Could a dire new infection sweep the world in a matter of weeks? Might the disease be so strange it alters the behaviour of people beyond recognition, making them predatory and fearless?
World War Z, the latest Brad Pitt action thriller, is premised on these disturbing possibilities, and there's a seed of science in them. The film is loosely based on a book by Max Brooks, history major and son of film director Mel Brooks.
The terror of a zombie plague is deftly realised in this film. The plot centres around seemingly inexorable logic: infection deletes personalities and creates zombies, infected individuals infect others faster than they can be killed, and the infected have lost all self-preservation intent, so can't be awed or reasoned into stopping their destruction of humanity.
The chilling idea that a single bite can transform loved individuals into automata intent only on transmitting the infection, is reflected in some real illnesses, some of which we can't always cure.
Rabies may be transferred by a bite and cause mania, violence, brain damage and death, and can be transferred from animals to humans.
The toxoplasma virus in mice causes them to become fearless, get near cats and get eaten. Other diseases that attack human brain tissue and can change behaviour and apparent personality include neurosyphilis and CJD (Creutzfeldt-Jakob disease) - the human form of mad cow disease.
Director Marc Forster has created a film that juxtaposes the personal scale with that of cataclysms of nature - lead character Gerry Lane (Pitt) reluctantly leaves his family, using all the skill and judgment he learned as a former UN operative to combat a threat that is biological but mindless. And again in scenes of zombies running and flowing up and over a giant wall like a river of ants, indifferent to their personal survival, using each other's fallen bodies as a self-growing ladder.
These two themes: critical personal choices by individuals, versus mass behaviour, are reflected in the existing mathematical literature modelling zombie attack - yes, such literature does exist.
The paper, When Zombies Attack!: Mathematical Modelling of an Outbreak of Zombie Infection, by an Ottawa-based Australian mathematician and his students, defined the genre when they applied standard mathematical disease-modelling techniques to a hypothetical zombie plague.
In that model, infected and non-infected persons contact and infect each other at random, at a rate which, in context, determines the demise or survival of the human race. A follow-up book due next year includes articles by a range of academics and explores different scenarios via mathematical modelling techniques that take into account human agency, skill and choices, leading to different outcomes.
Both mathematics and films allow us to explore the world of what might be. The power of the human imagination, supported by the insights provided by mathematics and computer simulation, allows us to plan and prepare for the future, including major threats.
Mathematical modelling is routinely used to estimate the effectiveness of different plans for vaccination, medication, education programmes, in extreme cases quarantine, and other strategies used to try to control deadly diseases such as tuberculosis.
The maths of zombies turns out to be not so different to that arising in the analysis of any infectious disease, with three main possible outcomes. There's the chance that the disease infects every member of the population. There's the chance that the disease dies out because of death or cure of the hosts. And the third possibility is that rates of transmission and death or cure balance in such a way that the disease persists in the population without overwhelming it.
The original Zombies Attack paper showed how the chances of the survival of humanity vary based on whether interventions such as quarantine, treatment or impulsive eradication are available.
In the film, we follow Pitt's character as he seeks the origin and cause of the outbreak, in the hope he'll find an insight that can be used for humanity to survive.
In a real plague, could we rely on a hero emerging to bring us the insight we would need to survive? Understanding is seldom achieved quickly: it is more often built up slowly by many people working on the same problem from different points of view.
Might we be better placed to invest now in understanding all the vagaries of nature including our own human nature? World War Z has a strong enough premise behind it to give us pause to think.
• Judy-Anne Osborn is a lecturer in mathematics at the University of Newcastle.