Science Fiction Studies

#60 = Volume 20, Part 2 = July 1993

David N. Samuelson

Modes of Extrapolation: The Formulas of Hard SF

[The original version of this article was written with the assistance of a grant from California State University, Long Beach.]

John Cawelti considered the artistic claims of various kinds of formula literature in Adventure, Mystery, Romance (1976). Distinguishing formula from convention and chronicling development within each genre, he identified the Western with a kind of setting, the detective story with a kind of plot, and the best-selling social melodrama with a kind of moral view, one that supported traditional moral values. That he failed to consider in depth another popular genre is not too surprising. SF is distinctly formulaic, but its formulas are multiple and various, ranging from myth to mathematics. Future battles in space may define its film image, but few readers would limit SF to any particular time, place, or type of action. Moreover, most books and movies called SF are hard to distinguish from other kinds of fantasy. Always a patchwork creation, the field of "science fiction'' has less coherence today than ever.

Like the monster Victor Frankenstein created, SF is made up of bits and pieces of other literary traditions in various stages of life or decay. Writers trace its heritage from myths and Märchen, "high'' fantasy and romance, travel and adventure tales, as well as from utopias and dystopias, satires and philosophical disquisitions, horror and ghost stories, even something as late and variegated as Surrealism. Becoming self-aware in the '20s and '30s, the monster lay claim to this ancestry, yet it also held itself a new thing because of its sometime allegiance to science and technology and the rational projection of futures. Many literary critics and scholars also find the productions from this period on through the Golden Age unconscionably infatuated with hardware, insufferably smug and arrogant, incomprehensibly optimistic, and barely literate in their narrative and expository style.

Whatever apparent shape SF had in the '40s, it shifted toward politics in the '50s and toward life styles in the '60s, perhaps never to regain a consensus center. Expanding since mid-century to 20% or more of fiction sales, it spread like "The Blob,'' took over its literary neighbors like "The Body Snatchers,'' and changed forms like "The Thing.'' Drawing attention to itself as if it were the complete corpus, each innovation deformed what the body of the genre had previously seemed to be. Each devoured form, however, refused to die, jostling with its predecessors to claim its share of the new conglomerate being.

The quasi-Surrealist "New Wave'' of the '60s gave way in turn to feminist counterculture quasi-utopian speculations in the 70s, followed by grungy "cyberpunk'' visions of human-computer interfaces in the '80s. Postmodern theorists like Larry McCafferey lay claim to all three, conflating them with other non-realistic, counter-realistic, and self-reflexive art around the world. Commercial publishers meanwhile continued to profit from both hard and soft SF, using formulas of adventure, satire and social criticism, and trading on resurgences in fantastic romance and horror stories. The latter were spurred on by the high sales figures respectively of J.R.R. Tolkien and Stephen King, themselves influenced by the coherence SF imposes on fantasy. Often trashy and melodramatic, sometimes dauntingly literate and philosophically provocative, SF does not always rely on science and technology for authority, nor is it limited to verbal expression.

SF images and concepts have long occupied the covers of the genre magazines. They were also part of film from its beginning, involved in the medium itself as well as its stories. Since midcentury, however, SF has invaded pop music, tv commercials, interactive video and computer games, and now "virtual reality.'' Saturating these markets, it reached new heights of public consciousness, however distorted that might seem to purists. It is now popularly said not just of atomic energy and space travel, but also of miniaturization and biogenetics, even the end of the Cold War or apartheid, that they were once "only science fiction.'' Today, SF embraces virtually all eccentric visions, past and present, whatever theoretical relevance to reality traditional supporters claim. Even the "paraliterary'' label by which critics like Samuel R. Delany distinguish it from literature with academic credentials hardly does justice to its protean existence.

Since SF's formal characteristics are continually in flux, the accretive model is clearly too amorphous for a single formula to categorize. This is not how it seemed to SF readers in the Fifties, when I was first infected. Provincially assuming a homogeneity exploded in the next decade, most definitions then focussed primarily on features distinguishing SF from fantasy. These characteristics never really dominated SF writing, let alone visual or musical media. By no means ``missing matter,'' however, even in today's SF constellation, they are still responsible for its flavor in the universe of fantasy. As representations of scientific values, they are especially visible now in SF we call hard (or "hardcore'' by analogy with other addictions).

Hard SF relies on a defining characteristic of all SF, which I called in a previous book the individual "science fiction.'' Darko Suvin's novum achieved wider currency in criticism, as a far more inclusive term, covering almost any change in society, psychology or science. To narrow the meaning again, I offer the term "hypothetical'' for a model of something not yet known, theoretically possible, but beyond historical human experience. All writers of fiction hypothesize virtual interactions of invented entities. Like science and engineering, however, SF makes plausible models of beings, places, and times nobody has yet encountered. Beyond "minimal'' SF like "Flowers for Algernon,'' highlighting only a single small shift, most SF stories feature a generous assortment of hypotheticals. Though hard SF mainly derives these through extensions of reigning scientific theory, this is not to say that hard SF is always scientific. Even science is not always scientific.

For science to be 100% accurate all the time is impossible, even disregarding experimental error and interfering variables. Table salt may always divide chemically into sodium and chlorine, water into hydrogen and oxygen, but that was not always known and its significance has not always been understood as we think we understand it now. The answers science provides vary with time, often yielding progressively more accurate results. While "normal'' science, in Thomas Kuhn's formulation, solves "puzzles,'' new ways of seeing emerge to make better sense of the data (such as heliocentrism, genetics, and plate tectonics). Such "paradigm-shifts'' make different questions meaningful, rendering the old science incomplete or at least dated, sometimes simply wrong. Insofar as hard SF ties itself to scientific findings and theory, it risks obsolescence almost as surely as an athlete setting a new record.

In SF, however, scientific accuracy is also limited by the competing demand for fantasy. Even hard SF requires an element of the unknown, into which writers cast a net fashioned of reigning theory. Building on what does not yet exist, all SF writers "cheat'' on known science, as Gregory Benford argues, calling hard SF "a class with no examples.'' A writer who actually could apply the new theory or build the machine would hardly settle for selling a story to a basically low-paying market. Much SF story-telling, moreover, requires hypotheticals defying contemporary theory: faster-than-light travel, breathable atmospheres and edible foodstuffs on other worlds, not to mention easy communication with alien intelligences. Without such fast answers to difficult questions, story may turn into lecture.

SF typically ignores these impossibilities (a practice ubiquitous in films) or conceals them with verbal legerdemain. The trick in hard SF is to minimize cheating, not just disguise it with fancy footwork. Claiming never to invent, Jules Verne larded his voyages extraordinaires with scientific information as a foundation for his extrapolations. Late in his career, H.G. Wells claimed he had allowed himself only one "impossibility'' per story. He did not always hold to this limit, but his goal was never simply toying with scientific ideas for their own sake. Others have rarely paid more than lip service to this rule in its most limited form, but old SF hands call it "playing the game'' to minimize violations of natural laws. Given a coherent fantasy, extending science rather than simply contradicting it, descriptions of the material universe should approximate to what is contemporaneously known to scientific investigators.

Of all the kinds of storytelling in the SF constellation, hard SF is least likely to be confused with other literature. The branch most closely allied to the hard sciences, hard SF makes extensive use of machine technology and material causation, empirical diction and relativistic morality, and the toughness and skepticism of experimental method. It permits but does not demand the elevation of certain literary qualities attributed to it. Robert A. Heinlein, Tom Godwin, and Jerry Pournelle may demand macho qualities for survival. Isaac Asimov, John Brunner, and Frederik Pohl may foreground serious consideration of social consequences. Ideas that transcend the human condition tend to preoccupy Greg Bear, Gregory Benford, and Arthur C. Clarke. All three groups—which tend to overlap and do not span the entire spectrum—show a distinct propensity for posing and solving puzzles, whether or not they propose new paradigms.

The mixture of science and fiction that makes up SF in general and hard SF in particular is complex and sometimes subtle. Space permits me only to sketch the outlines. In the context of fantasy, I suggest the importance of building bridges to relevance, one of which is extending the known. In the context of science, I posit the importance of empiricism, determinism, and relativism. Conditioned by these constraints, extensions in SF subdivide into extrapolation, speculation, and transformation. Elaborating on extrapolation, hardest of the three, I can only allude to examples of it in the literature of SF, not demonstrating it in individual texts.

1. The Relevance of Fantasy. A latecomer to Western culture, SF can justify its name in a sense on its mixture of old and new elements. On the one side a late blooming avatar of fantasy, it is on the other a romantic simplification of scientific processes. From a psychological standpoint, all literature is founded in fantasy. Theories of the imagination identify as fantasizing the basic situation of making in words what is absent from our senses. "Intertextual'' theory, both literary and psychological, analyzes the storehouse of images, conventions, and unconscious beliefs shaping both our tales and the basis of the narrative process. Familiar vocabulary, character types, settings, plot situations, social and sequential structures, underlie stories we tell ourselves about history, science, art, and religion, not just those claimed as fiction. Fairy tales and myths, the oldest extant stories, underlie our "humanistic'' views far more than we like to admit, and color our resistance to upstart sciences that give short shrift to such wish-fullfilment.

Overtly fantastic stories bulk large among humanity's entertainments, even in the last three centuries of Western culture, when the demands of science and industry tilted approved reading matter toward the practical and ostensibly realistic. Homer and Chaucer thought nothing of using verisimilitude in tales of wonder, but Horace Walpole had to justify the first "Gothic novel'' to philosophes and hard-headed businessmen. However credulous audiences ever were about myths and scriptures, epics and romances, 18th-century novelists felt the need to claim they wrote "histories,'' not time-wasting fiction. Driven partly underground, writers of overt fantasy became self-conscious that theirs was not the only way to tell stories. They either had to admit their flights of fancy were not worth the time of serious people or connect to the "real world'' as the reader conceived it on some grounds of practical relevance.

Jonathan Swift and Samuel Johnson, Montesquieu and Restif de la Bretonne tied their allegories and satires to the workaday world by traditional methods like extension, inversion, and exaggeration of the known, individually or in combination. Like Don Quixote before them, Candide and Rasselas mentally extend their educations into an unknown world as well as inverting the known. Lemuel Gulliver meets homunculi, giants, obtuse savants, and wise horses; differences in size and wisdom reach cosmic proportions in "Micromegas.'' Thomas More, Tommasso Campanella, and Francis Bacon took science more seriously than Cyrano de Bergerac, Swift, or Voltaire, but all gave it passing reference. Karl Guthke even credits the speculations of Bertrand de Fontenelle about other inhabited worlds with turning the tide of popular opinion toward science. Verisimilitude was barely a consideration, given the state of scientific education. Only in the 19th century could literary tools rendering the fantastic relevant mix with principles of scientific endeavor, allowing early (or proto-) SF to emerge.

2. Bridges to Relevance. Science, engineering, and literature make models of worlds we imagine; some of these we convince ourselves are phenomenally real. SF, especially hard SF, uses a number of model-making processes in creating narrative models of the future, of alien worlds, and of anticipated artifacts and phenomena, both alien and human. SF still uses inversion and exaggeration, for example, although it favors extension, enlisting naturalistic details and mimetic techniques in the service of fantasies. SF distorts realism in other traditional ways, as well, such as satire or allegory, but the method of distortion most characteristic of SF, and especially hard SF, is extrapolation, a process uniting science, realism, and fantasy in highly specific ways. Shared with and to some extent drawn from science and futurology, extrapolation is primarily used in SF for world-building and forecasting.

The models of science, engineering, and SF are supported by three philosophical principles (empiricism, determinism, and relativism) and two operating procedures (prediction and control) which serve as rules for everyday scientific activity. Empiricism, determinism, and relativism may be absolute only in Scientism, the belief that nothing is real except what can be observed by scientific means. On a human scale—between the atom and the star—scientists assume them at least for the duration of the study or the experiment. These scientific principles underlie all SF, even where the authors are not aware of it, but hard SF writers usually take them seriously and readers expect them to.

Everything in the universe may not actually be material, divisible, observable and measurable. Science works better with numerical precision, however, than with vague descriptive terms. Such numbers it basically derives from sense impressions, however much magnified by instrumentation. As practitioners of applied science, engineers are even more materialistic, working with physical models. Sense impressions are the stuff of fiction as well, with subjective coloration more prominent. To make credible to its readers experiences which can only be imagined, SF uses sense impressions, often magnified by instruments, and often puts numbers to them as well. Thus empiricism is a necessary if not sufficient element of both science and SF.

Sometimes in subnuclear physics, an effect may precede its apparent cause. Thus science itself seems to disprove absolute determinism on the subatomic level, from which all others are constructed in a material or empirical model of the universe. Outside physics as well, scientists have taken to speaking of probability more than causation, modifying the causal principle more than abandoning it. All thought and expression may not need linearity, but "natural language'' can not manage without it. Modernist and postmodern story-telling techniques fragment plot and question causation, suggesting that linearity is outmoded in fiction, but readers routinely reorder a complicated narrative structure as if a linear causal sequence predated the complication. If causality itself is outmoded, clinging to it probably reveals a limitation of the human mind. Richard Feynman argued that nobody can visualize the situation in an atomic nucleus; it's questionable how many people can visualize an indeterminate universe at human scale.

The most recent of the underlying principles to emerge, relativism is also quite exacting. It assumes that scientific findings are valid only in limited context, "relative to'' an observer, as well as to a measure we operationally call stable. What can be found in the lab may not exist outside it. Whether Sol circles Terra or vice-versa is less a matter of correctness than identification of an observer's physical frame of reference. Today's "correct'' position, that neither body provides a fixed center, eliminates an absolute frame of reference. Physicists don't know the fixed center of the Universe, if there is one, or if there is only one Universe. Compensating for past errors of anthropocentrism, we undoubtedly substitute new ones; we can hardly avoid a human viewpoint and a biased interest in what we investigate. Yet scientific discoveries have decentered past biases, transcended earlier frameworks focussed on more limited experience and conceptualizations, each step forward making us progressively less provincial. Relativism suggests the inevitability of such self-correction, if our frame of reference continues to expand.

Intellectually, engineers have an easier time of it; their real world assignments have less tolerance or "wiggle room.'' They can isolate a part of a system, as a "Black Box,'' disregarding what goes on inside it, concentrating on input, output, and ``throughput.'' Fiction writers cannot fully understand or describe all the behavior of their characters, let alone the world they inhabit. In a given context, they may also assume a moral relativism, measuring values by a standard not officially approved in the world in which they live. Hard SF writers echo the work of scientists, engineers, and fiction writers in general. They contextualize their stories in space and time, they avoid detailed description of a conception or invention that does not exist, and they measure characters' values against a world view at least partly scientific in origin.

Even more pragmatic than the axioms discussed above are two deterministic operating procedures, prediction and control. Some scientists discount prediction, but most accept that verification of theories, inside and outside the laboratory, depends on part of the material universe behaving as theory says it should. To test that prediction, they control the experimental situation.

