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Assume a spherical zombie…

<img alt=“zombie two.jpg” src=“” width=“239” height=“210” align=“right” border=0 hspace=“10px”/>Not so much following hot on the heels of the recent study on the spread of zombie infections, more shambling slowly and slightly aimlessly in pursuit, we have some new undead science for you.

But Davide Cassi, a physicist at the Università di Parma in Italy, might be slightly surprised to read this morning that he has published a paper about zombies. Cassi’s paper in Physical Review E – entitled Target annihilation by diffusing particles in inhomogeneous geometries – is actually about how long immobile targets will survive when they are being annihilated by “a population of random walkers”.

As he notes, this is of use to researchers exploring subjects such as how surface catalysts become ‘poisoned’ by molecules attaching to the catalysis sites (where your ‘immobile target’ is the catalyst site and your ‘random walker’ is the molecule sticking to it and not letting go).

This paper has now been press released with a zombie spin:

Though the paper itself does not specifically refer to fleeing from zombies, it describes “the survival probability of immobile targets annihilated by random walkers.” The conclusions suggest that the people trapped in a mall in “Dawn of the Dead” may be better off than the folks stuck in a farmhouse in “Night of the Living Dead.”

This is something of a stretch. First, it assumes that the potential zombie victim is immobile. Second, it assumes the zombies are engaging in a random walk, rather than their more normal behaviour of pursuing directly their next tasty brain. In other words, it’s rather reminiscent of the old joke about physicists assisting with milk production.

Still, if you happen to be chained to a wall and surrounded by randomly walking zombie you should hide in the mall not the farmhouse. Oh wait, you can’t get there: you’re chained to a wall.

Image: Mark Marek Photography.


  1. Report this comment

    James said:

    I agree, it’s a bit of a stretch to interpret the paper that way, but it sounds like you haven’t seen enough zombie movies. My favorite, Sean of the Dead, has zombies that act just like random walkers. The zombies in “I am Legend” are way too intelligent for my taste, and Cassi’s work wouldn’t apply there. Based on the ads for Zombieland, I’d guess those are more of the random walker type – that seems to work best for comedies.

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    Daniel said:

    James, I’m not sure that the zombies in Shaun of the Dead can be construed as random walkers. They actively pursue the protagonists and besiege them in a pub if my memory serves, that’s hardly random behaviour. If zombies were truly random walkers they wouldn’t be very scary, just a minor annoyance.

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    Oliver said:

    Whenever I walk at random I end up in a pub, too, but maybe that’s just me

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    james said:

    Don’t you remember the scene Shaun of the Dead where the people left the pub and, as long as they acted like zombies, the real zombies left them alone? The zombies all wandered about aimlessly. It wasn’t until the humans did something un-zombie like that the zombies pursued them. If there are no identifiable humans in range, they’re simply random walkers. Cassi’s particles do the same thing – they move randomly until a target particle is within range. The range around Cassi’s particles is basically the diameter of the particles. The range for Shaun of the Dead zombies is anyone within sight (who is acting human anyway). It’s a large range, of course, but that wouldn’t change Cassi’s math, it’s just like modeling interactions among larger diameter particles.

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    Daniel said:

    My reading of the paper was that – for this analogy to work – the zombies would have to physically bump into the (uninfected) human. Cassi’s particles can’t detect a possible reaction site at range and then move towards it.

    Either way, the characters in Shaun of the Dead are not immobile. They do eventually leave the pub…

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    james said:

    Ahhh, that’s the point exactly! Should they hide in the pub as the zombies walk randomly about outside? No, because the pub is not labyrinth-like enough and they would eventually be eaten when one of the undead stumbled upon a way in. They should have stayed in Shaun’s girlfriend’s apartment, which was much more labyrinth-like (considering how many steps you’d have to get right to make it up there). But then there wouldn’t have been much of a movie.

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