If the dissatisfaction with quantum mechanics is not caused by its physics, then it must arise elsewhere. The task of this post is to identify, as cleanly as possible, the point at which physics ends—and something else takes over.
That point is rarely marked. Indeed, much of the confusion surrounding quantum foundations can be traced to the fact that the transition is not recognised as a transition at all.
1. What Physics Actually Does
Physics constructs formal systems constrained by empirical adequacy. A physical theory proposes a mathematical structure, specifies how that structure connects to experimental procedures, and succeeds to the extent that its predictions align with observed outcomes.
Nothing in this description requires the theory to answer questions about what ultimately exists. Physics is answerable to experiments, not to metaphysical intuitions. Its authority extends precisely as far as empirical constraint extends—and no further.
Quantum mechanics fulfils this mandate with exceptional success. It tells us how to calculate probabilities for measurement outcomes under specified conditions. It does this reliably, repeatedly, and with astonishing precision.
This is the domain of physics proper.
2. Questions Physics Cannot Answer
Alongside this formal success, a different set of questions is routinely asked:
What is the wavefunction?
Does it represent a physical entity, information, or something else?
What really happens during measurement?
Is the universe fundamentally deterministic beneath appearances?
These questions have a distinctive feature: no experiment can decide between their competing answers.
Interpretations of quantum mechanics are constructed precisely to preserve empirical equivalence. If an experimental difference were available, the matter would cease to be interpretive and become physical. The fact that it does not is decisive.
When physicists argue about these matters, they are no longer doing physics.
They are doing ontology.
3. Ontology Without Admission
Ontology concerns what kinds of things there are, what counts as fundamental, and what sorts of explanations are acceptable. It does not proceed by experiment, because it is not about predicting outcomes. It proceeds by making commitments explicit and assessing their coherence, scope, and consequences.
Physicists often resist this description. They insist that they are merely extending physics, or making physics more complete. But the resistance itself is revealing.
The difficulty is not that ontology is being done. It is that it is being done without acknowledgement.
As a result, ontological commitments are treated as if they were forced by the theory, when in fact they are imposed upon it. Preferences for determinism, locality, realism, or observer-independence are smuggled in as if they were empirical requirements rather than philosophical expectations inherited from earlier frameworks.
4. Reality as a Demand Placed on Theory
A striking feature of foundational debates is the demand that quantum mechanics deliver a single, literal account of reality itself. The theory is treated as though it has failed unless it provides a clear answer to the question “what is really happening?”
But this demand is not itself grounded in physics.
It is grounded in a prior picture of what a satisfactory theory ought to do: namely, to mirror reality in a transparent and unambiguous way. That picture is rarely defended. It is assumed.
When quantum mechanics fails to meet this expectation, the failure is attributed to the theory rather than to the expectation.
5. The Illusion of a Neutral Standpoint
Much of the confusion turns on the notion of “reality” as an unproblematic reference point. Reality is treated as a single, determinate structure waiting to be described, rather than as something always encountered under a description, within a perspective.
Physicists slide between different senses of reality without noticing the shift: reality as measurement outcomes, reality as mathematical structure, reality as underlying mechanism, reality as observer-independent substrate. Each slide introduces a new commitment, but none are marked as such.
The result is a proliferation of disputes that cannot be resolved because they are not disagreements about facts, but about what counts as a satisfactory way of making sense of facts at all.
6. Why the Boundary Matters
Failing to distinguish physics from ontology does not make one more rigorous. It makes one less precise.
When ontological commitments are left implicit, they cannot be examined, compared, or revised. They harden into dogma while presenting themselves as methodological restraint. Debates become interminable because their terms are never clarified.
Recognising where physics ends does not diminish physics. It protects it.
It allows quantum mechanics to be acknowledged for what it is—a spectacularly successful physical theory—without burdening it with demands it was never designed to meet.
7. Looking Ahead
In the next post, we will turn to a particular self-image that sustains this confusion: the idea that one can be “just doing physics” while avoiding philosophy altogether. We will examine how this posture arises, what it conceals, and why it has proven so resilient in the culture of physics.
The boundary between physics and ontology is not a wall.
But it is a distinction—and failing to draw it has consequences.
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