In 1992, Hardy published a thought experiment that "makes nonsense of the famous interaction between matter and antimatter " — that when a particle meets its antiparticle, the pair "always annihilate one another" in a burst of energy. Hardy proposed the possibility that in some cases when said interaction is not observed a particle and an antiparticle could interact with one another and survive. But since the interaction has to remain unseen, no one would notice this happening, which is why the result came to be known as Hardy's paradox.