Is cross-posting allowed?

Does QuantumComputing.SE allow cross-posting of questions on multiple Stack Exchange sites?

The default Stack Exchange policy is that cross-posting is not allowed, as a general rule. However, individual SE sites can customize this policy and choose a different policy for their own site, if they like. (Many SE sites simply follow the standard network-wide policy, but some SE sites have chosen to allow cross-posting if certain guidelines are followed.)

What is QuantumComputing.SE's position on cross-posting? Do we have a custom policy, or do we follow the network-wide default?

The current informal "policy" has been that it is allowed, within limits. The main rationale is that there is no way to draw a consistent, meaningful boundary between the scopes of (some of) the different sites. This is especially true here, due to the intrinsically interdisciplinary nature of quantum information and quantum computation. "Within limits" means that there should be some rationale to ask the question on the different sites.

This also reflects what has already been mentioned and discussed on the general meta post. In particular, asking the same question on different sites (hopefully tailoring it to the different audiences) allows to reach different communities and gain different perspectives on the problem, as argued e.g. here. Moreover, there also seems to be a general consensus that different sites should stand on their own, and if a question is on-topic on multiple sites, it should be allowed to stand in all of them, see e.g. the answers to What to do with cross-site duplicates?. Quoting Roberto Cartano's answer there,

You can't assume that all users will be on all sites. Each site has to stand on its own merits and you have to treat each site as a separate community.

If a question is inappropriate on one site, users now have alternate places to go with it. It's a nice convenience if moderators choose to transfer it for them. If it turns out to be a duplicate, let the other community handle it with the means already in place. If the first moderator happens to spot it as a cross-site duplicate, it can simply be closed and the original poster can decide how to rework the question if they want to try it on another site.

In the edge case where the question is appropriate on more than one site, leave it on both sites and let the users of each community benefit from the information.

Now, I am not saying that cross-posting does not have its disadvantages. Some that I can think of are

1. It duplicates maintenance efforts as questions on different sites live independent lives.
2. If the OP does not link the other question on the other site, and someone else doesn't catch it, it potentially leads to a waste of time as people might give essentially equivalent answers without being aware that someone already did on another site.
3. We lose all the functionality provided by linked and related questions tabs.

On the other hand, what is gained is (potentially) different perspectives on the same topic (which can be very interesting and valuable information).

But regardless of pros and cons, I'm not even sure that we could devise a sensible policy to forbid cross-posting that doesn't involve software changes in the site. Sure, the situation in which the same person asks the same exact question on multiple sites can be handled: just close all but the first post (assuming we know that the question was cross-posted). But say Alice cross-posts a question on physics.SE and quantumcomputing.SE at the same time, the post on physics.SE is closed, and then a year later Bob, unaware of the previous post, asks a very similar question on physics.SE. Should this now be treated as a duplicate of a question that was answered on a different site? I think this sort of position would be hard to maintain. Also, different sites should stand on their own, not rely on discussions happening elsewhere. See also this relevant discussion on vi.meta.SE and this relevant post on the stackoverflow blog.

This said, it might be useful to have guidelines in place as to how cross-posting should happen. In particular, we definitely want askers to

1. Provide a link to the duplicate (or even just related) posts on the other sites.
2. Tailor the question to each site as much as possible.
• If you wanted to allow cross-posting, I think one could say: It is not permitted to copy the same question, word-for-word, onto two SE sites. (Or perhaps further limit that by "unless you have waited at least a week and gotten no answers".) That would avoid the concerns in your next-to-last paragraph, and cover most of the problematic cases. – D.W. Dec 1 '19 at 17:36
• @D.W. I would tend to agree that in those cases it's harder to assume good faith on OP's part. On the other hand, I am not so sure that even enforcing the rule that exactly duplicate posts are not allowed would work. I fear it would just lead to people (those that know about the policy) doing trivial changes to the post as an easy way to work around the policy. On the other hand, if the answer to that exact question is trivially found on another site by googling, there may be grounds to close the question with a "not enough effort" type of close reason. – glS Dec 1 '19 at 17:43
• really though, I'm curious how much of a problem this actually is. I mostly monitor cross-posting related to quantum-X tags via subscriptions, and there aren't that many of those. Does anyone know how to pull data about cross-posting from the data explorer? – glS Dec 1 '19 at 17:48
• This was prompted by my noticing a cross-posted question. I don't think there's any easy way to pull data from data explorer because cross-posting isn't recorded or marked in the database. When I encounter questions that are cross-posted on multiple sites, that experience diminishes my desire to answer questions on the site in the future by a tiny bit. I may be unusual in that respect. – D.W. Dec 1 '19 at 17:49
• In my experience it's usually pretty clear when someone is copy-pasting their question on multiple sites without putting any effort into figuring out which aspect is most relevant to each community. In my experience usually they just copy-paste, or they add a content-free sentence at the end that says "I am interested in the perspective of community X", or otherwise take the path of least effort. Of course if evasion of the policy became a significant problem one could always revise how it is handled at that point... – D.W. Dec 1 '19 at 17:49
• I would also note that earlier this year I flagged a question that was cross-posted here and on CSTheory.SE, and was copied word-for-word onto both sites, with one paragraph added on CSTheory.SE (that didn't seem to me to tailor it for that site); despite the flag, the question was not closed. – D.W. Dec 1 '19 at 18:08
• @D.W. I'm not able to write an answer right now, but I'd suggest editing/suggesting an edit to the question on both sites referencing the question on the other site (does that make sense?). Also, if it appears to be done in bad faith, pinging/flagging for a mod is reasonable, although I wouldn't necessarily expect a mod to do anything about a crossposted question purely on the basis of it being crossposted – Mithrandir24601 Dec 1 '19 at 19:15
• @Mithrandir24601, I would prefer to avoid trying to infer good faith or bad faith, especially when we don't have a clearly articulated policy. I'd rather focus on whether it meets our guidelines than attempting to guess the motivations of the asker. (I can understand why askers might cross-post; from a game-theoretic perspective, it benefits the asker to ask everywhere they can, because the more places they ask, the more likely they'll get an answer... it just doesn't necessarily benefit sites or answerers.) Personally, I'd prefer that mods close questions that violate the site's policies. – D.W. Dec 1 '19 at 19:36
• If you are proposing a policy of allowing cross-posting so long as the posts are cross-linked, that is not something I am personally enthusiastic about, but it's not really up to me. – D.W. Dec 1 '19 at 19:36
• @D.W. "If you are proposing a policy of allowing cross-posting so long as the posts are cross-linked"...that's the policy I'd propose, yes. If a question is well-written and on-topic on two or more sites they should be allowed on all those sites, period. I'm afraid people often tend to miss the forest for the trees while discussing the cross-posting policy: the overarching goal of the policy was not to prevent a question from being asked on multiple sites but to prevent new users from spamming multiple sites without knowing their scopes. – Sanchayan Dutta Dec 3 '19 at 17:26
• @D.W. [cont.] Time is limited for everyone and it's in nobody's interest to unnecessary waste time in making cosmetic changes to their question for a site B just because they already asked their question on some site A, given that they would not have to make that change if they hadn't previously asked their question on site A. Questions on a specific site should be judged independently per their individual merits rather than whether or not they have been asked on another site. To prevent duplicated efforts, cross-linking suffices. – Sanchayan Dutta Dec 3 '19 at 17:33