Let me begin by thanking Jon Negroni for this. Jon Negroni is the man behind the marvelous ideas of "The Pixar Theory." In 2013, Negroni wrote a thesis that states that all the Pixar characters live within one fictional universe, the Pixar universe. He also acknowledges that the ideas and concepts that form this theory come from the Cracked.com video series "After Hours," written by Daniel O'Brien.
Negroni wrote this theory with all the movies in a specific timeline and this is the order in which they go:1. "The Good Dinosaur" (post-Cretaceous Period).
2. "Brave" (14th and 15th centuries).
3. "The Incredibles" (1950s and '60s).
4. "Toy Story" (1997 to '98).
5. "Toy Story 2" (1999).
6. "Finding Nemo" (2003).
7. "Finding Dory" (2004).
8. "Ratatouille" (2007).
9. "Toy Story 3" (2010).
10. "Up" (2011 to 2016).
11. "Inside Out" (2014 to '15).
12. "Cars" (2100 to 2200).
13. "Cars 2" (2100 to 2200).
14. "Planes" (2100 to 2200).
15. "Planes: Fire and Rescue" (2100 to 2200).
16. "WALL-E" (2800 to 2900).
17. "A Bug's Life" (2898 to 3000).
18. "Monsters University" (4500 to 5000).
19. "Monsters, Inc." (4500 to 5000).
There is a website that specifically explains the time period and how it fits all together with evidence. However, as more movies have been released, they have not been added to that website, but to Negroni's personal blog instead. I for one had not heard of this until I stumbled across the SuperCarlinBrothers. It was specifically Jonathan "J" Carlin from the brother duo who made a video about "The Pixar Theory" which is where I first heard of this phenomenal idea. Negroni wrote a book that is available through his personal blog or you can read this theory on the website I mentioned earlier, or his blog, as I would not be able to explain it quite as well as he has. You could also watch the video by the SuperCarlinBrothers like I did as well, if you're more the auditory learner than the visual learner. However, you decide to investigate this theory, it is most definitely worth the time, as your mind will be blown!