> project out the E&M field. Voila, now you have a quantum description
There is no wavefunction describing the state of the subsystem because the system is not separable.
> Its dynamics may look funny, i.e. they may appear nonlocal, they may not conserve energy, etc. but that's different from saying "there is not a quantum description of these dynamics" which is what you're claiming.
What is the “quantum description of these dynamics”?
Quantum mechanics is usually based on something like the following postulate: “The state of a physical system is described by a well-behaved function of the coordinates and time, Ψ(q, t). The function contains all the information that can be known about the system.”
> project out the E&M field. Voila, now you have a quantum description
There is no wavefunction describing the state of the subsystem because the system is not separable.
> Its dynamics may look funny, i.e. they may appear nonlocal, they may not conserve energy, etc. but that's different from saying "there is not a quantum description of these dynamics" which is what you're claiming.
What is the “quantum description of these dynamics”?
Quantum mechanics is usually based on something like the following postulate: “The state of a physical system is described by a well-behaved function of the coordinates and time, Ψ(q, t). The function contains all the information that can be known about the system.”