The state of having two different parts, aspects, or natures that exist at the same time, often opposites or very different from each other.
From Latin 'dualis,' derived from 'duo' (two). The suffix '-ity' makes it an abstract noun meaning the quality or state of being dual or having a twofold nature.
Light is one of the strangest examples of duality in science—it acts like both a wave and a particle depending on how you measure it, and physicists still don't fully understand why the universe insists on this double life.
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