In special relativity the universal speed limit c is a postulate - the Lorentz transformation becomes singular at v = c, making infinite energy required to accelerate any mass to c. The mathematical statement is exact. The physical explanation is absent.
BFUT Paper 22 gives the physical explanation: c is the maximum propagation speed of the Spaticle substrate.
Why Nothing Can Exceed c
Nothing can travel faster than c because no physical process can reorganise the Spaticle substrate faster than the substrate's own maximum propagation speed. A physical effect - a force, a signal, a causal influence - requires substrate reorganisation to propagate. That reorganisation is bounded by c.
Massless excitations (photons, gravitational waves) travel at exactly c because they are purely propagating substrate deformations with no need to maintain internal condensation structure. Their entire propagation budget goes to spatial traversal.
Massive particles cannot reach c because they must continuously sustain internal condensation structure - the cooperative three-core rotation of Paper 16 - which requires a fraction of the propagation budget for internal maintenance. The constraint c² = v²_spatial + v²_internal means that increasing v_spatial reduces v_internal (the clock rate) and the particle can approach but never reach c.
c From Substrate Parameters
Paper 19 derives c from the electromagnetic coupling and condensation geometry - agreement 0.0001% with the measured value. The speed of light is a property of the medium, not a postulate about light. Any propagating disturbance in the Spaticle substrate travels at c, regardless of who produced it or who measures it. This is why the Michelson-Morley experiment returned a null result: if the apparatus and the light are both excitations of the same substrate, they drift together. No preferred reference frame exists.
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