Year: 2004 Pages: 10
In this paper we review the evolution of the concept of ?vacuum? according to different theories formulated in the last century, like Quantum Mechanics, Quantum Electrodynamics, Quantum Chromodynamics in Particle Physics and Cosmology. In all these theories a metastable vacuum state is considered which transforms from one state to another according to the energy taken into consideration. It is a ?fluid? made up by matter and radiation present in the whole Universe, which may be identified with a modern definition of ether.