Many of physics current issues stem from old unsolved issues in the classical theories, which are carried over to the modern theories that build up on them, or generalize them. Like for example the unknown origin of inertia, which is already present in Newtonian physics or the infinite self energies, which already are a problem in classical electrodynamics. We want to explore here such fundamental problems aswell as the remarkable consequences their answers have for theoretical physics. We're particularily interested in fundamental theoretical questions like the origin of Quantum mechanics, relativistic effects such as length contraction or time dilation, or the equivalence principle; the strength of gravity, the De Broglie relations or the structure of elementary particles. As a guiding line we use the dimensional constants of nature, each of which stands for an unexplained phenomenon in physics.