Video: Mosh pit simulation recalls random motion in gases
Metalheads in mosh pits act like atoms in a gas. Thatâs the conclusion of the first study of the collective motion of people at a rock concert.
The finding could add to the realism of computer-generated crowd scenes in films and games.; More importantly, it could help architects design buildings that ease the flow of chaotic crowds in an emergency.
Research into how humans behave in crowds had mostly been limited to fairly organised situations, like pedestrians forming lanes when walking on the street. But when , a graduate student at Cornell University in Ithaca, New York, took his girlfriend to her first heavy metal concert a few years ago, he witnessed a different and surprising form of crowd behaviour.
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âI didnât want to put her in harmâs way, so we stood off to the side,â he says. âIâm usually in the mosh pit, but for the first time I was off to the side and watching. I was amazed at what I saw.â
Metal fansâ favoured and mostly involves bodies slamming into each other. Silverberg wondered if the mathematical laws that describe group behaviour in flocks of birds or schools of fish could apply to moshers as well.
Like a random gas
Together with another grad student and two physics professors at Cornell, he pulled videos of mosh pits off YouTube and used software developed for analysing particles in a fluid to track the moshersâ motions. They found that the dancersâ speeds had the . Such particles move around freely, interacting only when they bounce off one another.
âThis presented a bit of a mystery,â Silverberg says. What makes a crowd of people with independent decision-making powers behave like a random gas?
To investigate, the team simulated a mosh pit with a few basic rules: the virtual moshers bounce off each other when they collide (instead of sticking or sliding through each other); they can move independently; and they can flock, or follow each other, to varying degrees. Finally, the team added a certain amount of statistical noise to the simulated moshersâ movements â âto mimic the effects of the inebriants that the participants typically useâ, says co-author Matthew Bierbaum.
They found that by tweaking their model parameters â decreasing noise or increasing the tendency to flock, for instance â they could make the pit shift between the random-gas-like moshing and a circular vortex called a circle pit, which is exactly what they saw in the YouTube videos of real mosh pits. .
âThese are collective behaviours that you wouldnât have predicted based on the previous literature on collective motion in humans,â Silverberg says. âThat work was geared at pedestrians, but what weâre seeing is fundamentally different.â
âThe fact that human beings are very complex creatures, and yet we can develop a lifeless computer simulation that mimics their behaviour, really tells us that weâre understanding something new about the behaviour of crowds that we didnât understand before,â says co-author .
Lane formation
The team also found a third mosh-pit mode that they hadnât seen on YouTube, which they call lane formation. âIf you increase the flocking or decrease the density of the simulated moshers, the active participants can break down the circle and just stream through the crowd,â Bierbaum says. âIâd be excited to see this, but it would have to be at a very large venue, so that the ends didnât collide with each other to form a circle pit.â
Although the project was mostly for fun, the researchers think it could have real-world implications for crowd animators and architects.
âWhen you have earthquakes or buildings on fire, people tend to panic when they escape. We donât have a good way of experimentally seeing whatâs going on,â Silverberg says. âBy going to these heavy-metal concerts, weâre able to ethically and safely observe how humans behave in these unusual excited states.â
âThatâs how we justify it after the fact, by talking about safety,â Sethna adds.
The correlation between moshers and random gases âseems very fitting to meâ, says Jon Freund, drummer in Ithaca-based metal band Thirteen South. âItâs kind of the same thing â a pure expression of energy thatâs just random.â
But he says knowing the physics behind it wonât change how he moshes â mostly because these days he stays out of the pit. âIâm a hide-on-the-stage-and-play-my-drums mosher,â he admits. âI donât want to get hit in the head.â
Silverberg notes that the studyâs main limitation was the quality of the data. âYouTube videos are typically shaky and taken from a poor viewing angle,â he says. Whatâs more, staff at venues âtend to baulk when you walk in with a cameraâ. He hopes to convince at least one venue to let him film with a camera suspended over the crowd. âThere really is so much to do and so much we donât know yet. Itâs really just beginning.â
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