Science Fiction
in Pseudoscience
The term
"science fiction" was invented to describe a certain genre of
literature popularized in the 1920s, when pulp fiction magazines
specializing in this type of fiction first appeared. But as a genre of
popular literature, under no particular name, science fiction is found
in general fiction magazines throughout the 19th Century.
Many of the themes invented by writers 100 to 150 years ago have
penetrated the public consciousness so thoroughly that pseudoscience
writers need only mention one or two key words to suggest a whole
scenario in the mind of the reader! What is really frightening, however,
is that the average reader probably thinks these familiar concepts
borrowed from nearly two centuries of fantasy fiction are actual,
well-established scientific fact
real phenomena of the real world!
In fact, the vast majority of these science fiction themes are fictional
clichιs without any fixed meaning, much less any correspondence to
anything in the real world.
Let's discuss some of
the more common themes that appear in 19th century fantastic
fiction. These include:
LOST
CIVILIZATIONS. The usual story goes that an explorer stumbles onto a
"lost" civilization in some isolated part of the world; a high
urban civilization that has no contact or communication whatsoever with
the rest of the world, is geographically isolated by jungles or
mountains, and, often, possesses a high technology. In the 19th
Century this fictional clichι, particularly exploited by British
novelist H. Rider Haggard, was a pleasant enough conceit, but it makes
little sense today, with the globe so thoroughly explored. Furthermore,
the concept of an advanced but totally isolated civilization has been
widespread trade and frequent cross-cultural contacts.
In 19th century fiction, the hero generally falls in
love with the local princess and gets her out of the country just as a
volcano or something similar destroys the civilization forever.
NEW
ANIMALS, BOTH FOUND AND MADE.
This was an especially popular theme in the latter part of the 19th
century. Still-surviving dinosaurs could be found on a remote plateau in
South America, as in The Lost
World, by Sir Arthur Conan Doyle; familiar small animals could be
made unrecognizably gigantic, as in The
Food of the Gods, by H. G. Wells; or animals could be surgically
turned into human beings, as in The
Island of Dr. Moreau, also by Wells. Hence our inheritance of two
familiar themes: those supposedly extinct animals are hiding out
somewhere, and those meddling scientists can create monsters to menace
us. Public fears of and legal interference with modern genetic
engineering experiments probably stem mainly from such fantasies, not
from any real threat or menace.
MECHANICAL
LIFE -- ROBOTS AND ANDROIDS. Many writers explored this theme during
the latter half of the 19th century, often as a social satire
on the ultimate influence of assembly lines -- assembling peoples rather
than products. In 20th Century science fiction the terms
"robot" and "android" have clearly established
meanings of which movie script writers and
many
others seem to be totally ignorant. A robot is any machine which can do
all or some of the work of a man without human supervision. An android
is an artificial human; it can operate mechanically or biochemically,
but it is manufactured. The concept of mechanical life grew up out of
the fad for clockwork automatons that continued from themid-18th
to mid-19th century. Typical is the Ambrose Bierce story, Moxon's
Master, in which a mechanical chess player ultimately murders its
designer.
VISITORS
FROM OTHER PLANETS. This is probably the single most familiar theme
from science fiction. As soon as people suspected that life is a natural
phenomenon, which may appear anywhere conditions are right, and that the
other planets are worlds like earth, the possibility that intelligent
creatures from other planets might visit us became a common topic of
discussion. Sometimes the visitors of fiction were peaceful and came to
Earth seeking knowledge; other times they were desperate and/or warlike,
and came to earth seeking conquest. Reality is quite different. There is
no evidence whatsoever that creatures from any other world have ever
visited Earth, and our increasing knowledge of the other planets of our
solar system -- none of which is suitable for life -- makes clear why we
haven't been visited. Visits from other solar systems are an extremely
remote possibility, in view of the vast distances between stars with
solar systems and the vast numbers of such systems to choose from.
VISITS
TO OTHER PLANETS. This tradition in literature goes back nearly
2,000 years, but only in the 19th century did writers of such
stories generally try to describe the other planets as they actually
were thought to be, rather than as imaginary Cloud-coocoolands in which
anything was possible. Nineteenth century fiction about visits from and
to other planets had a strong influence on the 19th century
pseudoscientific religion of Theosophy, and through it on much of 20th
century pseudoscience. (Did you know, for instance, that the Earth was
once colonized from Venus?!? Or that Atlantis had a death ray?!?)
