I was thinking about the principle of energy density and how sharp knives cut so easily because their surface areas are tiny and thus any force applied to them is imparted on this tiny area. So my question arises, does anyone know just how sharp the sharpest knife/ sword is? Lets no discuss microscopic knives, but rather macroscopic cutting instruments such as samurai swords. I would make a wild guess at a surface width of 10 microns, am I crazy? ** Mod note: there are now modern nanoblade surgical knives that cost hundreds of thousands of dollars.