That's how the survivors name the physics-defying powers that twist the world. Some theorize that the anomalies of the Oz are caused by the destruction of one of the alien ships that, apparently, loomed over the planet while the old civilization still stood. Everyone felt threatened, somebody lost the nerve and nuked several spaceship. The aliens retreated, but the planet was permanently hurt: the nuclear winter caused an irreversible global cooling, and the remnants of the broken spaceships got disseminated across the globe, twisting the physical laws as they fell. Now, they're also causing plenty of mutations among the local flora, fauna, and, well, humans. Collectively, this mind-boggling phenomenon is known as the Oz.