I was surprised to see this The multiplicative groups $\mathbb{Q}^\ast$ and $\mathbb{R}^\ast$ are not isomorphic question of mine, which is over 4 years old, closed today. I was alerted earlier today and asked to indicate whether the linked question was indeed a duplicate, to which I said "no", because while closely related, the questions are not identical.

What is the point of closing 4 year old questions as a duplicate? And how does the site take the OP's viewpoint into account when closing a question?

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    $\begingroup$ It's not an exact duplicate, but the other question answers your question. $\endgroup$ – Matt Samuel Feb 25 at 22:19
  • $\begingroup$ Some SEDE queries, just as a curiosity: Longest time between creation and closure and the same for deletion. $\endgroup$ – Martin Sleziak Feb 26 at 6:45
  • $\begingroup$ What I do not understand is why the duplicate arrow is this way round. The questions were asked roughly a week apart, and are basically identical (the same information can be obtained from either question). The key differences are: 1. The closed question is older. 2. The closed question contains the "easy" proof of non-isomorphism, based on cardinality (this is in the body of the question), while the other question does not, and so the closed question contains more information. 3. The closed question is better, as the other question is simply a PSQ and should be closed as such. $\endgroup$ – user1729 Feb 26 at 13:45
  • $\begingroup$ @hardmath Sorry, typo. By "older" I meant "newer". My point is that, although strictly speaking a duplicate, it is the better question. $\endgroup$ – user1729 Feb 26 at 18:44
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    $\begingroup$ @user1729: Opinions will vary. I feel the older Question asks the more incisive point, about a surjection and thus obviates a cardinality argument, while the newer needs to make an ad hoc objection to that. Also I think the essentially equivalent Accepted Answer to the older Question is a little better articulated, perhaps owing to its CW character. $\endgroup$ – hardmath Feb 26 at 19:32

The goal of Math SE is to create a searchable repository of high quality questions and answers. "Searchability" is important—if the same question is asked over and over again, then it becomes difficult for search engines (or users) to find the best answer to a given question. Duplicates create a lot of noise and clutter which make navigating the site harder. Closing a question as a duplicate helps to organize the site, and helps search engines to find canonical answers. Thus the point of closing an old question is to improve site organization and accessibility.

Regarding the specifics of your question, while the questions themselves are not identical, answers at the dupe-target seem to address your question. The point is not that the questions are duplicates, but that the question marked as a duplicate is answered at the dupe-target. Questions need not be identical in order for one to be closed as a duplicate of another.

  • $\begingroup$ But why has it taken so long for the decision to close it to be made? $\endgroup$ – Peter Phipps Feb 25 at 22:41
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    $\begingroup$ Some duplicates question have better answers than the original question. $\endgroup$ – Aryadeva Feb 25 at 23:21
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    $\begingroup$ Peter, being designated as a duplicate in no way indicates that your question shouldn't have been asked. It links it to a target question, as your question is linked on it's page. As long as the question is well asked, we typically do not delete dupes, because all good closely related questions assist a future asker. You did nothing wrong. $\endgroup$ – amWhy Feb 25 at 23:21
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    $\begingroup$ @PeterPhipps Math SE gets hundreds of new questions every day. Not every question which should be closed (for whatever reason) gets closed. Sometimes, an old question comes to the attention of users years later, and is dealt with then. $\endgroup$ – Xander Henderson Feb 25 at 23:44
  • $\begingroup$ I agree with all your points. I do think it matters that the questions are not identical; there may be ways to give an answer to the question I asked, that do not work for the other question. Closing the question as a duplicate makes it impossible to collect those answers on this site. $\endgroup$ – user133281 Feb 26 at 1:03
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    $\begingroup$ Your question asks for a way of doing a thing with a restriction (i.e. "don't use a cardinality argument"). The linked question asks for a way of doing a thing without any restrictions. The linked question is more general, thus any answer of your question will also answer the linked question, but the linked question admits more answers. Your question was appropriately closed as a duplicate. $\endgroup$ – Xander Henderson Feb 26 at 1:33
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    $\begingroup$ @XanderHenderson "The linked question is more general, thus any answer of your question will also answer the linked question, but the linked question admits more answers." That's a terrible justification - subquestions are not duplicates. Adding restrictions can dramatically change the nature of a question. "while the questions themselves are not identical, answers at the dupe-target seem to address your question." That's a better justification, but I'm still not sure I agree with it. $\endgroup$ – Noah Schweber Feb 26 at 2:11
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    $\begingroup$ @NoahSchweber In this case, none of the answers to the linked question make a cardinality argument. Strictly speaking, all of the answers to the linked question answer the closed question. $\endgroup$ – Xander Henderson Feb 26 at 3:34
  • $\begingroup$ True, and that's why I view the second as a better justification. But the first justification is just wrong. $\endgroup$ – Noah Schweber Feb 26 at 3:37
  • $\begingroup$ @NoahSchweber If a question with restrictions is answered below a question without restrictions, the question with restrictions is a duplicate. Thus, in many circumstances, a more specific question can (and should) be closed as a duplicate of a more general question. $\endgroup$ – Xander Henderson Feb 26 at 3:42

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