It is often said today that “experiments are interpretation-neutral” and that modern physics has moved beyond the Copenhagen interpretation. Yet historically and practically, almost all experimental work in quantum mechanics—and the subsequent development of quantum field theory—emerged within a Copenhagen framework.

By “relying on Copenhagen” I do not mean merely using Hilbert space and the Born rule. Rather, I mean the operational worldview introduced by Bohr and Heisenberg: the idea that physics requires a contextual division between the measuring apparatus and the quantum system, and that this division is not dictated by the formalism but by the experimental situation. No other interpretation supplies this operational intuition, and the formalism alone does not tell us where a “measurement” occurs or what counts as a classical device.

From the early quantum era through the development of QFT, all experimentally established theory and practice rested on this perspective. The detector designs that tested QED, the protocols for accelerator experiments, and even Feynman’s original vision of quantum computing all follow the same pattern: prepare, evolve, and then register a classical outcome. Modern quantum technologies continue to operate within this prepare-evolve-measure framework.

Later interpretations—Everettian, decoherence-based, relational, and others—appeared after the success of this Copenhagen architecture. They did not guide the original breakthroughs; rather, they reinterpret already-successful quantum practice and then claim parity with it. Decoherence, for example, is often presented as replacing the classical-quantum divide, yet what it truly does is formalize part of Bohr’s insight: classical behavior appears when a system interacts with a large environment. Decoherence explains how classical-looking states arise, but it does not eliminate the need for classical outcomes or the context-dependent cut—it simply pushes the cut outward in an elaborate way.

Quantum information theory likewise does not displace Copenhagen; rather, it reframes it. The information-theoretic language gives a modern re-expressions to Bohr’s view that quantum states reflect knowledge and constraints on prediction, not intrinsic properties of isolated systems. It is better seen as a translation of Bohr’s epistemic stance, not a completion that renders it obsolete.

In practice, quantum experiments still rest on what may be called a three-level Copenhagen ontology:

Potentialities: quantum systems before measurement, described by a non-classical structure of possibilities.

Wavefunctions as epistemic tools: mathematical devices that encode our knowledge and predict probabilities.

Actualities: concrete detector outcomes—irreducible classical events.

This architecture is unique to the Copenhagen spirit and remains implicit in all laboratory practice. One may adopt different philosophical stories, but the working structure does not change.

When considered in this light, the common analogy that “Everett relates to Copenhagen as Einstein relates to Newton” does not hold. Einstein introduced new mathematics and new testable predictions. Everett introduces no new mathematics and makes no new predictions. Nor does it mirror the Lagrangian/Hamiltonian reformulation in classical mechanics, which delivered powerful new calculational structures grounded in observables. The Everettian move instead introduces metaphysical commitments—many worlds, universal branching—without experimental or mathematical necessity. Put bluntly: Everett is metaphysics built atop decoherence, which itself was built atop Bohr.

This is not to deny the intellectual value of alternative interpretations. They explore conceptual territory that Copenhagen deliberately leaves open. But the operational backbone of quantum physics—the structure that actually touches experiment—remains Copenhagenian.

Perhaps the resistance to this observation is less about history or physics and more about sentiment. It is uncomfortable to accept that despite decades of debate, quantum practice still rests on Bohr’s pragmatic architecture.