According to our current understanding of physics, empty space, often referred to as a vacuum, is not truly devoid of particles or fields. Even in the absence of matter or observable particles, the vacuum is still filled with fluctuations and virtual particles arising from quantum field theory.
Quantum field theory describes the fundamental particles and their interactions as excitations of underlying fields that permeate all of space. These fields, such as the electromagnetic field, the Higgs field, and others, are present even in the absence of observable particles.
In the vacuum state, the lowest energy state of these fields, there is still a background energy associated with quantum fluctuations. These fluctuations give rise to virtual particles, which are particle-antiparticle pairs that spontaneously emerge and annihilate within very short time intervals dictated by the Heisenberg uncertainty principle.
These virtual particles are an inherent consequence of quantum field theory and have been experimentally observed through their subtle effects on physical phenomena. For example, the Casimir effect demonstrates the influence of virtual particles on the behavior of electromagnetic fields in the presence of boundaries.
Therefore, the concept of a completely empty space, devoid of any particles or fields, is not supported by our current understanding of physics. Even in what may seem like an empty region, the vacuum fluctuations and virtual particles persist, contributing to the dynamic nature of space.