The principle you mentioned, often referred to as the "exclusion principle" or "Pauli exclusion principle," states that two identical fermions (particles with half-integer spin) cannot occupy the same quantum state simultaneously. This principle applies to particles with rest mass, such as electrons, protons, and neutrons.
However, electromagnetic waves are not composed of fermions. They are described by a different class of particles called bosons, specifically photons. Bosons, which have integer spin, do not follow the exclusion principle. In fact, multiple photons can occupy the same quantum state simultaneously.
The behavior of photons and electromagnetic waves is governed by the laws of quantum mechanics, which describe the behavior of particles at the microscopic level. In quantum mechanics, particles like photons are described by wavefunctions, which are mathematical representations of their quantum states. The wavefunctions for photons allow for superposition, which means that multiple photons can occupy the same quantum state and travel together as a coherent electromagnetic wave.
It's important to note that while electromagnetic waves can overlap and occupy the same space, they still exhibit wave-like properties, such as interference and diffraction. These phenomena arise from the interaction and superposition of different electromagnetic waves with similar frequencies and wavelengths. However, at a fundamental level, the individual photons that make up the electromagnetic wave are distinct entities with their own energy and momentum.