The Copenhagen interpretation of quantum mechanics (QM) was developed by Niels Bohr and Werner Heisenberg in the 1920’s, and it remains the dominant interpretation among working physicists to this day (Tegmark, 1998; Schlosshauer et al., 2013).
Central to this interpretation is the notion that the physical world operates in two complementary modes: you are either making a measurement, which causes the wave function to collapse down to a single discrete particle-like point (via the Born rule), or physics is otherwise evolving according to the wave function, which critically preserves all the quantum uncertainty, and just rotates it around in a unitary manner over time.
During this wave-function mode, the mathematical picture suggests that there is no definitive underlying state of the world: everything is in some kind of probabilistic superposition of possible states. Only once you measure something does it actually exist in any kind of definite way, leading to the mantra that “the world only exists when you measure it”.
This strong discretization of the laws of physics is at the root of many seeming paradoxes and puzzles in understanding the quantum world: what exactly defines a “measurement” at a fundamental level? How can the wave function, which could conceivably spread out over large macroscopic spaces over time, instantaneously collapse down to a single point within that entire space?
Despite these conceptual difficulties, the mathematics of the framework allow straightforward calculations that match the outcomes of actual experiments, leading to a general attitude of “shut up and calculate”: don’t bother with unnecessary considerations of the actual underlying physical ontology, just do the math! This clearly puts this framework into the category of a calculational tool as discussed in tools vs models.
From a sociological perspective, the inability to properly appreciate the distinction between calculational tools and physical models has resulted in a century of the single most egregious form of “gaslighting” in any area of science. New students are trained that their own intuitions about the nature of the physical world are just “naive” biases inherited from the normal macroscopic realm, and that none of these things apply to this mysterious quantum world. You are just supposed to discard all such notions of what is physically plausible, and let the math tell you what is actually going on.
The whole thing is just so impossibly preposterous as to be hilarious, except that generations of serious people have somehow convinced themselves to swallow these absurdities. And they make sure to enforce the dogma on everyone else too: it is truly a cult-like dynamic, right at the heart of the most foundational branch of science.
The pilot-wave framework, while still incomplete, provides such a striking contrast to the paradoxes present in the Copenhagen interpretation, and yet it remains a “fringe” theory. Sure, if you’re actually needing to run some calculations, go ahead and use the Hilbert space formalism. But if you want to understand what might actually be going on in the underlying physics of Nature, the Copenhagen model is just obviously incoherent and nonsensical.