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Mark, if you can't distinguish between MO and your backyard...
+1 JDH. Isn't closing enough?
The question in question has 16 votes... The Real Mathematician would have to go to page 29 of the list of most upvoted questions to find it—I am sure a Real Mathematician has more Important Things to do than that!
I had the privilege of casting the final vote to delete. If that gets rid of the cicadas in my yard, that is a +++.
I do not have much against the deletions though I'd wish the process was a bit more transparent (this is actually a positive example, thank you Mark Sapir).
Yet, the gleefullnes and the feeling of superiority some display in doing so is a bit shocking.
After some complaints, I undeleted some questions that had answers with at least 5 votes, some with 10 or more votes. It would be preferable to ask permission from the authors before deleting their potentially significant answers.
+1 JDH. I think simply closing inappropriate questions is almost always sufficient, and I find the arguments in favor of being more aggressive with deletions to be very unconvincing. My impression is that this has not been much of an issue until very recently; in other words, MO got along just fine for two years using deletion only minimally. I see no compelling need to change course and start deleting any question which irritates three 10k users.
+1 for JDH.
I think the "a real mathematician" argument flawed. In fact, a closed question reflects better on MO since it shows that the community is able to identify poor questions (it also shows how politely (or not) people react to poor questions). An aseptic community is not attractive and might be argued to discourage just as many people.
If at some point the software can be improved again, it might make sense to prevent such questions from appearing on positive lists (such as "most votes"). Although they might serve their purpose in searches since they discourage the repetition of poor questions.
I don't think questions should be deleted if multiple high-reputation users want to keep them. I'd go so far as to say that if even one high-reputation user (and you can't get any higher than JDH) has expressed an interest in keeping a question on the site, it should be kept. I wish the voting system implemented that rule.
Mark, Andy, Bill, and others who want to delete this, you may not be able to understand what value others see in this question, but you'll observed that others do see value in it. I think that under those circumstances, it would be respectful not to prevent everyone from reading it.
The fact that there were almost no interesting answers is interesting in itself. Maybe the famous cicadas really are the only known instance of this phenomenon. Judging this question to be a failure for that reason is like judging a scientific experiment to be a failure because it did not produce the result expected.
I wasn't very impressed, either, with the unconstructive tone of some of the answers. Yes, the OP could have been clearer about the term "nature" and the role of coincidence, but I thought it was pretty obvious what was meant. If the question is undeleted I might have a go at improving it.
I think deletion should be kept for obvious homework questions that receive no answer, spam, and the like.
Mark, I still think that deleting is the wrong response. Closing already indicates that the question is not appropriate. Personally, I'm not even sure it should have been closed. I'd prefer it if it had been edited to make it better.
I'll say something about why I think this question is interesting (although not phrased particularly well). Mathematics has always been inspired by mathematical phenomena appearing in nature. By "nature" I mean everything in the physical world - physics, chemistry, biology etc., though for the purposes of this discussion I exclude human activity. There are examples of inverse square laws in nature, there are examples of exponential decay, and so on. Maybe there are directly observable examples of modified Bessel functions: who knows. Looking at how mathematics appears in nature often leads to new mathematics: take string theory, for instance, which may or may not be a good physical theory, but has certainly led to advances in mathematics.
So I think questions of the form "does such-and-such a piece of mathematics appear in nature?" are potentially interesting. Of course you could ask an unlimited number of such questions, but what makes this one stand out is that (i) there appears to be at least one example of prime numbers popping up non-coincidentally, and (ii) there don't appear to be so many examples that it's boring.
Out of interest, how would the pro-deletion people react to a question along the following lines? "I've been investigating such-and-such an abstract dynamical system, and when I ran some numerics on it, I discovered to my surprise that the period was always a prime number of units of time. Are there other examples of dynamical systems with unexpected prime number periodicity?" That's not phrased enormously well either, but would you consider a question of this type so beyond the pale that it deserved deletion?
Regarding the off-topic matter, if you have an easy deduction of the result described in that n-Category Café post from the result in your paper with Guba, I'd like to see it. I tried to find one years ago, when Fiore and I first did that work, but with no success: I couldn't see a direct way of deducing either characterization from the other. I also discussed this with Guba when he was visiting Glasgow in about 2005. But let's continue this discussion at the Café.