TIME
TRAVEL INTO THE PAST. There is no debate, even among science fiction
writers, that this is completely impossible. It not only involves
violations of the laws of physics, particularly the Second Law of
Thermodynamics, but literally and actually involves gross logical
contradictions. The idea is that mad Dr. Soandso gets into his time
machine (not clearly described) and somehow goes back to ancient Rome,
where he gives a translated handbook of physics and chemistry to a Roman
scholar, and thus utterly changes the course of human history
the
atomic bomb, for instance, is then invented by Claudius Festus Arpinna
in 350 AD. Despite the fact that even the writers agree time trips into
the past are an impossibility, they love to play with them, because of
the plot complications that can be generated by the logical
contradictions that arise. My favorite books of this type are Dinosaur
Beach by Keith Laumer and The
End of Eternity by Isaac Asimov. The time-travel short story to end
all time-travel short stories is All
You Zombies! By Robert A. Heinlein. Wells' 19th Century The
Time Machine is the genre's daddy.
SUSPENDED
ANIMATION OR TIME TRAVEL INTO THE FUTURE. Nothing impossible about
this, and a pseudoscientific rewrite of the Rip Van Winkle plot was the
easiest way for a writer to get his 19th century Every man
into the Utopian future to comment, marvel, and react. A classic example
is Wells' When the Sleeper Wakes. However, travel into the future (possible --
in fact, unavoidable!) is not much fun unless you can return to the past
to tell the home folks what you saw (impossible).
INVISIBILITY.
This theme was ever popular in the 19th century -- Well's
novel about the Invisible Man,
or Bierce's short story about a man eaten alive by an invisible animal,
are typical. Again, this is a physical impossibility. In order to be
invisible, an object would have to have two characteristics, which are
totally unrelated. It would have to be transparent,
and would also have to have an index
of refraction that is exactly equal to that of air. A transparent
object (like glass or quartz) is not invisible, because it does not have
the same index of refraction as air. But in fact no solid object (or
liquid object) can have an index of refraction anywhere close to that of
any gas at normal temperature and pressure. What is more, air does not
have a fixed index of refraction
it varies with pressure,
temperature, etc. But all solids and liquids have fixed indices of
refraction. To show that the idea of invisibility involves practical
contradictions, imagine an invisible boat. A transparent
boat with the same index of refraction as water would be clearly
visible in air (as is a splash of water), and thus "invisible"
only below the water line. If we instead made it have the index of
refraction of air, the part below the water line would be clearly
visible (like an air bubble in water). Also, a boat made of a
transparent material, like glass, would not be too seaworthy! In the
laboratory, one can find liquids, which have the same index of
refraction as certain glasses. If a piece of such glass is completely
immersed in such a liquid, it cannot be seen
(although it would easily be felt by putting one's fingers in the
liquid) -- but it would show up on radar or sonar. This does not seem
too practical!
Note also the
following: in general, there is no way to make a material that is not
transparent. Transparency is a more-or-less intrinsic property of
objects, determined by the way the atoms or molecules of the object are
bonded to one another. A final comment: an invisible creature would also
be blind! Eyes work by absorbing light.
"THE
FOURTH DIMENSION." The general claim is that there are
"other" space dimensions, somehow at right angles to the three
we know, and if we could "learn" to move in these other
dimensions (usually only one other, the fourth) we could do apparently
supernatural things, like instantaneously travel from one spot to
another, penetrate solid through solid, etc. The fact that all forces
whose ranges are not otherwise limited fall off with distance exactly as
the inverse square, to a very great measured accuracy, indicates
directly that there are no more than three space dimensions available to
matter and to forces
and everything in the universe is made of
matter and acted on by the same four forces. Physicists and
mathematicians routinely work in abstract spaces of arbitrary numbers of
dimensions
even infinite numbers of dimensions. Further, modern
efforts to unify the electromagnetic, weak, and strong nuclear forces,
which are understood quantum physically, with gravity, which is
understood only classically, sometimes involve working with many actual
space dimensions, 8 or more. This is a mathematical trick to make an
incomplete theory generate possibly realistic numbers, and has nothing
to do with the actual number of space dimensions. In these theories,
called "supersymmetric theories," all higher dimensions have
to be made compact, curled up on themselves, so that particles cannot
move or forces propagate along them, otherwise the theories would not
work at all! These theories are just things for physicists to play with
until they find a quantum theory of gravity, and have no particular
physical significance at present.