Scientists try to control the subject under study as much as possible, eliminating variables, making verification of a prediction less ambiguous. Least able of scientists to control objects of their study, even astronomers rejoiced in 1988 when a Supernova visible in the Southern hemisphere fulfilled most of their expectations. Like other hard scientists, they assume the virtual interchangeability of matter in a given state; nature is the control mechanism. Laboratory scientists, however, need to minimize contamination by chance or factors other than what is isolated for study. The soft sciences need "control groups,'' which they maintain and observe, to guard against the possibility that the hypothesized effect might occur even without the variations introduced for the experimental subjects.

Scientists try to establish measures of consistency and coherence internally, not just with the world of phenomena. Internal coherence means avoiding self-contradiction. "Mature'' sciences require self-consistent tenets, although specific findings constantly subject them to challenges for revision.

Internal consistency is usually valued in literature as well. As Rabkin points out in The Fantastic in Literature, wherever we locate a text on a continuum between extremes of pure realism and pure fantasy, we expect the game to have rules. Even books that seem to deny coherence are consistent in their denial, like Tristram Shandy, the "Alice'' books of Lewis Carroll, and David Lindsay's science fantasy novel, A Voyage to Arcturus.

Literary texts also follow conventions or codes marking them as literary, codes that create and exploit reader expectations. These codes are both internally and externally imposed. Jonathan Culler points to wholeness, continuity, and adherence to rules of grammar and punctuation as relevant to most texts, though some literary writers flout these rules to call attention to them. At a more self-conscious level, long-standing narrative conventions of myth and fantasy influence most if not all modes of story-telling. In fantasy, which rarely claims to represent phenomenal reality, many of these conventions are also metaphysical markers, establishing human relations with the supernatural.

Even fairy tales and quest romances, however, are consistent with external standards imposed in their times. They assume certain givens about the behavior of powers of good and evil, of royal or heroic personages, even of ordinary people. Based more on metaphysical than material causes, their simplistic conceptions of human psychology are still relevant to human experience. In more mimetic literary forms, such codes are still present, but they must vie with others standing for empirical experience and our theoretical processing of it. In Anatomy of Criticism and elsewhere, Frye calls myths "displaced'' in mimetic literature, but displaced how far? Humanistic values rooted in mythological thinking will seem natural to people if longevity and cultural inertia have embedded them in cultural consciousness.

External standards apply in all literature, including SF. Stories reflecting contemporary life are "historical'' in a sense, but the research involved is contemporaneous with the writing. Contemporary readers evaluate the credibility of narrative situations and events, taking for granted the same social codes and literary conventions. A story set even a generation in the past requires more research, if it is to reflect accurately the memories of readers. Since fewer readers are well-versed in more distant times or climes, we evaluate credibility in the distance by a mixture of criteria. Some are simple transpositions of present habits and mores, but educated readers also expect consistency with the historical record. A fictional attempt to kill Winston Churchill must not succeed in this timeline, if the story is to be regarded as realistic.

Like other writers, SF writers use measures of external consistency. They report concrete details to enlist the reader's senses on their side, and to let readers compare their images of reality with the phenomenal world they know. More so than other writers, however, they rely on theory to establish imagined reality. Historically, such reliance is not unique. One thinks of the "elements'' of Earth, Air, Fire, and Water; the psychology of "Humours''; Social Darwinism; the scientific ``religions'' of Marxism and Freudianism; even the recent attacks by Michel Foucault on the post-Enlightenment invocation of ``disciplines'' that have rationalized society's spreading control over health, crime, and sex.

Three things are new about the reliance on theory in SF, however. SF is oriented toward examining possible changes, not just maintaining the status quo. Beginning with physics, itself philosophically undermined by uncertainty, SF works outward into less predictable territory, including widely acknowledged pseudo-sciences. Finally, SF is both intellectually and aesthetically distanced from the theories it depends on. SF writers openly treat as hypothetical most aspects of the place, time, events, and characters they create. The fictional world of the "realistic'' is geared more toward facts, the world of the ``fantastic'' toward desire, both positive and negative aspects. SF seeks to occupy a fictional universe in the middle ground, toward which it constructs conceptual bridges, extending what we think we know into what we know we don't.

3. Extension Bridges. Regardless of its setting in time and space, SF depends on transgressions of what its readers think of as reality. To justify those transgressions, it establishes images of reality on grounds essentially theoretical. Extending scientific laws or facts into the unknown, SF treats what could be in theory but can not be verified in fact. This "scientific'' thinking connects the phenomenal present (and sometimes the past) with an imagined future (sometimes an imagined present or past). These connections typically cross three theoretical bridges: extrapolation, speculation, and transformation.

Depending mainly on what is verifiable, or at least that which is consistent with what is thought to be known, hard SF predominantly bridges the gap with extrapolation, extending trends or tendencies from one time frame (or domain of knowledge) into another. SF writers commonly use extrapolative techniques for building environments and ecospheres; they are more problematic when applied to cultural history. The open-ended phrase, "If this goes on . . . ,'' often associated with negative or cautionary tales, sums up the neutral essence of extrapolation.

Less bound to the knowable and more congenial to fertile imaginings, soft SF depends on more flexible techniques, labelled speculation. Congenial to philosophy, fantasy, even realistic fiction, speculation can have a special relevance to hard SF as inverted extrapolation, working out theoretical ways something imagined for other reasons might be judged possible. Speculation may flow from premises, ideas, even metaphors not based in science, but many SF writers feel an obligation to rationalize even outrageous speculations after the fact. Linking speculation to fantasy and philosophy, another open-ended phrase, "What if?,'' sums up its essence.

Some extrapolations from "hard science'' data or theories can lead to fictional worlds or world-views we can hardly recognize as emerging from modern society, however heavily influenced it may be by science and technology. Although grounded in science, such transformations cast doubt on basic categories of knowledge and thought, including science itself. We can see examples of these in the recent past. A conceptual revolution or series of revolutions in physics near the start of this century has had far-reaching influence. A revolution in geology near mid-century greatly altered our view of the crust of the earth. Such paradigm-shifts have also happened recently or are happening now in biology, brain science, and linguistics.

Far more often than in science, which is basically skeptical and conservative, SF "thought-experiments'' invoke far-reaching paradigm-shifts. Rarely do they test these for internal consistency beyond the scope of the story, let alone external consequences for science or the universe. Beyond such staples as travel in time and beyond light-speed, popular paradigm-shifts have included A. E. Van Vogt's "Null-A'' universe and William Gibson's "cyberspace.'' Some conclusions these changes lead to are incompatible not only with old scientific paradigms but also with the conventions of narrative fiction.

Absolute empiricism denies the existence of a soul, perhaps even of aesthetic experience, contradicting long-lived views of human sensibility. Absolute determinism, while allowing for chance, threatens to turn characters into puppets, denying traditional concepts of free will and human dignity. Absolute relativism makes every event unique and its experience contingent on shared reference grids; it casts doubt on most standards of behavior. The quantum-relativity transformation in physics not only introduces uncertainty on a subnuclear level; it also makes time and space contingent categories. Given multiple lines of reality (alternate time-lines or universes), the reading experience tends to degenerate into fantasy or selfmockery, neither of which invites belief.

Paradigmatic transformations may increase the impact of scientific principles on causal perception or introduce previously unknown areas of reality, from the mind to the universe (or universes). They may restore intuition to scientific enterprises, as Benford notes in physics. According to Fritjof Capra and Gary Zukav, however, intuition is just one parallel between physics and Eastern mysticism; implicit in their discussions is the sense that these parallels restore the value of old religions. Less rooted in science, the route from speculation to transformation may be less paradoxical, but no less disruptive.

Each of these bridges requires extended discussion, but space permits only the first to receive it here. Long as it is, the following analysis is suggestive rather than exhaustive; exploring every angle of extrapolation would take a book. SF examples are cited where possible, but none are subjected to close examination at this point. Discussion centers on identifying guiding principles of extrapolation, as well as its application in building alien worlds and constructing plausible futures.

4. Principles of Extrapolation. The bridge of extrapolation is familiar enough in SF that it became the name of the first academic journal devoted to critical and scholarly writing in the field. SF's use of extrapolation, however, is more extensive, complicated and subtle than its use as a catch-phrase might suggest. Simply put, extrapolation extends a series of numbers in logical order. Given 1 2 3, the next numbers for counting are 4 5 6. In the series 1 2 4 7 11, each enlarged by one more than the one before, the continuation is 16 22 29. Similarly, 1 4 9 16—all squares—lead to 36 49 64. Extending the principle of increase past a known end-point, all extrapolation stems from an exercise in mathematical logic.

Scientists and SF writers apply this logical principle to the real world. They extrapolate from the known into the unknown when they try to imagine conditions not observed in detail, based on similarities and continuity with what we think we know. What we have not directly observed, of course, includes a vast amount of territory. It comprises unexplored areas of the earth and the vast expanses of the universe beyond Earth, including the worlds of our solar system. Also beyond our observation are the future, the distant past, and most of the Microverse, the domain of the microscopically small: cells, molecules, atoms, and beyond.

SF's extrapolative practices build on the same sciences, but "world-building'' and "forecasting'' use different methods. World-building extends scientific processes; forecasting extends historical processes. Whenever intelligent manipulation of the material universe is involved, they overlap significantly.

Building alien worlds gives SF writers a chance to exercise their scientific ingenuity. The task is to construct environments alien to Earth which are still natural, consistent with what science knows about nature on this world and assumes about its continuity throughout the material universe. The writing itself is a product of human imagination, conditioned by language and history, but the builder of an alien world in fiction starts from scratch in a sense, treating it as untrammelled by human history. Ostensibly, this world may exist at any time since the Big Bang, even before or after the present dispensation, without regard for human history or biological scale. Olaf Stapledon's Star Maker is the outstanding example of such cosmic reach, but Poul Anderson's Tau Zero, James Blish's The Triumph of Time, and George Zebrowski's Macrolife also try to envision the end of our universe, if not its beginning.

In theory, the whole universe is the author's laboratory to experiment in with verbal models of matter and energy. Considerations of relevance and accessibility, however, tend to keep the creation within reach of modern times. The scope of understanding and sympathy of readers with minimal scientific education is limited. The theoretical operating constraints are the "laws of nature,'' conceptions or constructions about which scientists have achieved consensus at a given time. In this respect, writers of hard SF seek to be stringent, limiting themselves to what can be extrapolated directly from known science.

For the duration of the story, scientific conceptions are generally assumed to be timeless and universal. Taken to apply more or less uniformly throughout the universe, the laws of physics, for example, may be extended at will in space or on other bodies of matter (asteroids, satellites, planets, stars, galaxies, nebulae, etc.). Puzzle stories set within the solar system take for granted familiarity with such laws; for more distant climes, the author specifies the conditions early on. Many SF writers have written such stories, including Anderson, Benford, Clarke, Clement, Forward, Niven, and Sheffield.

Unlike the distant play of building alien worlds, forecasting is clearly relevant to contemporary concerns. Not a science in any serious sense, it is a combination of soft sciences that can be treated in fiction as if it had scientific rigor, like "psychohistory'' in Asimov's FOUNDATION narratives. In such exercises, writers extrapolate trends from a given historical base to arrive at a future. Forecasters may start from any time, future or past; usually choosing the 20th or early 21st century, they opt even more than world-builders for humanly comprehensible time lines.

The laboratory in this case is usually human civilization, i.e., its Western, technological variety, mostly on Earth or in its presumed expansion into space. Both hard and soft sciences set theoretical limits to forecasting, based on dominant ideas of what is susceptible to rigorous testing about human structures and conditions. Like the world-builder, the forecaster assumes a universe responsive to empirical, deterministic, and relativistic questions, but other assumptions separate the two methods. Barring a global catastrophe, forecasters assume a human future in which science and technology evolve and progress in an all but autonomous manner. They also typically permit intelligent beings to behave in ways not wholly predictable.

According to the first assumption, continuity and progress operate in science and technology as in no other area of human knowledge. Thus, the starting point of a given extrapolation may be further advanced than anything known by science at the time of the writing. Other dimensions of human experience are treated as even more variable, though authors try to extrapolate them as well, usually from a scientific or quasi-scientific base. Such a narrative may treat the social sciences as if they had empirical certainty, or were ideologically dependent upon harder science and technology. Alternatively, areas of human life less accessible to scientific analysis may be treated more as speculation than extrapolation, giving writers wide latitude.

Time factors are an important consideration. Some futurologists divide forecasts into near-future (15 years), mid-future (15-50 years), and far-future (over 50 years). This division implies a hierarchy of certainty, though few futurologists of standing would declare any projection certain. Extrapolations in SF also include longer time-spans, but they have their own constraints as well. Distance in time decreases the degree of certainty in one's extrapolations, leading back to world-building in the past, onward to speculation in the future.

In futurological usage, near-future projections are more plausible, though they can prove wildly errant if important elements are overlooked or under-valued. In SF, moreover, near futures usually lean heavily on technological and social forecasts, often with gloomy outcomes. Far-future projections are typically more speculative and more imaginative, less bound by contemporary obstacles past which we can not see our way. More distant futures often reflect more of our hopes and wishes, invoking the psychological sense of "projection.''

The severest form of extrapolation in forecasting concerns only one technological or social variable. The results of such an exercise may be wildly out of step with conceivable reality. At one time, for example, the U.S. Defense budget was increasing faster than the Gross National Product; a comparable argument today is made about health care costs. Such straight- line extrapolations show the impossible: a part becoming greater than the whole. Pohl, C.M. Kornbluth, and Robert Sheckley have imagined such states of affairs for satire, rather than for mimetic effect. Unmodified straight-line extrapolations are rare in fiction and futurology; both disciplines are more sophisticated than that, and allow many kinds of complications.

Futurologists have developed more precise terminology than SF writers, overtly routinizing many activities of their discipline. Used in computer models for highly complicated extrapolations, as well as in more intuitive studies, their terms place in broad relief similar procedures used in SF. The most important are probably "cross-impact studies,'' "second-order consequences,'' "wild cards,'' and "scenarios.''

Cross-impact studies bring into analysis factors which conflict with the continuation of an individual trend. Among them are limited resources, competing trends, and social intervention. A classic example is the vision-phone, a long-time expectation of electronic engineers as well as SF writers. Technology exists for widespread use of visual telephones; booths have been available for years for conference calls and electronics firms still try to market sets for the home. In television advertising, some companies still project routine home use for this technology. Consumer interest in the product, however, has always been limited. Cost, convenience, privacy, and the increasing availability of alternate means (faxes, electronic mail, computer bulletin boards) help keep large-scale spread of this product in the realm of SF.

Damping effects are another cross-impact. Actions may have consequences that radically change the conditions underlying the original extrapolation. In both physical and social environments, trends cancel themselves out, cyclically or irreversibly. Ecologically, population growth is always checked in some way. When deer overgraze their feedlands or predators their prey, they die back until there's more food per animal. History records many checks on human population, too: plagues, famines and infant mortality we share with most other animals, war with only a few. Less obviously deterministic, damping effects also affect human groupings (tribes, nations, etc.), which oscillate between such extremes as cut-throat competition and cradle-to-grave security.

