http://resonance.is/the-geometry-of-causality/
Exploring relativity from intuitively understandable geometrical descriptions. Understanding relativity is germane to understanding unified physics — from the relativistic structure of spacetime, to the geometry of strong gravitational objects, to Lorentz factors like time and mass dilation.
For instance, in Quantum Gravity and the Holographic Mass we see how the holographic ratio relationship of surface-to-volume Planck vacuum oscillators produces the observed rest mass of the proton.
Yet, calculations show that the spin of the Schwarzschild proton at the surface horizon is close to the speed of light. Angular momentum at this velocity means that there will be relativistic mass dilation, and the surface horizon will have the mass necessary for an object of that size to obey the Schwarzschild condition: the Schwarzschild mass.
This results in a gravitational force strong enough to bind nuclei, but which falls off at an exponential rate with distance, exactly matching the Yukawa potential.
This is just one example where the theory of relativity is necessary for fully understanding quantum phenomena — unified physics. The following video offers an interesting examination from geometrical considerations of how the invariance of the speed of light influences the nature of spacetime causality: