Physicists like Sean Carroll argue not only that quantum mechanics is not only a valuable way of interpreting the world, but actually describes reality, and that the central equation of quantum mechanics – the wave function – describes a real object in the world. But philosophers Raoni Arroyo and Jonas R. Becker Arenhart warn that the arguments for wave-function realism are deeply confused. At best, they show only that the wave function is a useful element inside the theoretical framework of quantum mechanics. But this goes no way whatsoever to showing that this framework should be interpreted as true or that its elements are real. The wavefunction realists are confusing two different levels of debate and lack any justification for their realism. The real question is: does a theory need to be true to be useful?

1. Wavefunction realism

Quantum mechanics is probably our most successful scientific theory. So, if one wants to know what the world is made of, or how the world looks at the fundamental level, one is well-advised to search for the answers in this theory. What does it say about these problems? Well, that is a difficult question, with no single answer. Many interpretative options arise, and one quickly ends up in a dispute about the pros and cons of the different views. Wavefunction realists attempt to overcome those difficulties by looking directly at the formalism of the theory: the theory is a description of the behavior of a mathematical entity, the wavefunction, so why not think that quantum mechanics is, fundamentally, about wavefunctions? The view that emerges is, as Alyssa Ney puts it, that

Reality isn’t fundamentally a collection of objects—particles, atoms—spread out in three-dimensional space or even four-dimensional spacetime, but instead, reality is fundamentally a wave function, a field-like object that exists in some higher-dimensional quantum reality.

This view is quite appealing to those philosophers keen to have a closer connection between science and philosophy, the naturalists. 

For naturalist philosophers, having our image of the world directly anchored to science is not just a preference, it is the whole game plan. Wavefunction realism promises to make that plan easier to achieve. The main advantage is the idea that we can “read off,” as it were, the ontology directly from our mature science—in this case, quantum mechanics. We can thereby furnish the inventory of the world in the most scientific way possible. That would seem to bypass the many messy interpretative difficulties that typically arise with quantum ontology, namely, when trying to say what quantum mechanics is really about.

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For a small price, the prize seems large: wavefunction realism would offer a direct path to closing the traditional epistemic gap in the metaphysics of science, that is, the gap betwen how theories say the world is and how reality actually is.

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