Comment by lkm0 | Hacker News Reader

Comment by lkm0 | Hacker News Reader

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Hidden variables are more about finding a way to derandomize quantum physics. The state |00> + |11> can collapse to |00> or |11> when measured. It appears to be that this randomness is baked into reality (God, meet dice, etc), and many people find this a bit distasteful, because it means measurements propagate faster than light (even if Alice and Bob can't communicate that info). If it turns out the theory is incomplete and there are missing/hidden variables, then it means whether it was |00> or |11> was determined from the start, before the measurement was made, and there's no faster-than-light interaction. Experiments around Bell's inequality prove that hidden variables don't exist, unless we start getting into scenarios that are as weird as entanglement itself. So the cat is truly alive and dead at the same time, and superposition is physically happening; this property is called quantum contextuality and is related to Bell/etc but still another discussion.

The important distinction in this case is about FTL existing but not being able to exploit it for FTL communication.

Thanks for taking the time to explain it further. This is a topic that keeps me up thinking about, not because a fundamental randomness is distasteful, but because it doesn't seem to match with what we see, and I'm wondering if we are getting caught up in describing laboratory/pure math isolated states rather than what actually occurs in nature.

In reality the entangled particle will interact with something almost instantly thus collapsing it. The cat is actually dead or alive from the perspective of the microscopic things in the box. A world never witnessed or measured by a being doesn't collapse it's entire history of interactions of every subatomic particle, atom, molecule and emergent property from the start of the universe to 'now' instantaneously upon being viewed. The photons from that world have been hitting earth continuously since earth existed after all.

No worries, explaining helps my understanding as well.

The new thing you're mentioning is a common observation about observers: if there are two cats in the box, should they be |dead dead> + |alive alive> or is one measuring the other and they've collapsed to a classical state? This depends on a person being outside the box; the scenario is called Wigner's friend. It's been used to show many other unintuitive aspects of quantum physics.

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