I progressively feel that a typical user interested in the mathematical-physics tag, like me, is not welcomed in the community; not to mention, that at least as I can tell, the community is not explicit enough on exactly what is acceptable, or not, under this tag.

Personal examples:

  1. My question "Geometric intuition for $\mathcal{L}^{-m} \oplus \mathcal{L}^{m} \rightarrow T^{2}$ Calabi-Yau threefolds was posted and voted-to-close four times on this site (PSE); at the end, it was migrated to Math Stack Exchange despite of the fact that I've received (and accepted) a really wonderful answer from a PSE user. My question manifestly was about the "physics way" to understand a mathematical idea used in physics papers (actually submitted to arXiv under the high energy physics label and no reference to mathematics) by famous physicists (Vafa and Jafferis). Honestly my question was about math, but, my point is that I consider my question as legitimate under the mathematical physics tag in PSE and not off-topic as the treatment it received from the community suggested.

  2. I offered an answer, "Connectedness on Special Kaehler manifolds". Again, this question is about a mathematical topic (special geometry) discovered by physicists, relevant for (black hole-) physics that is virtually not discussed by mathematicians at all. A moderator in the question comments immediately pointed that this question was off-topic in this site. To me, this is also a legitimate question in PSE.

  3. I had to close some drafts before posting the question "References on mathematical stacks for a string theory student". In all of them I received comments saying that this was off-topic in this site, until a version of the question was considered "acceptable" but still received comments saying: "this seems off-topic" or "I don't understand what you are saying"; despite of the fact that I specify that I'm a physics oriented student and my question was manifestly about the math-background needed to understand physics papers, written by physicists and that I didn't wanted an answer from a mathematician.

  4. Finally, I have the possibly subjective perception that the community was far more tolerant in this respect before I started to post in PSE (four years ago). For example, I find the following questions and answers nice and not evidently different from the examples I gave, except that they are apparently on-topic 1. To be honest, I find very discouraging and ambiguous the treatment a question in this tag receives.

Then my question is: How can I understand better what a permissible mathematical-physics question is? Is this a generalized attitude against the mathematical-physics community?

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    $\begingroup$ Related: physics.meta.stackexchange.com/q/164/2451 $\endgroup$
    – Qmechanic Mod
    Commented Jul 19, 2021 at 12:43
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    $\begingroup$ Physics SE is too big and there being such a thing as "the community" becomes too abstract of an idea to be useful in this context. I don't think Physics SE will split into more intimate and productive communities any time soon, so StephenG's suggestion about potentially better-suited sites is a good one. $\endgroup$
    – uhoh
    Commented Jul 28, 2021 at 12:17

