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A theoretical class of matter that violates one or more properties of normal matter as described by the Standard Model of particle physics. This isn't just weird stuff; it's stuff with properties like negative mass/energy density, which would cause gravity to repel rather than attract. While often purely hypothetical, some forms (like matter with negative pressure) are used in cosmological models to explain dark energy or to theorize about warp drives and traversable wormholes. It's the "what-if" building material of advanced cosmology and sci-fi tech.
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