Mark, I've moved our off-topic conversation to the n-Category Café, where it continues.
@Gil Kalai: a rough answer from memeory, no guarantee for correctnes. Score question +16. Two answers with lower score (3 maybe) but on-topic. Roughly the question was whether there are/to collect examples of prime numbers in nature. Giving as initially starting point, or was this an asnwer, an example of the now much discussed cicadas, different types of which have developmental cycles the duration of which in years are different prime
[ADDED: Sorry regarding the answers I was apparently completely off.]
Gil, the question was to give examples where prime numbers occur in nature. There were six answers, only one of which was substantive, and it simply and shortly described the cicada phenomenon, which had already been mention by the OP. This answer received 10 upvotes and the question itself 16 upvotes.
There is, IMO, zero mathematical content in the thread.
On the front page with the "newest" option there are 7 closed questions and at least two more that I guess will be closed soon. It is no wonder that many serious mathematicians take one look at MO and do not come back. Like Mark, I know researchers who choose not to participate because of irrelevancies on the site. Some lurk occasionally, but they no doubt miss threads that would be interesting due to the accumulation of irrelevant questions.
I have still not completely made up my mind regarding the deletions, but in view of what Bill Johnson said, I have a question:
In what way will deletions of closed month-old questions or also if it happens more quickly affect whether, to give a current example, user Mike Massa asks questions and they are thus on the front page for a while?
To be honest, the phenomenon described by Bill that
[certain] researchers who choose not to participate because of irrelevancies on the site
where irrelevancies means the occasional silly question, does not seem to me that important. I of course wish as many relevant people participate in the site, but I also expect people to be able to filter out a modicum of things they do not care for—even an Eminently Unimportant Mathematician like me manages to deal with it (I can't remember the last time one of my 'favorite tags' showed up in a question, although I know they do work because a semester ago a question by Kevin Lin appeared in yellow...)
I don't think the aspiration to have everyone on board is reasonable, and if some people are not willing to participate in the site, well, we will read their papers.
(My favorite example of prime numbers in nature is the following: when I go to my gim, I have to give a card to a guy sitting at a desk near the front door; at any given time, he has quite a few of them, and as he gets bored he plays with the cards, sometimes arranging them in rectangular arrays and rearranging them, and so on---a kind of solitaire; I once heard him make the observation to another guy that someones he can't make a real rectangular array, only one which is 1 x something or something x 1 and that that is very annoying, so he waits for someone to come or leave. He is annoyed by prime numbers getting in the way!)
The question has been deleted and undeleted several times in the last few days. (At the moment it's deleted, so I can't give exact numbers.) Apparently votes to [un]delete can be repeated (unlike votes to close), so this oscillation between deleted and undeleted could go on indefinitely. Perhaps the moderators should step in and propose/announce a policy for deleting non-spammy questions like this.
In answer to Andy Putman's question far above, I would propose limiting deletions to cases where the question, answers (if any) and comments (if any) are all clearly spammy/undergrad-homeworkish/crackpotish. If reasonable people might disagree on whether a question is in this class, then it shouldn't be deleted. I think the site would function just fine if there were no deletions at all.
Imagine a world in which the stackexchange software allowed only moderators to delete. Would MO be a disaster and unusable in this case? Of course not. I think that such a set up would be much preferable to the current situation, where any three easily irritated 10k users can delete a question.
Since 43397 went back and forth a few times, it has been undeleted and locked. (The default for deletion wars is 'undelete' and the default for closing wars is 'close'.) The question is likely to stay locked indefinitely, but feel free to continue the discussion here.
Apparently votes to [un]delete can be repeated (unlike votes to close), so this oscillation between deleted and undeleted could go on indefinitely.
I was completely unaware of this; I thought this was like for open/close. If I had known this my opinion would have been clear from the start (as opposed to undecided). In my opinion this obvioulsy implies that deletion should only happen in very clear cases or after discussion that leads to this conclusion essentially without oposition. If not this ccould lead to complete chaos. [Added: or significant extra work for the moderators]
Your policy on locking closed threads and deleted threads looks reasonable to me, Francois.