1.1.7. Einstein's Biggest Blunder?

Einstein also realized that, since gravitation is a universally attractive force, the universe is unstable to collapse. Newton, of course, realized this as well and postulated that the Universe must be infinite in extent to avoid collapse. Einstein's method to avoid universal collapse was to postulate the existence of another field which acts as a repulsive force. In the field equations, this can be identified with a term that represents vacuum energy and acts as a source of negative pressure in the universe. This source of pressure prevents the Universe from collapsing through an effective repulsive force which grows with distance. In this way, gravitational and repulsive forces are balanced. However, this balance is on a point of unstable equilibrium. A slight perturbation in either direction would send the Universe either into a state of terminal collapse or expansion. The possibility that the Universe was expanding on its own, without being assisted by Vacuum Energy Fields, was not considered by Einstein. The observational discovery of universal expansion by Edwin Hubble would come a few years later and would prompt Einstein to consider his vacuum energy term his "Greatest Blunder". Ironically, it will later turn out in this book that re-invoking the existence of this Vacuum Energy Field, may be the solution of some of out most profound current cosmological problems.