5 Answers 5

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    $\begingroup$ "should not have been migrated" -- A key issue seems to be the asymmetric situation with migration closures (with pre-defined paths): While usually, 5 close votes of users who don't like a question can be lifted by 5 who like the question, there is no way to vote against a migration process, and once it has happened, it does not matter if a question would have been considered on-topic by a majority of users. In effect, a small group of active users can thus kick out mathematical physics questions of PSE (which happens more than it should, IMO). Not sure there is a way to avoid this, ... $\endgroup$ Commented Jul 20, 2021 at 12:14
  • $\begingroup$ ... though - except for removing the pre-defined migration path, which gives time to vote to open after closure. $\endgroup$ Commented Jul 20, 2021 at 12:15
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    $\begingroup$ @Norbert Schuch: I agree. When Phys.SE got the pre-defined migration path to Math.SE everybody thought it would be a good thing. Well, it came with a price. $\endgroup$
    – Qmechanic Mod
    Commented Jul 20, 2021 at 12:23
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    $\begingroup$ Would it make sense to remove the pre-defined migration path? Or would this lead to a significant increase in moderator load? Or are there other obstacles? $\endgroup$ Commented Jul 20, 2021 at 12:59
  • $\begingroup$ @NorbertSchuch a small group of active users can thus kick out mathematical physics questions There is no evidence that this is happening. At least one post (I did not check them all) the OP mentions received an answer that the OP described as very useful on Mathematics SE suggesting migration was quite reasonable and even helpful. I think this is a storm in a teacup. $\endgroup$ Commented Jul 20, 2021 at 13:19
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    $\begingroup$ @StephenG The answer you refer to was written on Physics.SE and was migrated to Math.SE along with the question. $\endgroup$ Commented Jul 20, 2021 at 13:21
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    $\begingroup$ @StephenG I have seen a few questions recently which I felt were very well suited for here, and which I saw gradually being closed as OT and better suitable at math, and there was nothing I (or anyone else) could do. I do indeed feel that the migration path comes at a price, namely that there is no way to stop a migration (which I feel is a design bug, since every other type of closure can be changed by sufficiently many votes). $\endgroup$ Commented Jul 20, 2021 at 14:11
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    $\begingroup$ ... My feeling is that this way, the community can be shaped away from certain topics, simply because they can easily (and without any possibility for disagreeing) be migrated away -- even if there is a sufficient base of users who could answer it. Behold, even a satisfactory answer given here cannot prevent migration! $\endgroup$ Commented Jul 20, 2021 at 14:13
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    $\begingroup$ @NorbertSchuch Something to be careful of is just because there exist PSE users who can answer a question does not mean the question should not be closed or migrated. Even the fact that a question gets a wonderful accepted answer doesn't change whether or not a question belongs on PSE. I agree with your other comments that it shouldn't matter if the question could get a good answer elsewhere; it is also true that being answerable by PSE users does not mean it should stay open or on PSE. $\endgroup$ Commented Jul 20, 2021 at 14:14
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    $\begingroup$ @BioPhysicist Fair point. In the end, it of course boils down to what kind of mathematical physics questions we want to have - or not have - at PSE. --- In the end, what bothers me about the migration process is that it - unlike other closure processes - precisely does not allow the community to form such a consensus through majorities in the close/open voting process. $\endgroup$ Commented Jul 20, 2021 at 14:38
  • $\begingroup$ @NorbertSchuch You mean in terms of undoing, right? The vote to migrate is the same process as the vote to close. $\endgroup$ Commented Jul 20, 2021 at 16:05
  • $\begingroup$ @BioPhysicist Precisely. Once it is migrated (and even while the migration VtC is in process), there is no way to reverse (or interrupt) the process, except for leaving a comment. In that sense, it is an irreversible close vote (unless the other community rejects the migration, but that is done according to different criteria). $\endgroup$ Commented Jul 20, 2021 at 16:20
  • $\begingroup$ @NorbertSchuch But that is how normal closure votes work. If a question gets enough closure votes it gets closed. I don't see the issue with the vote to migration. The only issue would be the inability to vote to unmigrate just like we can vote to reopen. $\endgroup$ Commented Jul 20, 2021 at 16:21
  • $\begingroup$ @NorbertSchuch I am not sure how practical an "unmigrate" process would be to use or implement, but if you feel it might be useful you can always propose it via a new question on one of the Meta sites. $\endgroup$ Commented Jul 20, 2021 at 17:58
  • $\begingroup$ @StephenG I'm sure this has been brought up on SE before. However, a local solution might be do remove the default migration path - then, one can still flag for migration to math, but it does not happen automatically after closure, so the mods can wait a day or two before migrating it to see if any reopen votes trickle in. $\endgroup$ Commented Jul 20, 2021 at 19:45

I get the impression you are confusing the mathematical-physics tag on Physics SE with the one on Mathematics SE. They are not the same.

Physics SE :

Mathematical physics is the application of mathematics to problems in physics and mathematical methods suitable for such applications, e.g., partial differential equations (PDEs), functional analysis, variational calculus, and potential theory. It also includes the study of problems inspired by physics within a mathematically rigorous framework, such as rigorous derivation of an atomic energy spectrum, rigorous construction of a quantum field theoretic model, and rigorous description of a phase transition.

