For (meta) questions about the policy to disallow non-mainstream physics questions on the main site. For details, see the tag wiki.
Questions about non-mainstream physics are usually closed as off-topic with the following reason:
We deal with mainstream physics here. Questions about the general correctness of unpublished personal theories are off topic, although specific questions evaluating new theories in the context of established science are usually allowed. For more information, see Is non-mainstream physics appropriate for this site?