Vacuum is not empty

In physics, vacuum is a very old concept. On the one hand, the birth of relativity abandoned the classical concept of the vacuum filled with ether. On the other hand, the establishment of quantum mechanics provided the vacuum a very rich physical content. We will review the various structures and properties of vacuum revealed in the perspectives of relativistic quantum mechanics, quantum field theory, and quantum information. It is very interesting and instructive to find that the quantum theory of vacuum plays a very important and even fundamental role in many fields of modern physics. The further research on the nature of vacuum will bring a new revolutionary development of quantum physics.