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Are derivations of physical laws less important than the laws themselves?

This question is attracting a lot of attention, but there is a significant disagreement about whether it's on topic. I want to bring it up here to give the issue more exposure. I don't think I can give any summary that would be an acceptable substitute for reading it, so go read the question, and consider this: should it be on topic? Why or why not?

Secondary question: if it is on topic, what tags should it have? (other than )

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This question is off-topic as a mixture of too broad and primarily opinion-based.

However, I contend that this is not primarily due to its philosophical nature, but to the specific content of the question: It asks for the "meaning" of "derivations" in "physics". But there is no such unique meaning - the meaning of rigor and mathematical detail in physics varies from subfield to subfield, from person to person and from specific case to specific case. There is no general answer, although I am certain that a sizeable fraction of people will try and convince you their stance is the only one.

This means that there is no "meaning in physics" here. The question is too broad and primarily opinion-based simply because it will solicit many different answers which are neither right nor wrong - they're just viewpoints, which may be more accurate in some subfields and less accurate in others. So, while I can certainly determine what a bad answer to this question is, how do I determine a good one? Do I vote for the one that aligns most closely with my own? Do I vote for one that tries to list the advantages and disadvantages of each approach? Are those advantages and disadvantages universal, or again dependent on the specific case? So I find myself unable to objectively determine what a good answer would be although I expect many different ones to be given. That's pretty much the definition of being too broad and primarily opinion-based.

This is not really reliant on the question begin philosophical (although it is). I think the discussion of how much philosophy is too much philosophy is not relevant to this specific question, since it is already off-topic just by the broadness of its scope and the subjective nature of its answers.

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  • $\begingroup$ Methinks the adage Ask 10 people X and you'll get 11 answers applies to the subject. Which is definitively a case of opinion based. $\endgroup$ – Kyle Kanos Feb 19 '16 at 16:45
  • $\begingroup$ I'm sort of torn; I think you make a good argument here, but I do still believe the main reason to call the question off topic is its metaphysical/philosophical nature. $\endgroup$ – David Z Feb 21 '16 at 13:04
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I see the following two ways one could think of as what "Physics Stack Exchange" might be about:

  1. Physics Stack Exchange is a platform to ask questions about mainstream physics. Questions should ask about the concepts of the mainstream body of physical theories or how to probe them, which means that ideally, every question has a definite answer.

  2. Physics Stack Exchange is a platform to ask questions about mainstream physics. All conceptual questions when studying physics are allowed.

The first one actually describes the status quo and is a "physics based"-approach, while the second one is a "physics education based"-approach. Let me quote John Renie's answer above:

A good question and answer for this site will be one that future generations of physicists¹ will benefit from. That is, having encountered something they don't understand their Google search will lead them here and they'll find the answer to all their problems.

Here is my problem: A question about the rigour in mathematics or what one should focus on when learning theories is something that many (future) physicists stumble upon and need an answer to. This is also something all physicists have (at least implicitly) thought about at some point in their life. Ergo, many (future) physicists will benefit from answers to the question.

Questions about how to do physics are in principal a matter of philosophy. This does not mean that anything goes - quite the contrary - but it does mean that most users and even most expert physicists will be unfamiliar with many aspects that good answers should incorporate. On the other hand, (mainstream) physics is what physicists do and not what philosophers want them to do, so the answers, while lacking in certain aspects, could help students assess the situation.

The easiest possibility is always to just refer every question that touches about philosophy of science to philosophy.stackexchange. There, we have the experts. The problem is that the experts in philosophy might not know how it is actually implemented in reality.

Therefore: The Q&A-format can support questions about how things are done. They will generate a lot of bad answers (and one will have to enforce rigid non-discussion policies) but the mere fact that we allow for several answers to the same question and we have a sorting by votes means that meaningful answers will be swept to the top. We might want to have a tag "opinion-based" with a similar disclamer as the "resource-recommendations" and we would need to adapt the close reasons.

In order to illustrate what could be possible and might help physics students in understanding the field (although the answer is far from good - it would definitely need to elaborate and explain the last paragraph and even then, I'm not quite the expert on the matter that I would like to be), see this answer of mine.

Where to draw the line? Questions about how to write a paper or how to collaborate with other people are clearly off-topic - they are not about conceptual questions when studying physics. But many cases will be borderline, so this needs some discussion.

Therefore, those questions could be made on-topic, but we should create a special tag and special implementation rules.