Do not use just because your question involves math!

and on Mathematics SE it's :

DO NOT USE THIS TAG for elementary physical questions. This tag is intended for questions on modern mathematical methods used in quantum theory, general relativity, string theory, integrable system etc at an advanced undergraduate or graduate level.

I really think it's clear your questions fit the Mathematics SE definition better than the Physics SE one.

These are also very specialist questions and while I have no doubt there are people on Physics SE who can handle them the mathematical level required is more likely to receive a match on Mathematics SE. You say you want a physics related answer to them, but there seems little physics here (like a lot of String Theory IMO). In at least two cases you yourself say they're more suited to Mathematics SE and one question never (as far as I can tell) had a mathematical-physics tag.

It's unfortunate you find this a problem, but I think the nature of your questions may be more suited to Mathematics Overflow or Physics Overflow.

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    $\begingroup$ I don't think it matters where the OP is more likely to receive an answer. $\endgroup$ Commented Jul 20, 2021 at 12:14
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    $\begingroup$ @NorbertSchuch Do you think it would be more constructive or less to not suggest alternatives to the OP which might be better suited to their needs ? How does that help anyone ? $\endgroup$ Commented Jul 20, 2021 at 13:12
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    $\begingroup$ All I am saying is that the fact that the OP might have a better chance to receive answers somewhere else does not constitute a sufficient ground for closure. The question is about whether questions on mathematical physics are closed to quickly and/or incorrectly here, not whether they might have a higher chance of being answered somewhere else. $\endgroup$ Commented Jul 20, 2021 at 14:08
  • $\begingroup$ @NorbertSchuch Ultimately, from my view point, I don't think it matters where a user gets help as long as we are trying (in good faith) to help, and sometimes that means migration is a reasonable option. We'll never get a perfect system, IMO, and whether a closure is reasonable or not will always be pen to interpretation. I don't think (getting back to this case) that the OP has been unreasonably treated or handled in bad faith and I think that's teh best we can hope for from any system. YMMV. $\endgroup$ Commented Jul 20, 2021 at 14:34
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    $\begingroup$ The StackExchange-wide policy on migration is very simple: When a question is on-topic in more than one place, the OP gets to pick where to ask it. Migration is a subset of closure; you only migrate questions which are off-topic on the originating site. $\endgroup$
    – Kevin
    Commented Jul 22, 2021 at 18:04

I think that if the question is about mathematics per se, it is out of scope, even if the mathematics is commonly used in physics. It would be in scope if the question was about how to apply or interpret the mathematics in relation to physics. For example, if someone were to ask how to solve a quadratic equation, that would stand on its own mathematically and be out of scope, notwithstanding the fact that the solution of quadratic equations is a useful method in physics.

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    $\begingroup$ Mathematical physics is not primarily about how to relate mathematics to physics. $\endgroup$ Commented Jul 20, 2021 at 12:16
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    $\begingroup$ @NorbertSchuch I don't think that is what Marco is saying mathematical physics is. I think Marco is just saying for PSE that is what such questions should be about. e.g. Biophysics has topics that are not your "traditional physics" topics, yet there are some good biophysics questions that I would say aren't a good fit for PSE. $\endgroup$ Commented Jul 20, 2021 at 12:39

Perhaps it should be noted that the decision of this question is intimately linked with the question:

What should Physics do with String theory heritage?

It is an open secret among theoretical physicists that much of the String theory community has migrated during the past fifteen years to other questions than quantum gravity (the reasons are the positivity of the cosmological constant, the string theory landscape, and the absence of supersymmetry observed at LHC). Now it is concerned mainly with various QFT models that mostly find their application, if any, as highly idealized condensed-matter systems. The game is, for instance, to find various dualities that may translate various theories and their computable results into one another.

