I'm quite happy to delete this question if it is felt to be rubbish or if someone can say "nothing original".
I have an idea about how humans might explore the universe and obtain ridiculously huge amounts of power from (literally) nothing.
Isn't one of Dirac's theories that vacuum is in fact an ocean of feverish activity (the Dirac sea), where matter and antimatter are constantly and spontaneously coming into being and cancelling one another out?
So... what about the idea of harnessing this and using the resultant tanks of matter and antimatter to power a spacecraft? ... applying an acceleration of 9.81 ms2 constantly...?
If you could do that, I don't know how much time it would take (as perceived by those on board) to reach several of our nearest star systems... but it'd be pretty quick because you'd quickly get to 99% or closer to the speed of light... obviously the idea would be to accelerate to the mid-point and then decelerate from thereon.