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Science Fiction Today and Tomorrow

Page 27

by Reginald Bretnor


  But since there is less self-compression, have I given Cleopatra an impossibly high density? No, because I am postulating a higher proportion of heavy elements in its makeup than Earth has. That is not fantastic. Stars, and presumably their planets, do vary in composition.

  (Writers can of course play with innumerable other combinations, like that in the very large but very metal-poor world of Jack Vance's Big Planet.)

  The results of changing the gravity must be far-reaching indeed. Just think how this could influence the gait, the need for systematic exercise, the habit of standing versus sitting (are people in low weight more patient about queues?), the character of sports, architecture, engineering (the lower the weight, the smaller wings your aircraft need under given conditions, but the bigger brakes your ground vehicles), and on and on. In a lesser gravity, it takes a bit longer to fall some certain distance, and one lands a bit less hard; mountains and dunes tend to be steeper; pendulums of a given length, and waves on water, move slower. The air pressure falls off less rapidly with altitude. Thus, here on Earth, at about 18,000 feet the pressure is one half that at sea level; but on Cleopatra, you must go up to 21,000 feet for this. The effects on weather, every kind of flying, and the size of life zones bear

  A higher gravity reverses these consequences, more or less in proportion.

  In our present state of ignorance, we have to postulate many things that suit our story purposes but may not be true—for example, that a planet as small as Cleopatra can actually hold an Earth-type atmosphere. Other postulates—for example, that Cleopatran air is insufficient, or barely sufficient, to sustain human life—are equally legitimate, and lead to quite other stories. But whatever the writer assumes, let him realize that it will make for countless strangenesses, some radical, some subtle, but each of them all-pervasive, in the environment.

  (I must admit that certain of them scarcely look important. Thus, the horizon distance—for a man standing on a flat plain —is proportional to the square root of the planet's diameter. On Earth it is about five miles, and for globes not very much bigger or smaller, the change will not be striking. Often mountains, woods, haze, or the like will blot it out entirely. Yet even in this apparent triviality, some skillful writer may see a story.)

  If we have a higher proportion of heavy elements, including radioactive ones, than Earth does, then we doubtless get more internal heat; and the lesser size of Cleopatra also helps pass it outward faster. Thus here we should have more than a terrestrial share of volcanoes, quakes, and related phenomena. I guess there would be plenty of high mountains, some overreaching Everest; but we still know too little about how mountains get raised for this to be much more than a guess. In some areas, local concentrations of arsenic or whatever may well make the soil dangerous to man. But on the whole, industry ought to thrive.

  Conversely, and other things being equal, a metal-poor world is presumably fairly quiescent; a shortage of copper and iron might cause its natives to linger indefinitely in a Stone Age; colonists might have to emphasize a technology based on lighter elements such as aluminum.

  How fast does the planet rotate? This is a crucial question, but once more, not one to which present-day science can give a definitive answer. We know that Earth is being slowed down by Luna, so maybe it once spun around far more quickly than now. Maybe. It isn't being braked very fast, and we can't be sure how long that rate of deceleration has prevailed in the past or will in the future. Mars, whose satellites are insignificant, turns at nearly the same angular speed, while Venus, with no satellite whatsoever, is exceedingly slow and goes widdershins to boot.

  It does seem likely that big planets will, by and large, spin rapidly—such as Jupiter, with a period of about ten hours. They must pick up a lot of angular momentum as they condense, and they don't easily lose it afterward. But as for the lesser bodies, like Earth, we're still mainly in the realm of speculation.

  I assumed Cleopatra has no satellites worth mentioning. Therefore it has been slowed less than Earth, its present rotation taking 17.3 hours. This makes its year equal to 639 of its own days. But I could equally well have dreamed something different.

