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this post was submitted on 26 Jan 2026
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See, this is why I prefer the (terribly named) "Many Worlds" interpretation. Unlike the Copenhagen interpretation, it does not privilege measurement over other types of interactions between systems. That is, the wave function never collapses, it only seems to because you, as the observer, are part of the system.
The easy way to see this is to imagine that you put some other experimenter inside of a box. When they perform a measurement, from your perspective the wave function has not yet collapsed, but from the experimenter's perspective the wave has collapsed. Essentially, it is as if the system in a box has branched so that there are multiple copies of the experimenter within, one who sees each possible measurement result, but because you are outside of it you could, in theory, reverse the measurement and unite the two branches. However, it is important to understand that the concept of branches is just a visualization; it is nothing inherent to the theory, and when things get even slightly more complicated than the situation I have described, they do not meaningfully exist at all.
(Also, if it seems implausible that a macroscopic system in a box could remain in a superposition of multiple states, you actually are not wrong! However, the reason is not theoretical but practical: any system inside the box will interact thermally with the box itself, so unless it is perfectly insulated you cannot help but interact with it and therefore measure it yourself. This keeps going until essentially the entire world cannot help but perform a measurement of your system. Preventing this tendency from screwing things up is one of the things that makes building quantum computers hard.)
Hmm, you could say it instead privileges the subjective experience over other types of interaction. There's no reason in principle why you couldn't experience every "world" at the same time, in the same way a measurement could in principle return all possible results at the same time.
But you don't. Somehow your experience of reality is above unitary time evolution, even though "you" aren't.
I agree completely that that the Copenhagen interpretation makes an excellent phenomenological model in simple (albeit, very common!) settings. However, the problem is that it breaks down when you consider experiments such as the "quantum eraser" (mentioned in other comments here), which causes people to tie themselves into intellectual knots because they are thinking too hard about exactly what is going on with measurement; once one deprivileges measurement so that it becomes just another kind of interaction, the seeming paradoxes disappear.
Copenhagen interpretation doesn't break down for quantum erasure. Upon measurement you collapse the total quantum state into a result where the two measurements are consistent, that's simply what entanglement means.
The timing of experiments, and the choice of what to measure, are elements ultimately irrelevant to the above statement, as the quantum erasure experiment demonstrates.
To clarify my imprecise language, what "breaks down" is not its ability to give the correct answer, but the ability of the conceptual framework to give a clear explanation of what is going on, because it essentially defines measurement as "you know one when you see one", which can lead to confusion.
(However, separately, I do feel the need to point out that "entanglement" is not at all a term that is related to measurement results per se, but rather to the state of a system before you measure it. In particular, if a system is entangled, you can (in principle) disentangle it by reversing whatever process you used to entangle it so that you no longer get correlations in the measurements.)
I don't know, Many Worlds always led to more confusion than Copenhagen for me. But I suppose that's a matter of taste since they're equivalent.
As per the relationship between measurement and entanglement, from an empiricist viewpoint all quantum mechanical terms are related to measurement. If entanglement didn't affect the outcome of measurements, it wouldn't exist.
Indeed, you can disentangle an entangled system, which of course will change the outcome of measurements - that's how you know it's been disentangled.
I think to some extent we have been talking past each other. Very roughly speaking, I think that am more worried about what happens in the middle of an experiment, where you are more worried about what happens at the end. I actually completely agree with you that when a conscious being performs a measurement, then, from the perspective of that being, both interpretations of what happened when it performed the observation are equivalent. That is, the being has no way of telling them apart, and asking which interpretation is true at that point is, in my opinion, roughly along the same lines as asking whether the objective world exists.
(Just to be clear, it's not my intent to get mystical here. I think of consciousness as essentially just being a way of processing information about the world, rather than positing the existence of souls.)
Interesting framing. But without measurements there isn't really a need for different interpretations, is there? If that's what you mean by "in the middle of an experiment".
I will happily agree that before measurement, it's very useful to think of the system as existing in many states at the same time.
My main issue with Many Worlds is that it is always superfluous.
We know that the exponential complexity of the quantum state cannot be explained by saying every outcome simply occurs in another branch. That would make it mathematically equivalent to an ensemble, and ensembles can be decomposed into large collections of simple deterministic systems with only linear complexity. If that were how reality worked, quantum mechanics would be unnecessary. The theory could be reduced to classical statistical mechanics.
A quantum superposition, such as an electron being spin up and spin down, is not an electron doing both in some proportions. If it were, it would again be equivalent to an ensemble and fully describable using classical probability theory. If the quantum state has any ontology at all, it cannot merely represent particles doing multiple things at once. It must be something else, a distinct beable that either influences particles, as in pilot wave theories, or gives rise to them, as in collapse models.
Some Many Worlds advocates eventually concede this, but then argue that particles never really existed and are only subjective illusions, while the quantum state alone is real. Calling something a subjective illusion does not remove the need for explanation. Hallucinations are still physical processes with physical causes. You can explain them by analyzing the brain and its interactions.
Likewise, you still need a physical explanation for how the illusion of particles arises. Any such explanation ends up equivalent to explaining how real particles arise, and once you do that, Many Worlds becomes unnecessary. You can always replace the multiverse with a single universe by making the process stochastic instead of deterministic.
The crucial point is that we know a particle in a superposition of states cannot be a particle in multiple states at the same time. That is mathematically impossible and if that is what it was then it could be reduced to a classical description! Any interpretation which relies on thinking the quantum state represents an ensemble, i.e. it represents things "taking all possible paths" or "in multiple states at once," is just confused as to the mathematics as this is not what the mathematics says.
I go into this in more detail here: https://medium.com/p/f67aacb622d5