2025/09/15 by В. М. Симулик, Denys I. Bondar, Simulik, Volodimir +1
Physics and Astronomy · #Experimental and Theoretical Physics Studies #FOS: Physical sciences #Optics (physics.optics) #Physics Education (physics.ed-ph) #Relativity and Gravitational Theory
paper · pdf · doi:10.48550/arxiv.2509.12477
openalex publication_date 2025/09/15 · openalex created_date 2025/10/18 · openalex updated_date 2026/07/28
While the numerical value of the speed of light is known with extraordinary precision, its theoretical definition remains a subject of fundamental interest. We show that the definition of mass and velocity of light follow from the conserved quantities of the electromagnetic field. The proposed definition of the speed of light is always bounded from above by the phase velocity and equals it for plane waves. As a consequence, we obtain a generalization of Einstein's mass-energy relation for electromagnetic fields in media: m = εμE / c2. Hence, irrespective of the light's intensity, the electromagentic field in near-zero-index material is always massless. This approach offers new pedagogical insights into the fundamental nature of light propagation.