Lessons from PHOBOS

In June 2005 the PHOBOS Collaboration completed data taking at RHIC. In five years of operation PHOBOS recorded information for Au+Au at , 62.4, 130, and , Cu+Cu at 22.4, 62.4 and , d+Au at , and p+p at 200 and , altogether more than one billion collisions. Using these data we have studied the energy and centrality dependence of the global properties of charged particle production over essentially the full 4π solid angle and (for pions near mid rapidity) charged particle spectra down to transverse momenta below . We have also studied correlations of particles separated in pseudorapidity by up to 6 units. We find that the global properties of heavy ion collisions can be described in terms of a small number of simple dependencies on energy and centrality, and that there are strong correlations between the produced particles. To date no single model has been proposed which describes this rich phenomenology. In this talk I summarize what the data is explicitly telling us.