Vacuum still remains a mysterious medium from a physical point of view, especially its physical properties. The passaging of a monochromatic wave is examined through a vacuum of size L in our work. A monochromatic wave has a certain energy, and when passing through a vacuum it should not lose energy. At different values of the vacuum size, according to the properties of the vacuum, there should be no loss of energy by the wave. If energy loss occurs as a wave passes through, the cause of the energy loss is inhomogeneity. The inhomogeneity of the vacuum proves the existence of some particles in the vacuum, i.e. vacuum is ordinary matter. We can say that a certain part of the energy of a monochromatic wave is absorbed by matter, i.e. vacuum. In this work, the energy of a monochromatic wave is calculated before and after passing through a vacuum of size L. It has been proven that the ratio of the energy of a monochromatic wave before passing through a vacuum is less than 1. This means that the monochromatic wave was scattered in elastically in a vacuum and vacuum is a dense medium. After the passage of the vacuum wave, the length of the monochromatic wave decreases. A monochromatic wave loses energy in a vacuum.