I never really internalized it until I went to my first launch but one way to look at the Saturn V/Eagle combo is that it takes a 40-story building full of kerosene and liquid oxygen to get a VW bug with three dudes in it to the moon and back. The Voyager probes are that same VW beetle, without the dudes, on half the rocket... and it's taken 30 years to get them past Uranus. We're still spitballing the technology to get so much as a post-it note to Alpha Centauri which, true, outlines the argument of the author... but we're four generations from learning to fly and three from learning to split the atom which is about 20 generations less than the Romans lasted and they pretty much accomplished "concrete" so it's not like technological progress is predictably linear or anything. We don't have any little green men visiting us at night because the energy cost to travel to another solar system with life is astronomically more than the resources you'd gain in doing so.