What is the best way to handle a case where a question was asked a long time ago and received several incorrect answers but no correct ones? To be more concrete, this was the situation with this question: If photons have no mass, how can they have momentum? I've done the obvious things: (1) submitted a correct answer; (2) downvoted the incorrect answers; and (3) explained my downvotes in comments. However, the question is 9 months old, and one of the incorrect answers has been accepted and heavily upvoted. I would interpret this as a situation arising from the fact that physics.SE is relatively new, and is still in the process of attracting a critical mass of users. With a small number of users, someone can make an honest mistake in an answer and not have it corrected. The problem is that there are certain questions that are FAQs, and those FAQs got asked and answered early on. Now we're stuck with them. Students or other people without solid expertise of their own will come along and believe the incorrect answer, which has been upvoted and accepted and effectively frozen in place.
This is not about crackpottery, as discussed in this question: Answers they are a-changin' I'm talking about answers that are wrong, but not wrong in a crackpottish way. I'm sure the folks who gave these answers are competent at physics, but everyone makes mistakes sometimes, even people who are highly competent.
How have the older, more mature SE sites dealt with this?
The problem is that once a question has sat around for 6 or 12 months, nobody is likely to participate in it anymore. It's off everyone's radar, and if its answers are broken, they aren't going to get fixed.
For comparison, Wikipedia has mechanisms where you can try to attract people's interest in improving an article that needs work. For instance, you can nominate it as a good article, which initiates a review process; you can tag it as needing attention from an expert; you can nominate it for deletion; etc. SE, on the other hand, doesn't seem to have any mechanism (that I know of) for getting up on a soapbox and alerting people that a certain question is broken and needs fixing.