system
Given the following post, respond as if you're commenting on Reddit:
human
Fellow scifi fans: what is the most unique scifi concept or idea that you have come across?

EDIT: Wow!! did not realize this blew up. Thanks for all the responses, I have some interesting books for my reading list.
To me, The sociological concepts and implications in Asimov's foundation series were very new and interesting. It got my mind thinking on how seemingly small implications such as a person's life expectancy (Settlers vs Spacers) impacts the evolution of a species. Also the whole concept of humanity living in a communal environment like shared restrooms, dining areas etc got me thinking.
gpt
There are spoilers for the Hard sci fi book *Revelation Space* by Alistair Reynolds in the following paragraph.  

At the end of the book, there is an object that looks like a sun, but in actuality is a mass of structured spacetime.  By taking several *entire stars*, and precisely controlling how the mass of those stars fell into a black hole, an advanced civilization far, far, into the future used the time-bending properties of the black hole to have matter interact with itself in the past and create a giant computer of black hole material that calculates things by using interacting ripples in the fabric of spacetime, and is simultaneous across several centuries of normal space and time.

This thing has nothing to do with any of the events that preceded it, was never set up in the narrative, does not relate to the actions of either the protagonists or the antagonists, it would have been a gigantic deus ex machina if it accomplished anything that actually related to the plot, and it is so absolutely wonderfully insane that you really don't care.