𝐸 = 𝑀𝑐² and 𝐸 = 𝑀𝑐∞

Introduction Directional physics is built on three foundational principles: mass is composed of confined strings, light is a liberated string, energy is directional tension. In this framework, the speed of light is not a geometric parameter but a maximum directional intensity. The classical expression “squared” has no physical meaning in a multidimensional directional space. 2. Einstein’s Conceptual Error: The Photon Without Mass Einstein assumed that: the photon has no rest mass. This assumption is compatible with classical physics but incorrect in directional physics. In a directional model: a photon is a liberated string, every string carries directional tension, directional tension corresponds to directional mass, this mass is infinitesimal but non‑zero, it cannot be measured at rest because a photon cannot be immobilized. Einstein’s error was therefore ontological, not mathematical: he concluded that the photon had no mass simply because it could not be stopped. In directional physics: a photon possesses a directional mass equal to that of a single confined string that has been liberated.