Hi, I've had this question in my mind for a long time.. When we say that the electrical energy stored in a vacuum is U=1/2[tex]\epsilon0[/tex]*E^2, we assume that the energy is stored in the electric field right? But physically what does that mean? For eg: In a dielectric one can say that the energy is stored in the form of potential energy of atoms and molecules by polarizing and stretching them. So in the case of the vacuum where is the energy stored physically? Its stored in the field means what?