I think Solaristics is basically a metaphor for religion or God. How people would be able to communicate with God or a super-being if we get the chance to experience it directly. Solaris keeps cloning the psychic/memories of the visiting scientists. It can’t communicate with people, but it digs through memories to understand, what are the most important thing to each scientist. But this is freaking them out. Memories are the DNA of the individuality. Without memories people would like a bulb of collective consciousness, like Solaris itself. I think Tarkovsky avoided the religion subplot because the Soviet Union's restriction to discuss religoin. Highly recommended read or watch.

funny note: it seems no one reads posted articles on hacker news... people just talk about other stuff related to the topic of the article..