Actually, according to quantum physics, the world is functional. The Universe can be described by completely by a function (the universal wave function) and is completely time-reversible; you can run it forwards or backwards because it has no side-effects.
The collapse of a wave function into a single state that apparently happens on observation is as far as we know non-deterministic. The wave function itself is a probability amplitude. So I think it's a misinterpretation to say that "the universe can be described completely by a function" when everything we can actually know about the universe is observable and has necessarily collapsed from a probability amplitude of possible states into the observed state.
My interpretation is the exact opposite. Newtonian physics suggests the fundamentally deterministic world that QM can't because in the latter the only thing that is deterministic is probabilities.
Collapse of a wave function occurs when one wave becomes entangled with another. If I shine a photon on a particle to measure it, and the particle emits a photon back to me, I am now entangled with that particle through mutual interaction. But to a distant observer, there is no wave collapse. If our universe is purely quantum and exists alone (not being bumped into by other universes), then its wave function would just be evolving unitarily according to it's Hermitian - totally deterministically (the wave function, that is).
I don't know what it means for the universe to be "purely quantum", or what it means to be a "distant observer" yet somehow not interacting. A wave function in itself is not observable. Is it real? Definitional. Is it a physical phenomenon? Dubious. All we know is that as a model it is consistent with what we observe. What actually can be measured (and can reasonably be considered real and physical in that sense) can only be predicted probabilistically using quantum mechanics. It's like saying that I can perfectly predetermine the outcome of a dice roll—it's between one and six.
Since I got downvoted let me elaborate: it isn’t relevant that the universe is a function. What matters is whether the universe can be modeled better as the composition of pure functions or as some stateful composition (e.g. interacting stateful objects).
Programming languages aren’t about the final result but about how you decompose the result into modular abstractions.