An obvious comment is
that if actual higher dimensions did exist, nothing could
"prevent" matter, forces, or us from moving in those
directions to begin with, and we would know about them from the
beginning, just as we know about forward, sideways, and up.
COEXISTENT
WORLDS. These are
usually confused by pseudoscientists with the "fourth"
dimension and "parallel" worlds, two totally unrelated ideas.
The original 19th Century fantasy fiction theme of coexistent
worlds is that since we see only a very limited part of the full
electromagnetic spectrum, maybe there are features of the world of which
we are unaware
for instance, if we could see by ultraviolet light
maybe New York City would also be a jungle! We wouldn't be aware of the
jungle since it can be seen only in ultraviolet light. If this claim
makes sense to you, you have a lot to learn about nature. In each of the
last three themes, writers almost always confuse
"invisibility" with "intangibility." A blind man
can't see the curbstone, but that doesn't prevent him from tripping over
it! An object, which could not be seen, could still be felt, and its
existence would be obvious! Furthermore, an object, which reflected only
ultraviolet light, for instance, would be clearly
visible. Why? An object, which does not reflect visible light,
appears black to our eyes. A jet-black tree is just as visible as a
regular tree, at least in the daytime.
VIBRATIONS.
Physicists in the 19th Century were very interested in
vibrations and waves. Writers of popular fiction, and pseudoscientists,
took only these words, and used them as buzz words. (A buzzword is a
word, which is meaningless in context, and usually is applied too
broadly to so many things that no meaning could
possibly be assigned to it in its customary -- non-scientific --
applications.) Thus writers started saying things like "everything
is made of vibrations, and the only difference between one thing and
another is the rate at which is vibrates, its frequency. If I could
change my vibration rate to that of platinum metal, I would become
platinum metal." This is the 19th Century origin of the
20th century buzz word "vibes." "The vibes are
not right today for me to do this job." It makes no more sense to
say that things are "made of" vibrations than it does to say
they are made of "sidewise motions" (what is moving?) or that
they are made of "temperature" (what has the temperature?).
Matter is made of atoms. Atoms may or may not vibrate; it's the atoms
and their properties that are important.
ENERGY.
Nineteenth
century physicists were also extremely interested in the concept of
energy. In physics, "energy" is a bookkeeping device for
keeping track of the amount of work that has been done on or by a
system. In popular fiction, "energy" became a buzzword, and
finally a kind of substance. Science fiction writers and
pseudoscientists today talk about things made of "pure
energy." Since temperature, for instance, is a direct measure of
internal kinetic energy, to say something is "pure energy"
makes no more sense than to say something is "pure
temperature." This is gibberish, without any connection to the
world we live in. Energy is not a substance or a thing. It is a number
(with units of work) and it is not the number of anything.
PARALLEL
WORLDS. Another
ever-popular idea from 19th century fiction was, "what
if?" What if the South had won the Civil War? What if Napoleon had
not invaded Russia? Characters were struck by lightning or something and
woke up in another world in which history had taken some other turn. It
makes a good novel, but it has nothing to do with the world we live in.
In its purest form, this is a naοve "concrete" interpretation
of the abstract concept of probability
the claim that if the coin is
50% likely to fall heads, and 50% likely to fall tails, it has to do
both
the universe splits into two universes, in one of which the
coin falls heads, in the other of which it falls tails. Since almost
everything that happens in the universe is a matter of probability, and
since an almost limitless number of processes are taking place in each
split second, one is talking about an almost limitless number of
"new" universes being born every split second. Of course, one
can talk about anything. There is, however, nothing in the real world
corresponding to the concept of parallel worlds. In modern physics one
does encounter what are called "multiple vacua." The present
state of the universe is not the only possible state. For all we know
the whole universe could suddenly make a "phase transition" to
a different vacuum, in which all the fundamental constants and laws of
nature would be totally different, and things as we know them would
cease to exist. But this possibility has nothing whatsoever to do with
the concept of "parallel universes," which are instead more
often confused with "higher dimensions," "coexistent
worlds," etc. A good 20th century science fiction novel
dealing with parallel worlds is Keith Laumer's Worlds
of the Empirium; see also H. Beam Piper's "Pratime"
series.
