Wednesday, October 30, 2013

How to Outsmart the Zombie Apocalypse

Created using ZombieMe
Zombies seem to be incredibly popular lately.  "Mythbusters" just did an episode on zombies, "The Walking Dead" is more popular than ever, and zombie movies have been a bit of a trend, so I decided to make this month's bog post about zombies.  I won't focus on the martial arts since zombies aren't exactly skilled opponents, and punching range is already "too close," (don't even get me started about how ridiculous it is that a zombie-bite can transmit disease, but getting covered in zobmie blood while killing them never seems to be a problem in the movies). If you are looking for advice on fighting the zombie horde, I am very sorry to inform you that the best approach in a survival scenario is typically the most boring; stay well fortified and out of reach, conserve your energy, set traps, and use weapons that allow you to dispatch zombies from safely inside your fortification.  If you want to train to be prepared, changes are, a little bit of cardio training will help you out much more than any hand-to-hand skills you may have.

To some degree, zombies are just fiction, and we can't force them to adhere to reality, but at the same time, even in fantasy worlds, logic, math, and physics still need to apply.  As a friend of mine in the video game industry once told me, in a world with laser guns and plasma swords, you don't try to make it "realistic", you make it "believable."

Keeping this in mind, let's take a look at what physics and math can tell us about how to survive a zombie apocalypse:

1)  Energy is Conserved... So Let Them to Starve.
As I mentioned in a prior post about levers, energy can neither be created nor destroyed, but it does change form all the time.  So where do zombies get the energy to shuffle around and bite people?  For newly turned zombies, fat tissue may be a great source of energy (35 lbs of body fat at 3,500 calories per pound), but eventually they will have to get their energy from food (although, don't ask me how they are going to digest that food, or get that food and oxygen to the muscles without a functioning circulatory system...)

Calories in:
Zombie food is living flesh (usually human, definitely not other zombies), eaten raw.  Zombies still have human stomachs, so we must assume they are not capable of eating any more than a few pounds of flesh in any one sitting.  World records for competitive eating tend to lie somewhere around 10 lbs, and non-competitive eaters tend to tap out at about one tenth of that extreme.  For the sake of our calculations here, let's assume zombies get a little bit of that competitive-eater magic and are capable of eating 3 lbs of meat at a time.

Beef has about 1,300 calories per pound, and fatty bacon has around 2,600 calories per pound, with most of the variation in calories coming from the fat content.  This means that every time a zombie bites someone it get somewhere between 0 calories (bite only, no eating) and 7,800 Calories (3 lbs of raw chubby-guy meat fully digested).

Calories Out:
Zombies are most likely cold blooded (depending on what fictional universe you are entertaining), without a beating heart (otherwise they would bleed out).  In addition, we can assume they are only using a small portion of their brains, and your brain burns about 20% of your resting calories.  Given all this information, let's assume a zombie only burns only a tenth of a regular human's resting calories, or about 130 calories per day.

Zombies can be very active, however, walking around looking for food, and walking with a limp or a shuffle actually burns more calories than normal walking because our regular gait is a very efficient process that lets gravity do most of the work for us, and deviations from that natural gait are typically much less efficient.  Normal humans burn 170 calories an hour walking, so if zombies spend an extra 50% more energy doing their zombie walk, they burn about 255 calories per hour walking.  It is difficult to know how many hours a day zombies spend walking around looking for food, but 8 hours seems like a reasonable low estimate, given they are seldom dormant in the movies.

This puts total calorie expenditure by zombies at 130/day when dormant, or 2,170/day when active, meaning a dormant zombie needs to eat at least once every two months, and an active zombie needs to eat at least twice a week.

Starvation Timeline:
There are a lot of very sophisticated and intelligent mathematical models for how diseases spread, but for our purposes here, all we really need to know is that the infection curve is exponential, and according to the movies, 99.9% of humans are infected within a few weeks.  We can use this information to determine how often zombies eat and how quickly the starve.  You can download the excel file used for these approximations here if you want to follow along a home.

First, the infection curve, showing how quickly people turn into zombies, based on 100-perople-a-day interaction, and 1% chance of being bit by any given zombie you interact with.  I also assumed 0.1% of the population would successfully get themselves to safety.

The first two weeks are slow,  and the third and forth weeks are when the shit hits the fan.
Considering the fact that zombies only get to eat when they make new zombies, this means they will run out of food just as quickly as the infection spreads, and calories consumed per zombie drops to nearly zero by day 25.  From that point on, the zombies will slowly starve to death.

If your fictional universe involves dormant zombies, it will take them somewhere around two and a half years to burn up all their energy and either "die" or no longer pose any danger.  If the zombies are out walking around for eight hours a day, that time span shortens to two and a half months:

Make sure you have a few good books to read while you wait it out.

