This 4th D as C*tau will be a joining point between Relativity and Quantum mechanics with local time as the accumulation of quantum intervals tau. C*tau reveals the wavelength Lambda of energy and it is linked to the other 3D´s, as managed by Lorentz and Einstein, where Length contraction is due to the kinetic energy. Later Einstein showed that any type of energy (including mass-energy) will produce a curvature of space. Because of this length contraction, the observable three longitudinal dimensions need their energy content to be complete; a 4D scenario or a math of quaternions (a scalar Lambda plus the 3 longitudinal vector). Poincare's invariance is also understood as a greater energy content will imply a smaller Lambda and also a contraction of 3D values [(Delta r)^2 + (iDelta C*tau)^2 = constant]. This proposition is the first step of a 2021 novel interpretation (Theory of Space); I´d appreciate any opinions regarding this 4thD (C*tau), thanks