Related: this Meta question, which has no answers after five years.
There seems to be an issue with the "hard science" tag. First, it should have an automatic banner to remind potential answer authors that it's either a) been applied in error, or b) the questioner should be encouraged to clarify, when it's not really a hard science question, else c) it really does merit equations and references.
Second, there really needs to be a clear policy on when to remove the tag. For instance, this question is tagged "hard science" but isn't asked in a way that can really be answered with equations etc. -- it's not a hard science question at all (I answered based on the question content without noticing the "hard science" tag, and can't even hide my accepted answer now that L.Dutch has added the reminder banner).
Third, there needs to be a way to delay acceptance of answers that don't meet the tag, if it's genuinely warranted. As things stand, a new user can post a question that isn't worded like "hard science" and isn't really answerable with equations and references (perhaps because the answer is such common knowledge that people who know the answer don't recall where or even how many times they've read it), and without a reminder banner an experienced user can answer the question in the spirit it was asked, and be caught out with an unacceptable "may be removed" answer that's been accepted by the new user.
For the reference question, the simple solution is to remove the "hard science" tag -- but the fact this can happen points to flaws related to this tag that really need to be addressed. I can see where it makes sense to have the tag for certain questions -- like ones about stability of multi-body stellar systems with planets, for instance -- but it needs to be better guarded, perhaps even vetted.
Edit to add: this question is a fine example of what I was seeking a solution for: even the asker has admitted they misunderstood the
hard-science tag, but the question has been closed because unanswerable with
hard-science and one or more answers have been deleted because "not a hard science answer".