  Information avalanches in social media are typically studied in a similar
fashion as avalanches of neuronal activity in the brain. Whereas a large body
of literature reveals substantial agreement about the existence of a unique
process characterizing neuronal activity across organisms, the dynamics of
information in online social media is far less understood. Statistical laws of
information avalanches are found in previous studies to be not robust across
systems, and radically different processes are used to represent plausible
driving mechanisms for information propagation. Here, we analyze almost 1
billion time-stamped events collected from a multitude of online platforms --
including Telegram, Twitter and Weibo -- over observation windows longer than
10 years to show that the propagation of information in social media is a
universal and critical process. Universality arises from the observation of
identical macroscopic patterns across platforms, irrespective of the details of
the specific system at hand. Critical behavior is deduced from the power-law
distributions, and corresponding hyperscaling relations, characterizing size
and duration of avalanches of information. Neuronal activity may be modeled as
a simple contagion process, where only a single exposure to activity may be
sufficient for its diffusion. On the contrary, statistical testing on our data
indicates that a mixture of simple and complex contagion, where involvement of
an individual requires exposure from multiple acquaintances, characterizes the
propagation of information in social media. We show that the complexity of the
process is correlated with the semantic content of the information that is
propagated. Conversational topics about music, movies and TV shows tend to
propagate as simple contagion processes, whereas controversial discussions on
political/societal themes obey the rules of complex contagion.
