This is the second idea that I've had for a while and which has always kept me wondering.
If there was some reason why all of humanity went away except for a small group of people, how could/would they recreate the world? How would they reproduce all of our inventions and achievements? Would they do things differently? What skills would be required, and what people would you want there with you if it was you and others? What if it was just you alone?
I come to think of these questions when I appreciate the simplest conveniences in life. For example, the house or building you're sitting in right now. There are so many subtle yet complicated innovations and improvements that have allowed us to have such comfortable lives in modern buildings that I have very little knowledge about. Or our electronics, like computers, iPods, and telephones. I understand the most basic concepts behind how these devices work and if I had a long time by myself with a lot of basic tools and resources, I could probably replicate them eventually, but they would be much, much more primitive.
If I were responsible for rebuilding civilization, what knowledge would I want to have? This is to some extent what motivates me to learn in life: to become as capable as I can be if I ever have to rebuild something myself, less in a disaster-preparedness sort of way and more in a community-responsibility sort of way.
Would I want to study certain specialties like mechanical and electrical engineering much more than I did in college? Or would I want to go for breadth instead of depth so that I could build at least the most basic versions of each important part of civilization.
And the above is just about our "stuff." What about us? How would I/we structure our lives and our environment socially and politically? What systems would we keep from what we have now and what systems would we try anew? What historical mistakes would we avoid, and which would we commit again because of our human nature?
I hope that this sort of situation never happens literally, but the same sort of questions apply in a different way to our lives in our current society. Even though we are not rebuilding old stuff from scratch, we are building new stuff all the time, and we have our current government and political systems. We don't have the power to change everything at once or start from scratch in a totally new direction, but we do at least each have the responsibility to learn and advance the knowledge necessary to be good citizens and members of society. If each person believed he or she was responsible for our entire world, would we be in a better place than we are now?
I think so.