James Cameron shot “Avatar 2” and “Avatar 3” back-to-back and is now going to resume production on “Avatar 4.” “We go back to work on it in a month and it's big,” actor Sam Worthington tells PEOPLE of the fourth instalment, set for release in 2029. “It's bigger than you can imagine.” Already a third of “Avatar 4” has been filmed. Cameron has also hinted that it might be called “Avatar: The Tulkun Rider.”