  In modern democracies, the outcome of elections and referendums is often
remarkably tight. The repetition of these divisive events are the hallmark of a
split society; to the physicist, however, it is an astonishing feat for such
large collections of diverse individuals. Many sociophysics models reproduce
the emergence of collective human behavior with interacting agents, which
respond to their environment according to simple rules, modulated by random
fluctuations. A paragon of this class is the Ising model which, when
interactions are strong, predicts that order can emerge from a chaotic initial
state. In contrast with many elections, however, this model favors a strong
majority. Here, we introduce a new element to this classical theory, which
accounts for the influence of opinion polls on the electorate. This brings
about a new phase in which two groups divide the opinion equally. These
political camps are spatially segregated, and the sharp boundary that separates
them makes the system size-dependent, even in the limit of a large electorate.
Election data show that, over the last 30 years, countries with more than about
a million voters often found themselves in this state, whereas elections in
smaller countries yielded more consensual results. We suggest that this
transition hinges on the electorate's awareness of the general opinion.