Quantitative change leads to qualitative change, in both environmental and socio-historical frames of reference. Most life on Earth is utterly dependent on the planet's oxygen-rich atmosphere, originally produced by one-celled animals that made the earth unlivable for their own kind. If it is not checked, human pollution of the atmosphere with the residue of fossil fuels and chlorofluorocarbons could make the earth just as uninhabitable for us. Stephen Jay Gould in Wonderful Life shows the natural history of Earth replete with examples of species that died out for many reasons; the most impressive of course were the dinosaurs that ruled the planet for 150 million years. There is no scientific reason to exempt human beings from extinction.

In the 1960s, Alvin Toffler coined the term "future shock'' to describe the qualitative psychological effect on modern human populations of continual, increasing, and apparently irreversible change, citing numerous cases in 20th-century history. The findings of archaeology and physical anthropology suggest similar effects during the Neolithic Revolution, when humans invented agriculture, domesticated animals, built cities, and founded other enduring institutions. A long time on the scale of a single human life, the 10,000 years between then and now is barely a blip in the lifetime of the planet.

Following the axioms and assumptions identified earlier, straight-line extrapolation and first and second-order complications are roughly calculable in a temporal context, but few futurologists or SF writers settle for simplistic determinism. Too many events have taken experts by surprise, even after the tools of scientific forecasting were developed. Participants in both disciplines develop "scenarios'' introducing indeterminacy, a term borrowed from physics.

The object of study in any field of science usually reveals emergent properties impossible to predict from a constituent science. Chemistry is a constituent of biology, which must be consistent with its laws, but neither the voluntary activity and life cycles of biology emerge inevitably from laws of chemistry. Similarly, while rapid changes of state in chemistry are consistent with physical laws, they can not be predicted from those laws. At the subatomic level, even physicists are limited in what they can know or predict, in keeping with the "principle of uncertainty'' associated with Werner Heisenberg.

The indeterminacy factor in behavior stems partly from the impossibility of knowing enough details about the system under study, but also from the willfulness of intelligent beings as objects of study. The classic example of the resistant subject produced the "Hawthorne Effect,'' named for a study of employee-management relations in a Western Electric manufacturing plant in Chicago. This study found a rise in efficiency when management increased the lighting—as it did when the lighting was reduced. Knowing they were being studied, workers were concerned to make a good impression or fearful of making a bad one.

Principles of indeterminacy are extended into otherwise sober technological forecasting, as various surveys have shown (cf. Arthur C. Clarke's Profiles of the Future). Experts literally guess when—not if—hydrogen fusion or anti-gravity will be developed. Strictly outside anyone's expertise, these breakthroughs are still considered possible. Other wild cards are at the breaking point of speculation. Contact with extraterrestrial intelligence and control of extra-sensory-perception may seem on the edge of possibility. Others are clearly past the edge of present conceptions of physical law, e.g., invisibility and miniaturization of biological entities, reversible time travel, faster-than-light speed, and two-way communication with the dead. Such questions subject even experts to psychological projection. From a science-fictional viewpoint, however, once we impose our hopes and fears and desires on an unpredictable future, extrapolation can work from that situation, assuming a predictable state of human society and human technology from the point of impact.

All three kinds of complications may be invoked in terms of the "Gaia Effect,'' James Lovelock's theory that the planet Earth itself maintains a relatively stable climate. Physical scientists are understandably skeptical of this hypothesis, but some have sought material ways to proved or disprove it. Insufficient data, inadequate computer modelling, and highly questionable interpretation yield indeterminate results to date. Neither known nor disproved, illustrating emergent properties, social expectations, and psychological projection, the subject of a living planet maintaining its balance may seem a natural for SF. Writers who have imagined planet-wide beings have included Le Guin, Lem, and Stapledon, but the dramatic potential is limited, as for a hero with no known weaknesses.

5. Extrapolating Scientific Processes. Centered in the physical sciences, world-building should be the more reliable of the two methods of extrapolation SF commonly uses. It even underlies forecasting, supplying the ground rules, but its immediate relevance is less obvious. We take for granted that our world exists as it is; we are bred to be well suited to it. Imagining other worlds, SF writers are not so complacent; all aspects of world-creation are in play. Playing the game seriously, hard SF writers must construct a setting, an environment, usually a culture with a history, all of them differing from ours, yet consistent with present-day scientific knowledge.

The general principles of world-building are fairly simple, based on what hard evidence we have. That limited evidence depends on long-term and large-scale, but not exhaustive, explorations of one watery planet, a few trips to its satellite, and a few dozen instrumental probes of its rocky and gaseous neighbors. What science has won, however, by hard-fought analysis with many missteps, SF reconstructs by relatively easy synthesis with no assurances about accuracy.

In building a fictional world, writers who do not simply assume an "earthlike'' planet are obliged to work within existing constraints of cosmology, planetary science, and biochemistry. Hard SF writers rarely question the consensus cosmology of physicists concerning the formation of planets or the assumptions of biologists concerning the material causes for life. Fictional extrapolations differentiate themselves from the hard sciences largely in terms of considering potential alternatives not yet found. In imagining an alien world's inhabitants, writers have more freedom. If they do not simply allegorize or satirize human history, however, they must rely for plausibility on extrapolation from the social and behavioral sciences treated more or less deterministically. The greatest weakness in Hal Clement's classic of world-creation, Mission of Gravity, is the characterization of its aliens. They look like centipedes with lobster claws, act and think like Renaissance sailors, and talk largely like '50s engineers, at least as they are represented in American SF.

For anyone studying nature, two conflicting principles seem to govern material bodies in the universe we know. According to the Second Law of Thermodynamics, entropy increases. Energy levels even out over time, ultimately eliminating variations so that everything is a kind of low-temperature soup. In contrast to this great equalizer, Louise Young argues in The Unfinished Universe that the history of the universe so far shows energy differentiating itself into various states and shapes. The energy state we call matter extends and varies itself enormously, even before reaching the levels of life and culture. At each next level of complexity, the differentiating process rises to a higher mathematical power. The tension between entropy and differentiation allows writers considerable imaginative play.

Consensus cosmology among physicists holds that some 15 billion years ago, all the energy in our universe exploded from a single point in a Big Bang, unfolding in a lumpy, differentiated state ever since. Nebulae begat stars which begat planets; at least one of these begat life, which in turn begat culture. Assigning stars to nine letter classifications, largely based on temperature, we treat novas, supernovas, neutron stars, and black holes as special cases. Given fewer known examples, we classify the debris circling Sol as planets, satellites (including rings), asteroids, and comets. Distinguishing between gas giants and balls of rock, we find several variations in this system. While everything may even out in the end, matter and energy seem multifarious; this apparent decrease in entropy the Second Law permits in a "local'' situation.

On the biological level, we chart the development of life from simple proteins to DNA and RNA, from one-celled beings to colonies of similar but somewhat differentiated cells to creatures like ourselves with multiple organs consisting of specialized kinds of cells. Each level may include numbers of symbiotic relationships on internal and external levels, culminating (in our anthropocentric interpretation) with our vaunted intelligence, which we typically deny or denigrate in other species. In terms of the variety we know has existed, differentiation seems to be winning, but more species have died out than are now alive, and the number of those alive today is dwindling.

Viewed anthropologically, not as a possession of polite people, culture is a set of value distinctions shared by a group of humans. Whether or not there are empirical reasons for such distinctions, their major social function is to differentiate the group from gross physical matter, other animals, and other people. The origins of such values are buried in contemporary consciousness, where they form the assumptions and emotional bases of logic, aesthetics, and other cultural values. The most deeply held of these are typically the "numinous,'' the supernatural element of values we call religious. The most arbitrary values of all, their material basis consists of shared values about the unknown (e.g., contact with divinity, the origin of life, the existence of the "soul,'' and survival after death).

Each group's distinguishing set of values inevitably changes over time, however much effort is spent on trying to preserve it. While it is in place, moreover, people are willing to shed their own blood over it, as well as the blood of others with whom they differ. Here, too, entropy conflicts with differentiation. Each culture may be arbitrary, but that arbitrariness is precisely what distinguishes it from other cultures. People centered in technology may think technology decreases differences along with distances between cultures, another staple SF assumption, but we wear ethnocentric glasses. Other cultures become more alike to the extent that they buy into our technological way of life, but even then they typically maintain "spiritual'' differences, arbitrary to a materialist's eye. Both decreasing and increasing material discrepancies may exacerbate spiritual differences.

For building a hypothetical world—and even the bodies of our solar system are partly hypothetical objects to us—physics sets the paradigm for other sciences. The most successful at prediction, control, and reduction to mathematics, it deals with the simplest levels of matter and energy, from which the objects of other sciences are constructed. Relativity and quantum mechanics must be admitted, but most spectators follow a paradigm constructed from physics as practiced and formulated in the 19th century and before. For operations above the subnuclear level and below the cosmic, the old physics works fine, perhaps especially in fiction. Oversimplified, this paradigm is analytical, mechanistic, and systematic, but not infallible.

The physics paradigm involves both analysis and synthesis. Analyzing an object of study into its smallest constituent parts, physicists build mental models out of their perceived interactions to suggest an understanding of the whole. Subnuclear particles and operations have been known for nearly a century, but "atomic'' and ``elemental'' are still useful terms for the smallest part of something that can stand alone.

For purposes of modeling a world, we generally regard laws ascribed to science as mechanistic, describing processes virtually inexorable once they start. These laws must be consistent in their application and part of a coherent system, not contradicting either rigorous observations or laws in that science or another. Physics constrains the other sciences, but this system of checks and balances also works in reverse. If a more complex science demonstrates something contrary to the assumed limitations of a simpler one, those assumptions must be adjusted.

This procedure does not simply operate like clockwork. All scientific explanations are partial, allowing the model-builder a certain amount of latitude, especially vital to a fiction writer. Two obvious limits to rigid determinism are those of perceptual indeterminacy and conscious intervention. Principles of indeterminacy arise partly out of physics, partly out of differences between the sciences, and partly out of the mathematical language sciences use to describe things and events.

At the subnuclear level, the impossibility of absolute knowledge is symbolized by Heisenberg's Uncertainty Principle. The position and velocity of a particle cannot be known at the same time, whether this be considered a failure of tools or concepts. Uncertainty is not limited to subnuclear conditions, however. It is impossible in any science to demonstrate perfect continuity of nature with laboratory conditions. The loopholes involved may be infinitesimal and it is risky to try to enlarge them, but change at the microcosmic level makes itself felt on our scale of the world. Like a nail in a horseshoe losing a battle, a wayward subatomic particle can affect the germ plasm or the synapses of a brain, resulting in the death of a person, a species, a planet.

Indeterminacy is also apparent in relationships between the sciences. Chemistry may not violate laws of physics, but physics cannot predict everything in chemistry. Biology has a similar relationship to chemistry. Changing the scale of study reveals unpredictable properties of matter and energy at the next higher level of complexity. Heat makes life possible on Earth, but life without access to sunlight, as at deep ocean heat vents, was not predicted by physics and chemistry, and the forms such life takes were not anticipated even in biology. Ascending the ladder of complexity takes us from physics to chemistry to biology to psychology to sociology, with stops in between (biochemistry) and to the side (biophysics, psychophysics, psychochemistry). In the simplest analysis, more complex fields just have more variables than the sciences that underpin them.

Gödel's Theorem underpins with mathematical certainty these practical uncertainties, establishing that no closed system can determine all of its contents. The theorem is strictly mathematical in scope, but the extent to which the sciences are mathematically coherent restricts them as well. Again the model-builder is freed to imagine something of which we have no experience, if it is consistent with the known.

SF involves literary as well as scientific models, but the fictional construction of worlds depends on a mixture of the sciences. Hard sciences directly impact on the soft, but social and behavioral factors usually drive activities of both science and engineering. Whatever we regard as natural, intelligent intervention leads to "artificial'' variations in evolutionary development or variations of technology, which includes not just artifacts and machines but also laboratory and social processes in chemistry, biology, language, and culture. Potential in every fictional world, this principle is inherent in SF creation.

6. Hard Sciences. For the astronomical situation and the composition of an alien world, the physical sciences are obviously primary. They cannot be taken for granted, as in mundane fiction or SF set on an "Earthlike planet.'' Cosmology is invoked for the astronomical situation and composition of an alien planet, and for anomalies in the Earth's situation (solar or planetary variations).

The history of a star's formation, as well as its specific size, color, and temperature, impacts on its possessing inhabitable worlds. Nurtured by a G-type star of nondescript size and temperature, we are suspicious of stars near the ends of the spectrum, like blue giants and red dwarves. Although neutron stars appear in several SF stories, only Robert Forward in Dragon's Egg has ever described characters inhabiting one. Black holes are so exotic, even SF finds them stella incognita. This does not prevent their being used as a Black Box of sorts: Anderson, Benford, Niven, Pohl and others have written about human encounters with them.

Compared to stars, planets are so small and dark that their very existence outside our solar system has never been conclusively demonstrated. To present telescopes, a slightly perturbed stellar orbit would demonstrate at best the existence of a very large world, possibly indistinguishable at this distance from a neutron star or a black hole. SF draws its planetary models from our solar system, possibly unrepresentative, and from guesswork about effects of different kinds of stars on their own families of planets. Based on what we know of our solar system, a young planet might be quite volcanic and subject to heavy bombardments of solid matter. We would not think that a good candidate for harboring intelligent native life. Its formative eons would also determine its radioactivity and atmosphere; a world too close to its primary may have too little of the former and none of the latter. Deposits of minerals can also be guesstimated from planetary size, astronomical situation, and historical formation.

Otherwise, what matters most for a fictional setting are a planet's distance from its primary, its rotation, inclination to the ecliptic, mass, and any satellites it may have. These determine its revolution, day, seasons if any, gravitational pull, and tides, respectively. The existence of satellites may also interest intelligent species in exploring space.

The world that emerges has specific mineral and atmospheric elements, as well as a distinctive geography and topography. For each of these today we have a "mature'' science, although extending terms like geology and geography is provincial, since they derive from "geo'' or Gaia. In such sciences, we think we can extrapolate the behavior of physical elements and structures under foreseeable circumstances. Scientific assumptions based on a single planet may be inappropriate for other worlds, however. Planetary scientists' predictions often went awry when the Voyager probes beamed electronic impulses back to us as they passed other bodies in our own solar system. Landings on Mars and the mapping of Venus also yielded surprises.

Physical science includes more than inert matter, however distinctively it is composed or disposed. Natural processes take place on worlds and in suns unaided by life forms. In our Earthly experience, matter changes state, depending on temperature, air pressure, and other factors. In solid, liquid, or gaseous forms, it may combine with other matter. If its atomic structure is unstable, it decays radioactively. Chemical changes also take place without intelligent intervention, but science and engineering can speed or slow changes and introduce others not exploited by nature, if the potential is there.

