The spread of disease has always followed a clear pattern. The outbreak begins at a specific place and time and then spreads in a wavelike pattern away from the source.
The speed of this wave is governed by the methods of travel. Historical records show that the Black Death traveled across Europe at about two kilometers a day. This spread of this particularly virulent form of bubonic plague that killed between 35 and 200 million in the 14th century was limited by the transport that was then available.
But something strange happened in the 20th century, when that wavelike form of spreading seemingly vanished. Air travel suddenly allowed diseases to jump from one continent to another at breakneck speed. However, network theorists found they could restore the wavelike nature of the spread if they account for the speed of travel. By normalizing the spread in this way, a wavelike spreading pattern reemerges.
Social phenomenon, such as songs, tweets, videos, and so on, are thought to spread in a similar way. And because this happens from person to person through a social network, it should follow a wavelike spreading pattern.
But observing this pattern is hard because the geographical spread of information is distorted by the social media networks along which it moves. And that raises the question of whether it is really wavelike or fundamentally different.
To solve this conundrum, network scientists would dearly love to have an emblematic example of the way a specific piece of information has spread across the globe in a measurable way.
Today, Zsofia Kallus and pals at Eotvos University in Budapest, Hungary, say they have found just such an example in the way that Psy’s Gangnam Style video spread across the globe in 2012, eventually becoming the first to receive over a billion views on YouTube. And the team say it is possible to recover the unique wavelike signature of information spreading, providing they properly take account of the social networks involved.
The story behind this video pandemic is extraordinary. This music video was produced in a style known as k-pop by a South Korean musician called Psy, who was relatively unknown outside his home country. It was released on July 15, 2012, and immediately become popular in South Korea.
But since Psy was unknown outside the country, the video’s later success was hard to predict. By December 21, 2012, however, the video had become the most viewed in history when it reached a billion views of YouTube across the globe. “In 2012, the record breaking ‘Gangnam Style’ marked the appearance of a new type of online meme, reaching unprecedented level of fame despite its originally small local audience,” say Kallus and co.
Just how this happened is the focus of Kallus and co’s work. To do this, they tracked the spread of the video by searching the historical Twitter stream for geolocated tweets that mention “Gangnam Style.” “Location information allows us to record the approximate arrival time of a certain news to a specific geo-political region,” say Kallus and co.
That reveals the way the video spread, initially to the Philippines and from there to the rest of the world. That’s probably because the Philippines is relatively close to South Korea but has stronger links to the rest of the world through its diaspora. It also has stronger English language links.
But none of that reveals the classic wavelike pattern that epidemiologists expect when viral events occur. Indeed, the spread of the video when plotted against geographic distance from South Korea looks more or less random.
That’s because geographic distance is not the key factor in the spread of information over social networks. That depends instead on the strength of links from one area to another—places that have lots of social ties are likely to receive information more quickly than those that have weak ties.
And indeed, that’s exactly what Kallus and co find. And that points to a way of replacing the geographic distance with an effective distance that captures the speed at which information can spread between them. Once Kallus and co do that—replace the geographic distance with this effective distance—the expected wavelike pattern emerged.
They are even able to cross check this pattern by searching Google Trends for the phrase “Gangnam Style” to see when people first searched for it in different parts of the world. Sure enough, the Google Trends results exactly match those from Twitter.
That’s interesting work that shows how the spread of modern memes occurs in just the same way as ancient diseases. So the “Gangnam Style” video pandemic spread in exactly the same way as bubonic plague!
That’s not really a surprise. But it does confirm the extraordinarily deep link between the physical world and the world of pure information. Just why these seemingly different things—matter and information—share these similar behaviors is not clearly understood. But it does provide ample reason for further investigation.
Ref: arxiv.org/abs/1707.04460: Video Pandemics: Worldwide Viral Spreading of Psy's Gangnam Style Video