In this talk, I will show how the general relativity and quantum mechanics can be combined consistently to establish the gravitational quantum field theory (GQFT), which motivates us to build the hyperunified field theory (HUFT) based on the maximum entangled-qubits motion principle as well as gauge and scaling invariance principle. Such a HUFT enables us to understand the nature of spacetime and gravity, and make issues on the basic questions: what is the fundamental building block of nature? what brings about the fundamental symmetry of nature? what is the fundamental interaction of nature? how does the fundamental symmetry govern basic forces? what is the basic structure of spacetime? how many dimensions does spacetime have? why is there only a single temporal dimension? why do we live in a universe with only four-dimensional spacetime? why are there leptons and quarks beyond one family? how does early universe get inflationary expansion? what is a dark matter candidate? what is the nature of dark energy? It is expected that the gravitational wave detections will provide a new window in probing the gravitational universe and exploring the nature of spacetime and gravity.