My son and I were watching Back to the Future the other day and this question came up: Marty McFly had heard Johnny B Goode on the radio played by Chuck Berry. Marty McFly traveled back in time. Chuck Berry heard Marty McFly play Johnny B Goode over the phone and recorded it. It was that recording that Marty McFly heard on the radio. Where did that song come from if nobody wrote it?