[kgwgk]

> In Quantum Mechanics things travel as waves and interact as particles. Between interactions, everything is described by the Schrodinger Wave Function, which evolves to include every possible path. But at the point of an interaction the wave function must collapse to satisfy conservation rules.

That would make some sense if by interaction you mean "interaction with the macroscopic environment". When small-enough quantum systems (like two particles) interact there is no collapse and the evolution is unitary.

> This interaction is enough to 'collapse the wave function'. No 'observation' is required.

How do you distinguish the interactions that 'collapse the wave function' from those who do not?

[HackOfAllTrades]

The idea that Measurement = "interaction with the macroscopic environment" is part of the Copenhagen interpretation, not a requirement of QM itself.

Aside: (Personally, I see this more as Bohr's way of dodging questions he had no answer to, and not a viable way to think about Quantum Mechanics. A better answer would have been "I don't know. Let's figure it out." But that was impossible for political reasons. Bohr was being attacked by Einstein for 's sake. He can be forgiven for adopting Ali's "rope-a-dope" tactics if he felt that Einstein was trying to destroy his entire field in its infancy. But I find "there is no quantum world" simply unacceptable.)

Now to answer your question as best I can, an interaction must collapse the wave function when it is required to fulfill a conservation rule. For example, if an electron is captured by a nucleus it becomes bound and emits a photon. This is an interaction that must conserve momentum, angular momentum, energy, and charge. Because of that, the electron can no longer be represented by a non-localized wave function. The universe must concentrate those properties down to a point in order to "do the accounting" necessary for the conservation rules.

No, I don't know how it does that. But then, NONE of the available interpretations answer that question. This indicates to me we are thinking about it wrong.

What I like about Stuckey's paper is that it adds another factor: besides conservation rules the universe seems to require that "measurements" obey the Relativity Principle (No Preferred Frame of Reference). I have yet to figure out how to incorporate that.

[kgwgk]

Is the idea of “collapsing the wave function” a requirement of QM itself? In that context, a “measurement” would be to be what you call “an interaction that must collapse the wave function”.

And your answer is simply wrong. An excited atom can emit a photon, for example, and the system will still be described by a “non-localized wave function”. It won’t even be well defined if the spontaneous emission has happened or not yet.

The evolution of a quantum system according to Schrödinger’s equation doesn’t violate conservation rules. And, in case it’s not clear, the quantum system described by the wave function in the example above is the atom-photon(-or-not) pair.

You’re definitely thinking about it wrong.