Quarto
Unknown Enemy
While I'm sure that science fiction is about as realistic as those medieval tales about the weird creatures that live on other continents (which, come to think of it, were exactly that - science-fiction), the thing that amuses me the most is when people start seriously debating about things they couldn't possibly have any idea about, such as whether or not it's possible to go beyond the speed of light or travel in time (well, all right, in that particular case, "it's impossible" is a pretty safe bet). Remember, a hundred years ago, people not only didn't think it was possible to break the sound barrier, but they didn't even have any understanding of the technologies that would eventually make this possible - so, back then, the claim that it's impossible to travel faster than sound would have been perfectly reasonable. It didn't turn out that way, however - and it's pretty arrogant for people today to seriously think that we know enough about the universe to make claims about the speed of light.