Summary Young Sheldon's inconsistencies with The Big Bang Theory canon could be explained by the concept of a multiverse, as established by Sheldon's work in string theory. By acknowledging the existence of a multiverse, Young Sheldon can justify its departures from The Big Bang Theory's storyline and maintain a lighter tone. Young Sheldon can introduce the idea of a multiverse without incorporating major sci-fi elements, allowing future spinoffs to change the show's universe without contradicting the original.
Surprisingly, Sheldon's job in The Big Bang Theory could explain why Young Sheldonkeeps breaking the earlier show's canon. Like a lot of earlier sitcom spinoffs, Young Sheldon often diverges from the canon of the show's predecessor. This can prove a problem sometimes since Young Sheldon is a prequel to The Big Bang Theory. As such, it can be hard for Young Sheldon to justify why Meemaw acts so differently in The Big Bang Theory, why Sheldon never mentioned Paige in that earlier series, or why he spoke so poorly of his father when George Sr. was a reasonably good guy.
However, all of these The Big Bang Theory/Young Sheldon inconsistencies could be explained via one surprising character detail. Not only can The Big Bang Theory's canon justify why Young Sheldon changes so many details of the show's story, but the character element that makes sense of this changing backstory was established long before the spinoff even began. In The Big Bang Theory, Sheldon was a physicist who worked with string theory. This job could hold the key to Young Sheldon justifying the show's many departures from The Big Bang Theory canon as the show could introduce the idea of a multiverse if Sheldon explained some remedial string theory to viewers.
Young Sheldon's narrator, the adult Sheldon, could mention that the show's events are just one of infinite versions of his life. His work as a physicist would make this especially fitting, particularly since the series wouldn't need to expand on this idea. Young Sheldon already expanded The Big Bang Theory's universe by fleshing out Sheldon's family, hometown, and personal history, so the show doesn't need to offer countless other versions of the character or alternate universes. Instead, Sheldon could simply note that there might be numerous different versions of his life story existing simultaneously and, in doing so, he would justify Young Sheldon's canon hiccups.
Most of Young Sheldon's divergences from The Big Bang Theory aren't all that substantial, from cutting Sheldon's bullying to making George and Mary's marriage more successful. However, as Young Sheldon season 7 continues to explore Sheldon's teen years, things will inevitably get a little more complicated. Sheldon's father George Sr. canonically dies soon and also has an extramarital affair that Sheldon walks in on. While these traumatic events shaped The Big Bang Theory's Sheldon, they wouldn't necessarily need to happen in Young Sheldon's timeline if the show casually acknowledged the existence of a hypothetical multiverse. This could allow the series to maintain a lighter tone.
Young Sheldon could do anything after establishing the idea that there are multiple versions of Sheldon's story, and the show wouldn't even need to necessarily incorporate major sci-fi elements outside of Sheldon acknowledging the idea of multiverse theory itself. Since Sheldon worked with string theory, it would make sense for him to reference the multiverse theory in Young Sheldon's narration and, in the process, plant the idea that the show is just one of many versions of his life. Then, Young Sheldon and future spinoffs could change the show's universe without contradicting The Big Bang Theory's existing story.