  We present measurements of elliptic flow and event-by-event fluctuations
established by the PHOBOS experiment. Elliptic flow scaled by participant
eccentricity is found to be similar for both systems when collisions with the
same number of participants or the same particle area density are compared. The
agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence
that the matter is created in the initial stage of relativistic heavy ion
collisions with transverse granularity similar to that of the participant
nucleons. The event-by-event fluctuation results reveal that the initial
collision geometry is translated into the final state azimuthal particle
distribution, leading to an event-by-event proportionality between the observed
elliptic flow and initial eccentricity.
