What's going on …
There is a trend that is very easy to explain.
- A question is asked.
- It gets a few answers, and because it's the first of its kind (i.e. topic-wise), it receives a lot of popularity
- Votes trickle in, but at some point they stop, because the question isn't "new" anymore.
- The question and its answers stay like this.
Now, sooner or later, this happens:
- A new question is asked. It covers the same topics as the older one.
- It gets a few answers, which are now state-of-the-art, gets discussion, comments, etc.
- Somebody looks for a duplicate and finds our previous question.
- Close votes trickle in, sometimes very fast, sometimes not.
- The new question is closed eventually.
I won't give any specific example here, because if you've used the site, you'll know that this is more or less the same for every duplicate closed. Some are worse, some are better.
What the problem with this is …
In the following "duplicate" is referring to the question linked to as the "exact duplicate".
The duplicate might be absolutely outdated. This means that either technology has changed, software is no longer updated, new features have been added, etc.
You can't really fix a duplicate. If the above is true, it is very hard to "fix" such a state. As the duplicate is linked to quite often, it will probably have accumulated a large number of votes and views. At the same time, its answers might not reflect the current state of the art anymore (for reasons given above).
In order to fix something like this, you'd have to go through the whole question/answer pair and see if you can salvage it. Even worse, you might even want to close the duplicate as "not constructive" or "off topic", or "too localized", if it happens to fall under any of these categories. You would then end up in a state where the "new" question is locked (in some sense), and the old one too.
You can't really add new information. Well, you certainly can. But if you post a great answer to a question that's a year old – or if you've finally found the solution to a big problem –, you'll start off with a score of 0, among many other low-quality answers like "I kinda had the same problem, and fixed it by …", or "This is a great solution:
<insert link here>".
How are you ever going to make it to the top again? You won't have the ability to gather all these votes that would allow you to outscore the other answers.
By closing the new question, you stop the process of getting new information. After a question's been closed as a duplicate, you eliminate the possibility for users to add new information to an old problem. This is not to say that they couldn't just post at the duplicate, but for the reasons in my previous points, this is not always useful.
Also, from my experience, I haven't really often seen users posting their answers at the duplicate, even when they are able to see the "possible duplicate of … " link.
Should we do anything?
Duplication is not necessarily a bad thing. Every once in a while, we need to come up with something new. I'm out of ideas how to approach this inherent problem of Stack sites.
What do you think we can do? How can we teach people to vote more on duplicates, sort out the crap that's accumulated, edit old posts, et cetera? It would take a lot of involvement that's much more time-consuming than just posting a new answer, not worrying about the fact that the question you're answering is a duplicate.