  The electric and magnetic fields are investigated on the basis of quantum
vacuum. The analysis of the electromagnetic energy and force indicates that an
electric field is a polarized distribution of the vacuum virtual dipoles, and
that a magnetic field in vacuum is a rearrangement of the vacuum polarization.
It means that an electromagnetic wave is a successional changing of the vacuum
polarization in space. Also, it is found that the average half length of the
virtual dipoles around an elementary charge is a=2.8 *10^(-15)m. The result
leads to the step distribution of the field energy around an electron, the
relation between the fine structure constant and the vacuum polarization
distribution, and an extremely high energy density of the electromagnetic
field.
