This question is a math question. It may use equations which are commonly found in physics, and it may refer to non-linear terms as "interactions", but the question itself is purely about math. It was not put on hold or marked as off-topic.

Here's another purely math question which was not put on hold.

On the other hand this question, which is also a math question, was put on hold as off-topic. The difference in this latter question is that the asker focused directly onto the mathematics, stripping away whatever physics may have been at hand in when they identified the mathematical problem at the heart of the issue.

The difference between these questions is cosmetic. There is no substantive reason to consider the first or second questions "physics" other than the fact that the math questions represented there was encountered in a physics textbook. For all we know, the same may be true for the latter question, and is in fact likely given that the asker came here rather than to the math SE.

Why do you think one of these questions was put on hold while the other was not?

P.S. I think the answer is pretty obviously that there are more users here who are familiar with the math relevant to the first two questions than the third. Is this a good reason to close the third question?

  • $\begingroup$ Might be worthwhile to scroll through the Meta post Should pure Math questions be on topic. $\endgroup$ – Kyle Kanos Sep 25 '14 at 16:13
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    $\begingroup$ Also, I disagree that the first question is a math question. $\endgroup$ – Kyle Kanos Sep 25 '14 at 16:16
  • $\begingroup$ I strongly disagree with the assertion that the first question is purely mathematical. In fact, the OP states: "It seems to me, at the [end] of the day, computational results are the same from adiabatic switching or LSZ", clearly acknowledging that they are mathematically equivalent. The OP is, instead, interested in a deeper physical reason to prefer approach over the other (if one exists). $\endgroup$ – Danu Sep 25 '14 at 19:04
  • $\begingroup$ I'm afraid that with your definition of 'cosmetic trappings of physics around the mathematics', even a substantial fraction of the experimentalists I know would end up as mathematicians. $\endgroup$ – Emilio Pisanty Sep 25 '14 at 20:00
  • $\begingroup$ @EmilioPisanty: That was kind of my point. $\endgroup$ – DanielSank Sep 25 '14 at 21:21
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    $\begingroup$ Well, then why use the name physics at all? Let's rebrand the whole thing as mathematics! $\endgroup$ – Emilio Pisanty Sep 26 '14 at 8:59
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    $\begingroup$ @EmilioPisanty: I'm not sure if sarcasm is helpful here. $\endgroup$ – DanielSank Sep 26 '14 at 9:10
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    $\begingroup$ Apologies. My point is that I don't find it helpful to have definitions of mathematics which encompass all of physics. It seems to me, from your comments, that that is your position. $\endgroup$ – Emilio Pisanty Sep 26 '14 at 9:19
  • $\begingroup$ @EmilioPisanty: My "position" is that we should be consistent about what questions we consider on and off topic. I didn't mean to say that I think all three questions should be considered "math" and thus off-topic. If anything I feel the opposite. $\endgroup$ – DanielSank Sep 26 '14 at 9:27
  • $\begingroup$ @Danu: Fine, what about the second one? $\endgroup$ – DanielSank Sep 26 '14 at 9:28
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    $\begingroup$ @DanielSank it asks (implicitly): How do I physically interpret the fact that this integral diverges. This, too, is physics to me. $\endgroup$ – Danu Sep 26 '14 at 9:31
  • $\begingroup$ To be clear, I don't think either of the first two questions you linked to are in any way pure math. Sure, they contain math, but so does most physics. Further, I don't think a mathematician would really be able to provide an answer to either of them in the terms that the OPs are looking for. They are both then on-topic here and off-topic at maths. Why should they be closed? $\endgroup$ – Emilio Pisanty Sep 26 '14 at 11:08
  • $\begingroup$ @EmilioPisanty: There was a critical typo in the question which I just fixed. I do not think any of the questions I linked should have been closed. More importantly, I think we should be consistent about what we close. $\endgroup$ – DanielSank Sep 26 '14 at 17:37
  • $\begingroup$ @Danu: I really think it sounds like you're giving benefit of the doubt to two of the questions but not the third one. Why? $\endgroup$ – DanielSank Sep 26 '14 at 17:38
  • $\begingroup$ @DanielSank Note that I did not vote to close on that question. I honestly just don't think there is a problem here. See David Z's answer. $\endgroup$ – Danu Sep 26 '14 at 17:40

I'm not going to bother looking at the questions you linked, not because I think it's not worth my time (something I couldn't judge without looking at the questions), but because the general issue you're addressing can be answered without referring to them.

Some questions posted on Physics.SE deal purely with mathematics, no sane person can deny that without being facetious. The reason we allow some and not others is because physicists are more suited to helping with some math problems. There are some problems we as physicists see over and over again, and on top of that, we have our own ways of solving and interpreting these problems that is different from the methods and interpretations of mathematicians or engineers. Thus, if some of these questions arise that cover purely mathematical problems but they approach it from a physicist's perspective (or that is to say, they have applied physics cosmetics), then it's more likely we will leave it open because there's a good chance that the solution might be more helpful coming from a physicist rather than a pure mathematician.

For questions where all the physics has been stripped away, we usually take that as a sign that the OP is not interested in the unique methods or interpretations that physicists use and that they are purely interested in the mathematical approach to the problem. For this kind of question, a mathematician is better suited, what with it being their expertise and all.

So while cosmology may be important in physics, cosmetology is important in asking physics questions.

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    $\begingroup$ "For questions where all the physics has been stripped away, we usually take that as a sign that the OP is not interested in the unique methods or interpretations that physicists use and that they are purely interested in the mathematical approach to the problem." But isn't that doing a disservice to the asker? The asker may have stripped the physics off precisely to help us see the real issue at hand, even if that issue were encountered in a physics context. $\endgroup$ – DanielSank Sep 25 '14 at 21:22
  • $\begingroup$ @DanielSank and the real issue would be purely of a mathematical nature. Wouldn't it be better for the people at Math.SE to answer it in that case? $\endgroup$ – Jim Sep 26 '14 at 14:01

Take a look at the reason the closed question was closed: it was because of our homework policy, specifically the part that says

It's not enough to just show your work and ask where you went wrong.

So this closure has nothing to do with whether it should be considered a physics question or a math question.

  • $\begingroup$ So if the OP removed the homework tag would everything be ok? $\endgroup$ – DanielSank Sep 26 '14 at 17:49
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    $\begingroup$ @DanielSank: No, it's not the tag, it's the policy. $\endgroup$ – Kyle Kanos Sep 26 '14 at 17:56
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    $\begingroup$ @DanielSank This question is a check-my-work question. Those are off-topic as per the current policy, and the consensus now seems to be to keep it that way. It is not closed for being maths-like, it is closed for being something that could be found in an exercise section, and easily looked up in the body of a classical mechanics textbook. $\endgroup$ – Emilio Pisanty Sep 26 '14 at 17:57

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