(zenodo.org) Introduction Electromagnetic waves are typically regarded as transverse, propagating without the need for a medium. However, their finite speed of propagation raises a fundamental question: what happens to energy in space during wave propagation? If energy cannot change instantaneously, then at some point in space, an energy gradient must form. If this is true, then it is logical to assume that electromagnetic waves generate not only transverse but also longitudinal energy oscillations. Energy Gradient and Its Consequences When an electromagnetic wave leaves its source, it alters the energy density in the surrounding space. As the wave propagates, the energy at the source returns to its original value, but at a distance R, the energy remains altered. This means that between these two points, an energy gradient exists, which can propagate as a longitudinal wave. Classical physics does not account for such a phenomenon, but that does not mean it does not exist. Instead, its effects might be too subtle to detect directly. Put differently,...