Hard SF

Hard science fiction is a category of science fiction characterized by an emphasis on scientific or technical detail, or on scientific accuracy, or on both.

The heart of the "Hard SF" designation is the relationship of the science content and attitude to the rest of the narrative, and the "hardness" or rigor of the science itself. One requirement for Hard SF is procedural or intentional: a story should try to be accurate, logical, credible and rigorous in its use of current scientific and technical knowledge about which technology, phenomena, scenarios and situations that are practically and/or theoretically possible, and later discoveries do not necessarily invalidate the label. For example, P. Schuyler Miller called Arthur C. Clarke's 1961 novel A Fall of Moondust Hard SF, and the designation remains valid even though a crucial plot element, the existence of deep pockets of "moondust" in lunar craters, is now known to be incorrect.

There is a degree of flexibility in how far from "real science" a story can stray before it leaves the realm of hard SF. Some authors scrupulously avoid such technology as faster-than-light travel, while others accept such notions (sometimes referred to as "enabling devices", since they allow the story to take place) but focus on realistically depicting the worlds that such a technology might make possible. In this view, a story's scientific "hardness" is less a matter of the absolute accuracy of the science content than of the rigor and consistency with which the various ideas and possibilities are worked out.

Examples of Hard SF include:

Arthur C. Clarke - A Fall of Moondust

Stanislaw Lem - Solaris 

F.M. Busby - The Star Rebel 

Kim Stanley Robinson - The Mars trilogy

Gwyneth Jones - Life