In 2013, Jon Negroni wrote a blog post that opened eyes. The gist: every Pixar movie exists across time within the same universe. He came to this conclusion because of easter eggs (clues left in the background or allusions) within the movies.
There are a couple of things to keep an eye out for in the Pixar universe, namely Buy-n-Large, or BNL for short. In Up, BNL is the company that wishes to purchase Carl’s house. In Wall-E, the spaceship where humanity survives is owned and run by BNL. They even power the batteries in Monsters Inc. They are the largest easter egg in Pixar as they exist throughout time.
Without further ado, from start to finish, here is a timeline of the Pixar Universe:
Brave is where it all starts. It introduces magic to the world and the concept of animals behaving like people. This establishes a lot of groundwork for how the universe works. It also ties back in, as the witch affects much of the universe. We will return to her.
Next is Ratatouille. Much time has passed, as human civilization now has cities like Paris and not castles in the woods. During this time, anthropomorphic animals have evolved from the animals affected by Brave's witch. Finding Nemo also takes place around the same time, although slightly more modernly. The anthropomorphic animals are reiterated by Finding Nemo.
The Incredibles is occurring more or less simultaneously too. Much like how many superheroes were created in the real world in the 20th century, The Incredibles and the need for super heroes develops during this time period. Here, we see the first signs of AI (artificial intelligence) as the robot becomes capable of thinking--and fighting--for itself. This is our first introduction to AI and sentient machines, which will be a huge part of the later universe.
Toy Story occurs next. This movie introduces fully sentient objects. Although they are not robots, The Incredibles provides an explanation for the toys’ consciousness. Syndrome mentions “Zero Point Energy” which is how he powers his weapons. This is a plausible explanation for where the toys draw their energy and life. Toy Story and its sequels also provide the groundwork of unrest that will eventually lead to AI and objects revolting against humans.
Enter the time period of Wall-E and Cars. Negroni hypothesizes that there is a war between humans and machine, which leads to the destruction of Earth being capable of supporting human life. BNL puts people on the Axiom and machines take over Earth. The people on the Axiom have no purpose outside of their addiction to machines, much like the relationship toys and machines used to have to humans. BNL is hypothesized to be run by the objects to control people, as the departure of people allows Earth to be only for machine. The captain on the Axiom is even AI set to keep the humans from returning to Earth.
And so, Earth becomes home to cars. Cars 2 has direct references to Earth, as they name countries, so we know it is taking place on our planet. The only plausible explanation for the lack of people is that humans have left, so it is while human life exists only on the Axiom. Cars 2 also introduces a fuel shortage, which eventually causes machines to die out (perhaps this will be seen in Cars 3). This is why Wall-E is the last life on Earth when humans return to start anew.
Enter A Bug’s Life (if you can even remember Pixar movies that old). The reason that humans don’t show up for so long in the movie is because there are so few on Earth. A Bug’s Life is thought to be set during this new period of human reintroduction.
Now, we have humans and highly conscious, higher level thinking animals recolonizing the planet together. This gives rise (over many, many years of evolution) to monsters. Enter Monsters Inc. This is the only explanation for how animalistic-monsters have a completely humanized society. The doors for gathering energy in Monsters Inc are using magic to travel the monsters back in time. There is even a home seen in both A Bug’s Life and in Monsters Inc when Randall goes to collect energy, but it has deteriorated when it is shown in A Bug’s Life.
Boo from Monsters Inc accidentally comes to this world, falls in love with it, and never forgets. Essentially, she saw too much and was too involved to not miss Sully and his world. She was exposed to magic, and becomes obsessed with traveling through time to find Sully. Here, we connect back to Brave. The witch in Brave is the only character to explicitly use magic, and Monsters Inc is using magic. Negroni hypothesizes that the witch in Brave is Boo. She is so far back in time because she is looking for the source of the magic: the wisps. This is also why she is obsessed with wood and wood carvings; she is trying to solve wooden doors being magic portals. This is also why she disappears during Brave and Merida cannot find her. She has traveled through time via her door. Not convinced? Here is a wood carving of Sully in her home in Brave so that you can question your disbelief of this entire theory.
With all this in mind, we have one final thought: we really hope Boo finds Sully again someday.