In sf Terminology – unlike Physics, where it has a different meaning – a force field (sometimes a force shield or energy screen) is usually an invisible protective sphere or wall of force. The term "force field" first seems to have been used in this sf sense in E E "Doc" Smith's Spacehounds of IPC (July-September 1931 Amazing; 1947). Throughout the 1930s and 1940s the force field performed sterling service, notably in Smith's Skylark and Lensman series, where force fields under attack routinely glow red and orange and then all the way up through the spectrum until they reach violet and black and break down. Isaac Asimov's "Not Final!" (October 1941 Astounding) uses force-field research as a vehicle for the message that absolute statements about scientific possibility tend to be unwise (see Clarke's Laws). A dome-shaped force field surrounds and protects the ancient artefact found on the Moon in Arthur C Clarke's "The Sentinel" (Spring 1951 10 Story Fantasy as "Sentinel of Eternity"; vt in Expedition to Earth, coll 1953).
There are conceptual precursors which would now be classed as force fields although not originally described as such. In William Hope Hodgson's The Night Land: A Love Story (1912; cut 1921), humanity's Last Redoubt is defended by the "Electric Circle" which generates the "Air Clog ... an Invisible Wall of Safety." Some kind of force-field Technology (though here more akin to the Tractor Beam) seems to underlie the invisible "flying loop" which provides action-at-a-distance effects in Rudyard Kipling's "As Easy as A.B.C." (March-April 1912 The London Magazine). Everett F Bleiler's Science Fiction: The Early Years: A Full Description of More Than 3,000 Science-Fiction Stories from Earliest Times to the Appearance of the Genre Magazines in 1930 with Author, Title, and Motif Indexes (dated 1990 but 1991) lists further examples including Florence Carpenter Dieudonné's Rondah, or Thirty-Three Years in a Star (1887) – perhaps the earliest use of the concept in Proto SF – and John Mastin's Through the Sun in an Airship (1909).
In golden-age sf, force fields are also a sovereign remedy against Rays, Death Rays and usually bullets as well – though not against "space-axes" in E E Smith's First Lensman (1950) or against swords in Charles L Harness's Flight into Yesterday (May 1949 Startling; exp 1953; vt The Paradox Men 1955 dos; rev 1984). In these books the efficacy of the shield is directly proportional to the cube of the velocity (Smith) or to the momentum (Harness) of the object it resists. This property of force fields gives Harness a good excuse to introduce swordplay, where the momentum involved is relatively small, into a technologically advanced society – an example of Medieval Futurism that other writers were not slow to follow, most notably Frank Herbert with his personal "shields" and knife-fighting in Dune (fixup 1965). Joe Haldeman's The Forever War (fixup 1974) features a "stasis field" within which electromagnetic radiation cannot exist and the maximum allowed speed is 16.3 metres per second; in this arena, effective weaponry is restricted to swords, spears, bows and arrows, etc. Robert Sheckley's "Early Model" (August 1956 Galaxy) tells of a protective force field so efficient that it renders its wearer almost incapable of carrying out any action at all that might conceivably endanger him. The eponymous device in Poul Anderson's Shield (June-July 1962 Fantastic Stories of the Imagination; 1963) can recharge its batteries by soaking up the kinetic energy of the bullets it stops. But these are comparatively late examples, when the concept was sufficiently familiar in sf to allow Parody and sophisticated variations. Still later force fields are often simply accepted as a given, as in Star Trek with its shields or in Iain M Banks's Culture stories – where, renamed as "electromagnetic effectors", force fields are capable of complex manipulations in addition to straightforward defence.
It is the essence of the traditional sf force field that by a kind of judo it converts the energy of an attacking force and repels it back on itself. Few writers, however, were able to give – or concerned to try to give – a convincing rationale for forces being conveniently able to curve themselves around an object and to take on some of the properties of hard, resistant matter. A well-ground mirror might more plausibly carry out the same function, at least against death rays. Indeed, Colin Kapp's "The Pen and the Dark" (in New Writings in SF 8, anth 1966, ed John Carnell) features an Alien defensive barrier which is essentially a 3D mirror, opposing each physical assault with a precisely similar reflection. James Blish nevertheless made an interesting attempt, using analogies from radar technology, to justify a kind of standing-wave force field placed around New York by some unspecified hostile power in "The Box" (April 1949 Thrilling Wonder). The true rationale for the force field and for its close relations, the Tractor Beam (which pulls objects towards the beam projector) and the Pressor Beam (which pushes them away), is that – like Faster Than Light travel – they help tell stories.
An interesting variation on the force field theme is the Stasis Field (which see). Christopher Anvil's "Gadget vs. Trend" (October 1962 Analog) features a "stasis field" which makes materials utterly impervious without imposing the usual Time-stasis within. One ingenious Weapon application is to enclose a small amount of fissionable material within such a container until field-reflected particle emissions build up to a state of nuclear supercriticality: when the field is turned off, this "wink bomb" explodes as a miniature nuke. Yet another imagined field offers viscous resistance rather than a solid-seeming barrier. Such a "tanglefoot field", slowing movement like a sea of molasses, is used for crowd control in Robert A Heinlein's The Star Beast (May-July 1954 F&SF as "Star Lummox"; 1954); a similar "radar Hobble-Field" appears in Alfred Bester's Tiger! Tiger! (October 1956-January 1957 Galaxy as "The Stars My Destination"; 1956; rev vt The Stars My Destination 1957; rev 1996). Precursors of these immobilizing fields, based vaguely on electricity, include the "ground-circuit" of Rudyard Kipling's "As Easy as A.B.C." (March-April 1912 The London Magazine); the "electric hedge" of George Bernard Shaw's Back to Methuselah (1921; revs 1921-1945), which is explicitly derived from Kipling; and the static-electricity immobilizer of W E Johns's Biggles Hits the Trail (1935), to which one character is luckily immune thanks to his rubber-soled shoes.
Shutting down invading Spaceships' protecting force fields to make them vulnerable to nuclear attack is a key plot point in Independence Day (1996). In such late-phase sf works that accept the established device without need for explanation, force fields of a more grandiose nature may surround entire solar systems – as an imposed quarantine for humanity in Greg Egan's Quarantine (1992) and for inimical Aliens in Peter F Hamilton's Pandora's Star (2004), or for more traditional defensive purposes in John Scalzi's Old Man's War (2005), whose aliens' impregnable shield is powered by the entire output of their sun's white-dwarf companion. [DRL/PN]
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