<span class="SFPTagline"> From SCIFIPEDIA </span>

Hard science fiction (often shortened to "hard SF") is the subset of science fiction that strives for accuracy in science. Although the precise definition is often a subject for spirited debate, the typical earmarks of hard science fiction require at a minimum that:

• the science in the story is accurate to what is known of science today, and
• (real-world) science or engineering is central to the plot of the story.

That is, in a pure "hard science fiction" story, the resolution of the story will not depend on invented science (for example, the invented "fact" that Krieger waves reflect off holographic surfaces), but will depend on real science (for example, the attraction of dust to an electrostatically charged surface, as in Hal Clement's story "Dust Rag."

Hard science fiction may more accurately be thought of as a spectrum and not a category; science fiction can be "harder" or "softer," depending on the accuracy of the science and the degree to which the science is integral to the plot. Some aficionados of hard science fiction claim that a story cannot be completely characterized as "hard SF" if it contains science fiction tropes such as faster-than-light travel or time travel, which contradict the currently known laws of physics.

Some writers whose works are usually considered to belong to the subgenre of hard SF include Gregory Benford, Arthur C. Clarke, Greg Egan, and Geoffrey A. Landis; the short story "The Cold Equations" by Tom Godwin is often cited as the exemplar of hard science fiction.