2)  Large Numbers are Still Finite... So Kill Them One by One
Zombie movies are great because even though the zombies are stupid, (sometimes) slow, and uncoordinated, the authors and screenwriters can have the protagonists overwhelmed by unlimited number of them.

Let's take another look at the green infection curve above.  Once 99.9% of the population has turned into zombies, the total number of zombies is not going to get any bigger and we still have 0.01% of the population alive.  Of those still alive, let's say only 25% are able bodied and capable of killing zombies, giving us a zombie-to-hunter ratio of 4000 to 1.  Even with those numbers, it is still reasonable for the remaining humans to quickly hunt zombies into extinction, and it just so happens that hunting things into extinction is a human specialty.

Let's say you've fortified yourself, and now you want to start killing zombies.  If you can manage to kill an average of eleven zombies a day, you will have done your part to eliminate zombies completely within one year.  Even if you were injured and unable to hunt down eleven a day, just adopting the philosophy of "if you see one, kill it" will help to ensure the number of zombies available to overwhelm you is always diminishing over time.

As an aside, humans already have a tendency to hunt down and systematically kill animals we believe to be a threat to us.  After the movie Jaws came out in 1975, shark hunting skyrocketed, and shark populations off the eastern coast of the united stated dropped by 50 to 90 percent in the following decades.

3)  Human Teeth are Dull... So Wear a Jacket
Humans are omnivores that primarily eat things they already killed using tools.  We don't usually kill things with our teeth, and we definitely don't defend ourselves with them.  We can, of course, still break the skin with our teeth, so it is not unreasonable to believe a zombie could take a bite out of a person, but it also doesn't take a lot of effort to make yourself bite-proof, either.

I decided to gather my own data for this topic, and bought a bag of apples.  It was pretty easy to break the skin of the apple using my teeth.  Next, I tried a variety of materials readily available around the house to see how easy it would be for a zombie to bite through it and infect someone.


  • One layer - No problem at all
  • Two Layers - No problem at all
  • Four Layers - Somewhat inhibited
  • Eight Layers - Difficult, but still possible

Notes:  Overall, the shirt was relatively bad protection from a zombie bite, even in layers.  In addition to being relatively easy to bite through, I could also taste the apple through the shirt when I broke the skin, implying zombie-infections may still pass through.  I also tested denim, with similar results, but one layer of denim behaved more like two layers of T-shirt.

Leather (very thin pig skin):

  • One layer - Moderately inhibited, **no penetration**
  • Two Layers - Difficult, **no penetration**

Notes:  Leather appears to be a great option.  The leather I tested was thin and soft, and could be torn with bare hands relatively easily.  Even though I was able to break the skin of the apple through a single layer, the leather was never punctured, and I could not taste the apple, implying you may get injured though very thin leather, but probably not infected.  A thick leather jacket would be practically impenetrable.


  • One layer - Somewhat inhibited
  • Two Layers - Moderately inhibited
  • Four Layers - Difficult, but still possible

Notes:  The scarf was a little bit perplexing.  It did not provide much more protection than the shirt or the denim, and I could taste the apple after every bite, but it did require a different sort of coordination.  Instead of just biting down on the scarf, I had to push in to overcome the fluffiness, and then bite down.  Would a zombie know how to do this, or would the zombie just bite down on the scarf?  Im not sure.  Fluffy clothing gets a maybe.

Duct Tape:

  • One layer - No problem at all
  • Two Layers - Moderately inhibited
  • Four Layers - Difficult, **no penetration**

Notes:  The duct tape is a second clear winner after leather.  Two layers of duct tape were insufficient, allowing me to puncture the tape and taste the apple, but at a thickness of four layers of duct tape, it was impossible to puncture, and difficult to bite.  This means that duct tape is a viable material for a zombie-proof outfit, and a perfect compliment to leather for ensuring there are no gaps (like taping your gloves to your jacket and your jacket to your pants).

How much duct tape do you need to be safe?  Let's assume you are going to make an entire zombie-proof suit from duct tape, four layers thick:
This took an hour and a half to complete (one layer only), and requires a partner.  The suit itself was surprisingly comfortable and flexible.  Running was not possible, but a brisk jog was fine.  We used a layer of paper towel underneath to keep the duct tape from tearing out body hair.
The one-layer duct tape outfit above (ignoring hands, feet, and head) took 70 yards of duct tape to construct.  Allowing for some mistakes and size differences, if you have 5 large (60 yard) rolls of duct tape in your home, you have everything you need to stroll around in the middle of a zombie apocalypse, completely care-free and invincible.