  Whether a spin-1/2 Fermi gas will become ferromagnetic as the strength of
repulsive interaction increases is a long-standing controversial issue.
Recently this problem is studied experimentally by Jo et al, Science, 325, 1521
(2009) in which the authors claim a ferromagnetic transition is observed. This
work is to point out the results of this experiment can not distinguish whether
the system is in a ferromagnetic state or in a non-magnetic but strongly
short-range correlated state. A conclusive experimental demonstration of
ferromagnetism relies on the observation of ferromagnetic domains.