  If it did have a moon, how would that affect things? Well, first, there are certain limitations on the possibilities. A moon can't be too close in, or it will break apart because of unbalanced gravitational forces on its inner and outer sides. This boundary is called Roche's limit, after the astronomer who first examined the matter in detail. For Earthlike planets it is about 2.5 radii from the center, 1.5 from the surface. That is, for Earth itself Roche's limit is roughly six thousand miles straight up. (Of course, it doesn't apply to small bodies like spaceships, only to larger and less compact masses such as Luna.)

  On the other hand, a moon circling very far out would be too weakly held; in time, the tug of the sun and neighbor planets would cause it to drift elsewhere. At a quarter million miles' remove, Luna is quite solidly held. But one or two million might prove too much in the long run—and in any event, so remote, our companion would not be a very interesting feature of our skies.

  (Cleopatra did have a small moon once, which got too near and disintegrated, forming a ring of dust and rocky fragments. But the calculations about this, to determine what it looks like and how that appearance varies throughout the year, are rather involved.)

  Within such bounds, as far as science today can tell, we are free to put almost anything that isn't outrageously big. But if the orbit is really peculiar, the writer should be prepared to explain how this came about. A polar or near-polar track is less stable than one which isn't far off the plane of the primary's equator; it is also much less likely to occur in the first place. That is, through some such freak of nature as the capture of an asteroid under exactly the right circumstances, we might get a moon with a wildly canted orbital plane; but it probably wouldn't stay there for many million years. In general, satellites that don't pass very far north and south of the equators of their planets are more plausible.

  Well, so let's take a body of some reasonable size, and set it in motion around our imaginary world at some reasonable average distance. (This is distance from the center of the planet, not its surface. For a nearby companion, the distinction is important.) How long does it take to complete a circuit and how big does it look to someone on the ground?

  The same principles we used before will work again here. Take Figures 4 and 5. Instead of letting "1.0" stand for quantities like "the mass of Sol." "the mean distance of Earth from Sol," and "the period of Earth around Sol" let it stand for "the mass of Earth." "the mean distance of Luna from Earth," and "the period of Luna around Earth." Thus you find your answer in terms of months rather than years. (This is a rough-and-ready method, but it will serve fairly well provided that the satellite isn't extremely big or extremely near.) Likewise, the apparent size of the object in the sky, compared to Luna, is close-enough equal to its actual diameter compared to Luna, divided by its distance from the surface of the planet, compared to Luna.

  But in this case, we aren't done yet. What we have been discussing is the sidereal period, i.e., the time for the satellite to complete an orbit as seen from out among the stars. Now the planet is rotating while the moon revolves around it. Most likely both move in the same direction; retrograde orbits, like polar ones, are improbable though not altogether impossible. Unless the moon is quite remote, this will have a very marked effect. For instance, Luna, as seen from Earth, rises about fifty minutes later every day than on the previous day—while an artificial satellite not far aloft comes up in the west, not the east, and virtually flies through the heavens, undergoing eclipse in the middle of its course.

  I would offer you another graph at this point, but unfortunately can't think of any that would be much help. You shall have to subtract revolution from rotation, and visualize how the phases of the moon(s) proceed and how they show in the skies. Bear in mind, too, that very close satellites probably won't be visible everywhere on the planet. Algebra and trigonometry
are the best tools for jobs of this kind. But failing them, scale diagrams drawn on graph paper will usually give results sufficiently accurate for storytelling purposes.

  The closer and bigger a moon is, the more tidal effect it has. For that matter, the solar tides aren't generally negligible; on Earth they amount to a third of the total. There is no simple formula. We know how tides can vary, from the nearly unmoved Mediterranean to those great bores which come roaring up the Bay of Fundy. Still, the writer can get a rough idea from this fact: that the tide-raising power is proportional to the mass of the moon or sun, and inversely proportional to the cube of its distance. That is, if Luna were twice as massive at its present remove, the tides it creates would be roughly twice what they really are. If Luna kept the same mass but were at twice its present distance, its tides would be 1/23 or one-eighth as strong as now, while if it were half as far off as it is, they would be or eight times as great. In addition, the theoretical height of a deepwater tide is proportional to the diameter and inversely proportional to the density of the planet being pulled upon. That is, the larger and/or less dense it happens to be, the higher its oceans are lifted.

