On Friends, Phoebe thinks that her grandfather is Albert Einstein.
The joke comes from Phoebe’s unusual family history and her grandmother’s unreliable explanation of an old photograph. Phoebe sees a picture of Einstein and accepts the idea that the famous physicist is her grandfather, treating the photograph with the same sincere confidence she often brings to her eccentric beliefs.
The gag fits Phoebe’s character: she is imaginative, unconventional, and frequently interprets ordinary events through a highly personal lens. Einstein’s unmistakable white hair and mustache also make the photograph instantly recognizable to viewers, even while Phoebe misunderstands its significance.
The storyline belongs to the broader family arc involving Phoebe’s biological father and the secrets surrounding her upbringing. Her family relationships are gradually clarified through later episodes, but the Einstein claim is played as a comic misunderstanding rather than a genuine genealogical revelation. Albert Einstein was a German-born theoretical physicist best known for the theory of relativity and the equation E=mc².