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Is it OK to downvote "impossible questions"? With impossible questions I mean questions that are not possible to answer or that are not possible to do (obviously, the OP doesn't know that). For instance:

Anyone knows if P = NP? >>> Not possible to answer

or:

Is there a way to sort an array with a O(logn) complexity? >>> Not possible to do

Related post , but no the same, I'm asking about downvoting, not closing.

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8  
Both have real answers, though: 1) No, nobody does. 2) No, it's not possible. The essence of such answers are lame assertions, but that's where reliable, authoritative references come in. –  Grant Thomas Dec 15 '11 at 16:58
5  
Since the tooltip for a downvote says "This question does not show any research effort; it is unclear or not useful" I'd say yes, it's okay to downvote such questions. Of course, voting is anonymous, and downvotes on questions have no reputation cost to the voter, so you can downvote for any reason whatsoever and no one will gainsay you. –  Al E. Dec 15 '11 at 17:06
1  
Are these real questions? –  Some Helpful Commenter Dec 15 '11 at 17:22
    
downvoter... care to share? –  juliomalegria Dec 15 '11 at 19:23

3 Answers 3

up vote 5 down vote accepted

Your first question is possible to answer.

Anyone knows if P = NP?

No. Nobody knows.

I'd still probably downvote that one, since it's almost certainly not related to a specific programming problem that the asker might have. Also, it's extremely well-known, and a Google search would have turned up the answer.

I think the second question is better.

Is there a way to sort an array with a O(logn) complexity?

That's answerable, as you already pointed out. It's also something that someone might reasonably want to do (reasonable other than the fact that it's provably impossible), so it's not a completely brainless question. I wouldn't downvote it.

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5  
Actually, P does equal NP. I have a proof, it's just too large to fit in this comment window –  Adam Rackis Dec 15 '11 at 18:43
    
Ah, the dilemma of upvoting a case of the funnies and risking that someone takes it seriously... –  l0b0 Dec 21 '11 at 15:39

Is there a way to sort an array with a O(logn) complexity?

This is not an impossible question. There is an answer: No!

Anyone knows if P = NP?

Although Anyone knows if ... usually does not indicate a good question, it might even be appropriate in this case.

Once again, the answer is No!, since the problem P = NP? has not yet been solved.

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Downvoting is a very personal choice, but I think would choose answer these questions rather than downvote them.

The downvote button tooltip reads

This question does not show any research effort; it is unclear or not useful.

Neither of your example questions here fits those criteria to my mind. Better to explain to the OP (and hence to any other user who comes along with a duplicate question in the future) why their question can only be answered by saying "No, no-one knows", or "No, that's impossible."

They aren't bad questions just because the OP doesn't know that what they ask is impossible or infeasible. They're badly-phrased, maybe, but I think I'd still answer. And I wouldn't downvote something I've answered.

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'Downvoting is a very personal choice' - Yes to whether you vote or not, but the reasons for voting shouldn't just be left to personal whim; we have established protocols for the why of it. –  Grant Thomas Dec 15 '11 at 17:36
    
I agree - but the key word there is shouldn't. In reality, people vote for all sorts of reasons. –  razlebe Dec 15 '11 at 19:03

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