The series finale of popular 1980s medical drama St. Elsewhere.
In that episode, the entirety of St. Elsewhere, including all its characters, are revealed to have been the dream of a minor character named Tommy Westphall, an autistic boy who possesses a snow globe containing a replica of the hospital where the series took place. At least that's the most widely held interpretation of St. Elsewhere's final moments. The ending has become an infamous example of the "it was all a dream" conclusion that's appeared in dozens of movies and TV shows over the years.
Where things get complicated is that characters from St. Elsewhere made guest appearances on another TV series, and characters from that series in turn appeared on other series. This expands the Tommy Westphall universe ever outward, to the point where over 400 shows now reside under its umbrella.
The Biggest Shared Universe Has Over 400 Shows
The first connection made in the Tommy Westphall universe is from St. Elsewhere to Homicide: Life on the Street, which shared a writer/producer in Tom Fontana. Characters from Homicide crossed over with multiple series, including The X-Files, Law & Order, The Wire and Arrested Development, with Richard Belzer's John Munch being the most frequent culprit. The Westphall universe just keeps expanding out in that manner from there, getting bigger and bigger in the same way as a snowball rolling downhill, which is appropriate considering Tommy's snow globe.
Just some of the other series that have ended up connected as part of the Tommy Westphall universe include Arrowverse shows also tie back to Westphall. The full list includes 419 shows as of 2016, the last time the curators of the Westphall theory updated its website. Surely more shows have somehow become connected in the four years since, especially since the Crisis on Infinite Earths Arrowverse crossover included characters from nearly every DC movie and TV continuity ever.
Of course, every party has a pooper, and there are those that consider the Tommy Westphall universe ridiculous. In their defense, the theory's original creator, Dwayne McDuffle, actually posited it while attempting to mock crazy shared universe theories based around guest appearances by one TV show's character(s) on another show. One prominent critic, Professor Brian Weatherson, argues that just because St. Elsewhere's characters appear in Tommy's dream doesn't mean they don't also exist in the show's actual reality, and thus the ending is being interpreted wrong, and by extension the universe theory is invalid. Even if that's true though, thinking about it remains an amusing diversion.