DETACHABLE
"MIND." What
if we could transfer your mind into the body of a spider? Or my mind
into the body of a whale? Makes for a good 19th or 20th
century fantasy story or satire, but what on earth are we talking about?
Not brain transplants. Some swami makes a mumbo-jumbo incantation -- the
movie All of Me features a classic example -- and minds shuffle around
among bodies like cards. What does the word "mind" mean
anyway? What the writers did is to take the ancient religious concept of
"soul," rename it "mind," and go on from there.
Again, there's no connection to reality at any point. But it's now a
common teaching in pseudoscience that you can "learn" --
there's that word again, and it's just $250 for easy lessons if you act
today! -- To detach your mind from your body and send it out to visit
distant places. Sounds like a primitive scenario to account for the very
natural phenomenon of dreaming.
REALITY
AS MENTAL IMAGE. Another
popular theme of 19th century fantasy fiction was to have a
character realize that his inner thoughts could reshape the whole
universe
by thinking that everyone should have two heads, he somehow
causes everyone to instantly and from then on have two heads. H. G.
Wells wrote a fine story along these lines, entitled The Man Who could Work Miracles, and 20th century writers
have used it too, as did Ursula LeGuin in The Lathe of Heaven.
As far as reality is
concerned, however, it is one of the most obvious facts of our
experience that the universe goes on totally independent of our
thoughts, desires, dream, and fancies. The fact that a dimwitted cook
doesn't know what temperature water boils at, or thinks water boils at
50°
F, does not alter the boiling temperature of the water on the cookstove.
The original 19th century nonsense has been re-treaded many
times, and most recently has shown up in crackpot
"popularizations" of quantum physics or in books about
"mystical physics," in which it is claimed that physicists
have shown that "your mind creates your own reality," and
similar vague gobbledygook. What goes on in the human brain has no more
effect on what goes on inside the Sun than what goes on inside the Sun
has on what goes on inside the human brain. How various processes affect
one another is the precise thing that physicists do study. There is no
question, experimentally, that thoughts alone do
not affect processes going on outside the body.
CIVILIZATION
AS PERIODIC. When in
the 19th century people began to realize the earth was
millions of years old (actually it's billions of years old), but knew
little or nothing about biology and evolution, they said things like,
"But recorded history only goes back a few thousand years! What
were humans doing the rest of that time?" In fact, humans didn't
even exist for most of earth's history, as was clearly understood by the
end of the 19th century. But writers and pseudoscientists
were going strong with the theme of civilizations rising and falling,
rising and falling. Half a million years ago some great civilization had
TV and microwave ovens and girls whom could kick off clothes even faster
than Bo Derek. But that civilization fell, and humans reverted to
savagery, and then a long climb began up to our present civilization,
which will also fall, etc. There is no question but that this idea is
totally wrong as it applies to the past. There is not one shred of
archaeological evident of any past civilization with a technology
anything like our own. The archaeological record is wholly consistent
with the usual idea that urban civilization is only about 10,000 years
old at most. (The human race itself, in its present form, is only around
50,000 years old
and for most of its existence lived a semi-nomadic,
hunter-gatherer lifestyle.)
WE'RE
PROPERTY. If there were
creatures on other planets that were much more advanced that we are -- a
very familiar idea in the 19th century -- they might not even
consider us intelligent, much less civilized. Maybe they consider us
like domestic animals on a far
or like exhibits in a zoo. Maybe they
own us, tend us secretly, cull out fat specimens and eat them. Lots of
good stories have been written about this, and early 20th
century pseudoscientist Charles Fort got a number of books out of the
theme. But alas, there is no evidence whatsoever of visitors from other
planets, advanced or otherwise, benign or malevolent. The other problem
is why visitors from other planets should have any attitude toward us at
all, pro or con. What's your attitude toward the squirrels in your back
yard? Or the ants? Or the crickets? If they don't bother you, you
probably don't even notice -- much less bother -- them. And they're
right in your backyard, not 100 light years away.
