From TheTime-Space Continua - an Open Forum:

"Most physicists believe that in any final theory of quantum gravity, space-time itself will be quantised and grainy in nature. Quantum mechanics implies that there is a tiniest measurable scale, called the Planck length, which is 10^-33 centimetres. Likewise, the Planck time is 10^-43 seconds. So the smallest possible volume in four-dimensional space-time, the Planck volume, is 10^-142 cubic centimetre seconds. If we assume that each of these volumes counts a single space-time quantum, this provides a direct quantification of bulk: a space-time volume of one cubic centimetre that lasts for one second is composed of 10^142 space-time elements. This number is large enough to make space-time appear smooth at all scales that we can currently probe experimentally. "