  Recently a simple military exercise on the Internet was perceived as the
beginning of a new civil war in the US. Social media aggregate people around
common interests eliciting a collective framing of narratives and worldviews.
However, the wide availability of user-provided content and the direct path
between producers and consumers of information often foster confusion about
causations, encouraging mistrust, rumors, and even conspiracy thinking. In
order to contrast such a trend attempts to \textit{debunk} are often
undertaken. Here, we examine the effectiveness of debunking through a
quantitative analysis of 54 million users over a time span of five years (Jan
2010, Dec 2014). In particular, we compare how users interact with proven
(scientific) and unsubstantiated (conspiracy-like) information on Facebook in
the US. Our findings confirm the existence of echo chambers where users
interact primarily with either conspiracy-like or scientific pages. Both groups
interact similarly with the information within their echo chamber. We examine
47,780 debunking posts and find that attempts at debunking are largely
ineffective. For one, only a small fraction of usual consumers of
unsubstantiated information interact with the posts. Furthermore, we show that
those few are often the most committed conspiracy users and rather than
internalizing debunking information, they often react to it negatively. Indeed,
after interacting with debunking posts, users retain, or even increase, their
engagement within the conspiracy echo chamber.
