We propose a theory to explain random behavior for the digits in the expans
ions of fundamental mathematical constants. At the core of our approach is
a general hypothesis concerning the distribution of the iterates generated
by dynamical maps. On this main hypothesis, one obtains proofs of base-2 no
rmality-namely bit randomness in a specific technical sense-for a collectio
n of celebrated constants, including pi, log 2, zeta (3), and others. Also
on the hypothesis, the number zeta (5) is either rational or normal to base
2. We indicate a research connection between our dynamical model and the t
heory of pseudorandom number generators.