  To understand the foundations of quantum mechanics, we have to think
carefully about how theoretical concepts are rooted in -- and limited by -- the
nature of experience, as Bohr attempted to show. Geometrical pictures of
physical phenomena are favored because of their clarity. Quantum phenomena,
however, do not permit them. Instead, the historical and dynamical aspects of
description diverge and must be expressed in different but complementary
languages. Objective historical facts are recorded in terms of objects, which
necessarily have an imprecise, empirical quality. Dynamics is based on
quantitative abstraction from recurring patterns. The "quantum of action" is
the discontinuity between these two ways of looking at the physical world.