Early 20th
century science fiction writers did not add that many new themes. The
four most often encountered are:
THE
ATOM AS A LITTLE SOLAR SYSTEM
OR, OUR SOLAR SYSTEM AS A GIGANTIC
ATOM. This is based on
a public misunderstanding of very early, primitive work on the structure
of the atom. In Bohr's early, pre-quantum model, electrons orbit the
nucleus of the atom vaguely like planets orbit the sun. But
this picture of the atom is not correct. An atom is absolutely
nothing like a solar system; electrons are absolutely nothing like
planets. The classical physical laws obeyed by planets are totally
different from the quantum-physical laws obeyed by atoms and their
constituents. This is a classic instance of a completely false analogy.
MATTER
TRANSMITTERS. I don't know who invented this concept, but it was
probably Ralph Milne Farley in the 1920s with his RADIO MAN series. The
idea is familiar from the later use in TV fantasy shows like STAR TREK.
Somehow your body is scanned and recorded -- and in the process
presumably destroyed. Then the information is transmitted some vast
distance and the body reconstructed somehow from the information
available, using raw materials lying around in the new location. That
this is not just difficult but essentially impossible can easily be
seen. There are about 10(28) atoms in a human being. Suppose that the
position of each atom could be measured in about the time it takes light
to cross an atom -- that is as fast as it could possibly be done,
assuming the measuring device literally peels away the body and so is
literally in contact with each atom it measures. The time for light to
cross an atom is about 10-18 seconds. So to scan a human body would take
about 10(28) x 10.18 sec or about 300 years! To reconstruct the body at
the other end, again as fast as possible, would take the same length of
time. Furthermore the reconstructed body would be just that
it would
not be the original individual who was destroyed more that 6 centuries
before, at the other end of the transmitter. Any activity of the brain
that involves dynamic behavior -- steady currents, makes and breaks of
contact, etc. -- would not get recorded. Only information stored in the
form of specific molecules would get across. In short, the reconstructed
body might have some of the memories of the original individual, but
might not have all of his personality, training, etc.
or any of it.
SPACE
WARP, HYPERSPACE, OR STAR DRIVE. Interstellar
travel is not too practical a prospect, because to travel any
significant fraction of the radius of our own galaxy would require
thousands of years travelling as fast as one can go, just under the
speed of light. Science fiction writers have invented various totally
imaginary ways to get around this problem so that they can use the usual
cowboys and Indians plots. You can't rescue Princes Layya from Barf
Tater if it takes 300 years to find out he has her and 400 years to get
to where she's held prisoner. Layya and Barf would presumably be long
gone by the time Luke Starkicker got on the scene with his faithful
robot companion DO-2-U-2. Apparently the first writer to consciously
avoid this problem was E. E. ("Doc") Smith, back in the 1920s
-- probably because he was also the first writer to do much with the
concept of interstellar travel, in his famous Skylark
and Lensman series.
"Doc" solved the problem by asserting that his space ships
could be made inertialess -- and thus (according to "Doc")
could in their inertialess state travel effortlessly at huge multiples
of the speed of light. In fact, however, an object without inertial mass
(for instance a photon or neutrino) must travel at precisely
the speed of light, neither faster nor slower, at all times.
"Doc," for purposes of his stories, was also unclear about how
one "goes inertialess," since inertia is an intrinsic
property of matter.
Later writers sought
to avoid these and other problems with physical law by literally
"writing" their way from one star to another; that is, by
cloaking the problem with a "solution" of swell-sounding
gibberish terms. The standard solution is that the space ship somehow
enters an alternate universe ("hyperspace") where almost
infinite speeds are possible. Terms like hyperspace and space warp,
common in science fiction literature since the 1930s, have become
familiar recently to millions of illiterates via their use in fantasy TV
shows and movies involving interstellar travel. Anyway, the space ship
"makes the jump to hyperspace," or "warps space,"
and then when it gets near (?) its destination (?) -- how it navigates
is unknown and unspecified -- it comes back into "regular
space." Now, this is all total gibberish, with no connection to the
real universe in which we live. Even considered as an abstract scenario,
it contains internal contradictions. Why should there be any relations
between position in "hyperspace" to position in "real
space?" Just moving straight up into the air ("making the jump
to the third dimension") doesn't get you from Rome to Buenos Aires.
Indeed, the entire concept of dimensions is based on the fact that
motion along one dimension is independent of motion along any other
dimension! And how does one go into hyperspace
or warp space
or
construct a star drive that "clutches at the very fabric of space
itself?" The writer, at his typewriter, has no troubles. He can
make up any convenient rules he wants, however inconsistent. But in our
real universe the rules are not so flexible. The fact remains, if you
want to go from one point in the universe to another point, you cannot
go at a speed faster than 186,000 miles per second, period.
