In an introductory QM class we are learning that some fundamental things in nature are quantized. For example, the energy states of a bound particle. But we have also learned that an unrestrained particle can have a continuum of energies.
Which things in nature are quantized? Energy is, but only under certain conditions? Are position and momentum quantized, or do they have discrete quantities we just can't measure exactly? Or is it that at some level all things are discrete?