Despite being called science fiction, a lot of writers in the genre are selective in how much science actually goes into their fiction, especially when it comes to portraying outer space. This is such a common tendency that there is a sub-genre, hard science fiction, that is specifically characterized by an emphasis on scientific accuracy, at least as it is best understood by the author at the time of writing. This leads to a lot of common mistakes and liberties when it comes to showing outer space. A common example is disregard for microgravity. This is the physical process that allows objects to seemingly float in space. It is commonly referred to as "zero-g" although this is a grossly inaccurate description. Contrary to popular belief, gravity does in fact exist in space, and it is actually gravitational forces that allow astronauts to float on the International Space Station. Learning to navigate microgravity is an essential part of being an astronaut.