The measurement results are mathematically necessary. The Copenhagen interpretation, that this means there is a physical collapse in the wavefunction, is not.
> To me, it seems that other theories are just disputing what the "collapse" fundamentally means.
If you substitute "collapse" for "measurement" this is pretty much true. What else could "different interpretations of a theory" mean?
One is about what actually happens. This contains Shrodinger equation and similar things.
The other is about what results will we get if we poke the particles with macroscopic objects disturbing them beyond recognition. That's the all math where the word "measurement" is used.
Somehow we think the science of what happens to a frog when you poke it with a knife is a part of zoology. It's important, it might be even more important than zoology, but that's a different domain of science.
That's perhaps the Narcissistic Many Worlds interpretation. Another way of thinking about Many Worlds is that there's only one universe, in which: after measuring a particle in a superposition of two states, you are now in a superposition of two states. Each of the superimposed you states thinks your instrument measured a single clear result.
The wavefunction of the universe goes on propagating as usual, including both of the superimposed yous, but within each of the superimposed states, that you thinks that it has witnessed wavefunction collapse.
In many worlds, collapse is a subjective and approximate phenomena, not something fundamental.
The way I see it, other interpretations have no purpose except to reconcile what we observe on small scales with incorrect statements such as "electron is a tiny ball", or "electron is a wave in the three-dimensional space", or "an observer which are themselves composed of quantum mechanical particles is independent of the system, and exerts free will to choose measurements while the observed system is purely deterministic".
The uncertainty principle says you can never know both the location and the momentum of a particle. This stems from the fact that because spacetime is the way it is, knowing either one of those things requires having made a measurement, which by its nature, prevents the measurement of the other thing.
The act of measurement is independent of there being an "observer" in the sense of some sort of intelligence or consciousness. The use of the word observer in early communications led to all sorts of woowoo garbage later on.
More recent interpretations suggest that instead of the requirement that particles be in a singular state, perhaps their fundamental nature is probabilistic. The wave function is the thing, the particle at a singular place and time is an illusion. There's no need for wave functions to collapse, and that view seems to be an imposition of human scale expectations on the quantum universe. An electron exists as a point cloud - what we observe is an artifact of the observation, not a fundamental property of the particle.
I am fond of the "universe is made of math" view suggested by Max Tegmark.
https://en.m.wikipedia.org/wiki/Mathematical_universe_hypoth...
We did not evolve to perceive the universe as it is. We have limitations built into the mechanics of our existence that have to be overcome and understood at every level of abstraction that our tools of reason and technology provide. The more degrees of separation between our evolved tools of perception and extrapolated and abstracted concepts about how the universe works, the more it will diverge from human experience and seem to be "weird." When we try to make weird things make sense to our monkey brains, we introduce a bias that can lead us astray.
https://www.quantamagazine.org/where-quantum-probability-com...
The Copenhagen interpretation is an attempt to make monkey sense of something that has no direct input into any of our tools of perception.
The Everett interpretation recognizes that any observation has to include the quantum states of the mechanism doing the measuring, the environment in which the mechanism resides, and the entities in proximity to the environment, and planet, solar system, galaxy, and universe - that by existing inside the universe, you are subject to the influence of everything else that exists within the universe, and that quantum states are one of the proxies we have for predicting the results of interactions between the states.
Stephen Hawking was an Everettian, and discounted the Copenhagen interpretation.
https://en.wikipedia.org/wiki/Many-worlds_interpretation
Tldr; there's no such consensus on Copenhagen, and the many worlds interpretation is gaining precedence, because it's got the most rigorous basis in mathematics.
> Quantum mechanics is intrinsically indeterministic.
> The correspondence principle: in the appropriate limit, quantum theory comes to resemble classical physics and reproduces the classical predictions. The Born rule: the wave function of a system yields probabilities for the outcomes of measurements upon that system.
> Complementarity: certain properties cannot be jointly defined for the same system at the same time. In order to talk about a specific property of a system, that system must be considered within the context of a specific laboratory arrangement. Observable quantities corresponding to mutually exclusive laboratory arrangements cannot be predicted together, but considering multiple such mutually exclusive experiments is necessary to characterize a system.
These are universally accepted facts now (it would be silly for any physical theory to contradict the second one). Even a kind of "out there" theory like many worlds theory (https://en.wikipedia.org/wiki/Many-worlds_interpretation) would not dispute these facts (it just reinterprets the indeterminism of quantum mechanics as taking different "branches" in a multiverse). The "interpretation" part of it is a bit historical, as no "interpretation" should contradict these facts (a la Bell's theorem).
Edit: As a philosophy, any "interpretation" built off of these facts is cool, but until you calculate anything, it's essentially useless as a physical theory.