There is a question asked a few days ago on "Reaching 50% the speed of light using a centrifuge" that is effectively answered by a very nice answer to a different question on "Does a spinning disk weigh more than when it is stationary?". The person who provided the nice answer, @PM-2Ring, notes this in a comment on the first question. Since comments are officially transitory and often not read by subsequent readers of a question, I think would be nice to have a permanent visible answer.

The first question has now been closed as a duplicate, with the duplicate target being a third question "How is length contraction on rigid bodies possible in special relativity since definition of rigid body states they are not deformable?" whose answers don't seem relevant to me, and all three questions seem distinct to me. For example, the answer to the first question might depend on how strictly one defines "centrifuge", e.g. does a Black Hole accretion disk or a cyclotron count? The second question could have been answered without answering the first. The third question and its answers seem to be about linear, not rotational, motion and require some expertise to apply to the first question.

I have noticed other cases where questions are closed as duplicates because another distinct question has the answer buried in its answers. When I look at that question and its answers it can take me some time to find the relevant component. Sometimes I can only recognize that it is relevant because I am an expert, which is unlikely to be the case for the person who asked the original question.

What should the protocol be when a second question is not a duplicate but has the answer to the first question somewhere in its answers. Should we ask the user who gave the relevant answer to mostly copy their answer over to the first question? (This would seem to be okay according to the answers to "Is it OK to copy and paste part of own answer over and over, to answer new questions?".) Or should the first question be closed as a duplicate but give specific directions to the relevant answers?

  • $\begingroup$ "that is effectively answered by a very nice answer" - in what sense Would the complete answer, copied and pasted, make sense to post as an answer to the other question? Or does it coincidentally, when read and fully understood, happen to provide the insight needed to answer the new question (perhaps as only part of the explanation)? Or somewhere in between? $\endgroup$ Commented Sep 21, 2023 at 22:38
  • $\begingroup$ Since comments are officially transitory... I have always been under the impression that the "Linked" posts on the right of the page exist even the comment containing the link is deleted. $\endgroup$
    – Kyle Kanos
    Commented Sep 22, 2023 at 1:56
  • $\begingroup$ @Karl-Knechtel All of the "very nice answer" is not relevant, but the part of that answer from "However, it's not possible for normal materials" to "and the nano-rotor is getting close to that speed." seems to me to be an almost complete answer to "Reaching 50% the speed of light using a centrifuge". $\endgroup$ Commented Sep 22, 2023 at 12:42
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    $\begingroup$ @Kyle-Kanos It does not appear that "Linked" posts are retained if the comment containing the links is deleted. Being an experimental physicist, I did an experiment. I posted a test comment here with a couple of links to relevant questions. The links immediately appeared in the "Linked" section to the right of the question. I then waited 10 minutes and then deleted my test comment. The two links in the test comment then disappeared from the "Linked" section. $\endgroup$ Commented Sep 22, 2023 at 12:49
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    $\begingroup$ @DavidBailey hmm, seems that behavior is status-by-design (cf. Meta.SE), which is unfortunate IMO. It would be nice if all such links were tracked. Oh well. $\endgroup$
    – Kyle Kanos
    Commented Oct 3, 2023 at 19:19

1 Answer 1


If the questions are not duplicates, they should not be closed as duplicates. Of course there is interpretational leeway in how similar questions need to be to justify closing one as the duplicate of the other, but if we buy the premise of this meta question that the questions are not duplicates, then they shouldn't be closed as duplicates.

But copying answers is also not the best solution: If the original answer is improved by an edit, the copy won't be. I think the preferred solution should be that an answer to the new question simply links directly to the relevant answers on the old question and explains how they apply to the new case at hand.


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