It's been over twenty years since theater audiences first had their minds blown by The Matrix. The 1999 movie revolutionized filmmaking and remains one of the best science fiction movies of all time. It boosted the careers of actors like Keanu Reeves and Carrie-Anne Moss, and it put the Wachowskis on the map as directors to watch.
Since then, The Matrix has gotten several sequels, which are better than people remember, and there's a fourth feature-length installment coming late in 2021. The film has spawned comic book and video game tie-ins, and it has never drifted far from the cultural imagination. For all the love The Matrix gets, there's still a massive plot hole in the first film that puts fans into debates to this day.
In the world of The Matrix, machines rule the planet. When machines became sentient they fought a war against humans, and the humans lost. The twist is, unlike other AI-dominated dystopias, the machines didn't kill everyone. They grow humans in fields and keep them sedated by making their minds live inside a computer-generated reality – the Matrix. It's a great plot, which is why The Matrix is a classic, but it does beg one question. Why would the machines choose to grow humans instead of killing them off? Unfortunately, the only answer the movie supplies is ludicrous.
Humans ≠Batteries
The only explanation viewers get for the "big question" in The Matrix comes from a conversation between Neo and Morpheus. In the scene, Morpheus is explaining the war between humans and machines to Neo. Morpheus tells Neo that in an attempt to deprive the machines of their solar power, humans used a weapon to block out the sun. The lack of sunlight didn't stop the machines, however, because they found a way to use the human body for energy. Morpheus claims that the Matrix and the human fields it helps maintain are a power source for the machines that now populate the planet.
While that might not seem like a particularly abhorrent plot point on the surface, the human battery issue is a real problem for The Matrix. Unfortunately, human bodies sitting passively in tanks wouldn't be able to generate any kind of society-sustaining energy for the machines. It's a physics problem. Energy can't be created or destroyed. Even though human bodies naturally produce lots of heat, they do so by absorbing other forms of energy. Humans call that food, the machines call it a non-starter.
The machines would have to put as much energy into their human fields as they wanted to extract from them. Without the sun, they can't grow food. If humans are their only energy source, they can't produce enough energy of any kind to keep their humans alive.
The Neural Network Draft
Apparently, a human-based energy source wasn't the original explanation for why the machines kept us all alive. The Wachowskis have said they had planned for the machines to being using humanity to create a neural network. That certainly sounds more in line with the science fiction anime stories that inspired the Wachowskis to create The Matrix in the first place.
No one has said definitively why the plan changed. One rumor has it that the studio thought the concept of a neural network would be too confusing for audiences. While that definitely sounds like something a big film studio might think, that theory seems unlikely. After all, the studio was entirely on board for The Matrix being an undercover trans allegory, a much more difficult concept for theater audiences to fully absorb.
Another theory relies entirely on the evidence present in The Matrix. It's much simpler, and honestly much more reasonable. Ready? Morpheus was wrong. Of course, he couldn't know firsthand what happened during the war between humans and machines. No human could. At the same time, no one alive could say for sure what the machines were doing with humans. It's likely the human battery concept was just "real world" humanity's best guess at what was going on.
Retcon Opportunity
The Matrix films have never directly addressed this last remaining plot hole in the franchise. Of course, that could change with the upcoming Matrix 4, set to release in December of 2021. At this point, it's anyone's guess.
The Wachowskis have been very secretive about plot details for Matrix 4. They haven't even officially released a title, though one may have leaked, and fans are lucky to even have an idea of the cast list. Keanu Reeves and Carrie-Anne Moss will be returning for Matrix 4, but other previous stars appear to be absent from the film. That might be an indication that the Wachowskis aren't wholeheartedly interested in dealing with the past of the Matrix franchise. Focusing on forward momentum would be a good move, even if it means leaving this plot hole unfilled.