Mohs Scale of Science Fiction Hardness/Speculative Science

Speculative Science: Stories in which there is no "big lie" -- the science of the tale is (or was) genuine speculative science or engineering, and the goal of the author to make as few errors with respect to known fact as possible.


 * The works set early in the timeline of Larry Niven's Known Space universe fall into this category, including Protector (which featured Bussard Ramscoops but no faster-than-light travel). The later in the timeline of Known Space you go, though, the farther the scale slides toward the soft side, with FTL, reactionless drives, inertialess drives, indestructible transparent hull material, and finally psychic luck all entering the fray.
 * Robert L. Forward's Rocheworld setting was quite hard through the first two books (it should be, he's a physicist). Points are lost to Sequelitis; In the third and later books, the science softens to mush, including finding native coffee beans on the moon of a gas giant circling a red dwarf.
 * Dragon's Egg, also by Forward, takes the idea of life on the surface of a neutron star with extreme seriousness.
 * In Eternal Sunshine of the Spotless Mind, the memory-erasure device is reasonably plausible from a scientific perspective, and as a story set Twenty Minutes Into the Future, there is little else that could be objected to.
 * Robert A. Heinlein's The Moon Is a Harsh Mistress: Minus Mike itself, pretty much everything is already around, or could easily be put together in the next half-century (the book is set in 2075-2076). The only fly in jam here is that we had a moonbase for a minimum of thousands by the 90s.
 * The Menace From Earth (also by Heinlein) posits a sublunar colony that doesn't require a ton of future-tech but would be absurdly expensive to build with today's technology. Beyond that, the story sticks tightly to realistic extensions of the current technology. The protagonist is even engaged in drafting the design for a starship that anticipates engines that haven't been invented.
 * I Miss the Sunrise is set far in the future, but doesn't rely on Applied Phlebotinum. Many of the technologies present are described in great detail and generally work according to real physics.
 * Orion's Arm falls at the softer end of this category. Things that are almost certainly impossible can be accepted but only so long as it is shown that they don't violate any known laws of physics. Wormholes that might violate causality undergo Visser collapse, extremely fast sub-light speed travel with Reactionless Drives has ridiculous amounts of math preventing violations of thermodynamics, brains the size of stars can be made but are subject to all the problems that come with it like light delay between different parts and the constant threat of turning into an actual star.
 * Charles Pellegrino's Flying To Valhalla and The Killing Star. The Valkyrie spaceships (and their alien equivalents) are a design seriously proposed by Pellegrino and Jim Powell. And, unfortunately, the major source of mayhem is pretty plausible too.
 * Steven Gould's Helm brings two major science-fiction elements: terraforming and technological Brainwashing. The former is described in significant detail in an early chapter, and the terrain depicted of the book reflects the planet's history. The brainwashing is treated in less detail, but its mechanism of operation is convincing nonetheless.
 * Quite neatly demonstrating that science fiction hardness is not perfectly correlated with plausibility: Car Wars. The only thing lifting it above Futurology on the Scale is the optional Body Backup Drive rules.
 * John C. Wright's The Golden Oecumene trilogy, which has interstellar travel that respects the speed of light, and Hermetic Millenium, which is Space Opera set as hard an SF future as he could write.
 * Moon: Minus the Space Is Noisy and  it was so spot on, NASA personnel who screen tested the film just to see how close they got it were pretty impressed. The best explanation is when one of them asked the Director, "Why does the base look like a bunker?", he replied that he figured that it would just be easier (and cheaper) to transpose stuff that already existed onto the moon -- and then another in the group stated that she's in fact working on just that.

Futurology: Stories which function almost like a prediction of the future, extrapolating from current technology rather than inventing major new technologies or discoveries. Expect Zeerust in older entries.

Examples

 * Gattaca: Set in a very near future that introduces no really new technology but speculates on the advance of subtle human genetic manipulation and fetal selection and the ethical and social implications of a society that quickly relegates the non-engineered to second class status. The gamete selection technology portrayed in the movie is a reasonable extrapolation from technology that already exists; indeed, the furthest-out thing in the film is a manned expedition to Titan (and given an entire world population of geniuses, it's not much of a stretch except for the fact they don't wear spacesuits or seatbelts).
 * Max Headroom: Strongly related to its Twenty Minutes Into the Future premise, though still spiced with the occasional TV commercial that makes people's brains explode. Which may be a comedic exaggeration of a Reverse Funny Aneurysm; certain TV shows have been known to trigger grand mal seizures.
 * Given that The Machine Stops by E. M. Forster dates back to 1909, Zeerust is painfully evident throughout -- but the idea of a globe-spanning information-processing system managing the delivery of food, operation of air travel, and aiding the dissemination of information is far from implausible, even if many of the details are distorted relative to what is now considered feasible.
 * Regenesis: Set in the present, showcases bleeding edge biotechnology for its science fiction aspects (most of the technology featured are real or in the "theoretical possible but impractical/expensive/unethical stage of development)". Sometimes it's less science-fictiony than CSI.
 * Anime and manga examples: Mighty Space Miners, Planetes, Moonlight Mile, Freedom Project, Rocket Girls.
 * Ghost in the Shell is for the most part completely plausible, although some of its elements are not so much impossible as Awesome but Impractical (eg. SpiderTanks, cloaking devices etc.). Others (sentient AIs developing self-awareness, full-body prostheses, Brain Uploading) are so realistically presented as to be almost frightening.
 * TV docudramas about near-future space exploration, such as Space Odyssey: Voyage to The Planets and Race to Mars.
 * Stephen Baxter tends to write in this category, with books like Titan, about a mission to the eponymous moon using a combination of decommissioned Shuttle, ISS and Apollo technology.
 * Michael Flynn's Firestar series, a near-future setting about averting an asteroid that might otherwise hit the Earth.
 * Neuromancer, the William Gibson novel, falls on the hard side of the spectrum, largely because his vague depiction of Cyberspace has preventing it from aging too badly (although Zeerust abounds nevertheless). His description of the Freeside space colony is not too far off from what humans could realistically create in the near future, although it gets some of the details about Artificial Gravity wrong. Ironically, the most difficult thing in the novel to create in real life might be the AI itself that the title refers to.
 * Jupiter Moon, a British Sci series taking place on a decommissioned space vessel.