An oddly large number of articles are titles with, or include in their opening line, a phrase like 'I have a doubt regarding gravity'; see the articles at the bottom, for examples.
In most cases, it doesn't seem that the OP actually 'doubts' that the physics in question are true. Instead, they seem to mean that they are generally confused.
Is there a particular language which this usage transliterates from? Possibly a particular thesaurus entry leading people astray?
Edit: See also (thanks to @Yrogirg)