THE CROWD AS A LIQUID: an invisible vortex that pulls people in

David Madero. Toro, 2021 / instagram.com

The 20th century is often referred to as the «century of crowds». This definition was given by Serge Moscovici, the author of the theory of social representations. Before him, the phenomenon of the crowd had been explored by psychologist and physician Gustave Le Bon, sociologist Gabriel Tarde, psychoanalyst Sigmund Freud, and others.

Modern science has also contributed to the study of crowd dynamics at a new level of technological development. Crowds are unpredictable and dangerous, which is why scientists are developing strategies to help reduce the risks that arise when large groups of people gather.

ENCIERRO, BULLS AGAINST PEOPLE

n one of the latest studies, the results of which were published in the international journal Nature, scientists focused their research on the massive crowds that gather for the San Fermín festival in the city of Pamplona, the capital of Spain’s Navarre province.

The tradition, dedicated to the commemoration of Saint Fermín, has existed for more than eight centuries. Saint Fermín, a Spaniard by origin, was beheaded in Amiens, France, at the beginning of the 4th century and, over time, became the main patron of Navarre and its Basque inhabitants.

The most important event of the festival is the encierro — the run of twelve enraged bulls from the pen to the arena along the city’s fenced-off streets. Unlike bullfighting, which has been repeatedly condemned by animal rights activists, the encierro does not face an official ban. Although activists protest against it as well, sometimes in exotic forms.

For example, by organizing similar «runs» — but with people instead of bulls.

A DEADLY GAME

In authentic encierro events, people are the most direct participants. Anyone can join — tourist or local, novice or experienced runner. Every day for a week, participants must sprint one kilometer ahead of a herd of bulls. Naturally, it is preferable to survive the run, managing to slip behind the fence before being trampled to death.

As you can imagine, not everyone succeeds. In 1924, bulls trampled and gored more than 200 people. For 13 of them, the games ended in death. Since then, tragedies of that scale have not reoccurred, although encierro still sometimes claims one or several lives.

The emotional intensity of the festival traditionally runs high, often leading participants and spectators to consume alcohol and drugs. Underestimating the risks while intoxicated, tourists tend to suffer the most. Nevertheless, this has done nothing to diminish the encierro’s popularity around the world.

Each year, between one and three million thrill-seekers attend the event.

IS HEMINGWAY TO BLAME?

In 1923, Ernest Hemingway witnessed the San Fermín festival. The running of the bulls in Pamplona gained worldwide fame thanks to his novel The Sun Also Rises, which some publishers occasionally title Fiesta.

This was, in fact, the original working title of the literary work, considered one of the most translated American novels. It carried the subtitle «The Lost Generation» — a phrase Hemingway borrowed from the writer Gertrude Stein.

Thanks to Hemingway, this expression took on a life of its own in world culture. It came to denote a particular type of hero — displaced, wounded by war or emigration, often prone to alcoholism, madness, and suicide.

VORTEX STRUCTURES DISCOVERED IN THE CROWD

If one were to seriously study any crowd, it would certainly make sense to choose one with the extraordinary background of the San Fermín festival. Taking on this fascinating task, scientists discovered that the massive Pamplona crowd was far less chaotic than previously believed. The study revealed a kind of structure within it — dense groups of people formed swirling «vortex patterns».

Such effects had never before been observed in mass human gatherings. The discovery resulted from an analysis of video footage capturing the behavior of the thousands-strong crowd in Pamplona’s Consistorial Square.

Researchers installed cameras on balconies overlooking the square and used computer models to analyze the footage. To understand the behavior of the crowd, they focused on one of its main characteristics — «fluidity». In the model, the crowd behaved like a typical liquid — a dense continuum composed of particles.

HIGH DENSITY CREATES «VORTICES»

This was a groundbreaking idea, as previous crowd models portrayed it as consisting of discrete, individual agents. In the video footage, one can trace how the crowd gradually begins to fill Consistorial Square from early morning. Eventually, it reaches a density of about four people per square meter.

It is at this point that something surprising happens. Once the crowd reaches a critical density, it starts to «twist». At first, this process is almost imperceptible. Then it gradually accelerates — swirling «vortices» begin to form within the crowd, each encompassing hundreds of people.

These vortex structures start pushing against one another. When maximum density is reached — 9 people per square meter — the period of vortex rotation increases, reaching up to 18 seconds. However, the movement is so slow that participants’ consciousness does not register it.

Most likely, they have no idea they are moving in a circle.

CAN A CROWD BECOME «SAFE»?

The work on the Pamplona project took French physicists from the École Normale Supérieure in Lyon for more than a month. The vortex patterns were discovered almost by accident: they were not visible in regular footage but became clearly noticeable in time-lapse videos.

It is worth noting that safety was not the primary focus of the study. However, the scientists believe that new findings in crowd dynamics could help event organizers prevent potentially fatal stampedes. Especially since the Pamplona crowd is not unique.

Physicists observed similar patterns while studying footage of other crowds — notably the Love Parade disaster, which occurred in 2010 in Duisburg, Germany. During that tragedy, a stampede at a massive music festival claimed the lives of 21 people.

Original research: