In light of the 552-episode marathon showing on FXX right now and living on for eternity in our hearts, "The Simpsons" show runner Al Jean has posited a potential finale for the show, should it ever end:
@EverySimpsons My idea for last episode -- ends w/arrival at Xmas pageant (beginning of first episode). Whole series a continuous loop...
— Al Jean (@AlJean) August 21, 2014
This is a reference to the first-ever episode, from the show's premiere in 1989, when the family gathers to watch Bart parody "Jingle Bells" and Lisa perform as Tawanga, the Santa Claus of the South Seas.
As the A.V. club notes, Jean's tweet is also likely a reference to "eternal return," a concept recently popularized by "True Detective" via Rust Cohle's fondness for post-Kantian philosophy.
In conclusion: time is a flat circle, preferably from Lard Lad with pink, sprinkled frosting.