At some point, life may emerge, in ways distinctive to the planet's biochemistry. Animate matter is subject to gravity and climate, length of day and seasons, and chemical constraints and incentives, such as fuel consumption, oxidation, and excretion of waste products. A constraint SF often overlooks or suppresses, perhaps even more than the limitation of the speed of light, is incompatibility of a world's biochemistry with another's life forms. The hard SF writer has some obligation to account for surmounting this obstacle. Engineering, even if it does not "terraform'' the planet, can equip prospective colonists mechanically with spacesuits or living quarters. Bioengineering may even be able to tailor colonists genetically to suit a world as suggested by Blish in The Seedling Stars and Le Guin in her Hainish Cycle of SF narratives.

Given a sun, a body in orbit, and an active chemistry, the writer needs life forms as well, even for a colony with an artificial support system. It complicates the model-making process, but biology also has rules worth observing—or imposing. In explicitly fictional constructs, we should not be surprised if biological needs determine the design of the world and its situation in space. At a step further back, of course, story-telling needs may dictate the choice of biological forms. In theory, however, the hard SF writer may simply start with cosmological invention, and let each step determine the next, as Clement and Forward have claimed to do on occasion.

Whichever the sequence of composition, physics and chemistry play a role in determining biology. A life form needs structure and support, and some means of sensing its environment. For it to survive and prosper, the functions it performs demand an optimum size. To move, it needs organs of locomotion large and strong enough to move its mass. Increased mental powers seem to require an ability to communicate and to manipulate elements in the environment. Its senses will be consistent with those functions and its environment. Means of communication will also be affected by its environment and the material of which it is composed. On Earth alone, life forms from dinosaurs to ants have found millions of solutions for these problems which worked for as long as the species lasted. These all have material bases and constraints.

Beyond physics and chemistry, biology has its own "emergent qualities.'' Life forms need an energy source, usually the nearest star, even if they use it only indirectly, i.e., living off stellar energy stored in a planet's molten core. Carbon, hydrogen, and oxygen, aided by heat, predominate in Earth's life forms, but life based on other chemical processes is conceivable. See, for example, Asimov's The Gods Themselves, Clarke's "Out of the Sun,'' Clement's The Nitrogen Fix, Niven's "The Green Marauder,'' and Stanley G. Weinbaum's ``A Martian Odyssey.''

The ability to move or at least grow means being capable of converting matter and energy into tissue. This restriction applies even to a life form of crystalline substance, for which expansion is the only means of growth, as in Benford and Eklund's If the Stars Are Gods. For these processes to work, physics and chemistry must permit ingestion, fuel consumption, and excretion. At the microscopic level, life forms "recognize'' complex hydro-carbons by their chemical shape, a talent subject to error which can be exploited by invaders, from drugs to viruses. According to our definition of life forms, they exhibit sensitivity to their environment and some ``decision-making'' capacity. Aliens interesting for fiction usually have other mental abilities, too. Brain functions in our experience require a substantial network of quickly functioning cells, even if they are not biological in origin. Even before the coming of computers, SF writers from Murray Leinster to Arthur Clarke speculated about electronic and inorganic brains. Analogies from computer science now crop up in discussions of human brains; using cybernetic models, we now find life forms and computers share electrical charges and switching capacity, if not chemical transmitters. SF writers from Stapledon to Theodore Sturgeon also have extended network functions to overcome the isolation of separate brains (analogous to cells in this context). The number and size of these networks vary, as does the degree of voluntary participation, though the material basis is largely sidestepped.

The most characteristically "emergent'' feature of life forms we know is the struggle for survival. Lacking mentation we can detect, inorganic matter moves and erodes involuntarily, although at least one Hal Clement story posits volition to underground pools of petroleum. With organic matter, volition is a familiar story. Given a finite economy, species compete for survival, and those that breed before dying bequeath the challenge to a new generation. Species which fail that test become extinct, and the number of extinct species far outnumbers those present at any one time. Natural selection is neither gentle nor relenting to species too slow to adapt. Life forms struggle to survive as individuals and as species, neither struggle being ultimately winnable. The chief means of biological survival are finding a niche, reproduction, stability, and flexibility.

Plants and animals do not come into existence, let alone maintain it, without raw materials, be those water and sunlight, symbiotic partners, prey (vegetable or animal), or a combination of these. Plants and animals that serve as prey must be fast, smart, tough, or inaccessible, to survive predators long enough to reproduce their kind. If no offspring survive to reproduce themselves, the species dies out, and with it every individual.

Niches are not permanent, either; floods, fires, climate shifts and overpopulation can turn a hospitable niche into a deadly trap. "Alien invaders'' (including humans) also change the balance drastically. Even winning the battle of survival is at best temporary; living things decay, generally at a faster rate than the inorganic world erodes, leaving only progeny behind to cope in the next generation. To survive as species, given this rapid decay, life forms develop strategies to make copies of themselves. The one planet where we have observed life reveals a profusion of reproductive strategies, from fission to fusion to sexual breeding, physically interpenetrating or at a distance.

New generations yielded by reproduction must resemble the old ones in most particulars, if they are to take advantage of the same or similar survival patterns. At the "atomic'' level, DNA and RNA ensure this consistency and continuity, but not exactly. Mutations, hybrids, and other adaptations are common, but generally less effective than the norm, otherwise they would become the species form. At higher levels of complexity, other conservative forces operate. A brain too slow or simple (and perhaps too fast or complex) may provide a meal. An unstable culture will disintegrate if it is not destroyed from without. Rigid stability is also counterproductive, given the potential changes affecting an ecological niche. All the eggs or offspring may be eaten, plants or people wither from drought.

Besides strategies for waiting out the change, migrating, and building defenses, nature has others in the germ plasm. Much of the DNA molecule is apparently "garbage,'' doing little to ensure stability; both there and in behavior, change can enable species survival—at the price of species modification.

As the organism interacts with its environment, survival requires both stability and flexibility. The biological imperative to survive and multiply conflicts eventually with the limits of the physical universe. The elasticity of these limits is evident from the success of ants, termites, beavers and humans in modifying their environment. The limits are finite, however, even if we don't know where the boundaries lie. Without intelligent intervention, ecological balance may be calculable; adding the potential for engineering changes the picture, but there's still a frame.

This interaction between organisms and the natural environment is ecology, the basic principle of which is not stasis but balance. Without environmental changes, change in organisms would have no survival value. The changes organisms go through, seeking an edge, themselves upset the equilibrium. Once evolution starts—i.e., when life begins—the "natural balance'' is continually in flux. If it is in the nature of human beings to manipulate their environment, the difference between natural and artificial virtually vanishes.

This continual change in nature Charles Darwin dramatized as the "struggle for existence.'' One of his major sources, Thomas Malthus, had recognized the mathematical nature of the problem, asserting that population, otherwise unchecked, will be stopped by exhausting its environment. The basic principles of Darwin's theory—natural selection and species variation—permitted calculation of the changes in balance. It was not until Gregor Mendel, however, that the ``gene'' was identified as the atomic principle behind the mechanism of stability and change.

The flexibility of germ plasm has caused Darwinists some difficulty in dealing with borderline classifications. Distinctions require language, making the problem partly semantic, like differentiating a cult from a sect, or a weed from a garden plant. At some point, however, just as old species die out, variation brings new ones into being. On our world, some of these variations are induced by other species. We must assume at least the possibility of comparable engineering projects on other worlds, but the evidence can only be drawn from human history.

Some symbiotic relationships (e.g., ants and aphids) may suggest forced breeding by species other than ours. The interventions with which we are most familiar, however, are wrought by human beings, from breeding domestic plants and animals to deliberate thinning out and accidentally strengthening pests. Unanticipated effects are common enough in ``vital engineering'' for fantasy and SF to find it a fruitful area of biological science. Almost as common as the monster motif in film is the superman in prose fiction.

Postulating radical changes in human form has been a popular entertainment since classical times, practiced by poets, prose romancers, and mostly anonymous travellers. Mary Shelley's Frankenstein is the first story to suggest even vaguely scientific means and motive for creating (or recreating) human life, though her minimal science, like most people's in that era, smacks of alchemy and magic. Intervention in natural biological processes appears in the proto-SF of Edgar Allan Poe, Nathaniel Hawthorne, Ambrose Bierce, and Fitz-James O'Brien, culminating in Wells, and continuing to the present. Fiction has treated three major areas for intervention; in ascending order of difficulty, these are changes in mechanisms, species, and habitat.

Good at analyzing and producing mechanisms, technological humanity has developed many ways to extend lifespan and preserve a reasonable facsimile of "mature powers.'' Eye-glasses, hearing aids, prosthetic devices, metal and plastic joints, iron lungs, kidney machines, and artificial hearts are some examples from the arsenal of medical technology. Their potential for fiction is mainly limited to the medical drama involved, when the technology is first developed; later they are usually trivial. Anyone relying on artificial aids could be termed a "cyborg,'' but this term in SF usually evokes a being of mixed identity, often unsure how much of it is human or machine. Asimov, Alfred Bester, Philip K. Dick, Damon Knight, and C. L. Moore have written classic stories on this theme. Increasingly porous interfaces between human and machine make the question progressively more relevant for humanity as well as for SF.

Transplants and transfusions have caused social problems on Earth for cultural reasons. Dramatic questions have been raised concerning supply and demand, as well as prejudice between groups regarding themselves as enemies. The employment of surrogate mothers has raised the spectre of poor women renting their wombs. Such "baby farming'' arouses both civil libertarians and religious moralists, though it largely escaped notice in Clarke's Imperial Earth.

At a sensational level, identity questions arise in a number of areas. The courts have already decided parental rights over eggs fertilized in vitro. Cloning, already achieved with less complex life forms, raises identity problems, as Le Guin speculated in "Nine Lives'' and John Varley in several narratives. Identity is also at issue in the highly speculative example of brain exchange, treated satirically in a Thomas Mann novella, "The Transposed Heads'' and a Steve Martin film, The Man With Two Brains. Varley's stories treat it as a serious medical procedure, while writers in many media have almost taken for granted the possibility of electronic storage and reproduction of brains alone, or brains and bodies. SF examples include Algis Budrys' Rogue Moon and every story involving ``matter transmission,'' which must record the entire being it transmits.

Discovery of the DNA molecule unleashed other potentials on the world, including isolation of faulty genes and chromosomes, and the manipulation of the germ plasm itself. Progress on the "human genome project'' portends not only medical advances, but also the selection and production of desired characteristics in offspring, such as strength, intelligence, height, color of skin, hair, and eyes. This prospect raises the historical spectre of "ethnic cleansing,'' but it goes further, suggesting possibilities for changes in what we now think the human race does or should consist of. J.D. Bernal raised that possibility over 60 years ago in The World, The Flesh, and the Devil; Pohl's best satirical take on it is the short story, "Day Million.''

In such projects, as in cloning, surrogate motherhood, and artificial wombs, some feminist science critics see efforts to free man from dependency on woman. Yet cloning and asexual reproduction raise other issues of gender, too, theoretically freeing women from childbirth, permitting gender shapeshifting, and rendering men unnecessary from a biological point of view. These issues have been raised in SF by Marge Piercy, Joanna Russ, Alice Sheldon, Delany, and Varley, as well as in the classic depiction of an alien world free of limiting gender roles, Le Guin's The Left Hand of Darkness.

Before manipulating ourselves radically, of course, numerous writers have suggested we will meddle with other animals, perhaps developing talking dogs as in Roger Zelazny's The Dream Master, or chimps designed for dangerous construction work, as in Heinlein's "Jerry Was a Man.'' Humans have bred other species for millennia, occasionally crossing the line into new species. The upper classes in human society traditionally attempt to breed their own subspecies, via arranged marriages, for example. The "Nobel Prize sperm bank'' makes similar eugenic possibilities available to any woman. Dr. Frankenstein's revival of cadavers gave way in fiction to Dr. Moreau's "beast-men'' created by vivisection. The technology is different but the goal comparable for inventors of "designer genes'' and newly patented organisms. On the horizon, moreover, are biologically-based computer chips, represented as causing unforeseen but essentially positive changes in the human race. Paul Preuss is basically extrapolative in Human Error, Greg Bear transformational in Blood Music.

Human beings have altered their habitat at least since they discovered fire and invented tools, with major changes for nature in the Neolithic Revolution, the invention of cities, and the coming of industrialization. Since the last ice age, technological developments have enabled the species to expand and multiply. Such development has made it possible for more people than ever to live longer, more productive lives. It has had its drawbacks, however, for humans have made other species extinct, and it now threatens extinction for the human race itself. SF has chronicled thousands of disasters, from the sober speculation of George Stewart's Earth Abides to the heated extrapolation of Brunner's The Sheep Look Up, to paranoid scenarios like Wells' War of the Worlds and Thomas M. Disch's The Genocides. SF cinema contains an even higher percentage of catastrophes, though Hollywood's ratio of positive endings is also higher.

SF writers have imagined ways out of this mess, once termed the World Macroproblem by the Stanford Research Institute. Some of these involve giving up the comforts as well as the drawbacks of technological civilization, returning to the more rustic lifestyles of Leigh Brackett's The Long Tomorrow, Russell Hoban's Riddley Walker, and Edgar Pangborn's Davy. To maintain a technological civilization indefinitely, SF narratives often require life support systems, underground (E. M. Forster's "The Machine Stops,'' Harlan Ellison's ``A Boy and His Dog''), underwater (Henry Kuttner's Fury, Delany's ``Driftglass''), or under domes (Evgeny Zamiatin's We, John Boorman's film Zardoz). Off-Earth, the Moon is a favorite domicile and other occupied planets are too numerous to mention. Space stations or colonies have proliferated from the simple extrapolation of Clarke's Islands in the Sky and Blish's Cities in Flight tetralogy to the elaborate self-replicating galaxy-wanderers of George Zebrowski's Macrolife.

7. Soft Sciences. Brains, communication, and culture seem to be inseparable, a three-way chicken-and-egg problem. Two brains in communication form a miniature sub-culture. Increasing the number of brains in communication makes cultural manifestations more unifying, simultaneously isolating encultured groups from each other. Brains and bodily expression are generally presumed to be material, though the shapes and means may bear little resemblance to those with which we are familiar, even among the profusion of life forms known on Earth. Communication and culture require these material attributes, but they need others, too. Communication demands a development of codes or conventions; unable to exist without them, culture develops out of and also enforces them.

With culture come social organization and engineering. Both bring new elements into the game of survival, contributing to and withstanding pressures of the social as well as the natural environment. Both involve effects of thinking and communication on the environment, from agriculture and habitat construction to other innovations already mentioned. Communication inevitably breeds conflict, and social rules breed transgressions, which turn into crime and war; war in turn potentially leads to wholesale destruction of a country, an entire world, or just possibly interstellar alliances of worlds. Attenuated as they are, the material bases of culture and communication are very real, and the potential for multiple interactions immense, making a true science of culture difficult if not impossible. Comparability, control, and measurement become possible only along statistical lines, a situation not totally inconsistent with the state of affairs in subnuclear physics.

