Statistical mechanics reveals the ideal hideout; and informs real
disease modeling
American Physical Society, Science
Daily
A team of Cornell University researchers focusing on a fictional
zombie outbreak as an approach to disease modeling suggests heading for the
hills, in the Rockies, to save your brains from the undead.
Reading World War Z, an oral history of the first zombie war,
and a graduate statistical mechanics class inspired a group of Cornell
University researchers to explore how an "actual" zombie outbreak
might play out in the U.S.
Why model the mechanics of zombies? "Modeling zombies takes
you through a lot of the techniques used to model real diseases, albeit in a
fun context," says Alex Alemi, a graduate student at Cornell University.
Alemi and colleagues' work offers a nice introduction to disease
modeling in general, as well as some techniques of statistical physics for
measuring second-order phase transitions. "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," points out Alemi.
All told, the project was an overview of modern epidemiology
modeling, starting with differential equations to model a fully connected
population, then moving on to lattice-based models, and ending with a full
U.S.-scale simulation of an outbreak across the continental U.S.
It involved a lot of computational results generated from
simulations the researchers wrote themselves. "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," Alemi explains.
The project's large-scale simulations are stochastic in nature,
meaning that they have an element of randomness.
"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 says.
In most films or books, "if there is a zombie outbreak, it
is usually assumed to affect all areas at the same time, and some months after
the outbreak you're left with small pockets of survivors," explains Alemi.
"But in our attempt to model zombies somewhat realistically, it doesn't
seem like this is how it would actually go down."
Cities would fall quickly, but it would take weeks for zombies
to penetrate into less densely populated areas, and months to reach the
northern mountain-time zone.
"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," he
elaborates. "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."
If you somehow happen to find yourself in the midst of a
fictional zombie outbreak and want to survive as long as possible, Alemi
recommends making a run for the northern Rockies. While not an entirely
practical implication, it's "fun to know," he says, and points out
the benefits of applying hard science to fun topics--especially to help make
learning more entertaining and enjoyable.
"A lot of modern research can be off-putting for people
because the techniques are complicated and the systems or models studied lack a
strong connection to everyday experiences," Alemi adds. "Not that
zombies are an everyday occurrence, but most people can wrap their brains
around them."
What's next for Alemi and colleagues? "Given the time, we
could attempt to add more complicated social dynamics to the simulation, such
as allowing people to make a run for it, include plane flights, or have an
awareness of the zombie outbreak, etc.," he notes.
Story Source:
The above story is based on materials provided by American Physical Society. Note: Materials may be
edited for content and length.
Cite This Page:
American Physical Society. "Zombie outbreak? Statistical
mechanics reveals the ideal hideout; and informs real disease modeling." Science Daily,
27 February 2015. <www.sciencedaily.com/releases/2015/02/150227112753.htm>.
