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Comment by everdev | Hacker News Reader

> Wigner can even perform an experiment to determine whether this superposition exists or not. This is a kind of interference experiment showing that the photon and the measurement are indeed in a superposition. From Wigner’s point of view, this is a “fact”—the superposition exists. And this fact suggests that a measurement cannot have taken place.

> But this is in stark contrast to the point of view of the friend, who has indeed measured the photon’s polarization and recorded it. The friend can even call Wigner and say the measurement has been done (provided the outcome is not revealed).

A bit of a stretch saying that protons lose their superposition based on the content of a conversation.

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From a Many Worlds point of view at least, they absolutely could, because the superposition represents ignorance in the mind of infinitely many Wigners, but once you remove the ambiguity you are just dealing with one specific Wigner, who would then know which Everett branch he is actually on (at least ip to the ambiguity of this particular experiment).

In this experiment, in both branches he receives the same information "A measure has been done.", so it doesn't remove the ambiguity, and it doesn't destroy the superposition.

I was talking about the case when the friend is told the outcome of the measurement, that’s the only part relevant to what the parent comment said.

Why?

Because it implies that receiving information affects the material world. And communication isn't infallible.

What if you kind of hear me and are pretty sure I said 'positive' but not 100% sure? What if you're 50% sure? What two people are listening and one heard me say 'positive' and one heard 'negative'?

It's hard to imagine a physical process being dependant on something external and near impossible to quantify or measure.

The general idea is that as long as your particles are not entangled with the system’s particles then from your point of view they remain in a superposition.

The conversation simply represents the idea that the causal cone of the observed system is now interacting with the particles of the observer, making them entangled and so ‘collapsing’ the wave function or whatever you want to calm it.

Well, you have Lucretius' clinamen.

> Because it implies that receiving information affects the material world.

Information is physical, although I agree that the conversation isn't the important part, it's just a useful metaphor.

The measurement is itself still in superpostion though. You know it's taken place, but not with what result. It's kind of like quantum eraser.

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