We are now departing on a voyage to the very sources of the river of time. What was it that happened at the very beginning of time? What triggered the expansion of the Universe?

We have seen in the chapter ‘Towards the sources of the river of time’ that the huge pressure of hot matter at time zero cannot be the cause of the high velocities of recession of matter, because the uniform Universe has no pressure drop, which is the only cause of force driving an expansion. What then was the cause of the expansion?

The key to understanding the ‘primeval push’ lies in the existence of the special vacuum-like state of matter at high densities and temperatures.

We have already looked at several vacuum-like states in the chapter dealing with Grand Unification. Theorists believe that a unique vacuum-like state with enormous energy density and the corresponding gigantic mass density is formed at the temperature of ‘superunification’. This density in grams per cubic centimeter is written as unity with ninety four zeros (!). The enormity of this number defies imagination. We have already mentioned in the preceding chapter that any vacuum possessing non-zero mass density must have huge negative pressure.

In accordance with Einstein's theory of gravitation, gravitation is produced not only by mass but by pressure as well. Pressure is usually not high and so the gravitation connected with it is negligibly small.