just picture what happens when you fill a 2 liter soda bottle with water (or any liquid) and try to pour it all out at once. it comes out in clumps. This means there will be competition, since all the water will try to escape all at once. the fact that there is competition means that there must be more than one seperate entity competing. if there were no spaces between the atoms, the water would all flow out uniformly and consistently. and I suspect, - maybe - , that the time intervals between clumps can be measured by avocadro's number and, in turn, can MEASURE avocadro's number.