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  • $\begingroup$ I'm divided about the issue. Since "keep off-topic"-pleas have already been made, I tried to argue for "make on-topic" to have this opinion present here. $\endgroup$ – Martin Feb 19 '16 at 14:19
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    $\begingroup$ "A question about the rigour in mathematics or what one should focus on when learning theories is something that many (future) physicists stumble upon and need an answer to." My response to this is always that many current and future physicists also stumble on what to make for dinner and how to cook it. That doesn't make food recipes on topic here, just because a physicist may want to find a quick lunch recipe for the rare downtime at the particle accelerator. There seems to be a general aversion from sending people to other sites -- like needing to go to multiple sources is somehow... $\endgroup$ – tpg2114 Feb 19 '16 at 16:14
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    $\begingroup$ confusing or represents an impossibly high barrier to entry. I don't look at physics.SE as a standalone site, but as part of a network where I can get information on all of my topics, and more, by going to various sites. I like to think that this is a site for physics and not a site for physicists. $\endgroup$ – tpg2114 Feb 19 '16 at 16:14
  • $\begingroup$ I disagree with your false dichotomy of what PSE is about. $\endgroup$ – Kyle Kanos Feb 19 '16 at 16:44
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    $\begingroup$ I do not want to claim that this is a dichotomy, sorry for that. I tried to rewrite the first passage to make clearer that I just want to discuss two (of maybe more) approaches. $\endgroup$ – Martin Feb 19 '16 at 16:52
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    $\begingroup$ I'm not quite sure your position is clear from the answer itself, although it is well argued. Naturally, I don't agree that the question should be on topic, but I do appreciate you posting a case for it. $\endgroup$ – David Z Feb 21 '16 at 13:02
  • $\begingroup$ @DavidZ: I'm not quite sure my position is completely clear to myself. I do think it is possible to give interesting and good answers (there will never be a definite answer though) to those kind of questions, yet I'm unsure of whether the place to do this is here or maybe at philosophy.stackexchange (wher would we get better answers?). Maybe I'll edit that part in. I did not think you'd agree with the position, but since I would not have thought about this argument a couple of years ago, I thought I'd post it for everybody (assuming that a few may not have seen it either). $\endgroup$ – Martin Feb 21 '16 at 17:34
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An answer to represent the reason I bring this up in the first place: I think the question is about the "meta-study" of how we do physics (epistemiology), or perhaps the process of physics, not about physics itself. It contains a specific example which is physics, yes, but the example is only used to illustrate the deeper issue actually being asked about, namely how derivations affect our knowledge of the validity of physical laws. I think this should be off topic.

I can't think of any topical tags we have that would meaningfully apply to this question, which I take to be evidence in favor of it being off topic. It's a pretty general rule that if question is on topic, there should be at least one topical tag which characterizes what it's about (so, not things like or ). We can, of course, create a new tag if the question really should be on topic but no appropriate topical tag exists, but we should think long and hard before doing so about why there was never a need for the new tag in the 5-year history of the site.

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  • $\begingroup$ I find myself in strong agreement with your position. The issues raised in the question are philosophical in nature, not physical. Furthermore, they rest on the invalid assumption that there are not more rigorous treatments - the OP just hasn't encountered them. So, the data used to support the question seems cherry picked. In particular, for the first example, it would not be 'rigorous' unless one were to perform the necessary integral over all possible volumes and shapes. Clearly, they are missing the point and do not have a handle on what 'rigorous' means. $\endgroup$ – Jon Custer Feb 18 '16 at 19:55
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    $\begingroup$ Devil's advocate -- is that question really much different from this one, this one or maybe to a lesser extent, this one? Those questions attracted little discussion of on-topic-ness, which isn't to say that it proves anything. After all, they all could be off-topic. But we have had some leeway with.. $\endgroup$ – tpg2114 Feb 18 '16 at 20:58
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    $\begingroup$ questions about "how we do things" to approach a problem. Perhaps it isn't so bad? Is there a huge difference between how a derivation affects our knowledge of physical laws and how measuring gravitational waves affects our knowledge? Would we have this conversation if somebody asked how observations of something gets mapped into a law? $\endgroup$ – tpg2114 Feb 18 '16 at 20:58
  • $\begingroup$ @tpg2114 I think this question is different from the last two at least, because those are about specific derivations or specific aspects of derivations that I would consider within the domain of physics. The first one you linked is more similar to the question we're currently discussing, since it's quite general. I would consider it possibly too broad. But I do believe that the current question is more clearly off topic than any of the three you linked. (Also, #1 and #3 may have the same issue of not having any applicable topical tags.) $\endgroup$ – David Z Feb 19 '16 at 8:17
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A good question and answer for this site will be one that future generations of physicists¹ will benefit from. That is, having encountered something they don't understand their Google search will lead them here and they'll find the answer to all their problems.

This is a lofty ideal, and in practice few questions and answers will reach it, but I think it's one worth striving for. However the question being discussed here is just a complaint that physicists sometimes appear casual about the level of proof they demand. There is no definitive answer to this, and I can't see how any opinions we express in an answer will benefit anyone including the OP.

Discussions like this are great fun in the coffee room (better still in the bar, especially after a few drinks have gone down :-) but they are out of place here. Leave it closed.


¹ basically that means physics students

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