Explore the revolutionary theory that redefines our understanding of the universe with ""Theory of the Four-Dimensional Electromagnetic Universe."" This groundbreaking work by Domenico Maglione presents the concept that our universe is a hypersphere composed of four real spatial dimensions. We live in its three-dimensional part, perceiving the fourth spatial dimension not as space but as time. In this enlightening book, Maglione introduces two fundamental postulates that challenge conventional cosmology. The first postulate posits a four-dimensional universe with a privileged reference system centered on the Big Bang, where the expansion of the time dimension occurs at the speed of light in vacuum. The second postulate, the restricted holographic principle, explains how we experience phenomena in the three-dimensional part of the universe differently, though quantitatively proportional, to their true nature in the four-dimensional reality. Readers will explore the derivation of fundamental equations that bridge quantum mechanics and relativity, shedding light on the wave-particle duality of electromagnetic waves and the nature of mass and energy. The book further clarifies how temporal waves, by their radiation pressure, cause the expansion of the universe, offering clear hypotheses on the true nature of dark energy and dark matter. Maglione's theory proposes that the entire universe simplifies into an immense four-dimensional electromagnetic field where static electromagnetic waves, the TWs, oscillate along the fourth dimension perceived as time. This perspective invites a reimagining of the universe as fundamentally composed of light.