  As said, there is such tremendous local variation that these formulas are only good for making an overall estimate of the situation. But it is crucial for the writer to do that much. How do the waters behave? (Two or more moons could make sailing mighty complicated, not to speak of more important things like ocean currents.) Great tides, long continued, will slow down the rotation—though the amount of friction they make depends also on the pattern of land distribution, with most energy being dissipated when narrow channels like Bering Strait are in existence. We must simply guess at the effects on weather or on life, but they are almost certainly enormous. For instance, if Earth had weaker tides than it does, would life have been delayed in moving from the seas onto dry ground?

  One clear-cut, if indirect, influence of tides on weather is through the spin of the planet. The more rapidly it rotates, the stronger the cyclone-breeding Coriolis forces. In the case of Cleopatra, we have not only this factor, but also the more powerful irradiaton—and, maybe, the greater distance upward from surface to stratosphere, together with the lesser separation of poles and tropics—to generate more violent and changeable weather than is common on Earth.

  Insofar as the matter is understood by contemporary geo-physicists, we can predict that Cleopatra, having a hotter molten core and a greater rate of rotation, possesses a respectable magnetic field, quite likely stronger than the terrestrial. This will have helped preserve its atmosphere, in spite of the higher temperatures and lower gravity. Solar particles, which might otherwise have kicked gas molecules into space, have generally been warded off. To be sure, some get through to the uppermost thin layers of air, creating secondary cosmic rays, electrical disturbances, and showy auroras.

  The weather is likewise affected by axial tilt. Earth does not ride upright in its orbit; no member of the Solar System does. Our axis of rotation slants about 23% off the vertical. From this we get our seasons, with everything that that implies. We cannot tell how often Earthlike worlds elsewhere have radically different orientations. My guess is that this is a rarity and that, if anything, Earth may lean a bit more rakishly than most. But it's merely another guess. Whatever value the writer chooses, let him ponder how it will determine the course of the year, the size and character of climatic zones, the development of life and civilizations.

  If Earth did travel upright, thus having no seasons, we would probably never see migratory birds across the sky. One suspects there would be no clear cycle of the birth and death of vegetation either.

  Then what form would agriculture have taken? Society? Religion?

  It is questions like these that science fiction is uniquely well fitted to ask. Simple permutations of natural law, such as we have been considering here, raise amazingly many of them, and suggest tentative answers.

  True, this kind of backgrounding work is the barest beginning. The writer must then go on to topography, living creatures both nonhuman and human, problems and dreams, the story itself— ultimately, to those words which are to appear on a printed page. Yet if he has given some thought and, yes, some love to his setting, that will show in the words. Only by making it real to himself can he make it, and the events which happen within its framework, seem real to the reader.

  The undertaking isn't unduly hard. It is mind-expanding in the best sense of that phrase. Or may I end by repeating myself and saying that, for writer and reader alike, it's fun?

  Poul Anderson

  Poul Anderson was born in Pennsylvania in 1926, of Scandinavian parents (hence the spelling of the first name), and was raised in Texas and on a Minnesota farm, with intervals in Europe and the Washington, D.C., area. He graduated from the University of Minnesota in physics, with distinction, but having already sold some stories while in college (first significant publication in 1947), decided to become a writer. Now a long-time resident, with wife and daughter, of San Francisco Bay area; wife, Karen, occasionally writes, too.

  He is the author of more than fifty books and two hundred-odd short pieces. Besides science fiction, they include fantasy, mystery, historical, juvenile, and here-and-now fiction; nonfiction; poetry, essays, translations, criticism, etc. Short stories and articles have appeared in places as various as the science fiction magazines, Boys' Life, Playboy, the Toronto Star Weekly, National Review, Ellery Queen's, and the defunct Jack London's magazine. Novels, nonfiction books, and short stories have appeared in fifteen foreign languages.