Still more complicated than biology, let alone physics, the soft sciences achieve quantitative prediction and control mainly by applying statistical methods to groups of people. Useful principles can arise out of the soft sciences, though they are hard to prove or disprove, and subject to rapid obsolescence in a fast-changing history. Complicated by sheer volume, multiple levels of interactions, motivation by symbols, and awareness of being observed, the human sciences are also limited in our society by laws regulating experimentation, unreliable testimony of witnesses, and a degree of resistance to the very idea of our being predictable. Their relevance to world-building is apparent only where intelligent life is involved, but readers of fiction have a limited interest in any other kind. We have evidence about only one intelligent species but the known history of its many distinct cultures yields a large variety of alternatives. Brain science, behaviorism, economics, and sociology, all relevant to the construction of alien beings, are discussed below in order of decreasing reliability.

Psycho-biology, psycho-chemistry, and psycho-physics have shown great progress and even greater promise studying the brain and nervous system as material objects. Brains of both sick and healthy animals, including humans, can now be analyzed in detail, practically without disturbing the subject. Speed of synaptic response can be measured and location of receptors determined. Charted in detail, effects of both physical and pharmacological stimuli (electrodes and drugs) can be quantitatively predicted. A legitimate category of biological (hard) science, brain science is a soft science in terms of how much it can not do, both legally and physically. In SF, however, less limited versions of brain science may be postulated and enacted, such as Pohl's "Purchased People'' stories, Niven's "Death by Ecstacy'' and Michael Crichton's Terminal Man.

Partly because adherents claimed too much for it, partly because human behavior varies so widely, partly because people—even scientists themselves (out of uniform)—bridle at the idea of reduction to stimulus and response, behaviorism has a bad name with the public, but it refuses to go away. Behaviorists treat human behavior like that of other animals, disregarding what may actually go on in the Black Box we call a brain (like brain scientists, they avoid the word ``mind''). They hold that human behavior can be explained in terms of physical constraints and cultural conditioning. Indeed, for simple operational procedures throughout the world of science, behavioral assumptions are largely accepted. Cultural conditioning is highly complex, of course, and this complexity is intensified by interaction with the autonomy claimed by individuals (including behavioral scienctists). As a result, behaviorism has never been mathematically predictable over a wide range of analysis, although its claimed potential enables SF writers to project behavioral assumptions into imagined worlds, human or alien.

The psychoanalytic theories of Sigmund Freud and his contentious disciples offer to explain individual behavior via simple principles complexly interpreted. Freud's background in medical research, scientific aims, and attempts at objective expression lent his discipline a measure of scientific standing. Softest of the sciences, more a pseudo-science, it is systematic and based on close observation, but its findings lack refutability. Partly as compensation, its adherents sometimes approach religious fervor in their own behavior. Both theory and therapy, psychoanalysis offers to explain and to cure. With a cure rate roughly equivalent to that of witch-doctors, however, and a metapsychology exploded by brain science, it has fragmented into myriad cults while maintaining some allegiance from literary critics.

The "talking cure'' does mirror how people process inchoate ideas bubbling up from the unconscious, including writers and critics. More an art than a science, psychoanalysis offers convenient labels for broad-scale behavior patterns. It has created a kaleidoscope of metaphoric constructions, such as the unconscious and its divisions (id and superego), the multiplication and fragmentation of images, and the repression of uncomfortable memories and bodily urges, especially those of sex and violence. SF writers making explicit use of psychoanalysis include Kuttner, Moore, Pohl, and Sturgeon; Le Guin's artistic allegiance is more to Jung, though intellectually she has claimed to lean toward Freud. The most prominent Freudian analyst of SF was Dr. Robert Plank.

In the long run, everything can be reduced to economics, as the struggle for existence by other means. Eventually, stars burn out, even the universe reaches a steady state, after all the essential but scarce goods of energy have been spent. The balance of nature is one branch of economics, but usually we reserve the term for the actions of intelligent beings organizing their material existence.

At one extreme, only Adam Smith's "invisible hand'' of supply and demand regulates the pure market economy. Given rational behavior by consumers and producers, price, service and accessibility determine survival of the fittest among producers and marketing outlets. The same principle should apply in the sale of ideas as in that of widgets. Pure laissez-faire economy only exists in the imagination, however, as nostalgia for communitarian open markets where everyone knew everyone else or as a set of libertarian principles best fitted to a society of wolves. Modified market economies do operate in the real world, and the invisible hand can be represented in a purer state in a work of fiction, operating in a nearly deterministic way, with obvious advantages for SF projections. Laissez-faire capitalism shares with Mercantilism the background of Anderson's "Polesotechnic League'' stories and novels. Heinlein's The Moon is a Harsh Mistress argues the necessity for a market economy, while a Libertarian position is represented in his Farnham's Freehold and J. Neil Schulman's Alongside Night.

Theoretically, one could design controls more efficient than those of the market for using raw materials, transportation, and personnel, educating or otherwise inducing consumers to buy what is available to sell. Utopian fictions may succeed as designed, but utopian communities don't, including nations that pretend to put "socialist'' principles into practice. Conscious design and deliberate planning, regardless of idealistic intent, run afoul of human desires for variety, uniqueness, and status. The conflict between pragmatic ideals for all and preferences for the individual impassions many a SF story, not just those with a dystopian theme foregrounded. Beyond Ivan Yefremov's Andromeda and Ernest Callenbach's Ecotopia, we can cite Heinlein's Beyond This Horizon and Pohl's The Age of the Pussyfoot.

Economic systems in the real world are much more complicated than either model. "Capitalist'' countries have safeguards to mitigate cutthroat extremes, to protect businesses as well as consumers, and to maintain an environment in which competition is worthwhile. ``Socialist'' countries have ``safeguards'' of their own, including black markets and competition for status and party favors. Stories reflecting this complexity express more verisimilitude than either extreme. Like physical laws, both models set constraints, though it is uncertain whether these limits are real or simply psychological barriers we can not imagine going beyond.

The most widespread attempts to apply deterministic principles in economics are the social dicta associated with Karl Marx and the heirs to his mantle, who made it a coat of many colors. Like psychoanalysis, Marxism is both theory and therapy, lacking even Freud's medical discipline or scientific reserve. Marx and Friedrich Engels attempted scientific analysis, but their expression of it rarely escaped polemic, since the analysis revealed to them both the need and means for action. As a cure, Marxism is a disaster, though victims of capitalist oppression still cling to its often laudable ideals. Various conceptual formulations of Marx and Engels, moreover, concerning ideological constraints, historical materialism, class struggle, and mutual interactions between economic interests and the rest of culture have found their way into the common fund of knowledge.

Heavily indebted to Smith and Friedrich Hegel, Marxist theory has been refined by several generations of intellectuals, at variant distances from revolutionary fervor and party discipline. The mechanistic laws Marxists tried to construct have been less fortunate, but they still offer potential for extrapolation. Soviet SF found use for them, not always by choice, but so have British and American writers, not all of whom were sympathetic to the Marxist cause. Communitarian futures appear in Aldiss' Enemies of the System and Benford's Against Infinity, variations on anarchism in Le Guin's The Dispossessed: An Ambiguous Utopia and Eric Frank Russell's "And Then There Were None.'' Since SF includes materialist futures alternative to capitalism, Marxist or Marxian critics of SF are common, the best known being Darko Suvin and Fredric Jameson.

Statistical evidence often serves as raw material for economic models, but sociology as a science depends mainly on statistical analysis of group behavior. Along with economic models, sociology has proposed a profusion of principles for understanding more or less rational behavior. Sociology does a better job anticipating many behaviors than leaving it to chance, but even the best models have a 5-10% error rate. Such models typically involve "controlled'' situations, large numbers of subjects, and research subjects largely unaware of their status. At best only snapshots of the moment of interview, opinion samples can easily be skewed by subjects dissembling. Dissembling is more or less predictable on controversial issues, but it can also embody contempt for surveys and surveyors in general. More reliable models are traffic patterns, in buildings and on highways, though mechanical breakdowns and accidents cramp the predictive model. Statistically, corporate and national behavior can also be predicted, or at least designed into an alien world.

Like psychology, sociology has a major split between its experimental and reflective sides. Experimental sociology is often a handmaid of sales campaigns, for political candidates as well as commercial products and company reputations; otherwise, it may only confirm the obvious in a complicated manner. The reflective branch builds elaborate theories on the basis of available information, which often wind up as intelligent but biased guesswork, impossible to disprove. Even where sociology is eminently sensible, it is more retrospective than predictive. From the standpoint of prediction and control, it may be less an empirical science than a pseudo-science, but that hardly incapacitates it for extrapolation. Delany's Triton, Pohl's Jem, and a number of works each by John Brunner and Mack Reynolds are just a few of the many SF examples of sociology in action.

From its origin in Saussure's linguistics, structuralism proliferated into other areas of cultural and literary study. Promising to be the quantum theory of cultural studies, structuralism seemed a way to quantify observation beyond the vagaries of surface irregularities. Its major exponent, Claude Levi-Strauss, extended the model of arbitrary and systematic language into kinship relationships, table manners, totemism, and other largely unconscious social contracts. He did not succeed in eliminating the role of the outside observer, however. Rather he imposed a set of arbitrary values into the analysis, such that his own interpretations often defied replication by others.

In literary studies, structuralism quickly fragmented into numerous analyses based on virtually any perceptible analogy to structure(s) of language. Language may be based in arbitrary distinctions, but literary use of language is a highly self-conscious use of verbal and social codes and conventions. This reflexive self-analysis may have made the disintegration of structuralism inevitable, leading to deconstruction and other post-structuralist positions. The most prominent SF writer and critic overtly associated with such concerns is Samuel R. Delany, but readings have recently emerged of Dick, Gibson, Lem, and the borderline SF of Italo Calvino, in which post-structuralism, postmodernism, and "chaos theory'' seem interwoven.

Psychoanalysis, dialectical materialism, and structuralism may technically be pseudo-sciences, but they have enough cultural respectability to escape that definitive judgment. Even less science or inertia supports certain other "disciplines.'' Just a gleam in Asimov's eye when he began his `"Foundation'' series, psycho-history may be an unconscious mirroring of Marxism, as Charles Elkins contends. It is also a more market-oriented attempt to treat social history as statistically predictable on a large scale. For Americans leery of Marx, it can provide a model, largely uncredited, for forecasts of human development, both on and off Earth, building up at one point what Donald A. Wollheim called a consensus ``cosmogony'' for the field. The best known is Heinlein's "Future History'' but Cherryh, Le Guin, Niven, Pournelle, even and "Cordwainer Smith'' have adopted their own versions for narratives set in a stable historical context.

8. Collaborative Efforts. Each story set on an alien world uses scientific principles and techniques to build up a picture of that world. Writers of hard SF make a virtue of this necessity, stressing it in essays based in their own writings. Interested mainly in story-telling, Poul Anderson has created in his fiction many alien worlds and relations with alien species, in which human protagonists are involved. He has also written non-fiction about making human-habitable worlds convincing. Clement was probably the first hard SF writer to detail in an essay, later an afterword to Mission of Gravity, its scientific extrapolations. He has since written about how both alien worlds and alien life forms can be developed in the imagination from scientific principles, and has carried out these techniques in a dozen novels and several dozen short stories. Clarke and Benford have also written non-fiction in support of their fiction. A great propagandist for space travel and the conceptual inventor of ``stationary'' communication satellites, Clarke wrote fiction and essays on parallel tracks. Benford's non-technical non-fiction tends to hone in on SF ideals, with obvious references to his own practice.

Perhaps the most extreme exponent of science for its own sake in SF is Robert Forward of Hughes Laboratories, whose research reports on space drives, anti-gravity, and other "far-out''' science have been made readily available to SF writers and critics over the years. Each of his novels published in the 1980s takes place on a world different enough from Earth that he has to rely as a guide for what could happen on the scientific principles according to which the basic situation could exist. They illustrate the point he made at the 1983 Eaton Conference on hard SF: when faced with a story-telling decision, he sometimes "lets the science write the story.'' The physics and chemistry of the situation themselves make characters' behavior inevitable or at least probable.

World-creation is an act of tremendous arrogance, for one writer or even a team of savants. The reason is not religious scruples but the need for knowledge in so many fields of science to do the job well. Even when it is done well, the accomplishment is only temporary. The project will eventually "date,'' either because its hypotheticals have come true or because some new discovery or historical event cancels out its assumptions. The complexity of the task has been recognized openly more of late than in earlier SF, which often has a slapdash quality. Writers today acknowledge and follow more scientific sources or openly pool various kinds and levels of expertise.

Such informal collaboration has gone on undercover for generations, but some of it now surfaces publicly. A community college in San Jose, California, hosts an annual conference at which scientists, writers and readers build and act out alien contact scenarios. An East Coast scientist regularly advertises in specialty publications his availability as a paid consultant helping design alien worlds. Scientists, many without SF affiliation, are credited in footnotes and afterwords, even in novels by established SF writers like Clarke and Preuss. Such credits have long been the practice in SF feature films from Things to Come (Wells, 1936) to Destination: Moon (Heinlein, 1950) to 2001: A Space Odyssey (Clarke, 1968), all made with advice from numerous scientists. For its setting and cultural behavior, even an unscientific a recreation of prehistory like The Clan of the Cave Bear (1986) had as technical advisor primate specialist Desmond Morris, also employed on 2001.

Two recent literary instances merit special mention. Supplements circulated with advance copies of Helliconia Spring (1982) by Brian W. Aldiss made explicit his indebtedness to members of the scientific community. Two things make this example stand out. No scientist himself, Aldiss enlisted a team of scientific advisors to aid and correct him in creating the alien world on which his trilogy was set. Moreover, it was apparent that his publisher thought making this news public was good advertising for an ambitious set of novels by an author not previously associated with hard SF.

In recent years, several shared-world anthology series have been assembled. Innocently proposed by the French critic and novelist Michel Butor, something similar was roundly attacked by SF writers and critics in the Sixties because of its dangers for higher concepts of art as well as for scientific ingenuity. Actually pioneered in "triplets'' of novellas published by Twayne in the 1950s, this concept is regularly used in the Star Trek universe and standard in virtually every film and television series. With the basic situation already worked out in the context of scientific constraints, each author can work changes on it, even affecting stories written by others. In microcosm, this is not unlike the fictional galaxy or universe SF writers have shared in a dialogue at least since the 1920s. It even has the beginnings of an artistic defense in Delany's argument for sequels in The American Shore: an invented world has more potential than an author can use up in any single narrative.

One notable example of such scientific and science-fictional teamwork is Medea's World, an anthology edited by Harlan Ellison, who is even less scientifically oriented than Aldiss. Derived from a Continuing Education Seminar at the University of California, Los Angeles, this book includes both stories set upon a consensus alien world developed during the course of study, and essays helping to set it up and explain it.

9. Extrapolating Historical Processes. Historical extrapolation is already implicated in world-building. Abstractly, each scientific prediction is a forecast, but we usually call "historical'' actions taken by human beings not bound to a traditional cyclical conception of time. Extraterrestrial beings may have a history, but their actions are part of our creation of their world as in Blish's A Case of Conscience or the Niven and Pournelle A Mote in God's Eye. Whatever the human allegory present, invoking the alien has a distancing effect. About their history we can be relatively neutral, if they do not threaten our survival. Regardless of which are the interlopers, moreover, the story will say something about our present precarious toehold in the universe or on our home world.

