You reached a point which is outside the map square system. The rectangle of map squares is set to the size big enough to include all the default ground that is set to have physical properties. Outside that, there are no map squares for your objects to be registered on.
The map squares system is designed to rapidly identify nearby objects to check for physical contacts during each frame's physics calculations.
The map squares system is designed to rapidly identify nearby objects to check for physical contacts during each frame's physics calculations.