I don’t need to rehash the plot of “Back to the Future” here, because only one scene actually matters. It’s the scene at the very end, after the girl is got and the day won, when Marty McFly takes to the stage and plays Chuck Berry’s “Johnny B. Goode.”
A vigilant observer, Marvin Berry, calls his cousin Chuck, announcing, “You know that new sound you been lookin’ for? Well, listen to this!” and holds the phone up to the music. In case you live under a musical rock (e.g. listen to “Fall Out Boy”), Chuck Berry is the musician often credited, alongside Elvis Presley, with the birth of rock ‘n’ roll with his song “Johnny B. Goode” in 1955 (a year after Presley’s “That’s All Right Mama”).
So the indication is that Chuck Berry learned the song from Marty McFly in the past. Marty McFly in the future, of course, learned the song from Chuck Berry. This is, in fact, a very common paradox of time travel. In this scenario, the information passed between the teacher (Berry) and the student (McFly), in this case the song “Johnny B. Goode,” has apparently arisen out of thin air. It is an effect without a cause. It is impossible, so the entire scenario is impossible. And a condition (time travel) that leads to an impossible situation is, therefore, also impossible.
Then who, you may ask, invented rock ‘n’ roll: Marty McFly, Chuck Berry, or Elvis Presley? None of ‘em. It was Muddy Waters.
