As a science-based stack, we do and will inevitable get questions that are, to put it mildly, not based on "mainstream science". Some examples:

• http://earthscience.stackexchange.com/q/6928/6
• Why aren't there more questions and concerns about chemtrails?

Over on Physics, such questions are off-topic and specifically closed as not mainstream science. We have discussed the same here before, and it seems the community agrees that it should be off-topic.

Should we add a custom close reason for questions not based on mainstream science?