I've just voted to close this post, which I will slightly paraphrase because I'm sure it will soon be deleted:
I would like to know in simple words why time slows down and lengths change when I am in my private rocket traveling near the speed of light.
Although I think that almost everyone will agree this should be closed, it's not so clear which of the close reasons to choose. (In fact, I ended up choosing one pretty much arbitrarily and no longer remember what it was.)
Yes, this question is a duplicate many times over, but I can't choose that reason without pointing to a specific prior question, which I'd rather not do, partly because I don't want to spend time hunting up that question and more importantly because I don't want to send a message that posters who can't be bothered doing their own searches can post questions like this and expect others to do their searching for them.
It's not really unclear what's being asked. "Too broad" and "primarily opinion based" don't seem to fit. That leaves:
This question does not appear to be about physics within the scope defined in the help center.
Well, that's pretty good, but unfortunately I can't choose it without choosing a sub-reason. And none of those sub-reasons seems to fit. This is not a homework-like question, it's not about engineering, and it doesn't (to my knowledge) belong on another site on the Stack Exchange network.
Is it non-mainstream physics? Well, sort of, in the sense that it seems to confuse a "change in (proper?) length" with a change in the assignment of coordinates, but I think there is a difference between being non-mainstream and being a little confused. Besides, there are many other questions at about this level which are even more mainstream than this one, but still equally in need of closing.
That leaves me with the option of formulating a custom close reason, which requires a little extra effort on my part --- all the more so because that custom close reason automatically becomes publicly visible as a comment, so that although all I want to do is cast a close vote and move on, I feel like I need to spend an extra minute or so making sure my comment is fit for public consumption.
For this and other such questions, I would be much happier if it were possible to close with the reason "This question does not appear to be about physics as defined in the help center", where it is stated upfront that this site is for active researchers, academics and students of physics and astronomy.
Let me close by saying that we get a lot of questions at this level, some of which show more thought than this one does (e.g. the questions that arise periodically where someone has actually given some thought to what it would be like to ride on a light wave, has discovered an apparent paradox, and wants to know how to resolve it). I think it's important to discourage such posts without discouraging the spirit of inquiry that lies behind them. Telling people that they are engaged in "non-mainstream physics" is, I think, likely to be perceived as disparaging --- which is doubly unfortunate because thought-experiments like this are mainstream physics. (Yes, these thought-experiments have already been done and other people know the results, but naively repeating someone else's experiment---thought or otherwise---is still mainstream physics.) So I don't want to choose that option, but I do want to dispose of these posts quickly and effectively, and "not within the scope of the site" seems like a far better option than "non-mainstream".
Question 1: Can we please be given the option of closing as "Not within the scope...as defined in the help center", without having to choose or formulate a sub-reason?
Question 2: Does someone have a better suggestion?
Edited to add: Some have responded that "Too Broad" fits this question perfectly. Whether or not that is the case, it does not dispose of the general issue. What about questions of the form "I imagined myself riding on a lightbeam, and I don't see how I can square the obvious consequences with the fact that the speed of light is supposed to be invariant"? This is (I think) far too specfic to be "Too Broad", far too honest an effort to think things through from first principles to be "Non-Mainstream", and a bad fit for all the others too.
Edited to add further: I've just noticed that moderators already have access to the exact close reason I'm asking for, for example here. Apparently someone thought it was a good idea for moderators to have this option, and apparently at least one moderator thinks it's a good idea to use it.