  Former regional vice-president of Mystery Writers of America and former president of Science Fiction Writers of America.

  Honors include: Guest of honor, world science fiction convention of 1959, and several regional conventions; four Hugo awards and two Nebula awards for best sf novelette of the year; "Forry" Award of Los Angeles Science Fantasy Society; special issue (April, 1972) of The Magazine of Fantasy and Science Fiction; Macmillan Cock Robin Award for best mystery novel; investiture in The Baker Street Irregulars, and twice winner of the Morley-Montgomery Prize for scholarship in Sherlock

  Holmes; Knight of Mark Twain. In the nonliterary field, knighthood in the Society for Creative Anachronism, for prowess in medieval combat.

  Among Poul Anderson's more popular books are Brain Wave, The High Crusade, The Enemy Stars, Three Hearts and Three Lions, The Broken Sword, Tau Zero. Most recent novels are, as of now: There Will Be Time and The People of the Wind.

  Hal Clement

  The Creation of Imaginary Beings

  The unheard-of creature and the unhuman character have been part of the storyteller's ammunition since long before the invention of writing, it seems safe to claim. Angel and demon, ghost and vampire, dragon and rukh, Homer's Cyclopes and Mandeville's headless men are all part of the basic human heritage. Telling how to create such beings might almost be taken as an insult to normal human imagination.

  In science fiction, however, we do try to maintain standards of realism (or at least believability) for a rather more knowledgeable and technically sophisticated audience than Homer faced. This is not to say that we have higher standards in these respects; Homer's gods and Sinbad's island-whale were as believable in their day as moon flight and atomic energy are now. Our standards are simply based on a better knowledge of the physical universe.

  Also, there is no intended suggestion that the ghost and his nonmaterial kin either have vanished or should vanish from the inventory. It is perfectly possible for a competent, informed, educated materialist of the late twentieth century to enjoy the works of Sheridan le Fanu or Lyman Frank Baum, not only with the full knowledge that they are not true histories but also safely above the need to prove his open-mindedness by saying that such things might be possible. However, I am confining my remarks to the rather narrow limits of "hard" science fiction, where I am qualified to hold a professional opinion. It has been charged that in restricting ourselves to "scientific accuracy" my colleague
s and I are narrowing the scope of usable story ideas available to us. My answer, mathematically rather horrible but defensible under literary standards, is that the square root of infinity is not really that much smaller than infinity as far as resource material goes. Our main point is that for many modern readers, a violation of the laws of thermodynamics by the author can spoil a story just as effectively as having Abraham Lincoln changing a set of spark plugs in a historical novel.

  Therefore, if we travel to Mars in a story, the vehicle must operate either along physical laws we currently think we know, or at least on more or less convincing extrapolations of those laws. Furthermore, when we get there the Martians, not to mention their lapdogs, saddle horses, dinner steaks, and rheumatism, must not strike too jarring a set of notes against the background which author and reader are, it is to be hoped, visualizing together. It is permissible and even desirable to take the reader by surprise with some of these details, of course. However, his reaction to the surprise should be the urge to kick himself for failing to foresee the item, rather than resentment at the author's ringing in a new theme.

  It follows that the "hard" science fiction writer must have at least an informed layman's grasp of biochemistry and ecology.

  Even in this narrowed realm, there would seem to be two basic lines of procedure for the storyteller who needs nonhuman characters and other extraterrestrial life forms. The two are not mutually exclusive; they overlap heavily in many ways. Nevertheless they represent different directions of attack on the problem, one of which is more useful if the basic story is already well set up in the author's mind, while the other is of more use in creating and developing the story possibilities themselves.

  In the first case, the qualities of the various life forms have to a considerable extent already been determined; they are demanded by the story events. Excellent recent examples occur in some of Keith Laumer's "Retief' novels, such as the wheeled metallic natives of Quopp in Retief's War and the even more peculiar Lumbagans in Retief's Ransom.

 

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