>NEO: I've kept quiet for as long as I could, but I feel a certain need to speak up at this point. The human body is the most inefficient source of energy you could possibly imagine. The efficiency of a power plant at converting thermal energy into electricity decreases as you run the turbines at lower temperatures. If you had any sort of food humans could eat, it would be more efficient to burn it in a furnace than feed it to humans. And now you're telling me that their food is the bodies of the dead, fed to the living? Haven't you ever heard of the laws of thermodynamics?
>MORPHEUS: Where did you hear about the laws of thermodynamics, Neo?
>NEO: Anyone who's made it past one science class in high school ought to know about the laws of thermodynamics!
>MORPHEUS: Where did you go to high school, Neo?
>(Pause.)
>NEO: ...in the Matrix.
>MORPHEUS: The machines tell elegant lies.
>(Pause.)
>NEO (in a small voice): Could I please have a real physics textbook?
>MORPHEUS: There is no such thing, Neo. The universe doesn't run on math.
My personal headcanon is that the machines were laboring under something akin to Asimov's three laws, which required that they preserve humanity. The Matrix, then is a loophole, something which technically satisfies the requirements of their core programming, but in a way that is advantageous to the machines.
But then, once you've got all those people hooked up, you might as well make some use out of them. They aren't the most efficient battery around, but if you've got to keep them anyway, they might as well serve as a load balancer. The people of Zion just came later and mistook an ancillary benefit for the machine's primary purpose.
MORPHEUS: Where did you hear about the laws of thermodynamics, Neo?
NEO: Anyone who's made it past one science class in high school ought to know about the laws of thermodynamics!
MORPHEUS: Where did you go to high school, Neo?
(Pause.)
NEO: ...in the Matrix.
MORPHEUS: The machines tell elegant lies.
(Pause.)
NEO (in a small voice): Could I please have a real physics textbook?
MORPHEUS: There is no such thing, Neo. The universe doesn't run on math.
[0] https://scifi.stackexchange.com/questions/1263/is-the-basic-...
It's probably the kind of thing that will be easily debunked by a real physicist (if you are one, go ahead) but I find the idea quite mind-blowing if I think about it for too long.
I've seen this as an explanation for quantum uncertainty.
but then some shit-for-brains hollywood producers read the script, decided it was too intellectual/nerdy and had it rewritten as "humans are batteries" which is gibberish to anyone with an education, but hollywood loves the lowest common denominator.