ESP,
PSYCHIC POWERS; PSIONICS. Two
themes became so immensely popular in the 1950s that they almost
completely dominated science fiction for more than a decade. The first
theme was the aftermath of a global thermonuclear war, with a world sunk
back into savagery and inhabited by weird, dangerous mutants. The second
theme was the awakening of fantastic, generally godlike human mental
powers. This latter theme has been so popular that fiction writers,
movie scripters, pseudoscientists and newspaper reporters tend to forget
that no such powers have ever
been demonstrated in any real laboratory inhabited by real scientists.
Popular fiction from the very first has been full of mysterious
individuals with godlike powers -- the same powers possessed by the gods
themselves in the various mythologies associated with the world's
popular religions. In the 19th century, two new
religions, Spiritualism and Theosophy, summarized conveniently, and
named or renamed, the powers that the gods would have -- but that we
poor humans never seem to possess. These powers include the ability to
read minds, telepathy; the ability to foresee the future, precognition; the ability to "see" what is behind
windowless walls and within locked drawers, clairvoyance;
the ability to move or alter objects without touching them, by sheer
"mental force," psychokinesis;
the ability to cause oneself to vanish at one spot and instantaneously
appear at another, teleportation;
the ability to "take over" another's body, animating it and
"looking out of" its eyes and other senses, possession;
and so on. As has been pointed out many times, the only thing these
imaginary powers have in common is their tendency to recur in the
daydreams of frustrated adolescents. "If I could only
. "
"I wish I could
" "Boy, if I could
"
Pretending that such powers "really do" exist, although we of
course don't have them yet
or rather we aren't trained
is merely wish fulfillment, of a rather pathetic kind. In the 1930s,
the catchall term ESP (Extra-Sensory Perception) was adopted for all
these powers, a rather poor name since many of them don't involve
perception. Thus science fiction writers introduced another term, psi
powers. The imaginary
science of such powers was then called "Psionics." People with
ESP were called "esp-ers" and so on.
The two themes of
post-nuclear war and psi powers sometimes blended, as in stories where
imaginary mutants created by peacetime or wartime radiation developed
such powers. Or the human race was depicted as evolving toward such
powers. Indeed, a standard science fiction picture of a highly advanced
or highly evolved race, since the 1930s, give them not only the physical
but also the mental powers attributed in mythology to the gods
themselves. This saves any necessity for the science fiction writer to
exercise any imagination or originality, regarding what an
"advanced race" would really be like.
IN
CONCLUSION: The great
danger of all the things we have discussed here is that some people tend
to accept everything that appears in works of fiction, no matter how far
fetched, as somehow "real," as if the authors of the stories
have no imaginations, no tradition of fantasy and religious theme to
draw on, and no ability to invent things of their own. Science fiction
is in no way science fact; it is a literature of entertainment, not of
instruction. There is little or no science involved in the usual science
fiction story, which since the 1950s ha anyway turned increasingly on
political and social issues. Even the handful of writers who do know a
little about science -- such as Hal Clement, Poul Anderson, and Arthur
C. Clarke -- will always ignore unpleasant facts if they get in the way
of the plot or the characters. Any fiction writer is out to interest
you, then to entertain you and amuse you. He does not try to function as
a scientist or as a teacher; he does not feel any obligation to depict
the actual universe in which we live, and generally he does not depict
such a universe.
Sadly,
pseudoscientists regularly take advantage of public familiarity with the
common themes of science fiction, just as they regularly take advantage
of the public's ignorance of most real scientific facts and authentic
science discoveries.
Acknowledgments
ASTOP -- The Austin
Society to Oppose Pseudoscience -- has prepared fact sheets on various
topics for the benefit of teachers and others interested in promoting
critical thinking. Dr. Rory Coker, Professor of Physics at the
University of Texas at Austin, is the author of this fact sheet.
The International Cultic Studies
Association (formerly American Family Foundation), a professional research and
educational organization concerned about the harmful effects of cultic and
related
involvements, prints and helps distribute these fact sheets. Because ASTOP fact sheets
seek to stimulate critical thinking, rather than advance a particular
point of view, opinions expressed are those of the authors.
These fact sheets may be copied for educational purposes, but
they may not be reproduced for resale.