Mosh pit madness ... it's a gas
Atomic reaction Heavy metal music fans in a mosh pit act like atoms in a gas - a finding that could advance emergency evacuation design and planning.
The study originated when Silverberg took his girlfriend to a heavy metal concert, but in deference to her, stayed out of the mosh pit.
"I saw things happening in the mosh pit that I hadn't noticed before from the inside," he says.
For the study the team, which includes professors James Sethna and Itai Cohen, examined YouTube videos of mosh pits from countries including the US, UK and Australia.
They then used particle imagery velocimetry, which tracks particle speed in fluids, to measure the collective motion of the moshers.
The researchers found the moshers' speed distributions reached the same equilibrium distribution of 2D gases - their seemingly random collisions in mosh pits could be predicted using simple models.
Silverberg says the next issue was to understand why "an inherently non-equilibrium system exhibits equilibrium characteristics".
To answer this question Bierbaum developed a flocking simulation - that describes the collective movement of groups such as birds and fish - and found the behaviour in the mosh pits was consistent with the predictions of this model.
Flocking simulations model living beings as simple particles, reducing complex behavioural dynamics to a few basic rules.
By playing with noise levels and the tendency of moshers to follow their neighbours, their model moved between two phenomena found at heavy metal concerts - the circle pit, where moshers exhibit an "ordered and vortex-like state" and the disordered, gas-like state.
Silverberg says previous research on human collective motion is based on pedestrians walking in lanes.
"If you want to understand what is happening in a riot or protest do you want to use pedestrians or a mosh pit?" he asks.
"Studying how people behave in mosh pits helps us better understand how people will behave in extreme circumstances such as riots, protests and emergencies."
He says further studies of this unique environment could lead to new architectural safety design principles that limit the risk of injury at extreme social gatherings.