Figure 1.
Critical length scales for some of the key inventions from the history of humanity. A shift across this scale towards ever smaller dimensions paralleled the advancement of humanity from the stone age to the modern age. Hence, as the products of the most sophisticated technologies of the day progressed from prehistoric huts, cutting tools and garments to modern musical instruments, automobiles and mechanical clocks to computers, nanocopters and nanomotors, the critical lengths shifted from millimeter to micrometer to nanometer scale, respectively.