What does the immortal sky of Zhang Han Temple describe?

The most formal and romantic story of "The Sky for Teenagers" is nothing more than correspondence, but the time left after letters is every ten years, which is very touching. The story is put into the future of environmental collapse. Although human science and technology have reached a breakthrough in life time, the environment is broken and human beings can no longer survive in such an environment. So, two male and female workers who were left waiting for the external environment to be processed by robots to start human embryos began to sleep, woke up in turn every ten years to see if the environment was restored, and left letters to each other explaining the situation ten years ago. In this way, they have gone through more than one hundred years. Later, the male engineer found that the living quarters of the female staff were leaking, so he gave her his own. Male engineers in the collapsed environment did not begin to age normally until they were in their sixties. He finally saw the sky and the signs of environmental improvement, so he decided to wake up the 25-year-old female employee.