  The online echo-chamber effect is a phenomenon in which beliefs that are far
from common sense are strengthened within relatively small communities formed
within online social networks. Since it is significantly degrading social
activities in the real world, we should understand how the echo-chamber effect
arises in an engineering framework to realize countermeasure technologies. This
paper proposes a model of the online echo-chamber effect by introducing the
concept of spontaneous symmetry breaking to the oscillation model framework
used for describing online user dynamics.
