Much of quantum theory depends on distinguishing a system from its environment. Decoherence theory, for instance, explains the emergence of classicality by describing how quantum systems become entangled with their surroundings, effectively “leaking” coherence into an external reservoir. But this model presupposes that a system can be meaningfully separated from what it is not.
From a relational perspective, such a division is neither ontologically fundamental nor epistemologically neutral. The system–environment split is a cut within a field of relation, enacted by a modelling stance or experimental setup. It is a perspective-dependent configuration, not a boundary found in the world.
1. The Classical Assumption
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Classical physics assumes bounded objects with internal dynamics and external influences,
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This logic carries into quantum theory in disguised form: systems evolve according to unitary dynamics, unless “interrupted” by measurements or environmental entanglement,
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But these boundaries — between system, observer, and environment — are drawn, not discovered.
2. The Relational Turn
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In a relational ontology, no system exists independently of its constraints and co-definitions,
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The “environment” is not external to the system; it is part of the same relational field,
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The act of identifying a subsystem is a punctuation of potential, a modelling decision that foregrounds some coherences while backgrounding others.
3. Decoherence Without Division
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Decoherence theory often presents the environment as a kind of repository of lost information,
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But if coherence is a distributed property of a whole field, then so-called “loss” is simply redistribution within the system-as-a-whole,
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There is no environment in the absolute sense — only relational gradients of entanglement and constraint.
4. Implications for Modelling
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The choice of what counts as the “system” shapes the formalism: different cuts yield different reduced density matrices, observables, and predictions,
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This is not a flaw, but a feature of quantum description: it reveals that what we treat as ontological boundaries are in fact epistemological partitions,
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From this standpoint, quantum theory doesn’t describe isolated systems, but how selections in a field of coherence yield observable structure.
Closing
There is no system without environment, and no environment without a system — because both are cuts in a continuous field of relation. The quantum world resists partition not because it is inherently mysterious, but because its ontology is not atomistic. What we call a system is an instance of selective attention, not a pre-existing object.
In our next post, we will return to the question of measurement, reframing it not as a collapse or observation, but as an event of actualisation — a relational transition under constraint.
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