The Hitchhikers Guide to the Galaxy address's the present's issue of space travel as well as the impending doom of being destroyed by Aliens. Put in a more comical way, Arthur and Ford escape the evaporation by hitchhiking on the offending ship. I really enjoyed listening to the radio show, the characters are great and comical and the robot Marvin is by far my favorite character in the series. In the Earth's present world, pre-evaporation, Aliens were already on the
planet under the guise of a Human form. Arthur at least seems unaware of that other creatures had infiltrated into the human population.
Ford being a 'being' that has set his goals on updating the Guide saves Arthur from getting evaporated and then has to deal with Arthur's questions throughout. The issue of the Earth getting destroyed is a common one that people worry about, though the likeliness of us experiencing in our current lifetime is minute. Though maybe we have Aliens among us, who knows.
Another thing that has been in constant thought of, if there are other beings out there, what is their thought of us? Most people think that they probably perceive us as undeveloped, unknowing and naive, borderline stupid on some occasions. When Arthur questions about the Earths entry in the guide, Ford has put the entry as 'Harmless.' Arthur of course is offended and then the entry is amended to 'Mostly Harmless.' It's funny to thing about it, but inherently we are probably mostly harmless to other lifeforms as they are probably more advanced than we are. Though that's just speculation.