  Cold interacting fermions in two dimensions form exactly solvable Luttinger
liquids, whose characteristic scaling exponents differ from those of
conventional Fermi liquids. We use the AdS/CFT correspondence to discuss an
equivalence between a class of helical, strongly coupled Luttinger liquids and
fermions propagating in the background of a 3D black hole. The microscopic
Lagrangian is explicitly known and the construction is fully embeddable in
string theory. The retarded Green function at low temperature and energy arises
from the geometry very near the black hole horizon. This structure is universal
for all cold, charged liquids with a dual description in gravity.
