Portals 2 is an exploration of differences. The initial part of the video shows a sphere-cloud machine discovering spaces. When the sphere-cloud machine travels, the landscapes and spaces are transformed: they elongate, they multiply, and they shift to upside down. The sphere continues the trip accelerating and de-accelerating and finally passes through the clouds to an outer space where it meets other sphere-planets. These planets move around each other as if in a beautiful dance. In this dance, they touch each other, with the touch transforming each planet and they acquire the characteristics of the other "partner" sphere. They also multiply, showing many differences. This interaction is an amazing dance where worlds don’t collide into each other but mix and differentiate.