Among the most confidently asserted claims in the foundations of quantum mechanics is the declaration that “the wavefunction is not real.” It is usually offered as a mark of sophistication: a refusal of naïve realism, a safeguard against reifying mathematical tools.
Yet this declaration, too, conceals more than it reveals.
For the question is not whether the wavefunction is real, but why this particular entity is so often singled out as unreal while others are allowed to pass without comment.
A Selective Suspicion
Physicists routinely manipulate objects that have no straightforward physical analogue:
state vectors in Hilbert space,
operators with no classical counterpart,
probability amplitudes whose squared magnitudes alone are observable.
None of these are directly observable. All are indispensable. Yet only the wavefunction is regularly subjected to ontological suspicion.
This selectivity is revealing.
Instrumentalism with Exceptions
When physicists say the wavefunction is not real, they often mean something modest:
The wavefunction is a calculational device, not a physical object.
Taken strictly, this would amount to a thoroughgoing instrumentalism. But that is not how the claim is actually used.
For the same physicists will often speak without hesitation of:
particles existing,
fields interacting,
systems evolving in time.
The result is a hybrid stance: realism where it feels comfortable, instrumentalism where it does not.
This is not a principled position. It is an affective one.
The Anxiety Behind the Claim
Why does the wavefunction provoke such resistance?
Because it refuses to behave like the things physicists would like to be real. It lives in a high‑dimensional space, evolves deterministically until it does not, and resists localisation in ordinary spacetime.
Declaring it unreal is therefore less an ontological conclusion than a coping strategy.
The discomfort is metaphysical, not mathematical.
Reality as a Reward
Underlying the slogan “the wavefunction is not real” is an implicit criterion of reality:
to be real is to resemble familiar physical objects,
to be real is to occupy spacetime straightforwardly,
to be real is to behave classically when unobserved.
Entities that fail these tests are demoted. Entities that pass are rewarded with ontological status.
But these criteria are nowhere justified by quantum mechanics itself.
What the Denial Actually Commits One To
Ironically, denying reality to the wavefunction often increases ontological commitment elsewhere.
If the wavefunction is merely epistemic, then something must exist that it is knowledge of. Hidden variables, underlying states, or deeper realities are quietly reintroduced to carry the burden the wavefunction is forbidden to bear.
The denial of reality thus functions less as restraint than as displacement.
The Question That Refuses to Go Away
The persistent return of interpretive debates suggests that the wavefunction cannot simply be dismissed without remainder. Its role is too central, its success too intimate.
What remains unresolved is not whether the wavefunction is real, but what kind of ontological commitment its use entails.
Pretending the question has been answered by denial only ensures it will return in more confused forms.
Ontological Hygiene
Ontological responsibility here would not require declaring the wavefunction real or unreal. It would require stating explicitly:
what criteria of reality are being employed,
why those criteria are appropriate,
and what follows from adopting them.
Quantum mechanics does not force us to reify the wavefunction. But it does force us to confront the fact that selective realism is still realism—and selective instrumentalism is still metaphysics.
The wavefunction is not the problem. The refusal to own one’s criteria of reality is.
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