  In this paper, a modified formulation of generalized probabilistic theories
that will always give rise to the structure of Hilbert space of quantum
mechanics, in any finite outcome space, is presented and the guidelines to how
to extend this work to infinite dimensional Hilbert spaces are given. Moreover,
this new formulation which will be called as extended operational probabilistic
theories, applies not only to quantum systems, but also equally well to
classical systems, without violating Bell's theorem, and at the same time
solves the measurement problem. A new answer to the question of why our
universe is quantum mechanical rather than classical will be presented.
Besides, this extended probability theory shows that it is non determinacy, or
to be more precise, the non deterministic description of the universe, that
makes the laws of physics the way they are. In addition, this paper shows that
there is still a possibility that there might be a deterministic level from
which our universe emerges, which if understood correctly, may open the door
wide to applications in areas such as quantum computing. In addition, this
paper explains the deep reason why complex Hilbert spaces in quantum mechanics
are needed.
