What is wave function collapse?

As humans, we never perceive superpositions of matter waves. There are lots of different ideas about why that should be. One of the oldest, called “the Copenhagen interpretation” after a conference where lots of famous physicists met to talk about quantum physics, is that somehow when we measure a quantum system, the wave function undergoes a sudden, discontinuous change. There are many problems with this idea. “If it worked the way its adherents say it does, it would be:

1. The only non-linear evolution in all of quantum mechanics.
2. The only non-unitary evolution in all of quantum mechanics.
3. The only non-differentiable (in fact, discontinuous) phenomenon in all of quantum mechanics.
4. The only phenomenon in all of quantum mechanics that is non-local in the configuration space.
5. The only phenomenon in all of physics that violates CPT symmetry.
6. The only phenomenon in all of physics that violates Liouville’s Theorem (has a many-to-one mapping from initial conditions to outcomes).
7. The only phenomenon in all of physics that is acausal / non-deterministic / inherently random.