In stories explicitly involving Earth in the next century or so, a key component is the extrapolation of ongoing historical processes. While the fictional elements of world-creation can usually take for granted the physical elements of world-creation, interaction between homo sapiens and its planetary environment is almost always significant. Unlike the extrapolation of scientific processes, that of historical processes seldom takes a convincing pose of neutral objectivity. Whether the human race has a future, and what kind it will be, is of vital interest to both writers and readers of SF. It is something over which there are profound disagreements as well. The future in American (and Soviet) SF dominant through the 1950s usually assumed widespread technological expansion. At some level, writers may have seen technological expansion more as a threat than a promise, as Barry Malzberg argues in Engines of the Night. Itself a creature of an age of science, however, the corporate entity of SF has a vested interest in technological innovation and relatively free scientific inquiry.

Forecasters deal in predictions of a sort, but they have virtually no chance to control the situation under study, or even to isolate it. What they study is not replicable, since historical circumstances are never identical. While their forecasts may come true, realization of a single prediction does not validate the techniques or make a prophet reliable. Less a science than an art, forecasting has degrees of validity and plausibility, invaluable for writers of SF. It also has a variety of applications, in the hard sciences, soft sciences, and fiction writing.

Forecasting is not prophecy; it does not read palms, tea leaves, the stars, auguries of birds, or entrails of animals. Forecasters make no claims of infallibility. A human exercise in anticipating the disposition of the material universe by both human and environmental forces, forecasting deals in estimates of probability. Among its verbal outcomes are predictions, projections, and scenarios, all of them limited in scope, assumptions, and degrees of certainty.

Predictions focus on very narrow segments of activity, closely limited in context. Astronomical predictions are pretty sure bets, and weather forecasting is more accurate than it gets credit for being. Predictions involving human behavior are more problematic. The record of technological forecasting is not bad, and economic and demographic predictions provide moving targets, while market research best functions as self-fulfilling prophecy. Often wrong, and surrounded by fuzzy borders even when they're right, predictions at least are definite about something.

Projections are more broadly conceived, generally in the plural, and indefinite to a fault. Even if certain conditions hold true, and barring catastrophe, the expert consensus usually suggests multiple foreseeable outcomes of a present combination of factors. ``Alternative'' futures describe a range of possibilities and probabilities, extended from analyses of intersecting and contradictory trends. Projections may be couched in mathematical terms, but equations can not encompass all the myriad decisions and exceptions that determine real futures.

More imaginatively realized, scenarios are not just numbers on a graph. If not minimally dramatized, a scenario is at least depicted as involving people, like an architectural model. It shares with predictions a narrow focus. A scenario is also likely to be more speculative than a projection. If the term is borrowed from cinema, the activity is familiar in fictional treatments of future possibilities (utopia, dystopia, and SF).

Reputable forecasters phrase their pronouncements in restrained language. They specify as much as possible their operating assumptions; if the underlying assumptions are wrong, the forecast may be worthless. Forecasters typically underline their forecasts' relationship to context and offer alternative scenarios. They condition their degree of certainty about an event's occurrence and when to anticipate it. They also sometimes objectify numerically the probability of their forecasts' coming true. Inexact as forecasting is, it has its values, in business, government, and fiction for anticipating the expected and the surprising.

Even in ancient Babylon, where astronomers read their nation's future in the stars, forecasting had many applications, but its track record is always spotty. Then as now, farmers wanted reassurance about the weather, business about the economic climate, rulers about their term of office. Of today's wide variety of forecasts, only celestial mechanics is fully reliable. Paradoxically, however, as forecasting gets less reliable from meteorology to social psychology, our desire for guidance in facing the future becomes greater, prompting us virtually to feast on shadows. This gap leaves SF writers a lot of free play in areas that matter a great deal both to them and to their readers.

The most reliable predictions are in the hard sciences, out of which fictional world-creation proceeds. Eclipses are safe to predict, as are "sunrise'' and "sunset,'' even in cloudy weather. Tidal ebb and flow are consistent, meteor showers periodic. Even sunspots are cyclic, though not all flareups are predicted. Among physical phenomena, over which human actions have no sway, the decay of radioactive substances is virtually invariable. Scientists are only starting to offer rough predictions, however, of seismic activity and vulcanism. Where human contributions are variable, as in the depletion of the atmosphere's ozone layer and the phenomena of global warming, we can sensibly project only a range of probabilities.

The principles of meteorology are so well-established and systematic that its components can be reduced to mathematics. Observation stations around the world are supplemented by satellite snapshots, of visual phenomena, humidity, air pressure, air and sea temperatures, and wind velocity. The general patterns of movement induced by the Earth's spin and by temperature gradients between the poles and the equator are well-known. So are the differential effects on weather patterns of passing over land and sea, mountain and desert, country and city. Yet for a physical science, its predictions are not as reliable or precise as everyone wants.

Generally speaking, weather predictions are most reliable in a middle range. If rain is falling 10 miles west of you with the winds moving east, expect precipitation soon in your vicinity. One-day predictions for a larger geographical region are less precise. Five-day prediction is risky, one for six months to a year chancier still, but much less precision is expected. At either extreme of scope, the picture becomes fuzzier. Climate change over a long period and a large area (e.g., the world) is a subject of speculation, but seldom of certainty. Micro-climates, centering on tall buildings and topographical anomalies, can defy the experts. Part of the imprecision may stem from incomplete modelling techniques. Computer models are no better than the information fed them and the assumptions built into their programs. On both counts there are factors not fully understood.

Precise observations are not feasible for every square inch of the globe, and historical records are woefully inadequate, reconstructed from such evidence as tree rings and sedimentary beds, over time-periods virtually inconsequential in the history of the planet. For eons longer than the outside estimate of the human race's three million years, Earth was too hot or cold for human survival, let alone civilization. Even in historical times, the temperate zones have known periods uncomfortably warm and chilly, but the cycles and causes are not well understood.

Meteorologists deal with an interdependent global system, in which there are puzzling instabilities. The jetstream over North America does not always stay in its typical range of latitudes, for example. Pronounced and prolonged upwellings of warm water like El Ni˝o in the central Pacific are unpredictable. Pockets where the ozone layer has been compromised by human waste products presumably have or will have an effect on the whole system. Even the planned shutdown in production of chlorofluorocarbons will yield no noticeable improvement in the depletion rate for 15-20 years, as residual chemicals waft their way up. Since the overall weather system is a continuous process with no apparent beginning or end, simple cause-and-effect thinking is inadequate.

The other major problem in producing satisfactory weather predictions is customer demand. Hurricane and typhoon watches are generally but not universally successful in warning people of needed evacuation measures, because so much instrumentation and attention is directed on a relatively small pocket of weather. Tornados are smaller and considerably more sudden; forecasters can only project warnings of probable tornado activity, leaving individuals to safeguard themselves at the signs of imminent disaster. The temperature range in which humans can survive unaided is small in cosmic terms, the comfort range smaller still. Weather forecasters actually give good probabilities for precipitation and temperature ranges over a moderate geographical range. The average person often wants to know how to dress for the day or night in specific geographical areas, and that range of precision just isn't available.

If weather forecasting is problematic, where the components are inanimate and basically understood, much chancier are the varieties of social forecasting, where human beings are involved and the determining mechanisms are broadly outlined at best. Technological, economic, and sociological forecasting methods are the best tools available so far. They at least give planners and fiction writers something to shoot for. Of the areas considered, technological forecasting has the best track record. It also has the most sophisticated tools and the narrowest scope of study. Technological forecasters routinely predict not only whether something will be developed, but also when, sometimes within narrow parameters.

In the short range, engineering developments can be found on drawing boards and their exploitation anticipated along a ``development curve.'' A typical 15-year period for new technology lasts from inception to mass availability, taking into account competing solutions to a problem. Over a longer range, forecasters consider more universal long-term demands, based on the potential of existing technology, priority direction of resources, and pure guesswork. A private firm or government agency trying to develop a technology has its own timetable, affected not only by problems resisting engineering solutions, but also by organization and financial problems often unrelated to technological feasibility. Cost-overruns are not infrequent, especially if the federal government foots the bill.

Technological forecasting outside one's immediate project is more problematic. It largely depends on a consensus of experts in a discipline. Researchers outside a project have limited access to proprietary information, via conferences, periodicals, telephone calls, E-mail, and even industrial espionage. Surveys like the DELPHI method, however, ask general questions about the likelihood of a certain problem being solved. Recycling a first round of answers through the same experts produces a high degree of probability, even if many participants are hesitant to reveal their own activity. The DELPHI method is particularly effective for ongoing or anticipated activities where the capacities of the market and the technology are established, and the skill of the questioners is highly competent. Even then, technological feasibility may not suffice, as picture-phones demonstrate.

Forecasts for ``breakthrough'' technologies or ``wild card'' activities are less reliable, almost by definition. Forecasters sometimes reach beyond the realms of their expertise as well. Some technological advances, for example, are widely anticipated with no hard data available on the solution of the problem. They include controlled nuclear fusion, safe hydrogen fuel, cryonic brain preservation, space drives more economical than rockets and/or capable of a significant fraction of the speed of light, and space elevators (continuous loop transporters between earth and a body in synchronous orbit around the equator), not to mention cures for cancer and the common cold.

Technological advances such as these are a staple of SF, vying with alien contact for central position in the genre. The SF writer lacks the engineer's responsibility for making something work, or the marketer's problem of getting people to buy it at a price that makes a profit. The writer's obligation is to make plausible both the science and the demand behind the advance. Some stories basically stop there, yet the writer also has the option of treating the workings of an advance as a Black Box. A story with social relevance and resonance will also suggest possible effects of an advance, especially unintended consequences. As an entertainer, moreover, the writer has the responsibility of finding a striking or dramatic way to incorporate the advance into a narrative.

"Economic man'' is assumed to make decisions in his self-interest, rationally analyzed. Less reliable than technological forecasting, the economic variety is more suggestive for dramatic conflict, despite its reputation as the "dismal science,'' an adjunct to accounting. This model is adequate to many spheres of action, and extendable to the greater economy of time and effort expended, not just money. Economic forecasting is notoriously unreliable, however, even at the macro level. Governments, businesses, even individuals depend on economic forecasts for management, budgeting, and planning (each in itself a kind of forecasting). Soviet-bloc planners are prime examples of the impossibility of accounting for all relevant factors, including human obstinacy, and planning effectively for all contingencies. A market economy also involves a variation of the Hawthorne Effect. Knowledgeable people in positions of power can react swiftly to forecasts and actions by both government and business, slowing or even reversing their effects. Ordinary consumers can have a similar effect acting in concert, acting strictly for themselves, with no premeditated social effect; fear of a shortage can lead to hoarding, which makes the shortage certain.

If technological forecasts succeed within certain limits, and economics reliably measures desire, sociological forecasting is still in its infancy, seeking a purpose as well as a sound methodology. For fiction, this leaves a lot of room for arbitrary or thematically-linked invention, however constrained by natural law, technology, and economics. Examples of applied sociology include demographics (population statistics), market research (politics and products), and fashions (including fads).

Human population growth must have limits; it can not be the only component of Earth's biomass, let alone the planet. Nobody knows, however, which constraints will kick in when, if growth is not slowed voluntarily. With modern medicine greatly reducing the brake of infant mortality, voluntary birth control (correlated with higher material living standards) is the only means of compensation we regard as humane. Other killers persist, however, and large families are the norm in many parts of the world, for rational economic reasons as well as traditional religious teachings. Factoring in war, pestilence, and birth control, demographers typically work with low, medium, and high estimates over short, medium, and long terms. Projections are largely guesswork, with breeding decisions in the hands of individuals, but business, religious, and governmental policies can have significant effects. Besides plague, war, and programmatic reductions in fertility, SF writers like Aldiss, Blish, Brunner, Pohl and Kornbluth, and Robert Silverberg, have considered varied effects of continued growth.

Applied demographics, using such estimates for financial gain, attempts finer gradations of cultural and economic difference. While education has been notoriously fallible in predicting future needs, some business ventures have been more successful. Researching what people buy, wear, eat, and watch and how they vote has become a major industry, with computerized inventory records and market profiles tracking behavior by postal zones, voting districts, even city blocks. Forecasting future behavior has limited scientific validity, however, based as it is largely on straight-line extrapolations, often static or inertial.

Demographers may turn up solid economic data based on what people do, but pollsters can only measure what people are willing to say, at the time they are being polled. Rarely disinterested, such research affects behavior primarily if followed by immediate efforts to reinforce or rechannel the opinions revealed, something competitors are also attempting from a different angle.

At the level of culture, history and sociology chronicle changes in taste and fashion, but cannot predict them with any accuracy. To create self-fulfilling prophecies, the fashion industry uses enforcement mechanisms like the cabals that decide the colors to be marketed each year, but none is foolproof. Fashion also has material causes, including availability of textiles or composites. Over time, Clothes even make broad symbolic statements that no individual may actually have planned. Black suits and stovepipe hats embodied the grimy industrial cities of the 19th century; white gloves and high heels suggest a woman of leisure. Sociologists have also found fashion cycles keyed to such indices as gender ratio, economic conditions, war and peace. Rising and falling necklines and hemlines may adhere to regular periods, but they are only part of a style, and not everyone follows the dictates of haute couture.

Fads generally have a shorter and largely predictable lifetime, the inevitable end of which businesses often fail to anticipate. Forecasters can offer generalizations about typical cycles; some, like Faith Popcorn, even work at a level comparable to astrology in offering guidance to business. SF writers like Brunner, Delany, and Spinrad also invent changes in fads and fashions, new slang and customs as well as major clothing styles and individual fashion statements. Subject only to constraints of contemporary plausibility, such inventions are entertaining but usually date quickly. They rarely succeed as prediction.

Forecasting is not strictly a scientific activity. The factors to be considered are many, few of them simple, and chief among them is the unpredictability of the isolated individual. Only on a wider scale and a longer time- frame, subordinating individuals to statistical analysis, can forecasting hope to reach a high degree of scientific reliability. Even then, interpretations will differ. A mixture of possibility and desire, social forecasting is primarily an affair of words and ideas, i.e., a literary activity.

10. Literary Forecasting. In addition to having tools of hard and soft science at their disposal, with some pretense to objectivity, SF writers have a major interest in subjective issues. Human desires, largely unsatisfied, are constants in their trade, and powerful counters in SF with its emphasis on potential. A wide variety of characters will share some of these desires, with consequences that are sometimes foreseeable. The behavior of individuals sometimes can be forecast from character and situation. On the level of motivation, however, the SF writer must keep in the forefront goals a writer of contemporary realism can take for granted as shared background. Primary factors shaping the world-views of characters include long-term human desires, short-term economic preferences, and the effects of both on the environment and human survival within it.

Inventions in history as well as in SF are largely efforts to secure things or situations people wanted long before modern technological society, as Kurt Marek points out. Cultural practices, stories and myths illustrate the need of homo sapiens for food and shelter, transportation and communication, medicine, social organization, understanding, even disinterested knowledge. SF, engineering, and science often reflect desires enshrined in prehistoric myth and material practices of both past and present, as well as technologies seen today as capable of realization.

