Quantum states are the key mathematical objects in quantum theory. It is therefore surprising that physicists have been unable to agree on what a quantum state represents. One possibility is that a pure quantum state corresponds directly to reality. But there is a long history of suggestions that a quantum state (even a pure state) represents only knowledge or information of some kind. Here we show that any model in which a quantum state represents mere information about an underlying physical state of the system must make predictions which contradict those of quantum theory.
So, it turns out it is more than "just" a useful mathematical tool after all. Does this confirm the universe basically runs on maths?