Many-a-theorist in "String theory/HEP theory/..." will admit to you that they are just doing some interesting mathematics and that they have no illusion of the applicability of their work to real systems. They will also admit that putting a "String theory heritage" label on their work allows them to work on the topics in high-status settings with a large and active community (unlike the case of a number of areas in Pure Mathematics). This is a self-sustaining effect, since research institutions are often largely financed on a citation-metric basis, and String theorists still hold tenured policy-making positions at Physics departments. Very often, String theory itself is not even involved any more, instead field theories and dualities that were discovered in the course of investigating String theory are used. This is why I call this field String theory heritage.

However, the way the work is motivated is nowadays more similar to Pure Mathematics. It would be simply untrue to say that Pure Mathematics has no applications in the real world. For instance, number theory has immensely important applications in banking. But would we call Number theory a branch of Banking? Do Pure Mathematicians working on Number theory really choose goals with banking applications in mind? Of course not, they have their own criteria. I feel similar statements are in order about at least some of the sectors of "HEP theory" that come from String theory heritage and their relation to Physics.

This being said, I certainly do not want to say that the work done in String theory heritage is not generally scientifically interesting or done badly. Also, there are many areas of Theoretical and Mathematical physics where the very same statements would be possible; Exact solutions of Einstein equations are particularly close to home for me personally in this regard. Or, e.g., the proof of the positive-mass theorem not in dimension 4, but in general dimension.

For example, there are "singular sets" causing problems in the proof of the theorem for dimension larger than 7. Would I consider a detailed question about these sets as on-topic on PSE? No, I would not, but I am not ironclad. The line is really quite thin, because if you restrict these types of questions too much, you restrict the possibility of diversity and exploration.

So really no final judgment here, I just wanted to point out that this is not the issue of just PSE, but of the entire Physics community at the moment. This is a choice the PSE community has to deal with, but either choice makes some sense!

  • $\begingroup$ There aren’t that many string theorists - the dominant groups of physicists are in condensed matter/solid state and optics - so it’s a bit rich to suggest they hold policy-making power. Except for select (and rich) institutions, the cost benefit analysis is simple: as overheads are % of grants, it is better to get experimentalist, who can more easily get larger grants. Of course there’s the prestige factor, but few reach star or superstar status a la Witten or Arkadi-Ahmed. $\endgroup$ Commented Jul 29, 2021 at 23:07
  • $\begingroup$ @ZeroTheHero I guess this is really about perspective. Most STEM people are not physicists, rather people in Life sciences (biochemistry, medicine). However, physicists still largely determine science policy within their field. What I meant by policy is more like university/department hiring policy or grant panels picking which projects will get money and so on. In most countries the institution receives not only overheads but also separate money for "research output"/"research excellence" measured by citation metrics. This is why they roll the red carpet for string heritage people. $\endgroup$
    – Void
    Commented Jul 30, 2021 at 6:10

I disagree.

  1. For one, I don’t think you’re a typical user. Check the tag to see typical questions.
  2. For another, you present your question in a way that maximizes hifalutin mathematical jargon.
  3. You admitted yourself - in reply to a comment of mine - that at least one of your question was basically a math question.
  4. In case of the specific question “ References on mathematical stacks for a string theory student”, you actually supply your own background, which suggest the answer is unlikely to be useful to the community at large.

I’m not quite sure why you think the community has little tolerance to math/phys questions. The activity in the mathematical physics and cognate tags shows otherwise. Your questions (or answers) require quite specialized knowledge to understand, which restricts the number of people with the expertise to view or answer. None of your questions or answers you give in examples have been downvoted. Sorry if this shatters any illusion that mathematical physics is somehow equivalent to string theory: it is just not.