Food and shelter are primary needs, which exfoliate into myriad practices, distinguishing cultures as civilized in their own eyes in contrast to others whom they see as barbarian. Some SF (Clarke's comes to mind) transforms agriculture by eliminating the need for human labor, or replacing organic forms via chemical transformations. This is not to ignore innovations like hydroponics and "green revolution'' hybrids already capable of feeding far larger multitudes than those who go hungry today for lack of distribution. Domestication of animals in SF extends to increasing their intelligence and capability, typically to handle menial occupations, and even to enslaving intelligent species, including ourselves.

SF's architectural imagination may be revealed less by its writers than by the ``ultra-modern'' visions displayed by its illustrators since the 1920s. On the covers of magazines and inside as well, graceful buildings soar into the sky, connected by fluid-appearing bridges and causeways. The urban complex becomes a "machine for living,'' consistent with the visions of Le Corbusier and Frank Lloyd Wright, and echoed in real buildings today, perhaps especially hotels (SF is in some ways a literature for tourists). Films often use a heavier hand to draw our architectural future, from the expressionistic horror of Metropolis and the defiant confidence of Things to Come to the miles-long computer of Forbidden Planet and the somber anarchy of Bladerunner.

To survive and to accomplish what a society values requires social organization. The six basic types defined by Aristotle were monarchy, aristocracy, and polity, and their ``perversions'' tyranny, oligarchy, and democracy. The intervening centuries have worked many variations on these, and social organization in the modern world is both aided and complicated by technologies. New means of production and distribution, communication and transport, inevitably affect it. Of primary importance are information access and power relations, not to mention mechanisms of fiscal credit. Innovations in these areas will impact and reflect changes in living quarters, health care, child-rearing and education. Add to that the potential for integrating into society various new species (robots, upgraded animals, other biological creations, even aliens) and this vast canvas becomes even more complicated.

The emergence of individual traits seems universal among humans, but its genetic base is given expression according to highly determining social constraints. Even what one understands as the "self'' comes from socially approved means of investigation and communication. Social sources determine what matters to us about our relationships with others, with our immediate environment, and with biology and physics. Writers typically find self-understanding important for characters and/or readers, but the SF writer also sees it as part of an alternate universe the fiction constructs.

Art, religion, philosophy, and science are both formal disciplines and informal activities through which we pursue meaning and self-understanding. They are not mutually exclusive or all-encompassing, however, since magic and psychology, for example, may be classified under any of them or all four. Everyone has a personal investment, however unconscious, in a society's image of the race and its place in the universe. Even a willingness to pursue knowledge without regard for where the search leads has a personal element. Yet practitioners of these disciplines sometimes become so deeply involved in the quest for truth as to seem disinterested.

These long-term desires are most often made real through relatively short-term economic decisions. It is also safe to assume that some decisions are based almost strictly on short-term economic preferences. These include survival needs in times of scarcity as well as questions of which product if any to buy in times of affluence. If the two interests do not coincide, the writer can play off the ``rational man'' of economics against irrational preferences based on deep-seated drives. Choices available to the rational self come from an irrational menu. Driven by long-term or even universal goals, pragmatically making short-term decisions, characters and whole societies in SF often live and cope with unintended effects of their choices (or those of their peers and predecessors).

Individual economic decisions may be rational or irrational, calculable or incalculable. The drama, in both real life and fiction, lies not in the mathematics of budgeting, but in the means by which agents and agencies try to bring the world and their budgets into conformity. In the broader scale of economics lies the most personal and perhaps the scarcest commodity of all, the time allotted to one's life, giving rise to speculation about the degree to which one can plan it, and even extend it.

Cultures as well as species take self-preservation into account, rearing and educating their young, regulating sex and marriage, organizing their mutual interactions so as to insure the survival of their "way of life.'' Like corporations, government and other bureaucracies may seem virtually immortal on the time scale of an individual's life. Yet governments and forms of government fall, businesses fail, and corporate culture continually alters as participants change places and go through transitions as individuals. Cultures also differ in terms of how much they encourage individuals to melt into or oppose corporate existence, or even to recognize the possibility of divergence. Utopian and dystopian fictions are built on forecasting such convergence or divergence of interests.

Individual planning is always subject to corporate behavior, in terms of one's role in a tribe or a company, and restrictions imposed by laws, regulations, mores, and leaders flexing their will. Tying one's future to that of the tribe seems far more common in human experience than keeping one's distance. Individual planning for retirement, economic security, and career advancement, as well as marriage and children, is especially encouraged in today's macro-culture misnamed "the West.'' While such planning is constrained by physics and biology, the resources of Western science and technology are also directed toward overcoming or at least relaxing those limits.

Though opinions differ about quality of life in industrial society, modern medical science has clearly increased the average human life-span. Reductions of death in infancy and surgery comprise a major portion of that increase, while the biggest headlines and headaches come from surgical and chemical advances extending the lives of the elderly and the infirm. SF stories imagine future medical facilities with mechanical and psychic healers able to mend breaks and ruptures of every kind, even to suspend animation until more specialized facilities can restore life itself. The ultimate goal in this direction is immortality, or at least greatly extended longevity, without debility.

Avenues with fictional promise in this perhaps chimerical quest include cryonics, cloning, and electronic transfer of personality. Parallelling ancient practices of mummification, cryonics is a delaying action, freezing the body immediately after death. Suspended animation with appropriate drugs might be preferable but earlier intervention with freezing is treated as murder. If cloning is carried out with human cells, it promises only cellular immortality, without a mechanism of brain or memory transplant. Individuals then would not have to be limited to the same body at a different biological age, but could change appearance including gender at will. Whether or not organic brain transplants work out, immortalists hope for electronic recording and transference of partial or whole personalities (Gregory Benford's Tides of Light and Great Sky River), or bodiless electronic being (Frederik Pohl's Heechee tetralogy).

SF offers a bewildering range of tools with which to forecast characters' behavior, or invent new behaviors, suggesting that character is only a complicated automated mechanism. But behavioral forecasting is by no means limited to SF. Even without the benefit of scientific vision, or modern science in particular, literary conventions alone require a certain amount of forecasting in order for plot and character to interact.

Plot is what characters do, and characters are the agents that carry out the plot. In a string of events causally united, character motivation must be established in terms of tendencies and potential. Characters are thin in fairy tale and romance and their behavior is almost completely predictable. The realistic novel or short story usually overlays such conventions with more complicated motivations. Said to be based on real life, such motivations may be described more precisely as partly based on observations of real life as it was lived among the Western middle classes in the 18th and 19th centuries. Seen against that highly constrained and constructed context, these tendencies and motivations may be legitimately described as plausible. The codes and conventions of realism are far less dominant in the 20th century, with its bewildering variety of media, genres, behaviors, attitudes, and techniques.

Characters are not strictly separable from story, but in any story the writer has to forecast how individuals would behave when subjected to certain pressures. émile Zola first articulated the deterministic assumptions governing naturalism. In The Experimental Novel, Zola pushed to extremes the analysis of people interacting with such pressures, pretending to substitute dispassionate research and neutral observations for subjective desires and aesthetic goals. Zola never fully put his ideas into practice in his novels—he was too good a writer for that—but SF owes much to Zola's conception, or at least to the 19th century Western scientific climate he expressed. Zola's "experimental method'' was ready-made for story-tellers lacking an observational base for how people actually behave in places and times that are only potential. SF writers following Zola's model can rely on technological forecasting for the initial impetus, basing character reactions on a variable mix of theory, history, and arbitrary invention. The first to do so was Zola's contemporary, Verne, the father of hard SF.

Verne meticulously researched scientific details for neutral presentation, but his fiction was by no means neutral about what people did with science and technology. More so than disinterested knowledge, neutral extrapolation is an oxymoron. Even writers who consciously avoid firing warning shots or rallying readers around a flag can not avoid utopian or dystopian interpretations of their work. Most SF writers have strong opinions on what is desirable in the futures they anticipate. Moreover, a writer need not anticipate, design, or desire a perfect world in order to write a utopian story. Classic tales of the '20s and '30s may have described a high-technology future to parade scientific marvels rather than examine their effects, but the not-so-hidden assumption was that technology was good for us. Soviet SF, even after the "thaw'' of the mid-50s, largely toed an ideological line reflecting real-life experience for few of their readers: already great, socialism was destined to be even better.

Typically, however, people in SF are neither angels nor devils, making utopian worlds not perfect, but only potentially better. Even B.F. Skinner's doctrinaire behaviorist utopia, Walden Two, accepts imperfections inherent in the biological creatures we are. SF generally meets the preference of readers since Dante's time for Hell over Heaven. Things can go wrong more ways than right, and complications make stories interesting. The "comic infernos'' Kingsley Amis found in the 1950s may be especially representative of American SF of that era, but cautionary tales have always abounded in the genre.

The outright dystopia, perfection inverted, is rare in SF, unlike the anti-utopia with its resistance to social planning. In history, private or corporate planning has always served mainly to enrich or protect an elite class. For those unable to reap its benefits, governmental planning may be the only defense, even if the rich also get a share. Elites probably could not buy better propaganda than anti-utopians' depiction of government planning as anti-populistic and likely to usher in stifling social controls. Yet the danger of too little planning is equally visible in future-scene stories of war, ecological catastrophe, and natural disaster.

10. Models are Destiny? The futurologist Frederik W. Polak maintains that every society is guided in part by the images it projects of its own future. In SF, forecasting and planning mean determining a future, in the sense of making it so. Perhaps nowhere is that more visible than in models for a future Earth and artificial habitats. In the far future on Earth, or after a catastrophe virtually wipes out technological civilization, a new model is needed. Even with changes in the astronomical coordinates, many physical conditions will continue. Artificial habitats are more complicated, involving both world-building and forecasting. Unlike with an alien planet, writers are not trying to outguess nature. Space stations and other artificial habitats anticipated for our near future obviously require technological forecasting, some based on what is on the drawing boards of several nations. Alien habitats must also be treated as future engineering projects, since we have no historical experience of many of the products and processes imagined.

Where human artifacts are concerned, we can start with tried technology, tested physical principles, and standard assumptions about what human beings need and want. The further we imagine into the future, however, the more technological innovations, cross-impacts, and secondary effects may interact. The result may be something far beyond anything we can do today. It may be something it is hard to feel we would even want, given our present cultural and biological configurations. Imagining what aliens would want and how they would realize it materially follows a similar continuum. The nearer the alien habitat to what we think we would want, the more it seems constructed for human beings in costume, as in many SF films and tv shows.

These principles clearly apply to space stations, the most obvious near future advance into space for the human race. They also apply to settlements on hostile worlds (i.e., any alien planet) and to any vehicle in which a species sets out to explore its solar system and beyond. Spaceships take various sizes and configurations in SF narrative and film, depending on function and motive power. Writers make vehicles of hollowed-out asteroids, commandeered planets, and total human fabrications, from space colonies in Earth orbit or visiting other worlds and star systems, to still larger structures. Niven's Ringworld postulates a structure surrounding a sun in the plane of the ecliptic; Orbitsville by Bob Shaw goes him one better, surrounding the sun in all directions. Ostensibly built by aliens, both are variations on Freeman Dyson's idea that a Stage Two technological civilization would harness all the energy of its star. A step further out is the human-built space-time structure in Greg Bear's Eon, which looks to be both infinite and eternal.

Imagining such artifacts clearly requires extrapolation of the engineering potential in alternative futures as well as the extension of human scientific categories and natural laws to the universe outside our immediate vicinity. In this context, at least, extrapolations of scientific and historical processes are complementary activities, two ways of modelling the same thing, but world-building and forecasting coalesce in another sense. Imagining either alternative futures or alien worlds is a process of extending the empire of human understanding into unknown time and space. All ``worlds'' of SF are imagined artifacts, models of how we think things are or could be.

A Partial Secondary Bibliography for Extrapolation

This list supplements the "hard SF'' secondary bibliography for the introduction, mainly with works about science and literature cited or otherwise used in preparing this essay. Everything from the other list should apply here as well. This list does not document fiction or films cited.

Aldiss, Brian W. "Helliconia: How and Why.'' The Pale Shadow of Science. Seattle: Serconia, 1985 [not the publisher's flyer].

Allport, Gordon. The Nature of Prejudice. 1954. Abr. Garden City, NY: Anchor, 1958.

Amis, Kingsley. New Maps of Hell: A Survey of Science Fiction. London: Gollancz, 1961.

Augros, Robert, and George Stanciu. The New Biology: Discovering the Wisdom in Nature. Boston: Shambhala, 1988.

Balling, Robert C., Jr. The Heated Debate: Greenhouse Prediction Versus Climate Reality. San Francisco: Pacific Research for Public Policy, 1992.

Barber, Bernard. Science and the Social Order. 1952. Rev. ed. NY: Collier, 1962.

Bernal, J.D. The World, The Flesh and The Devil: An Enquiry into the Future of the Three Enemies of the Rational Soul. 1929. Bloomington: Indiana UP, 1969.

Berry, Adrian. The Next Ten Thousand Years: A Vision of Man's Future in the Universe. 1974. Bungay, England: Coronet, 1976.

Beveridge, W.I.B. The Art of Scientific Investigation. 3rd ed. NY: Vintage, [1957].

Bleibtreu, John F. The Parable of the Beast. NY: Collier, 1969.

Blish, James. "Of Science Fiction Criticism'' [response to Butor, q.v.]. Riverside Quarterly 3:214-17, August 1968. ALSO Clareson, 166-70.

Bohm, David, and F. David Peat. Science, Order, and Creativity. NY: Bantam, 1987.

Bracewell, Ronald N. The Galactic Club: Intelligent Life in Outer Space. San Francisco: San Francisco Book Co., 1976.

Bretnor, Reginald, ed. The Craft of Science Fiction. NY: Harper, 1976.

Bronowski, J[acob]. The Common Sense of Science. NY: Vintage [1963].

—————. The Identity of Man. Garden City, NY: American Museum Science Press, 1966.

—————. Science and Human Values. 1956. NY: Harper, 1959.

Brooke-Rose, Christine. A Rhetoric of the Unreal: Studies in Narrative and Structure, Especially of the Fantastic. 1981. Cambridge, UK: Cambridge UP, 1983.

Brown, Robert, ed. Rules and Laws in Sociology. Chicago: Aldine, 1973.

Butor, Michel. "Science Fiction: The Crisis of Its Growth,'' Partisan Review 34:595-602, Autumn 1967. ALSO Clareson, 157-65.

Calder, Nigel. The Weather Machine. NY: Viking, 1975.

Calvin, William H. The Ascent of Mind: Ice Age Climates and the Evolution of Intelligence. NY: Bantam, 1991.

Capra, Fritjof. The Tao of Physics: An Exploration of the Parallels Between Modern Physics and Eastern Mysticism. Boulder, CO: Shambhala, 1975.

Carr, John F., ed. "Science Fiction Future Histories.'' Special issue, Bulletin of the Science Fiction Writers of America, 14.3, Fall 1979.

