You know it’s coming. You’ve got your shotgun, your food and water, and useful barricades for blocking doors and windows. But, the numerous fictional portrayals aside, what would really happen in the event of a zombie outbreak? Or perhaps we should ask instead: what couldn’t happen?
They just keep going and going and going…
Zombies should not be the Energizer Bunny, any more than humans are.
The most obvious limitation is that the zombies are decaying. Wait long enough, and they’ll presumably stop moving. There’s a reason normal humans shut down after they’ve taken that degree of trauma. If the spinal cord has been significantly damaged, the zombie can’t be walking anywhere. Even if the nerves are structurally intact, inadequate blood flow will lead to nerve damage very quickly: within 5 minutes for the central nervous system, maybe 20 minutes for the spinal cord, digestive organs, and muscles. Since the trauma that turns someone into a zombie is usually accompanied by lots of blood loss, how are their tissues getting oxygen and why aren’t they permanently down within tens of minutes?
If we grant that the zombie is structurally sound and getting enough oxygen that it doesn’t immediately go into an ischemic cascade, there are still problems. Consider energy. If a zombie doesn’t eat, how far can it go?
There is enough ATP in normal human muscles for a few hundred meters of walking. So clearly the zombies still have ATP synthesis going, or they’d be notably non-threatening. If we assume glycolysis but no way to replenish sugars, after thirty or forty kilometers the zombie will drop – hitting the wall like any endurance athlete. If zombies have massively up-regulated fat metabolism, they can go a couple of hundred kilometers before they run out of body fat to burn into motion. This would be a convenient way to explain why the zombies would like high-fat foods like brraaiinnss, but as we’ll see that distance limit makes zombies relatively easy to contain.
If the zombies can eat each other and/or humans, then they can go further. But absent an external food supply, the population of zombies will exponentially decay with distance (the math is the same as the rocket equation), with an e-folding distance of ~200 km. That means that any initial population of zombies will die off quickly. Shambling around twenty-four hours a day looking for brains is energy-intensive. At normal walking speed, the population of zombies will die off with a timescale of a couple of days.
All of this assumes that the zombies are limited by their food supply. Omnivorous zombies or zombie cows are much more dangerous – there are far more grains than brains. But the normal human-eating zombie is pretty easy to contain, because the infection dies off so quickly. All you need to do is give the zombies something to chase until they drop dead (or un-undead, or more dead, or whatever). It’s persistence hunting in reverse: in the zombie apocalypse, you survive by having the zombies chase you.
In the interests of not losing the zombies when you run far enough ahead of them to have a snack and refill your water bottles, it’s probably best to start with a car with a full tank of gas. Have a couple of your friends serve as rear-guard to make sure the zombies don’t get too close, and drive in a big loop around the infected area, pied-pipering the zombies to their doom. With 600 km of driving, almost all of the zombies trailing you will be dead. Just 5% will survive if they can eat each other and run at the same time. You don’t need to do anything silly like armor the car. A zombie limited to normal human strength can’t break the windows, and the extra weight would cut into the gas mileage.
Speed and Transmission
Slow zombies. Why do these work at all? In that case, it’s not even a matter of outrunning your friends. These zombies are so slow, it just doesn’t make sense that they’ve been able to infect anybody beyond the initial carriers without something else going on.
Which brings up the problem of the transmission of the zombification. The zombies, regardless of speed, want to eat your brains. And in most cases, a zombie without a head isn’t going anywhere. So, assuming transmission via bites or other bodily fluids, the only people who get turned into zombies and not just eaten will be those slow and unlucky enough to get bitten or scratched, but fast enough to get away afterwards. This is a big limit on infection. In order for the outbreak to spread, each zombie has to bite far more people than the one-per-two-days limit from the energy content of their muscles and also avoid getting eaten by fellow zombies.
The Resident Evil series gets around all of this by having the virus become airborne or blood-borne depending on the situation. But then all of the characters that are fighting the zombies should have been infected as soon as they got into the same room as one. And of course those zombies are far too fast and too long-lived to be consistent.
You can avoid a lot of these issues by ignoring physics by means of magic. Dungeons & Dragons includes zombies, of course, generally under the control of some sort of evil necromancer. More necromancy shows up in Dead Beat, a book in the Dresden Files, where the zombies require an ongoing rhythm, metaphysically replacing their heartbeats, in order to keep moving. Either way, physics is not the limitation.
That said, the usual issues with zombies still apply — just stabbing one won’t stop it, though head shots probably work better. On the plus side, they’re generally not contagious.
Preferred solution for D&D? Bring a cleric.
For Dead Beat? Bigger zombie. No, really. We’re talking getting your undead pet T-Rex to munch the evil zombies for you.
Of course, with the zombie apocalypse, an ounce of prevention is worth a pound of cure. You know it’s a nasty virus? Fine. Treat it like ebola and stash it in a biosafety level 4 lab. Biohazard suits with positive air pressure (to avoid contamination even if there is an accidental puncture) are mandatory, along with multiple airlocks and serious decontamination of anything from inside. And all of the air vents run through micropore filters and then directly into furnaces, to burn up anything airborne that escapes (there goes Resident Evil). Similarly, if you’re testing some experimental new retrovirus on humans or animals… keep them in a nice, safe quarantine, long enough to check for weird side effects. And really, test the animals first.
So the zombie apocalypse is really quite ineffective as apocalypses go. So we’ll end this with a few funny things.
Here’s a take on the corporate zombie by Jonathan Coulton.
And, regardless of your political affiliation, we present what should be an entertaining “endorsement” by Joss Whedon.
Both of us wrote this one – RMR & MWB.