Abstract
Alternative views of quantum states are often expressed using the language of representation. It is important to distinguish three questions here: What is a quantum state? How may a quantum state be represented? What, if anything, does a quantum state represent? I defend answers to these questions against alternatives. In brief, a quantum state is an objective relational property of a physical system that describes neither its intrinsic physical properties nor anyone’s epistemic state. A quantum state is representational (in my preferred sense of that term) and many quantum states are real. Since its primary role is to assign Born probabilities to certain physical events involving the system, a quantum state may be represented in quantum theory by any mathematical object that facilitates this role. If it represents anything, a quantum state represents the objective probabilities it yields in this way.
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Notes
- 1.
When the subjectivist statistician Bruno De Finetti (1968) famously wrote PROBABILITY DOES NOT EXIST he meant to deny that the physical world contains any such thing, just as it contains no phlogiston, fairies or witches.
- 2.
Suarez (2015) has proposed an “intermediate” view with a dispositional velocity field defined at each point of space that also faces the following problem.
- 3.
- 4.
The state of an individual system can sometimes be prepared with no selection step by controlling its interactions with its environment, as in laser cooling or just letting the system relax when coupled to a vacuum (Fröhlich & Schubnel, 2016). While it is tempting to conclude this works by modifying its intrinsic properties, certification of the procedure by quantum tomography on many similarly prepared systems does not establish this conclusion.
- 5.
For further details see my (2012b).
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Healey, R. (2022). Representation and the Quantum State. In: Allori, V. (eds) Quantum Mechanics and Fundamentality . Synthese Library, vol 460. Springer, Cham. https://doi.org/10.1007/978-3-030-99642-0_20
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