Great Scott, this is heavy.

It never occurred to me until a few months ago during my latest viewing of the Back to the Future (BTTF) trilogy, probably because I just never examined the logic much before, but I was a little surprised at how obviously broken the logic is in BTTF 2.

So, 2015's 80-year-old Biff (Old Biff) steals the time machine and goes back to 1955 on the night of the lightning storm. (I definitely appreciate Doc pointing out the unbelievable coincidence of Old Biff choosing that of all possible days to travel back to, but I digress.)

So Old Biff goes back to 1955 and gives 1955's Biff (Young Biff) Grey's Sports Almanac, then returns straight back to 2015 and returns the Delorean where he found it (although it would have made more sense for him to just keep it, unless maybe Old Biff thought Doc had a spare time machine he could use to catch him, but I digress).

Doc and Marty go from 2015 back to 1985 where the world is turned upside-down. Doc realizes that Old Biff borrowed the time machine and Marty suggests they just return to 2015 to stop Old Biff from taking the car. This is where the science becomes fiction (yes, it was factual until now).

Doc replies that if they returned to 2015, they'd be going forward in the skewed timeline where Biff is a billionaire and has destroyed the world, so it wouldn't work. Hmm. Once Old Biff gave Young Biff the almanac, that changed the future and the timeline that Old Biff was existing on, right? That being the case, why is it that when he returned to 2015 he landed back exactly where he left from? And for that matter, why is it that Doc and Marty left from that very same 2015, but when they landed in 1985 it was on the skewed timeline?

Anyway, there's no real point to this little diatribe. It was just on my mind and thought I'd share. I do wonder, though, if I'm the last person on earth to have realized this paradox.