"Owing to departures from strict homogeneity, the actual world cannot be exactly of Einstein's form. The instability of Einstein's universe indicates that in general, a system which is nearly, but not exactly, of this form will tend to depart further and further from it with lapse of time. Consequently, Einstein's model cannot permanently represent the smoothed-out universe of nebulae. It is possible, or course, that the actual universe was much closer to this model in the remote past than it is now. ...It has even been suggested that the Einstein configuration was an unstable equilibrium state through which the universe slowly passed in expanding from an initial 'explosive' phase of small volume and high density."