摘要: 根据实际天文观测论述了膨胀着的宇宙系统的时间可以与空间分开来讨论；宇宙的空间是平直的。在宇宙质心坐标系中，由背景辐射温度、宇宙密度和宇宙半径（最远星系的距离）3个观测数据计算了宇宙这个引力系统的总能量，结果表明系统是一个引力束缚态，将来会收缩。在均匀分布的初始条件下计算了收缩过程，这是同步自由落体过程。在宇宙的膨胀过程与其收缩过程对称的假设之下，建立膨胀时间与背景辐射温度的一对一的对应关系。According to astronomical observation we point out that the time of our expanding cosmic system can be discussed separating from the space. And the space in our universe is flat. In the cosmic center-of-mass frame（CCF）, based on the temperature of CMBR, the cosmic density and the cosmic radii, the distance of the farmost galaxy, the total energy of our universe asa gravitation system has been calculated. It shows that our universe is in a gravitational bound state, and it will contract. In CCF the contracting progress is a synchronized freely falling body under initial condition of uniform distribution. Uder assumption of the symmetry of cosmic expanding and contracting progresses, th one-to-one correspondence of the expanding time to the temperature of CMBR can be obtained.