In a typical zombie apocalypse book, once the infection arrives it spreads rapidly and within a few months the entirety of the United States and possibly the world has been affected, leaving only small pockets of survivors.

However, according to a group of researchers at Cornell University that is not how it would happen. Large cities might fall in a single day but more remote areas could be completely unaffected for months.

Inspired by reading “World War Z, an oral history of the first zombie war” a graduate statistical mechanics class attempted to simulate how a zombie outbreak would play out in the U.S.

“Modeling zombies takes you through a lot of the techniques used to model real diseases, albeit in a fun context. It’s interesting in its own right as a model, as a cousin of traditional SIR [susceptible, infected, and resistant] models—which are used for many diseases—but with an additional nonlinearity,” says Alex Alemi, a graduate student at Cornell told Phys.org.

The project used the techniques of modern epidemiology modeling, starting with with equations to model a fully connected population and lattice based models and ending with a full scale simulation of a U.S. outbreak.

“At their heart, the simulations are akin to modeling chemical reactions taking place between different elements and, in this case, we have four states a person can be in—human, infected, zombie, or dead zombie—with approximately 300 million people,” said Alimi.

“Each possible interaction—zombie bites human, human kills zombie, zombie moves, etc.—is treated like a radioactive decay, with a half-life that depends on some parameters, and we tried to simulate the times it would take for all of these different interactions to fire, where complications arise because when one thing happens it can affect the rates at which all of the other things happen,” he continued.

According to the results of the simulation, the less densely populated an area is the safer it is from a zombie outbreak, with the northern Rocky Mountains being the safest spot in the US. According to the team, people in that area might have months to prepare before the arrival of the walking dead.

“Given the dynamics of the disease, once the zombies invade more sparsely populated areas, the whole outbreak slows down—there are fewer humans to bite, so you start creating zombies at a slower rate. I’d love to see a fictional account where most of New York City falls in a day, but upstate New York has a month or so to prepare.” said Alimi.

Alimi and his colleagues are not the first to use the zombie apocalypse for practical purposes. The Centers for Disease control has, for the past several years, maintained a “Zombie Preparedness” page.

The site is meant to be fun and educational at the same time. It contains educational materials, a downloadable graphic novella, zombie preparedness posters and information on how to prepare for a zombie outbreak. More practically however, if someone were to take the steps recommended for a zombie outbreak they would be better prepared for other potential disasters such as an earthquake or hurricane.

The Cornell researchers will present their findings at the 2015 American Physical Society March Meeting in San Antonio, Texas.