Can a particle be in two places at once?

The answer

In quantum mechanics, particles exist in a 'superposition' of multiple states simultaneously until measured. The famous double-slit experiment demonstrates this: a single electron fired at two slits creates an interference pattern as if it passed through both slits at once. The moment you observe which slit it passes through, the superposition collapses and the interference pattern disappears. This remains one of the deepest mysteries in physics.