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I just noticed that the question

was closed as off-topic a couple of months ago, and I don't understand why. The topic is basic quantum field theory: the entanglement structure of the vacuum is fundamental to understanding basic things like the interplay between causality and the structure of two-point correlation functions, understanding why a strict position-operator doesn't exist in relativistic QFT, and so on, not to mention its central role in more exotic (but still very much mainstream) things like Hawking radiation, the black-hole information paradox, and the AdS/CFT correspondence. In case the fundamental importance of the vacuum entanglement topic in quantum field theory is unfamiliar, note that Edward Witten wrote a review paper about it (Notes on Some Entanglement Properties of Quantum Field Theory, arXiv:1803.04993). This particular question is about harvesting entanglement from the vacuum, which is not something that has any practical utility, but it does have pedagogical utility.

There is plenty of precedent on this site for regarding theoretical physics as on-topic as long as it's mainstream, even if it is purely a pedagogical thought experiment with no forseeable practical applications. I'm curious to understand why this particular question about basic quantum field theory was deemed to be off-topic. Not complaining, just sincerely curious to know what the reasoning was, in case I'm overlooking a good reason.

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  • $\begingroup$ Note: as of two hours ago, the question has been reopened. $\endgroup$
    – rob Mod
    Oct 4 at 20:21
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    $\begingroup$ The question has been reopened, but my meta-question is less about lobbying for reopen-votes and more about wanting to understand the reason for the original close-votes. Usually I can understand why a question was closed as off-topic, even if I think it's debatable. But in this case, I don't. I reviewed What topics can I ask about here? carefully and re-read the question carefully, and I'm still unsure. Are "what would happen if" questions automatically off-topic, even if it's a device to learn something about well-established physics? $\endgroup$ Oct 5 at 0:36
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    $\begingroup$ Perhaps any of the users who originally voted to close can share their thought process. $\endgroup$ Oct 5 at 10:45
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    $\begingroup$ I wasn't involved in either the closing or opening, but my best guess for the reason is that if you just skim the question, it sounds nutty. It asks about a website that talks about harvesting something from the vacuum. Like time crystals, this is a subject that attracts a lot of nonsensical popsci speculation, and it ends up easy to forget that there's something real at its foundation. $\endgroup$
    – knzhou
    Oct 5 at 18:15
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    $\begingroup$ @knzhou That's a good observation. I can totally see how nutty it could look on the surface. On the one hand, I would suggest that we really shouldn't be casting votes (including regular up/down votes) on posts that we don't understand. On the other hand, some questions can't be understood (at least not with physics) and should be closed for that reason. How can we always be sure which is which, without spending inordinate amounts of time investigating every nutty-looking post? I suppose the best solution is to design the system to allow reopen-votes... exactly like the SE designers did. $\endgroup$ Oct 6 at 0:33
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I voted to close the question (before I was a mod), and I have racked by brain to remember what I was thinking, but I just don't recall.

I suspect that I read the question and misunderstood something—so that it just sounded "nutty" (as some of the above comments put it).

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    $\begingroup$ Thank you for the feedback! You raised a very good point... I can't always remember my reasons for doing things last week, nevermind two months ago, so it probably wasn't fair for me to think anybody would remember specific reasons after such a long delay. I probably wouldn't have posted this meta-question if I had thought about that before. $\endgroup$ Oct 7 at 1:43
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    $\begingroup$ And by the way, congrats on being selected as a mod! I loved your "familiarizing myself with all the new controls." :) $\endgroup$ Oct 7 at 1:44

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