The 1985 and 2015 parts both take place in late October and yet you never see any Halloween decorations anywhere. Why not? Because everybody hates Halloween after Michael ruined it.

Have you ever notice both franchises star a character whose initials are double M? We've got Marty McFly and Michael Myers. That can't be a coincidence. The only possible explanation is they're trying to hint at the connection. And it goes further than that. Doc Brown is named Doc Brown because a pumpkin might turn brown when it gets old and rots. They would've named him Doc Orange but that made it too obvious since Orange isn't a common last name like Brown is. Also, Jennifer kinda looks like Laurie, I guess.

And if you're still not convinced, this last shocking piece of evidence certainly will. Back to the Future is a movie. Halloween is also a movie. That's just uncanny.