When a meme becomes popular, we often say that it has gone “viral”. This word suggests that memes become popular by being particularly infectious. In analogy to epidemics, a particularly viral meme hits a critical threshold where it just won’t die, because each new infection spreads it to even more people. But is this epidemic model actually true?
A paper titled “The Structural Virality of Online Diffusion” puts into question the very idea that popular memes are viral. They point out another mechanism by which memes can become popular: the broadcast. Rather than infecting multiple generations of followers, a meme may become popular simply by infecting one person with a lot of followers.
Figure 1 from the paper. The tree on the left illustrates a broadcast, while the one on the right illustrates viral spreading.
The paper considers a massive amount of Twitter data to determine whether the most popular links are broadcast-like or virus-like. On average, they more resemble broadcasts, but there is a huge amount of variation.