CompuServe subscriber James Baugh argues that at best, a computer simulation of quantum mechanics will result in an exponential-time algorithm. At worst, it is impossible. The reader is surely aware of the standard many-body Schroedinger equation. Baugh is asserting this as a general principle. This is the quantifiable ontological difference between classical mechanics and quantum mechanics.
Ontological arguments are common currency.
To put things another way, the formalism of quantum mechanics has to respect the possibility that all the particles will suddenly amalgamate into one large particle or several large particles, which may then disintegrate again. There may be other conservation laws which prevent such amalgamations, but these laws are unknown to the formalism. This requirement of the formalism saddles us with the exponential-time algorithm, unless perhaps we are content to stick to very low energies where amalgamations and disintegrations are unknown. Exponential-time algorithms are practically useless. We may be able to view a computer simulation of the collapse of the wave function in a simple geometry, which will give us great intellectual satisfaction, but that is the best we can do.