read "The Last Question" by Isaac Asimov
He wrote: This is by far my favorite story of all those I have written. After all, I undertook to tell several trillion years of human history in the space of a short story and I leave it to you as to how well I succeeded. I also undertook another task, but I won't tell you what that was lest l spoil the story for you. It is a curious fact that innumerable readers have asked me if I wrote this story. They seem never to remember the title of the story or (for sure) the author, except for the vague thought it might be me. But, of course, they never forget the story itself especially the ending. The idea seems to drown out everything -- and I'm satisfied that it should.
The last question, posed in 2061, was this: Will mankind one day without the net expenditure of energy be able to restore the sun to its full youthfulness even after it had died of old age?
Or maybe it could be put more simply like this: How can the net amount of entropy of the universe be massively decreased?