The Classical Assumption of Separateness
Among the deepest and most pervasive assumptions of ordinary thought is that separate things are genuinely separate. Two objects on opposite sides of a room have their own independent properties, their own histories, their own futures. What happens to one has no direct bearing on what happens to the other, unless there is some physical mechanism — some chain of cause and effect, some signal travelling through the space between them — connecting them. This is the assumption of local realism: that reality is local (influenced only by what is nearby) and real (possessed of definite properties prior to and independent of observation).
It is a good assumption, verified by the overwhelming majority of everyday experience. The cup on the table does not know what the pen across the room is doing. The planet Mars does not feel the gravitational influence of a distant star in any practically significant way. Separateness, at the scale of ordinary life, is an excellent approximation. We build our social and moral world on it: each person is an individual with their own history and responsibility, not determined by what is happening to someone on the other side of the world.
Quantum mechanics does not overturn this assumption at the level of ordinary life. Decoherence ensures that macroscopic objects behave classically. But it does reveal, at the quantum level, that local realism is false. The universe is not, at its foundation, a collection of independently existing things with their own separate properties. It is, in some deep sense, more fundamentally connected than any classical picture allows.
Bell's Theorem and the Experimental Proof
John Bell's 1964 theorem is one of the most important results in the history of physics because it turned a philosophical dispute — about whether quantum mechanics was complete — into an empirical question. Bell derived a mathematical inequality that any theory respecting local realism must satisfy. Quantum mechanics predicts violations of this inequality. Experiments can test which prediction is correct.
The experiments, beginning with John Clauser's work in the 1970s and culminating in a series of increasingly rigorous tests in the 1980s and beyond — including Alain Aspect's landmark experiments in 1982 and the loophole-free tests conducted in Delft, Munich, and NIST in 2015 — have consistently found violations of Bell's inequality. The violations are exactly as quantum mechanics predicts. Local realism is ruled out.
This result has been described by physicist David Mermin as among the most profound discoveries in the history of science. It means that no matter how one interprets quantum mechanics, the universe cannot be described by any theory that assigns definite local properties to physical systems. Either the properties of quantum systems are genuinely indeterminate prior to measurement (as most interpretations maintain), or there are non-local influences that propagate instantaneously across space (as some interpretations, such as pilot wave theory, propose). Either way, the classical picture of a universe of locally independent, separately existing things with their own definite properties is wrong.
What Non-Locality Is and Is Not
It is important to be precise about what quantum non-locality does and does not imply. It does not imply faster-than-light communication. The correlations between entangled particles cannot be used to send a message instantaneously, because the result of any individual measurement is, from the measurer's perspective, completely random. It is only the pattern of correlations — visible only after comparing results by conventional means — that is non-local. The non-locality is real but it is not a channel for information.
Quantum non-locality also does not obviously imply a universe that is, in some mystical sense, 'all one' or 'fundamentally unified.' The non-local correlations are specific, structured, and constrained. They are not a general condition of universal interconnection. Two particles that have never interacted are not entangled. The non-locality operates through the specific quantum states that systems share as a result of past interactions.
What non-locality does imply is that the assumption of separability — the assumption that the state of a composite system can always be fully described by describing the states of its parts independently — is false at the quantum level. This is precisely what entanglement means: the state of two entangled particles cannot be factored into separate descriptions of each particle. The pair has properties that neither particle has alone. The whole genuinely contains something not present in either part.
Philosophical Implications: Holism and the Limits of Analysis
The philosophical tradition of reductionism holds that complex systems can, in principle, be fully understood by understanding their parts. This approach has been enormously productive in science: the properties of molecules are explained by the properties of atoms, atomic properties by nuclear and electronic structure, nuclear properties by quark dynamics. Reductionism, as a research strategy, has produced the most powerful scientific theories in history.
Quantum entanglement introduces a precise and experimentally established limit on this strategy. For entangled systems, the parts do not tell the whole story. The correlations between entangled particles — the non-local, non-classically-explicable patterns of correlation that Bell's theorem confirmed — are properties of the joint system that are not reducible to properties of the individual particles. The whole, in this specific and non-mystical sense, is more than the sum of its parts.
This does not invalidate the reductionist research programme. Most systems, at most scales, are not in highly entangled states, and reductive explanations work. But it does suggest that completeness — the ideal of a fully reductive account in which all the properties of a complex system can be derived from the properties of its components — is not always attainable. Some properties are genuinely emergent, not in the weak sense of being merely complex, but in the strong sense of being absent from the parts and present only in the whole.
The doctrine holds that genuine understanding requires openness to this kind of complexity. The love of clean, reductive explanations — the desire to dissolve every question into simpler pieces that can be handled separately — is a powerful intellectual tool that can become a form of Iron Certainty when it refuses to acknowledge that some questions have holistic answers. The quantum world is one domain where this refusal is demonstrably wrong.
Towards a Humbler Picture of Relationship
The deepest implication of quantum non-locality may be less about physics than about the concept of relationship itself. Classical physics modelled relationship as interaction: two separate entities, acting on each other through forces that traverse the space between them. Quantum mechanics reveals that some relationships are constitutive rather than interactive: two entangled particles are not two separate things with a special connection between them, but in some sense one thing with two aspects. The relationship is not between them; it is part of what they are.
This is a difficult concept to cash out with full philosophical rigour, and caution is warranted in extending it beyond its well-established quantum mechanical context. But as a model — an instance of genuine, rigorously established holism at the foundation of physical reality — it invites reflection on what kinds of connection, in other domains, may be more fundamental than our habit of treating things as separate allows us to see.
The doctrine does not derive metaphysical conclusions from quantum mechanics. It does not claim that social bonds are quantum entanglement, or that compassion is a form of non-locality. But it holds that the habit of treating each thing as fully separate from every other thing, as the foundation of understanding, is an assumption — one that quantum mechanics has shown, at the physical level, to be false. The serious seeker holds assumptions loosely, and asks, in each domain of inquiry, what is genuinely separate and what is genuinely connected. That question is always worth asking, and quantum mechanics has given us an extraordinary reason to take it seriously.
Understanding grows stronger when pursued together in honesty.