I finally got around to watching The Road, although from what I gather this review will apply even moreso to the book. Like The Matrix, the use of humans in the story goes against the Laws of Thermodynamics. In short, eating a human yields less energy than it took to grow the human. (Hilariously, this Master’s in English Literature thesis about the theme of “entropy” in The Road completely misses the thermodynamic problem with cannibalism.)
It’s often said that The Road depicts a world with no ecosystem. In fact, the ecosystem is just extremely simple: non-replenishable vegetables, one species of herbivores (hereafter “good guys”) and one species of predator (cannibals).
In one of the most famous scenes, some cannibals are keeping humans imprisoned for eating later. But their prisoners are wasting away at 1500 calories per day – it would be far better to kill all of them as soon as they’re captured and preserve the meat. The only reason we keep livestock is if they can eat food we can’t, such as grass, to upgrade excess low quality food, such as grain, or to store food temporarily, such as a hog fattened for winter.
In another scene, a pack of carnivores chases down one or two herbivores. But with a subsistence ecosystem, we should expect to see a few solitary predators preying on a large base of herbivores. The rate at which predators would find prey would quickly lead them to turn on each other.
Based on these violations of physics, my conclusion is that the father and son are in fact in purgatory. The father is there for the sin of suicide: the two bullets in the gun represent not the two bullets left, but the two bullets used to get them there. The boy, born after The Fall, was never baptised, so when the father is freed at the end, the boy must keep walking the road with some of those other couples that the mother mentions “are doing it” (suicide).