  In this paper, we bring together our efforts in identifying and understanding
nonequilibrium phase segregation driven by active processes in the living cell,
with special focus on the segregation of cell membrane components driven by
active contractile stresses arising from cortical actomyosin. This also has
implications for active segregation dynamics in membraneless regions within the
cytoplasm and nucleus (3d). We formulate an active version of the Flory-Huggins
theory that incorporates a contribution from fluctuating active stresses. Apart
from knitting together some of our past theoretical work in a comprehensive
narrative, we highlight some new results, and establish a correspondence with
recent studies on Active Model B/B+. We point to the many unusual aspects of
the dynamics of active phase segregation, such as (i) anomalous growth
dynamics, (ii) coarsening accompanied by propulsion and coalescence of domains
that exhibit nonreciprocal effects, (iii) segregation into mesoscale domains,
(iv) emergence of a nonequilibrium phase segregated steady state characterised
by strong macroscopic fluctuations (fluctuation dominated phase ordering
(FDPO)), and (v) mesoscale segregation even above the equilibrium Tc. Apart
from its implications for actively driven segregation of binary fluids, these
ideas are at the heart of an Active Emulsion description of the lateral
organisation of molecules on the plasma membrane of living cells, whose full
molecular elaboration appears elsewhere.
