When is a research question "closed"? I am in Computer Science. I read a survey today. The author gave such a good result by the end of the article that I think the research question can be called "closed": the result performance is ideal and I think the problem is not worth researching any more; future developers can simply use the algorithms proposed and things should be fine. However, the author of the survey did not say so -- they did not say that the problem is solved, nor did they said anything about future work.

I believe (in this specific case), that the problem is solved:


The research goal is to reduce network latency. By the time the survey was written (year 2008), the result latency was 100ms. With such latency, human users won't notice a network delay, because that only happens when the latency exceeds 150ms.
The authors of the survey did not publish any paper on optimizing the algorithms after that survey.


Does these mean that the problem is safely closed? If so, why didn't the survey authors say that? If not, why didn't they continue working on it? How would I know whether a research question is solved or not?
I don't think a research question is every “closed”, as you say, though it's of course a matter of vocabulary. In the example you mention, it seems clearly that there is no current incentive to design better solutions, but unless it is actually proven that there can be none, it's not a solved-and-closed question, it's a “we don't actually need to do better” question. This makes all the difference in the world.