I just asked a question regarding how protons remain together in a nucleus despite their electromagnetic repulsion, but I just found that exact question already asked and answered on Physics.SE Regrettably I deleted the question as it is an exact duplicate, but I thought I'd bring up the discussion here on meta.

How do we decide where questions that straddle the physics/chemistry border belong? The field of particle physics seems like it could potentially belong on both sites, so how should we choose where specific questions should go?

  • $\begingroup$ To me personally, the question about protons in a nucleus is a chemistry question, not a physics one. Yet, both chemistry and physics use math to answer it. $\endgroup$
    – picakhu
    Commented May 3, 2012 at 19:21

5 Answers 5


Whatever general boundaries are agreed upon, I suggest that we do not expend too much effort debating edge cases. It is valid for a question to be on-topic on more than one Stack Exchange website, so only in particularly egregious cases should we migrate questions.

Borrowing from the debate over our neighbor to the west (Biology), some overlap is acceptable and unavoidable. From a user point-of-view, one who chooses to post in either Chem, Phys, or Bio hopefully does so with the intent that they have (or desire) greater familiarity on that topic. Needlessly shuffling their posts around across multiple sites dilutes rep.


I believe the canonical criterion is that chemistry deals with chemical bonds. So, you need electrons, and you typically needs more than one atom. But there is some leeway, in that questions about the evolution of, say, ionization energy along the periodic table can be considered a chemistry or a physics question.

My position would thus be: if it concerns molecules (more than one atom), chemical bonds, intermolecular or intramolecular interactions, we don't migrate it to Physics. If it concerns atomic properties, we migrate unless it's a question about the difference between various chemical elements (which is a fine chemistry question, somehow).


Obligatory xkcd

I've been a member of Physics.SAe for a while now, so I think I've gotten the hang of it's scope.

One thing I've noticed about overlap is that questions falling within overlap regions of two sites get migrated to wherever the question is bound to get more answers. So, "where a question belongs" is something that really depends upon the question, especially the intent of the question.

That being said:

  • Nuclear physics: Phy.SE only
  • Thermodynamics: If it relates to thermochemistry--the thermodynamics of reactions, then keep it. Also free energy related questions--free energy ismore used in chemistry. If it has to do with general thermodynamical processes and parameters, keep it at Physics.SE.
  • Electrochemistry: Chem.SE, but Phy.SE does accept these (See comments here)
  • Chemical Equilibria, kinetics: Chem.SE only
  • Gas equations &c: Fine on both sites. Just let them stay on whichever site they are asked on--unless it is likely that they may get better answers in migration.
  • Solid state: Either is OK, leaning towards migration to Chem.SE.
  • Quantum mechanics: orbital questions are welcome on phy.SE, but not really Molecular Orbital Theory and hybridization. On chem.SE's side, we need not do much-all of this is on-topic.

Are there any more?

We may also need to think about biochem. (think there was an area51 discussion on this).


There is a fairly large overlap between many SE sites. Unix.SE, for instance, overlaps quite a bit with both SuperUser and ServerFault, and all three have nontrivial overlap with SO. So we don't need to draw a line saying "This goes here only, that only goes there." If a topic is likely to be of interest to someone in the field of Chemistry, it is on-topic here. Even if it would also be of interest to a physicist and on-topic on P.SE.


Chemistry is a central science. We can discuss whatever we feel capable of discussing. The difference between fields is really more arbitrary and only matters for budgets in schools.


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