World#bounds

The World has no fixed size, but it does have a bounds outside of which objects are no longer considered as being "in world" and you should use this to clean-up the display list and purge dead objects.
By default we set the Bounds to be from 0,0 to Game.width,Game.height. I.e. it will match the size given to the game constructor with 0,0 representing the top-left of the display.
However 0,0 is actually the center of the world, and if you rotate or scale the world all of that will happen from 0,0.
So if you want to make a game in which the world itself will rotate you should adjust the bounds so that 0,0 is the center point, i.e. set them to -1000,-1000,2000,2000 for a 2000x2000 sized world centered around 0,0. Bound of this world that objects can not escape from.