"The collective mood is influenced by the combination of loud, fast music, synchronized with bright flashing lights, and frequent intoxication." What the science behind mosh pits can tell us about human behaviour

Ever wondered about the physics of mosh pits and circle pits?

If so, you're not alone, because earlier this week, Max Sebastian, a subscriber to the podcast The Rest Is Science, posed a question for hosts Hannah Fry and Michael Stevens on this very subject. He asked, "Can you talk a bit about mosh pits and fluid dynamics, and how that links to crowd safety at large concerts?"

Before answering the question, mathematician Fry referenced an academic paper published by Cornell University in 2013 titled Collective Motion of Humans in Mosh and Circle Pits at Heavy Metal Concerts. The paper, authored by Jesse L Silverberg, Matthew Bierbaum, James P Sethna and Itai Cohen from the Department of Physics and Laboratory of Atomic and Solid State Physics at the New York-based university, drew comparisons between 'moshers' and the behaviours of particles.

"What they did," Fry explains, "is they attended a number of heavy metal concerts, and also watched videos of them on the internet, and it is written as a proper academic paper would be."

The paper reads: "Here, we study large crowds (102–105 attendees) of people under the extreme conditions typically found at heavy metal concerts. Often resulting in injuries, the collective mood is influenced by the combination of loud (130 dB), fast (blast beats exceeding 300 beats per min) music, synchronized with bright flashing lights, and frequent intoxication."

"What a way to distill the joy of a good night out with your friends," Fry laughs, later revealing that she is "very much not a mosh pitter".

"Anyway, here's the thing," she continues. "f you stop thinking of people as people and you start thinking of them as particles, actually what you see in mosh pits is this behaviour that is common across sort of systems of fluids essentially.

"Each person effectively is like a particle, right? They're propelled.... they're constantly colliding, and they're reacting to what's going on around them locally, not the whole global system. They're not all following a series of rules, they're just reacting to what's going on around them. So these physicists, what they did is they made this mathematical model, this computer simulation - adorably good sense of humour here - they called it the Mobile Active Simulated Humanoids model, otherwise known as Mashers.

"There are two different tendencies that people have when they're in this sort of crowd situation," Fry continues. "Either we tend to copy what people are doing around us, flocking behaviour, which is what you get when you see big flocks of birds where they're sort of copying the average speed and direction of their neighbours. And humans are doing the same thing, right, if the crowd is moving in a particular direction, we tend to copy what's going on immediately around us.

"But then we also you have sort of more random, unpredictable movement when we're acting as an individual. You know, say somebody spots a friend, or whatever it might be. And what they found is that actually these mosh pits, they do have this gas-like state. They essentially form the same patterns that you would see if you were looking at a box of atoms, this sort of disordered gas, the Maxwell Boltzman distribution is what it's known, but people are sort of pinging around from each other in this in this disordered way.

"But then when you get more people going in, people organise into this vortex-like state, this sort of circular motion, that you see precisely as you do in fluids, where people are sort of rotating with the audience, and this is like something... these circle pits that emerge from nowhere, it's this emergent property, nobody ever says like, 'Okay, off you go, start rotating in this direction!'

"These are people with their own personal wills and they haven't organised any of these patterns," Stevens interjects.

"No, it's just something that happens when you stop behaving like people. and start behaving like particles," Fry concludes.

Watch the explanation from the 3 minutes 45 seconds point of the podcast.

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If you've any further questions, please direct them to the good people at The Rest Is Science, not us, because we'll have as many questions as you, tbh.