement Networks

A comprehensive historical survey of atmospheric instruments (15th–19th century) organised by epistemological function across six analytic layers: state, transport, integration, radiation, electrical, and sentinel. Includes primary-source citations, historiographic references, and a detailed timeline. This is the Coastline document — it maps the historical territory.

Version 0.1.3 (frozen) · ~12,000 words

Essay: Amplifiers at the Boundary

An interpretive essay arguing that the sentinel tradition was displaced because its devices were non-invertible, and that the question sentinels were trying to answer — how close is a system to a qualitative change? — is now central to modern science. Connects storm-glass physics to bifurcation theory, critical slowing down, early warning signals, and non-Hermitian quantum boundary sensing. This is the Sail document — it interprets and argues.

Version 0.4.1 (polished) · ~6,010 words

Quantum Dossier: Quantum Systems Near Critical Points (in progress)

A trapped-ion-centred survey of quantum systems near structural, spectral, topological, and dissipative boundaries. Organised by boundary type, not by platform. Includes a dedicated treatment of the EP sensing controversy (signal enhancement vs. noise penalty). This is a second Coastline document — it maps the quantum territory.

Section 0 frozen (v0.1.1) · Section 1 drafted · Sections 2–8 pending · Projected ~18,000 words

How the documents relate

The historical dossier is documentary. It establishes facts, dates, attributions, and sources. Its categories are explicitly marked as analytic rather than actor-native.

The essay is argumentative. It takes the sentinel concept from the dossier and develops it into a physics argument about the relationship between sensitivity, invertibility, and proximity to regime boundaries. It is self-contained but references the dossier as a companion.

The quantum dossier is technical. It extends the boundary-sensing framework into quantum systems, using trapped ions as the anchor platform. It is standalone — it can be read without the other two documents — but shares the same organising principle: amplified response near a boundary, with attendant degradation of information recoverability.

Source: github.com/threehouse-plus-ec/near-critical-sensing · Licence: CC BY 4.0