4. Chuck Berry Existed Before Marty McFly Went Back To The Future - Back To The Future (1985)
Likely the most arbitrary plot hole on this list - given
Back to the Future's knowing and comedic nature - but a plot hole nonetheless. During a scene towards the end of the film, in which Marty is brought up on stage at the climactic "Enchantment Under The Sea Dance," he performs a version of the Chuck Berry classic "Johnny B. Goode." Marvin Berry - the man Marty is filling in for on guitar - hears Marty's rocking noise and proceeds to call up his cousin, Chuck Berry (yep, the famous musician) to tell him about "that new sound looking for." But we already know that
Back to the Future has established itself as existing in a universe where the future
can be changed, not one in which everything that happens has already happened. Simply put, there's not a single fixed history (one which is self-consistent and unchangeable), and the things that happening in the present (despite time travel interference), aren't running in a perfect loop with the past.
Back to the Future clearly employs a "history is flexible" attitude, what with the "changed" 1985 that Marty comes back to at the end of the movie. The point is, by the movie's logic, Marty McFly apparently "inspired" Chuck Berry's sound by returning to the fifties. But we know that Chuck Berry and Johnny B. Goode
already existed without Marty's intervening in the regular 1985. The movie takes several liberties in this vein, and ultimately mixes cinema's two most-popular time travel notions over the course of the trilogy (not to mention a third, which involves "parallel universes").