Rationale behind downvote button

Question

First: as a new non-scientist member of Physics SE I want to say thank you for the wealth of knowledge, interest and patience with my ignorance I have encountered here.

Second: I was very surprised to see that there is a "downvote" function for posts and answers. After trying to think of scenarios where such a function would enhance the quality of scientific discourse I am still at a loss.

The strength of this f̶o̶r̶u̶m̶ question-and-answer website is that it is highly specialised, and it's assumed that the vast majority of questions are not understood or of interest for the vast majority of people, be they physicists or not. I for one would be very busy if I would take the downvote button seriously and start voting on all posts that are "unclear" or "not useful" to me, the same way I upvote those that I find interesting. (Edit after comment: by this I mean that I don't understand 99% of the questions, but that says nothing about their quality, sincerity or usefulness for others, only my lack of knowledge.)

I do understand the 'upvote': it gives an indication on how popular a questions is, which means that there's a higher possibility that I will find it interesting. And it gives me an opportunity to send a small appreciation to those who taken the time to answer my question, or asked questions that enlightened me. But how can the distinction between a post with 0 votes (not popular) and one with -10 (very unpopular) help me to find the information I want?

So my honest question is:

What exactly is the rationale for the ability to downvote?

Can you point me to a specific case here where downvotes has achieved the intended function, that could not be achieved with other tools available? Is there research and/or data that shows that such a button enhances the quality of questions and answers?

Note after comments: I fully understand that the caretakers of this site are rightly proud and protective of it. I see myself as a grateful guest on PSE, and by no means am I criticizing or proposing changes. As a naive empiricist I am honestly curious on how exactly downvoting can have the function stated over and over again on the site and in comments below, as for me it seems counterintuitive. I apologize if this was a provocative issue. Please feel free to express your critique by downvoting this question.

Answer 1

Low quality questions on the front page send a signal to first-time visitors that this is not a site worth exploring. Downvoting low-quality questions helps to keep them off the front page.

Answer 2

After trying to think of scenarios where such a function would enhance the quality of scientific discourse I am still at a loss.

I think the first problem is that it's no scientific discourse we're aiming for here. This site is a question and answer site to which we are (voluntarily) providing (potentially) useful information to readers. Whether the content is useful or not is intended for the community to decide, literally why voting is important.

I suspect that it might be useful to consider scores on posts as being akin to grades on homework or tests: it provides a useful metric to others as to the knowledge content in the assigned work. While we may be used to the percentile grading system, it wouldn't be too difficult to adjust the scoring to see how far above or below the median (or even passing) would be. For instance, instead of a 90%, you got +5 to a mid-B or a 60% being -25 to the mid-B. In this sense, it is easier to see how bad you did (due to negative score) versus how good you did (positive score).

Downvotes are very much the same here: they convey a measure of knowledge content in the post: those with useful content are positively scored while posts with little useful content are negatively scored. So really it's just a measure of the relative worth of a post, given our own understanding. And this measure of relative worth is a nice by number attached to the top of your post.
Comments, on the other hand, are tiny and buried under the post. So not only do you have to read the entire post, but then what could be dozens of comments to parse the usefulness or potential issues of the post. It should be obvious that a big fat $-X$ at the top is a lot more clear indicator of problems than a tiny "this is wrong!" at the bottom.

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In regards to alternatives you've proposed,

1. No expressed consensus
   • Then everything is correct and there is no reason to vote up or even comment on anything. In fact, why bother asking or answering?
2. Comment the mistake/error
   • This is a good first step (I've argued so previously), but it does not, by itself, work to replace votes because (a) comments are generally temporary & such a comment mentioning the error might be irretrievably erased and (b) there is no guarantee that future viewers will actually read the comments to find the error.
3. Ignoring the post
   • Then not only is everything correct, but you are actively damaging the site because users who don't know better might think the bad post is actually good when you really know it is wrong (#2 below addresses the case when you cannot judge the content).
4. Flagging it for moderators to review
   • Flags, as discussed in the Help Center, are for specific instances of posts (e.g., someone using an answer to reply instead of a comment, spam), rather than a catch-all for bad content. Using moderator intervention in this manner is actually not in line with their wants and, even worse, then relies on these 6 people being, effectively, the ultimate arbiters of truth.

Hence, none of these provide any meaningful way to convey an incorrect/problematic post; voting is the only reliable mechanism to indicate a usefulness measure (positively or negatively) while an answer still exists (for deletion, see this and this Help Center article).

For other remarks on downvoting in general,

1. Don't have the time to downvote
   • Well this doesn't preclude you from actually downvoting, it just says that you're either not interested in curating or plain lazy (it really doesn't take much time or effort to hit that button as you see posts).
2. One may not understand the content
   • Great, it happens to all of us (because we're not all experts in all fields). Fortunately, this doesn't preclude you from voting on subjects you do know, just the ones you don't know.
3. There's more people who don't know enough about a given topic than who do know about that topic
   • This is probably an idea you had based on your experience with the Hot Network Question effect (see this Meta post and links therein), but in most cases, this is not true. Most posts only get a few upvotes. More advanced or specialized topics get even less.

Answer 3

Think there is a mechanism like, you cannot change the vote of a downvoted and commented answer, before the answer is not re-worked. Accordingly, I would love to see the common attitude, that a downvote comes with a qualifying comment, so the author has a chance to re-act and common quality of both, Q & A, is raised.

Else downvoting remains on the level of selectionism.