One of my favorite things about The Walking Dead is the fact that producer and head of make-up and special effects, Greg Nicotero, has taken pains to ensure that the zombies on the show decompose a little more each season, which mirrors the decomposition of bodies in real life. You can see the fascinating aging of the zombies over the course of the series here.
The problem with that, however, is that in attempting to capture the realities behind a corpse’s decomposition, the show has written itself into a corner. According to this piece from Moviepilot, a little more than 500 days have passed since the zombie outbreak. That’s about a year and a half. According to the way that bodies decay, the walkers on the show look about right for bodies that have been dead for a year and a half.
However, here’s the catch: According to this article, it takes eight to 12 years for a body to decompose if its buried 6 feet underground. On the other hand, above ground bodies decay at a rate of about four times faster than that, which is to say: A dead body will decay into a skeleton in two to three years (in fact, according to that article, “A corpse can become a moving mass of maggots within days, even hours in hot climates.”)
Assuming that the vast majority of the Earth’s population was infected by the walker virus a year and a half ago, that means that there’s only another six months to a year and a half before those bodies have completely decomposed. Now, if you can kill a zombie with a shot through the brain, that suggests that zombies do need a brain in order to continue operating. However, if their brains have completely decayed within three years, then the threat of zombies mostly disappears, save for the few people who have died more recently.
In other words, Rick Grimes and the rest of the survivors only have to hole themselves up in Alexandria for another six to 18 months before the threat of walkers essentially evaporates outside of those walls. At that point, the only threat that will remain is in newly dying people, who will continue to turn to walkers until a cure for the virus is finally discovered by Eugene.
DAMMIT. NEVER MIND.