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    Suppose you have a mathematical question, and you know a small number of specific people who you believe can answer that question. Suppose at least some of these people regularly participate on MO. Also suppose that the question is one that (possibly with some small amount of work to make it slightly more general) is suitable for MO.

    What are the benefits and drawbacks of asking this question on MO rather than e-mailing the specific people? I am interested in answers to this question both from the viewpoint of the mathematics community as a whole, as well as from the viewpoint of the questioner.

    From the point of view of the general community I think the advantages of asking on MO is that the question and its answer are available on the internet for posterity.

    From the point of view of the questioner the advantage is that you may get a good answer from an unexpected person. Furthermore, it seems plausible to me that you might get the answer faster on MO as more people will see it. The main disadvantages for the asker are that some people won't speculate as freely in public, and that the askees may not see the question on MO depending on timing (which may result in the question getting answered more slowly or not at all).

    From the point of view of the potential answerers the main advantage is that you go to MO when you're in the mood to answer math questions, whereas you might be checking your email for lots of reasons. Furthermore, you're less likely to waste your time answering it, because you can see more easily if it's already been answered.


    More specifically, I often find myself in the situation of wondering if I should email a fusion categories question to Pavel Etingof, Victor Ostrik, and Dmitri Nikshych (the first two of whom occasionally appear on MO), or posting it on MO. My experience is that more often than not my MO question gets answered by Evan Jenkins (or David Jordan or Pasquale Zito) before ENO even see it. That seems to me to be a better outcome for everyone. And if Evan, David, and Pasquale don't know the answer, then it's probably a hard question and I don't feel as bad asking more senior (and thus much busier) people.

    In graduate school, you have the convenient thing that if you want to ask Prof. X a question, you can first ask one of X's graduate students. Often that'll get you an answer, but if it doesn't then you know it's a hard question. To some extent MO automates this process, where younger people with more time probably check MO more often, but then the unanswered questions stick around for other people to answer.

    • CommentAuthorgrp
    • CommentTimeAug 6th 2011
    The primary drawback to asking on MathOverflow is that more people will know that some entity (and some might know that it is you) is asking the question. This could be a drawback in that someone else might consider it their question (because they have an answer that they are using as a major part of getting their degree), or it is a question that might be easily answered (which may lead to some personal embarrassment), or it is a question which others might consider bad form in asking ("Hey, I found this on my friend's desk, by the way, she works for the NSA and her computer password is grigori, and it seemed like a cool problem to ask..."). If you are imaginative enough, you can probably find other reasons for not making the question so public; all the ones I can think are along the lines of it would help some people to keep it private or semi-private.

    There are more convoluted reasons for not making questions public, but they involve unfounded assumptions which may not hold between a grant asker and a grant provider. If your intentions are good and you know of no harm that can come from making the question public, go ahead and ask it on MathOverflow. (For this post, harm includes things like not following MathOverflow guidelines.)

    Gerhard "Paranoia Can Fuel The Imagination" Paseman, 2011.08.06

    Someone even made a tag called [ask-johnson]

    ...which suggests that I spend too much time on MO. Still, it is more productive to waste time on MO than to do most of my other activities.

    Generally I ask a few experts before I post on MO, but that is mostly because it is more time consuming to frame a question properly for MO than for a specialist.
    • CommentAuthorWill Jagy
    • CommentTimeAug 7th 2011
    If you look at the one question with the ask-johnson tag, the OP said something about how his question really ought to have such a tag.

    So I put one. Then one of the comments suggested a no-pressure-bill tag, but I felt the joke was more of a one-time type.
    Bill Johnson makes a very good point when he says: "it is more time consuming to frame a question properly for MO than for a specialist." For a simple enough but technical question, it would be enough to discourage me from asking MO.

    I have another one that's been rattling in my brain for the past couple of days: it's a terminology question. On the one hand, I feel like asking it on MO because I wonder if there are several terms used by different areas for the same concept. On the other hand, it doesn't seem like this question is serious enough to warrant the MO posterity.
    • CommentAuthorWill Jagy
    • CommentTimeAug 7th 2011
    I've really never asked on MO about the spinor genus for ternary quadratic forms. So very much background is required even to frame the questions. Now, the other side is that various experts have gotten tired of answering my questions. So I try to balance things. As Pete Clark's Euclidean quadratic forms were introduced on MO, I mostly kept my part of the discussion visible on MO. But the largest progress happened because of hints from individuals off MO, in the end making it obvious that I needed to understand a few pages in a certain book. My summary is that you get a certain number of answers per expert, people are busy.
    This is an interesting thread. Here are a few observations: A question not directed to a particular expert but to the community is not as much of a direct demand on the expert's time, and leaves the expert to respond if the question is indeed interesting to him/her. This fact leads to more questions being carefully formulated and asked, which is good for mathematics in general. There have been a number of occasions where my questions have been cheerfully answered by people I wouldn't have dared to bother.

    This aside, I have a stockpile of specialized questions that I'm pretty sure would be answerable by only a couple of experts. Aside from the benefit of recording these for posterity, I can't see why these wouldn't be better handled by a quick e-mail to the person who can answer them.

    I guess that a good rule of thumb may be: If you know someone who has a 90% chance of answering your question, and wouldn't mind doing so, ask them first. If you don't have luck with this for whatever reason, THEN bring it to MO.


    Ask your expert if they would be willing to post the answer on MO. If they say yes, ask the question on MO, then direct your expert to it. Everybody wins: MO potentially gets a new user, you potentially get answers from people you didn't have in mind, posterity gets a potentially valuable discussion easily searchable using Google.


    I like to use something like Qiaochu's approach. I sometimes post a question on MO, and then email a link to the person I think might have an answer. This has a number of benefits:

    1. posterity
    2. MO potentially gets a new user
    3. it puts less pressure on the expert, and sometimes I get an answer from an unexpected source
    4. the process of writing the question up for MO often clarified the question (I've answered a number of my own question only after thinking for a while about how to pose the question on MO)
    5. the math renders on MO, but not in an email
    6. the expert has options for how to reply (sometimes they email me an answer instead of posting it on MO)

    If I'm really worried about wasting their time, I wait a few days before sending the link. If I haven't gotten a good answer on MO after a few days, it suggests the question isn't an easy one.