What is underneath the social self-organization of large human crowds clapping in unison?
When large groups clap chaotically (and not synchronized) — i.e. right after a good performance has ended — they clap quickly.
Thus, in order to clap together, they must clap slower which leads to a necessary doubling of the signal period.
However, as the audience gradually decreases the period (clapping faster) to increase the average noise intensity (to express their enthusiasm for the performance, theoretically) the combined signal slips back into fast-clapping mode — with a larger dispersion of frequencies — making it impossible to maintain synchronization.
Thus, people must know that they need to slow down their clapping in order to achieve it
The authors posit that this is why synchronized clapping is a daily event in more homogenous eastern-European countries, while it happens much less often in other parts of the world.
Often when the roar of a crowd clapping will suddenly become synchronized.
This paper explains the dynamics of this phenomenon
To do so they tested placed a microphone on the ceiling of several theatre and opera performances in Romania and Hungary
Typically after a few seconds of incoherent clapping a periodic signal develops (Fig1A)
Interestingly, we find that the increase in amplitude leads to a decrease in average noise intensity (Fig1D)
To understand the origin of this conflict they record and analyze the sound created by an unaware group of individuals (Fig1B)
By correlating these two signals they learn that:
The decrease in the average noise intensity is therefore a consequence of the period doubling, because there is less clapping per unit time.
However, the decreasing clapping period gradually brings the synchronized clapping back to the fast clapping heard in the early asynchronous phase, and synchronization disappears.
It seems the conflicting desire of the audience simultaneously to increase the average noise intensity and to maintain synchronization leads to the sequence of appearing and disappearing synchronized regimes.
These results indicate that the transition from random to synchronized clapping is accompanied by a period-doubling process.
In order to test if this is a necessary condition for synchronization they asked students to clap in two different ways:
The two modes of clapping clearly display separated frequencies and the average period doubles from mode I to mode II (Fig. 1F).
Importantly, the width of the frequency distribution and the relative dispersion of mode II clapping is considerably smaller (Fig. 1G)
This result was also reproducible for a single individual
Notes by Matthew R. DeVerna