"The fun, and the material for this article, lies in treating the whole thing as a game. I've been playing the game since I was a child, so the rules must be quite simple. They are: for the reader of a science-fiction story, they consist of finding as many as possible of the author's statements or implications which conflict with the facts as science currently understands them. For the author, the rule is to make as few such slips as he possibly can."Speculative Fiction fanatics are always raving about how "hard" the science is in various stories — but it's not like you can rub a story with a piece of quartz and see if it leaves a scratch on the plot. So what is "hardness" in SF? Why do some people want it? And how do we put a number to it? Beginning with the first question: "Hard" Science Fiction is firmly grounded in reality, with only a few fantastic flights of fancy not justified by science, or with the technology being nonexistent in today's world but probably scientifically possible at some point. "Soft" Sci-Fi is more flexible on the rules. Even the fantastical aspects of the story will show a divide — in hard SF, they operate through strict, preferably physical, laws, where in soft SF they work in whatever way suits the story best. What this leads to for hard SF is a raised bar for the amount of scientific research the writer must put into the story, and usually this is shown quite clearly. Example: a character is shown a machine for traveling into the past and asks, "How does it work?"
—Hal Clement, Whirligig World
Notes (please read!)
Note: The works mentioned below are sheerly for illustrative purposes — please add new examples to the subpages. Note 2: Contrary to what one might expect, there is no apostrophe in "Mohs" — the name is a reference to the Mohs scale of mineral hardness, named for Friedrich Mohs. (Grammatically speaking, an apostrophe after the 's' would be permissible; its addition would produce a possessive, i.e., "Mohs' scale", denoting the scale created or promulgated by Mohs. However, it's apparently not used in the standard name for the scale, so its use here would approach a degree of informality utterly unacceptable on The Other Wiki.) Note 3: While the term "soft science fiction" is used above as the antonym of "hard science fiction", another common use of the term is to describe soft science fiction: sociological and psychological science fiction. This can, in some cases, make it appropriate to talk about "hard soft science fiction", but doing so is likely to confuse people. Note 4: Sometimes a study hits the news that, if confirmed, would reassign many works on the scale. For example, the the September 2011 OPERA experiment which measured faster-than-light travel by neutrinos might have moved works whose One Big Lie was FTL Travel into the Speculative Science category. There are three reasons to be cautious about doing so: first, because mass media reporting of scientific results is often inaccurate due to the difficulty of presenting technical results to a non-technical audience; second, because revolutionary new results (and results in the news are generally new) are far more likely to be overturned than they appear (indeed, the OPERA anomaly seem to have been caused by faulty equipment); and third, for purposes of the Scale, the yardstick of scientific plausibility is what the science said at the time the work was written, not what scientists discovered later. Note 5: As far as this wiki is concerned, Tropes Are Not Good and Tropes Are Not Bad. "Hard" and "soft" may be considered as denotations of the quality of the story by those who prefer one over the other. We don't hold to that here. Note 6: In science fiction fandom, classifying something as hard science fiction generally relies on more than just the plausibility of the technology used. "Hardness", in that sense, also depends to the level of scientific explanation used in the story. This scale, however, is based mainly on closeness to real world science and the consistency of the science fiction elements. For this reason you may find examples of works on the higher end of the scale that are not generally described as hard science fiction. Note 7: Keep in mind that Science Marches On when categorizing older works. If the story in question was based on a scientific model that, while now discredited, was widely accepted in its day, it still qualifies as "hard" science fiction because the author did his best with the information available at the time. Note 8: When adding this trope to a work page, don't simply put down the number and leave it at that. This would require a troper to visit this page to learn more about it. That's fine if the troper is interested, but if who is already working down the work's page (and only at the M's) who probably doesn't want to wander off on a Wiki Walk. You can say the number, but please go on a bit explaining what the number is. For instance: