  We will show how both elliptic and radial flow generated during the first
fm/c at RHIC can be expressed in a form which is quasi-independent of the state
of matter and depends only on the initial energy density profile. Descriptions
based on partons or classical fields, thermalized or highly anisotropic, all
lead to the same collective velocity given a few easily satisfied conditions.
This significantly narrows the uncertainty for initializing hydrodynamic
prescriptions.
