Werner Heisenberg's uncertainty principle, formulated in 1927, states that a small bit of matter--an electron, for example--cannot have both a well-defined position and a well-defined momentum at the same time. What's more, measuring one of those properties inexorably disturbs it--you can never know what an electron's position was before you measured it, because the act of measurement changes its position. Dime-store philosophers have had a field day with this concept, using it to explain all manner of things. Pundits have been known to maintain, for example, that since the presence of a reporter exerts an influence on the people being observed, the journalistic endeavor is an example of the uncertainty principle. But in practice, Heisenberg's principle only applies to the subatomic world.