And here, you didn't think Up could get any sadder. OH, BUT IT CAN.
There are some Disney and Pixar theories that, quite simply, blow our minds (Frozen, Tangled and The Little Mermaid are all connected! Boom! Mind blown!). This one is more of an it-was-all-a-dream, whatever-happened-on-Lost sort of deal. But if you want a gut punch right in the feels, read on.
Credit where credit is due: This isn't a particularly new interpretation of the movie (and that's what it is, an interpretation, more so than a fact-based fan theory). It was recently resurfaced by Buzzfeed via Cheezburger, which seems to be adapted from this post on Reddit.
To really rip the band aid right off this emotional wound of a theory: Carl is dead.
He died at the beginning of the movie and everything after is his journey to heaven. When did he die? In his sleep, the night after the court tells him he needs to leave his house and move to a retirement home.
Russell is Carl's guardian angel, of sorts.
Russell needs one last badge (a badge for "Assisting the Elderly") in order to become a "Senior Wilderness Explorer." Or, in this interpretation, that last act is what would earn him his wings.
"I could help you cross the street. I could help you cross your yard. I could help you cross your porch," Russell says. "Well, I gotta help you cross something." What he eventually helps Carl cross is over into the after life.
Carl's guardian angel is a kid because he and his late wife, Ellie, were never able to have one (you'll remember this from the absolutely HEARTBREAKING opening sequence of the movie).
The theory says: "[Russell's] final badge requires him to help a senior citizen. This makes sense; Russell's other badges were preparing him in various ways for the final test, which is to help a senior citizen into the afterlife...Russell's innocence and devotion shows his purity, and the example he sets through that purity helps Carl see the error in his ways of thinking."
The house "represents Carl's attachment to the physical world," while Paradise Falls is heaven, or at least how Carl imagines heaven, based on a particularly utopian locale he saw on TV as a youth.
They theory says: "The raising of the house represents Carl's initial transition from the physical world to the spiritual world. He 'rises up' in the same way as people who have near-death experiences relate the feeling of floating above their body and watching as the doctors resuscitate it."
And when he finally lands at Paradise Falls after having a transformative journey (and without his home, which he finally let go of), Carl has finished his transition, presumably reuniting with Ellie in heaven.
Yes, the theory is a bit problematic:
Why does Carl find his My Adventure Book with a letter from Ellie telling him, "Thanks for the adventure. Now go have a new one!"? Why would Carl return to earth (and Russell's ceremony) after finding Heaven? What is the montage of Carl and Russell's adventures during the credits?
But it's fun (or, maybe the right word is depressing?) to think about.
Here's another take. Actually, here's almost the exact opposite take:
"Carl knew he never stood a chance in that jungle. It was his lifelong dream to go with his wife and be with her there. What was he going to do there? Hunt his food and clean his own water, in his age? Carl was planning to die at Paradise Falls. That way he'd be with his wife again. When he chose to leave the Falls he chose to live."
And here's just a completely different one that your Tea Party grandpa could get behind:
"Carl spends his entire life saving and losing and saving and losing from financial crisis to windfall and back again...He's tired of the new generation sweeping him under the rug. He takes whatever he has and flies his house halfway across the world in an effort to finish what he'd always dreamed of. Much like, say, an American senior citizen cashing in on their 401k. However, his whole plan goes awry when a selfish, obese, and poorly educated child tags along...Carl does everything he can to make his dream come true, but in the end learns that the best he can manage is to make peace with the new generation at the expense of everything he ever worked for or cared about."
Oh woof. That one might be the most depressing theory of all.