  The theory of echo chambers, which suggests that online political discussions
take place in conditions of ideological homogeneity, has recently gained
popularity as an explanation for patterns of political polarization and
radicalization observed in many democratic countries. However, while
micro-level experimental work has shown evidence that individuals may gravitate
towards information that supports their beliefs, recent macro-level studies
have cast doubt on whether this tendency generates echo chambers in practice,
instead suggesting that cross-cutting exposures are a common feature of digital
life. In this article, we offer an explanation for these diverging results.
Building on cognitive dissonance theory, and making use of observational trace
data taken from an online white nationalist website, we explore how individuals
in an ideological 'echo chamber' engage with opposing viewpoints. We show that
this type of exposure, far from being detrimental to radical online
discussions, is actually a core feature of such spaces that encourages people
to stay engaged. The most common 'echoes' in this echo chamber are in fact the
sound of opposing viewpoints being undermined and marginalized. Hence echo
chambers exist not only in spite of but thanks to the unifying presence of
oppositional viewpoints. We conclude with reflections on policy implications of
our study for those seeking to promote a more moderate political internet.
