In “Mirror Image,” a chilling episode in the first season of “The Twilight Zone,” a woman sees herself sitting on a bench. It’s not a reflection. It’s not a hallucination. It’s just — herself.

She begins to wonder if she’s crazy, but she finally settles on the theory that the doppelganger is a result of the collision of two dimensions. It smiles menacingly at her, and she’s convinced it’s there to take her place.