  We introduce a 2-state opinion dynamics model where agents evolve by majority
rule. In each update, a group of agents is specified whose members then all
adopt the local majority state. In the mean-field limit, where a group consists
of randomly-selected agents, consensus is reached in a time that scales ln N,
where N is the number of agents. On finite-dimensional lattices, where a group
is a contiguous cluster, the consensus time fluctuates strongly between
realizations and grows as a dimension-dependent power of N. The upper critical
dimension appears to be larger than 4. The final opinion always equals that of
the initial majority except in one dimension.
