Bohmian mechanics holds a special status among interpretations of quantum theory. Unlike the Copenhagen interpretation, which dissolves ontological questions into epistemic ones, and unlike Many-Worlds, which multiplies unobservable realities, Bohmian mechanics offers a clear, realist picture: particles have definite trajectories, guided by a “pilot wave” encoded in the wavefunction. No collapse, no superposition, no ambiguity—just hidden variables restoring classical determinism beneath quantum formalism.
But while this interpretation resolves some puzzles, it introduces others—and, as recent experiments on quantum tunnelling show, it may be ontologically inadequate to the phenomena it claims to describe. This post explains why Bohmian mechanics, despite its appeal, inherits the very metaphysical assumptions that quantum theory has outgrown. It cannot accommodate phenomena like tunnelling without contradiction, and it misconstrues what kind of system quantum reality actually is.
1. Bohmian Basics: Particles and Pilot Waves
In Bohmian mechanics:
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Particles have definite positions at all times, even when unmeasured.
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Their velocities are determined by the quantum potential, which is calculated from the wavefunction.
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The wavefunction evolves according to the Schrödinger equation and acts as a pilot wave guiding the motion of particles.
This framework allows one to reconstruct quantum predictions in a deterministic setting. But its ontological commitments are strictly substance-based: there are particles (with position and trajectory) and a wavefunction (which guides them). Even nonlocality is tolerated, so long as particles behave consistently with the pilot wave.
2. The Problem of the Barrier
Consider now the case of quantum tunnelling into an infinite barrier—as in the Sharoglazova et al. experiment.
According to Bohmian mechanics, if a barrier is infinitely extended and the wavefunction is exponentially decaying, the velocity of the particle drops to zero. The particle is “stuck” inside the barrier—its dwell time becomes infinite.
But the experiment shows something else: photons exhibit finite dwell times, and their tunnelling speed increases with the depth of potential (more negative kinetic energy). In other words, the system behaves dynamically, not statically, inside a region Bohmian mechanics would treat as a zone of rest.
This isn't just a failed prediction. It reveals a fundamental limitation: the Bohmian model assumes that the particle exists inside the barrier and that its motion stops due to boundary conditions. But from a relational standpoint, this framing is already misguided.
3. Ontological Misalignment
The real problem is not the velocity. It is the ontology of particle-in-space.
Bohmian mechanics assumes that:
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There is a particle,
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It is located at a position in space,
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It follows a trajectory governed by a wave,
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Its motion can be halted by conditions in a region.
This is precisely the metaphysical apparatus that quantum mechanics undermines. Entanglement, superposition, nonlocality, and measurement all suggest that quantum systems do not consist of localisable particles with hidden trajectories. They are not substances in space; they are structured fields of potential undergoing transformation under constraint.
Thus, Bohmian mechanics may be formally coherent, but it is ontologically incompatible with the structure of quantum phenomena. It tells a story that cannot accommodate the behaviour we observe—because its story is about things moving through space, rather than relations reorganising within a system.
4. The Collapse of Explanation
When substance ontology fails, its models collapse into contradiction or ad hoc patchwork. In the case of Bohmian mechanics:
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To explain nonlocal correlations, one must postulate instantaneous effects across space, undermining relativity.
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To explain tunnelling into barriers, one must assert infinite dwell times, contradicting observation.
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To preserve realism, one must add unobservable variables, violating parsimony.
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To maintain determinism, one must reinterpret probability as ignorance, undermining the core statistical structure of the theory.
These are not elegant trade-offs. They are symptoms of a misapplied metaphysics—an attempt to shoehorn quantum formalism into a classical mould.
5. Relational Recovery
A relational ontology does not attempt to recover classical substance. It accepts that localised particles with intrinsic properties are not fundamental. What exists are relations, structured fields of potential, undergoing actualisation according to systemic constraints.
In this framework:
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There is no particle “in” the barrier. There is a reconfiguration of coherence under topological tension.
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Motion is not trajectory, but change in relational patterning.
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Speed is not velocity through space, but rate of transformation across constrained affordances.
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The “failure” of Bohmian mechanics is not empirical but conceptual: it fails to see what quantum theory is telling us about the structure of reality.
Conclusion: Letting Go of Substance
Bohmian mechanics deserves credit for confronting the ontological question head-on. But its commitment to particles and trajectories locks it into a classical metaphysics that quantum systems do not support. Its failure to account for recent tunnelling experiments is not a matter of detail—it is a sign that substance-based thinking has reached its limit.
If quantum theory is to be interpreted without paradox, we must look beyond the ontology of things, and attend instead to the relational dynamics of transformation. The real task is not to save classical intuitions, but to develop a new metaphysical vocabulary—one in which coherence, potential, and constraint take precedence over entity, motion, and location.
In the next post, we will begin exploring what such a vocabulary might look like—not merely as an interpretation of quantum theory, but as a foundation for understanding reality as such.
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