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    $\begingroup$ Checking the tag to see "typical" questions is mostly good to see how much people abuse the mathematical-physics tag. $\endgroup$ Commented Jul 20, 2021 at 12:15
  • $\begingroup$ @NorbertSchuch Yes the tag is used - you would say abused - (very) liberally and is a reflection of the way the community feels about the topic. $\endgroup$ Commented Jul 20, 2021 at 12:37
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    $\begingroup$ I don't agree it is a way the community feels about the topic. It is mostly that many people don't know what mathematical physics is, and think the tag is meant for questions involving mathematics. The same way, the measurement-problem tag is abused (introducing [quantum-measurement] helped a bit, I believe.) Otherwise, the fact that a tag is mis-used would automatically render questions on that topic off-topic. $\endgroup$ Commented Jul 20, 2021 at 13:01
  • $\begingroup$ @NorbertSchuch the community does have misconceptions as to what mathematical physics is (I certainly believe the tag is abused). Not sure how to undo this given the distribution of expertise. It's one reason why I think most of the posts would have higher chances of answers in MSE. $\endgroup$ Commented Jul 20, 2021 at 13:12
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    $\begingroup$ @ZeroTheHero Thanks for your answer and your time. I think your answer cleverly clarifies the perspective of most of the users in the community about my questions. I really appreciate this perspective. $\endgroup$ Commented Jul 20, 2021 at 14:03
  • $\begingroup$ @ZeroTheHero A comment on your last paragraph (about why I talk about "little tolerance in math/phys" questions). Is not about the number of questions in this category. It's about the subjective struggle I experience in posting a question, plus some isolated cases from others that I don't objectively understand why they recieve bad comments (like the question in point 2.). Reading old questions gave me the (perhaps wrong) impression that some years ago (> 5 years) the math/phys community was richer and widely open to math questions than is today. $\endgroup$ Commented Jul 20, 2021 at 14:04
  • $\begingroup$ @ZeroTheHero Obviously I don't have objective arguments, just the vague feeling that I don't understand clearly what is acceptable under this tag, to me, my first question was legitimate, although not for the community. Thanks ! $\endgroup$ Commented Jul 20, 2021 at 14:08
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    $\begingroup$ @ZeroTheHero As commented under StephenG's post, the mere fact that a question might have a higher chance of being answered somewhere else does not render it off topic here. $\endgroup$ Commented Jul 20, 2021 at 14:09
  • $\begingroup$ @NorbertSchuch Oh I agree with that: it doesn't make off topic at all. It doesn't make the community "intolerant" either. It simply means that the OP could get a faster answer elsewhere. $\endgroup$ Commented Jul 20, 2021 at 15:11
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    $\begingroup$ @NorbertSchuch I'm just pointing out that the OP writes questions in highly mathematical language without linking much physics to the questions - contrary to what most people who use or abuse the math/phys tag do - and then turns around to suggest the community is intolerant. $\endgroup$ Commented Jul 20, 2021 at 15:16
  • $\begingroup$ You appear to be gatekeeping the definition of 'mathematical physics'. You suggest to the OP to use existing examples of questions on mathematical-physics as a guide to new ones. That circular logic doesn't keep a tag on-topic. Whether the OP's questions require specialised knowledge to answer has no relevance to the question or to the use of tags. $\endgroup$
    – Myridium
    Commented Jul 23, 2021 at 0:28
  • $\begingroup$ @Myridium I don't follow. How is it circular logic to suggest looking at questions that haven't been closed to know how to ask questions that won't be closed? $\endgroup$ Commented Jul 23, 2021 at 0:32
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    $\begingroup$ @Myridium This answer isn't trying to define the tag or the questions on it. We are assuming we have a mathematical physics question already. The suggestion is, given that, if you want to know how to have success with a mathematical physics question, go look at ones that have succeeded. $\endgroup$ Commented Jul 23, 2021 at 0:36
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    $\begingroup$ @Myridium sorry I don’t get it either. I’m just reacting to the statement that typical users of the tag are not welcomed (when there’s no evidence of this) or to the overly broad statement that the community shows little tolerance to math/phys (again, without evidence). How can it be gate-keeping when I actually suggest its use is broader than what the OP appears to suggest (in fact abusively broad)? $\endgroup$ Commented Jul 23, 2021 at 2:13
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    $\begingroup$ @Myridium what is clear is that the pool of people in this forum who can answer the questions of the OP as they are phrased now is small, and possibly larger on another forum. $\endgroup$ Commented Jul 23, 2021 at 2:15

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