re: How are dreams possible?
We may not be able to fundamentally alter the size of the universe that mankind inhabits, but I think we will fundamentally alter our experience of the universe.
Yes, I also think we don't have a good idea of what will matter to future generations.
Ours is very much influenced by the enormous developments of airplane technology. We (wrongly I believe) transpose it to the aerospace technology, helped by a great number of SF stories.
But other scientific discoveries or developments are catching up (computers, genetical engineering, etc) and should shape us more astonishingly than the dream of leaving our planet for another one in our present form.
Raoul