Randomness, pseudorandomness and models of arithmetic

Pseudorandmness plays an important role in number theory, complexity theory and cryptography. Our aim is to use models of arithmetic to explain pseudorandomness by randomness. To this end we construct a set of models $\cal M$, a common element $\iota$ of these models and a probability distribution on $\cal M$, such that for every pseudorandom sequence $s$, the probability that $s(\iota)=1$ holds true in a random model from $\cal M$ is equal to 1/2.