Is there a specific category in WikiAnswers for theoretical physics?

The Category "Definitions and Word Differences" is the best place for those questions. You can find a link to the Category in the "Related Links" section of this answer.

Because it's fun and mind-blowing. Theoretical physics predicted many things that you see in science fiction.

Yes, it's called "Questions about WikiAnswers" and this question is in that category!

As of August 27, 2011 here are the Primary and Secondary categories, 144 in total, without supervisors: Veterinary Medicine Zoology or Animal Biology Real Estate Antique & Classic Cars Auto Parts...

No, but you can request it by emailing your idea to WikiAnswers @ Answers.com (no spaces).