Carter, Paul A. The Creation of Tomorrow: Fifty Years of Magazine Science Fiction. NY: Columbia UP, 1977.

Cawelti, John. Adventure, Mystery, Romance: Formula Stories as Art and Popular Culture. Chicago: Chicago UP, 1976.

Chase, Stuart. The Most Probable World. Baltimore: Penguin, 1970.

Clareson, Thomas D., ed. SF: The Other Side of Realism: Essays on Modern Science Fiction and Fantasy. Bowling Green, OH: Bowling Green University Popular Press, 1971.

Cole, Jonathan. Fair Science: Women in the Scientific Community. NY: Free Press, 1979.

Corbusier, Le [Charles-Edouard Jenneret-Gris]. The Radiant City: Elements of a Doctrine of Urbanism to be Used as the Basis of Our Machine Age Civilization. NY: Orion, 1967. [French edition, La Ville radieuse, 1933].

Corea, Gena. The Mother Machine: Reproductive Technologies from Artificial Insemination to Artificial Wombs. New York: Harper, 1985.

Culler, Jonathan. On Deconstruction: Theory and Criticism After Structuralism. Ithaca NY: Cornell UP, 1982.

—————. The Pursuit of Signs: Semiotics, Literature, Deconstruction. Ithaca NY: Cornell UP, 1981.

—————. Structuralist Poetics: Structural Linguistics and the Study of Literature. Ithaca NY: Cornell UP, 1975.

Dawkins, Richard. The Selfish Gene. NY: Oxford UP, 1976.

Day, John A. The Science of Weather. Reading, MA: Addison-Wesley, 1966.

Degler, Carl N. In Search of Human Nature: The Decline and Revival of Darwinism in American Social Thought. NY: Oxford, 1991.

Drexler, K. Eric. Engines of Creation: The Coming Age of Nanotechnology. Garden City, NY: Anchor, 1987.

Drucker, Peter F. The Future of Industrial Man. 1942. NY: New American Library, 1970.

Dublin, Max. Futurehype: The Tyranny of Prophecy. NY: Viking, 1989.

Dyson, Freeman. Disturbing the Universe. New York: Harper, 1979.

Eagleton, Terry. Literary Theory: An Introduction. Minneapolis: University of Minnesota Press, 1983.

—————. Marxism and Literary Criticism. Berkeley: University of California Press, 1976.

Ehrlich, Paul R. The Machinery of Nature. NY: Simon and Schuster, 1986.

Elia, Irene. The Female Animal. 1986. NY: Holt, 1988.

Elkins, Charles. "Asimov's Foundation Novels: Historical Materialism Distorted into Cyclical Psychohistory,'' SFS 3:26-36, #8, March 1976. Expanded: Isaac Asimov. Ed. Joseph D. Olander and Martin Harry Greenberg. NY: Taplinger, 1977. 97-110.

Ellison, Harlan, ed. Medea: Harlan's World. NY: Bantam, 1985.

Ellul, Jacques. The Technological Society. Trans. John Wilkinson. NY: Vintage, 1964. [French edition, La Technique ou l'enjeu du siècle, 1954].

Ettinger, R.C.W. Man into Superman. NY: Avon, 1972.

Evans, Christopher. The Micro Millennium. NY: Viking, 1979.

Feinberg, Gerald. The Prometheus Project. Garden City: Anchor, 1969.

Ferkiss, Victor C. Futurology: Promise, Performance, Prospects. Washington DC: Center for Strategic and International Studies, 1977.

—————. Technological Man: The Myth and the Reality. NY: Mentor, 1969.

Florman, Samuel C. The Civilized Engineer. NY: St. Martin's, 1987.

Flynn, Michael F. "An Introduction to Psychohistory.'' Analog Science Fiction/Science Fact 108:60-78, April 1988, and 108:38-64, May 1988.

Forward, Robert L. Future Magic. NY: Avon, 1988. [Cover bears subtitle: ``How Today's Science Fiction Will Become Tomorrow's Reality'']

Foucault, Michel. The Archaeology of Knowledge (trans. A.M. Sheridan Smith) and The Discourse on Language (trans. Rupert Sawyer). NY: Harper 1972. [French editions, L'Archeologie du Savoir, 1969, and L'Ordre du Discours, 1971].

—————. The Birth of the Clinic: An Archaeology of Medical Reception. Trans. M. Sheridan Smith. NY: Vintage, 1975. [French edition, Naissance de la Clinique, 1963].

—————. Discipline and Punish: The Birth of the Prison. Trans. Alan Sheridan. NY: Vintage, 1979. [French edition, Surveiller et Punir: Naissance de la Prison, 1975].

—————. The History of Sexuality, vol. 1, An Introduction. Trans. Robert Hurley. NY: Vintage, 1980. [French edition, La Volonté de Savoir, 1976].

—————. Madness and Civilization: A History of Insanity in the Age of Reason. Trans. Richard Howard. NY: New American Library, 1967. [French edition, Histoire de la Folie, 1961].

—————. The Order of Things: An Archaeology of the Human Sciences. NY: Vintage, 1973. [French edition, Les Mots et les Choses, 1966].

Franklin, Jon. Molecules of the Mind. NY: Dell, 1988.

Frye, Northrop. Anatomy of Criticism: Four Essays. Princeton NJ: Princeton UP, 1957.

Gadet, Franšoise. Saussure and Contemporary Culture. Trans. Gregory Elliott. London: Radius, 1989.

Gerber, Richard. Utopian Fantasy. 1955. NY: McGraw-Hill, 1973.

Giere, Ronald N. Explaining Science: A Cognitive Approach. Chicago: University of Chicago Press, 1990 [1988].

Gilder, George. Microcosmos: The Quantum Revolution in Economics and Technology. NY: Simon and Schuster, 1989.

Gleick, James. Chaos: Making a New Science. NY: Viking, 1987.

Gorney, Roderick. The Human Agenda. NY: Bantam, 1973.

Gould, Stephen Jay. Wonderful Life: The Burgess Shale and the Nature of History. NY: Norton, 1989.

Greenstein, George. The Symbiotic Universe: Life and Mind in the Cosmos. NY: Morrow, 1988.

Grinnell, Frederick. The Scientific Attitude. Boulder, CO: Westview, 1987.

Guthke, Karl S. The Last Frontier: Imagining Other Worlds from the Copernican Revolution to Modern Science Fiction. Trans. Helen Atkins. Ithaca, NY: Cornell, 1990. [German edition, Der Mythos der Neuzeit, 1983].

Hagstrom, Warren O. The Scientific Community. Carbondale: Southern Illinois UP, 1975 [1965].

Halacy, D[aniel] S. The Weather Changers. NY: Harper, 1968.

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Haraway, Donna J. Simians, Cyborgs, and Women: The Reinvention of Nature. NY: Routledge, 1991.

Harland, Richard. Superstructuralism: The Philosophy of Structuralism and Post-Structuralism. London: Methuen, 1987.

Harman, Willis W. An Incomplete Guide to the Future. San Francisco: San Francisco Book Co., 1976.

Harrington, Alan. The Immortalist: An Approach to the Engineering of Man's Divinity. NY: Avon, 1970.

Harrison, Edward. Masks of the Universe. NY: Macmillan, 1985.

Hawken, Paul, James Ogilvy, and Peter Schwarz. Seven Tomorrows: Toward a Voluntary History. NY: Bantam, 1982.

Hawkes, Terence. Structuralism and Semiotics. Berkeley: University of California Press, 1977.

Hawking, Stephen W. A Brief History of Time: From the Big Bang to Black Holes. NY: Bantam, 1988.

Heilbroner, Robert L. The Future as History. NY: Grove, 1960.

Heppenheimer, T[homas] L. Colonies in Space. Harrisburg, PA: Stackpole, 1977.

—————. The Real Future. Garden City, NY: Doubleday, 1983.

—————. Toward Distant Suns. Harrisburg, PA: Stackpole, 1979.

Herbert, Frank. "Men on Other Planets.'' Bretnor. 121-34.

Hofstadter, Douglas. Gödel, Escher, Bach: An Eternal Golden Braid. NY: Vintage, 1979.

Hume, Kathryn. Fantasy and Mimesis: Responses to Reality in Western Literature. NY: Methuen, 1984.

Huntington, John. Rationalizing Genius: Ideological Strategies in the Classic American Science Fiction Short Story. New Brunswick, NJ: Rutgers UP, 1989.

Jameson, Fredric. Marxism and Form: Twentieth-Century Dialectical Theories of Literature. Princeton, NJ: Princeton UP, 1974 [1971].

—————. The Political Unconscious: Narrative as a Socially Symbolic Act. Ithaca, NY: Cornell UP, 1981.

—————. Postmodernism or, The Cultural Logic of Late Capitalism. Durham, NC: Duke UP, 1991.

—————. The Prison-House of Language: A Critical Account of Structuralism and Russian Formalism. 1972. Princeton, NJ: Princeton UP, 1974.

Kahn, Herman, and Anthony J. Weiner. The Year 2000: A Framework for Speculation on the Next Thirty-three Years. NY: Macmillan, 1967.

Keller, Evelyn Fox. Reflections on Gender and Science. New Haven: Yale UP, 1985.

Knight, David. The Age of Science: The Scientific World-View in the Nineteenth Century. Oxford: Blackwell, 1986.

Köhler, Wolfgang. The Place of Value in a World of Facts. NY: Mentor, 1966 [1938].

Kumar, Krishan. Utopianism. Milton Keynes, England: Open UP, 1991.

Lamb, Hubert H. Weather, Climate and Human Affairs. London: Routledge, 1988.

Landsberger, Henry A. Hawthorne Revisited: Management and the Worker, its Critics, and Developments in Human Relations in Industry. Ithaca, NY: Cornell, 1958.

Laszlo, Ervin. Evolution: The Grand Synthesis. Boston: Sham-bhala, 1987.

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Levi-Strauss, Claude. Structural Anthropology. Trans. Claire Jacobson and Brooke Grundfest Schoepf. NY: Harper 1963. [French edition, Anthropologie Structurale, 1958.]

Linstone, Harold A., and Murray Turoff, eds. The Delphi Method: Techniques and Applications. Reading, MA: Addison-Wesley, 1975.

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Lovelock, J[ames] E. Gaia: A New Look at Life on Earth. 1979. Oxford: Oxford UP, 1987.

Lutgens, Frederick K., and Edward J. Tarbuck. The Atmosphere: An Introduction. 3rd ed. Englewood Cliffs, NJ: Prentice Hall, 1986.

Macksey, Richard, and Eugenio Donato, eds. The Structuralist Controversy: The Languages of Criticism and the Sciences of Man. Baltimore: Johns Hopkins UP, 1972.

MacLean, Katherine. "Alien Minds and Non-Human Intelligences.'' Bretnor. 136-57.

Malzberg, Barry. The Engines of the Night: Science Fiction in the Eighties. Garden City, NY: Doubleday, 1982

Manuel, Frank E. and Fritzie P. Utopian Thought in the Western World. Cambridge, MA: Harvard UP, 1979.

Marek, Kurt W. Yestermorrow: Notes on Man's Progress, Trans. Ralph Manheim. NY: Knopf, 1961 [German edition, Provokatorische Notizes, 1960.

Margulis, Lynn, and Dorion Sagan. Microcosmos: Four Billion Years of Microbial Evolution. NY: Summit, 1986.

Maruyama, Magoroh, and Arthur Harkins, ed. Cultures Beyond the Earth. NY: Vintage, 1975.

Maslow, Abraham H. The Psychology of Science: A Reconnaissance. Chicago: Regnery, 1974 [1970].

Matson, Floyd W. The Broken Image: Man, Science, and Society. Garden City, NY: Anchor, 1966 [1964].

McCaffery, Larry, ed. Postmodern Fiction: A Bio-Bibliographical Guide. NY: Greenwood, 1986.

McHale, John. The Future of the Future. NY: Ballantine, 1971 [1969].

Meadows, Donella, et al. The Limits to Growth. NY: New American LIbrary, 1972.

Minsky, Marvin. The Society of Mind. NY: Simon and Schuster, 1986.

Monod, Jacques. Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology, Trans. Austryn Wainhouse. NY: Vintage, 1971 [French edition, Le Hasard et la Necessité, 1970].

Morgan, Robin. The Anatomy of Freedom: Feminism, Physics, and Global Politics. Garden City, NY: Anchor, 1984 [1982]

Moylan, Thomas. Demand the Impossible: Science Fiction and the Utopian Imagination. NY: Methuen, 1986.

Murray, Bruce C., Michael C. Malin, and Roland Greeley. Earthlike Planets. San Francisco: Freeman, 1981.

Nagel, Ernest, and James R. Newman. "Gödel's Proof.'' The World of Mathematics. 4 vols. Ed. James R. Newman. NY: Simon and Schuster, 1956. 3:1668-95.

Naisbitt, John. Megatrends: Ten New Directions Transforming Our Lives. NY: Warner, 1982.

Nourse, Alan E. "Extrapolation and Quantum Jumps.'' Bretnor. 73-86.

Pagels, Heinz R. The Cosmic Code: Quantum Physics as the Language of Nature. NY: Bantam, 1983 [1982].

—————. The Dreams of Reason: The Computer and the Rise of the Sciences of Complexity. NY: Simon and Schuster, 1988.

—————. Perfect Symmetry: The Search for the Beginning of Time. NY: Simon and Schuster, 1985.

Panshin, Alexei and Cory. The World Beyond the Hill: Science Fiction and the Quest for Transcendence. Los Angeles: Tarcher, 1989.

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Polak, Frederik W. The Image of the Future: Enlightening the Past, Orientating [sic] the Present, Forecasting the Future, Trans. Elise Boulding, 2 vols. Leyden, Netherlands: A. W. Sijthoff, 1961 [Dutch edition, De Toekomst is verleden tije, 1961].

Ponte, Lowell. The Cooling. Englewood Cliffs, NJ: Prentice-Hall, 1976.

Poster, Mark. The Utopian Thought of Restif de la Bretonne. NY: NYUP, 1971.

Pournelle, Jerry. "The Construction of Believable Societies.'' Bretnor. 104-19.

Prehoda, Robert W. Designing the Future: The Role of Technological Forecasting. Philadelphia: Chilton, 1967.

Rabkin, Eric S. The Fantastic in Literature. Princeton: Princeton UP, 1976.

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Richter, Maurice N., Jr. Science as a Cultural Process. Cambridge, MA: Schenkman, 1972.

Roethlisberger, Fritz J. Management and the Worker: An Account of a Psychological Program Conducted by the Western Electric Company, Hawthorne Works, Chicago. Cambridge, MA: Harvard UP, 1939.

Rosen, Stephen. Future Facts: A Forecast of the World as We Know it Before the End of the Century. NY: Simon and Schuster, 1976.

Rosenfeld, Albert. Prolongevity. NY: Avon, 1977.

—————. The Second Genesis: The Coming Control of LIfe. NY: Arena, 1972.

Ross, Andrew. Strange Weather: Culture, Science and Technology in the Age of Limits. London: Verso, 1991.

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Schell, Jonathan. The Fate of the Earth. NY: Avon, 1982.

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