In my point of view, science fiction is not only the story of the future but also is the present. It is a great imagination about the future world. In most science fiction novels, the fear of unknown present many times. Such as Alien invasion, disasters because of too advanced technology, the nuclear war and so on.

How to create the unknown? It is a problem that challenges many writers. For science fiction, besides good writing skill, writers also need to acquire tons of scientific knowledge. If people write for the future, sometimes the future must be reasonable, or science fiction novel will change to the fantasy novel. 

However , only the fear cannot create a good science fiction novel; it must contain the discussion about humanity itself.  When I was in high school, I like to read science fiction novels, such as the Three-Body Problem. In the book, it has the alien- the Trisolarans. The Trisolarans never show up in the novel, and the story is people fight against people. From what I understand, the Trisolarans are the catalyst but not the core of the story. Without the Trisolarans, the alien, people still will fight against each other for different reasons. That is what I comprehend about the science fiction. It writes for the future but server for the readers in nowadays.