Hello everyone. I need help with a thing, which correct name is unknown for me 
So I’ll try to explain, whot I’m actually going to achieve: I have made large world (~20 000 square kilometers) and the world is built with help of world composition, and its square. The world itself working like a charm, but now I want to make it endless, like… planet. So if the player will reach level border, he will see oppositeside of the level, and if he try to walk further - he will be transitioned to the opposite side of world. How can i achieve this effect, or maybe someone know how the effect is called?
One additional question: my game is based on physics, so physics must be as presice as possible at moment of the transition… and the transition must be seamless…