In physics, a hypothetical mirror universe made entirely of antimatter, or in science fiction, an opposite or inverted parallel world.
Combines 'anti-' (opposite) with 'world', emerging in mid-20th century physics and science fiction literature as scientists discovered antimatter and theorists imagined what a universe made of it might be like.
Physicists seriously considered that somewhere in the cosmos there might be an 'antiworld' made of antimatter—and if matter and antimatter ever touched, they'd annihilate each other in a burst of pure energy, which is exactly what scientists observed in particle colliders!
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