In his paper of 1927, Heisenberg was careful to point out that the
inescapable uncertainties px and x do not arise from imperfections in
practical measuring instruments. Rather, they arise from the need to use
a large range of wavenumbers, k, to represent a matter wave packet localized in a small region, x. The uncertainty principle represents a sharp
break with the ideas of classical physics, in which it is assumed that,
with enough skill and ingenuity, it is possible to simultaneously measure a
particle’s position and momentum to any desired degree of precision. As
shown in Example 5.8, however, there is no contradiction between the
uncertainty principle and classical laws for macroscopic systems because of
the small value of .