Modeling Gravitational Clustering without Computing Gravitational Force

The large-scale structure in the Universe is believed to arise out of smallrandom density perturbations generated in the very early Universe, that areamplified by gravity. Large and usually intricate N-body simulations aretypically employed to model the complex nonlinear dynamics in a selfgravitating medium. We suggest a very simple model which predicts, on largescales, the correct density and velocity distributions. The model does notinvolve an explicit computation of the gravitational force. It is based on asimple transformation of the variables and local conservation laws of mass and{\it generalized} linear momentum. The model demonstrates that the overallappearance of large-scale structure in the Universe is explicitly determined bythe initial velocity field and it reveals the most significant large-scaleeffects of gravity on the formation of structure.Comment: Latex file (needs, epsf.sty, aaspp4.sty); postscript figures; 10 pages (including figures); To appear in ApJ Letter