Luke Skywalker leads a group of Rebel X-wing fighters in an attack on the Imperial Death Star. As the fighters bank and roll towards the gargantuan spacecraft, you see laser weapons firing from both sides. Luke does some fancy flying, fires his weapons, lands his torpedo in the vent, and, with a loud explosion, the Death Star is no more. This climactic scene from "Star Wars: Episode IV" is typical of many action science fiction movies. It makes for a great movie going experience, but is the science real? Could spacecraft really move like this? Could you see laser blasts? Will we hear the deafening explosions? And should we care about any of these things?
We'll answer the last question first: "Yes, definitely!" Science is essential to any work of science fiction; in fact, it separates science fiction from fantasy or other works of fiction. Furthermore, sci-fi fans are very discriminating. Sometimes, minor errors in the science do not detract from the story and may not be noticeable, except by the discriminating viewer. In other cases, the mistakes in science are so blatant that the story becomes totally unbelievable and the movie falls apart.
In this article, we'll explore some major mistakes and misconceptions in sci-fi movies and TV shows. A few notes before we begin:
- Our list is not comprehensive ? we have chosen several topics, but there are many more.
- You may disagree with our choices. Discussion of sci-fi is always a good thing.
- We love sci-fi movies, TV shows, novels and short stories. Our goal is to inform, not to "pick on" a particular work.
- We realize that the primary goal of moviemakers is to entertain, not necessarily to educate. Sometimes emphasizing the science may not make the scene work.
- We realize that sci-fi movies are constrained by budgets, technical capabilities and matters that are critical to entertainment.
With this in mind, let's look at how science fiction doesn't work.
Willing Suspension of Disbelief
There is a principle in movie making called "the willing suspension of disbelief," in which moviegoers can accept a certain level of implausibility in favor of the story. For example, fantasy stories rely on magic and readers and viewers accept this. This also happens with some science fiction stories. For example, the work may be dated. Jules Verne's "Journey to the Center of the Earth" was written before geologists knew anything about the internal structure of the Earth or plate tectonics, so you can suspend belief and enjoy the story. Finding the line at which viewers are unwilling to suspend their belief can be tricky.
So, science is important to make a work of science fiction and authors and film makers should strive to make the science in their works as real as possible. If the science is not real, the responses can vary. Some viewers may be willing to suspend their disbelief. "Star Wars" fans are certainly willing to suspend disbelief. However, if the science is too "out there," Viewers can be turned off. "The Core" was so unbelievable that it bombed at the box office. How filmmakers choose to tackle the believability factor could mean the difference between a success and a bomb.
How Spaceships Move
We opened this article with a description of banking X-wing fighters and other spacecraft, from "Star Wars." You can see similar movements in the Viper fighters of the original "Battlestar Galactica" TV series. Designers modeled these spacecraft after modern jet aircraft fighters (like the F-14 and the MiG) and they engage in dogfights like those in "Top Gun." The banking of an aircraft is a consequence of air moving over the surfaces of the wing, ailerons and rudder. When a plane turns, the ailerons on one wing move up on one side and down on the other, which causes the aircraft to roll in the direction of the turn. Simultaneously, the tail rudder moves in the opposite direction of the turn and deflects air to make the turn. These combined air movements cause the plane to bank in the direction of the turn as the plane continually thrusts forward. They could not happen without air.
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While an aircraft moves through the medium of air, a spacecraft moves in a vacuum. Newton's Third Law of Motion ("for every action, there is an equal, but opposite reaction") governs the movement of a spacecraft. For a spacecraft to turn, it must fire a rocket thruster (eject mass as hot gasses) in the opposite direction from where it must go. There are three axes of rotation: pitch, roll and yaw. If the pilot wants to turn right, then the rocket thrusters fire left and usually the roll and yaw thrusters fire simultaneously. Such maneuvering thrusters are located in various places along the body of the spacecraft and allow it to move in all three axes of rotation. So, the turn of a spacecraft looks like an abrupt flip in one or more directions simultaneously rather than a smooth bank. You can see such movements of the Apollo spacecraft in the HBO miniseries "From the Earth to the Moon" and in the Viper fighters of the new "Battlestar Galactica" series on the SciFi Channel.
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Next, we'll learn about sci-fi mistakes with planets and asteroids.
In "Star Wars Episode I: The Phantom Menace," Qui-Gon Jinn, Obi-Wan Kenobi and Jar Jar Binks are in the underwater Gungan city on the planet Naboo. They must reach Queen Amidala on the other side of the planet. So, the Gungan leader says that the fastest way is to go through the planet's core and gives them a submarine. As they travel, several sea monsters pursue them and they escape before surfacing on the other side. While this scene seems harmless, it defies what we know about planets. Planets do not have rocky surfaces and watery cores.
In our solar system, we have small rocky planets (Mercury, Venus, Earth, Mars) and gas giants (Jupiter, Saturn, Uranus, Neptune). The planets formed when material from the early solar disk (planetismals) collided and clumped together to form the planets. The material in the inner solar system was mostly rock, dust and metal that could exist in the warm environment. The planetismals in the outer solar system were mostly gas, water ice and dust that could exist in the cold environment. As the planets formed, gravity held the aggregated planetismals together and caused them to spin. Naboo is an Earth-like planet, so let's look at the formation of the Earth.
On the early Earth, collisions of planetismals produced heat that melted the material, which was not uniform. In this molten medium, materials of different densities settled. Iron and nickel within the molten Earth were the densest and sank to the center to form the core. Less dense materials settled above to form layers (outer core, mantle, crust). Geologists refer to this process as differentiation. (Note: In the outer gas giant planets, the cores may be composed of dust and water ice with liquid gas layers around them).
Water is less dense than nickel, iron and rocks. It would float on these substances. So, you would not find water in the center of the Earth. Similarly, Naboo would not have a liquid water core.
In her book "The Science of Star Wars," Jeanne Cavelos states that Naboo supposedly is made of irregular rock aggregates with watery caves between them. However, gravity would attract these pieces and they would heat up. Any caves would collapse, water would disappear and Naboo would assume a spherical shape with differentiation just like the Earth.
In "The Core," scientists discover that the Earth's inner core has stopped rotating. This disrupts the Earth's magnetic field leaving the Earth vulnerable to deadly microwave radiation (Bad science alert: the Sun does not put out enough energy in the microwave band to be a danger and the Earth's magnetic field does not deflect microwaves). To correct this situation, the scientists travel through the mantle and the molten layers of the outer core and attempt to jumpstart the core's rotation with nuclear bombs. While the depiction of the Earth's structure is better than other movies, "The Core" has many other science problems (see detailed reviews on Bad Astronomy and Insultingly Stupid Movie Physics).
Mars in the Movies
Mars has long been a fascinating subject and Hollywood has tried to respond. In the 1950s, "The Angry Red Planet" depicted life on the red planet with scenes where the surface was entirely red and strange rat-spiders attacked the crew. "Robinson Crusoe on Mars" showed Mars as a desert-like planet with a thin atmosphere, and the hero survives there with an alien, human-like companion. We can forgive these movies as they used the famous astronomer Percival Lowell's descriptions of the surface of Mars and came out long before we ever sent a probe to Mars to see what it was like.
Mars is a cold desert planet where we think that water once flowed, and that water may still exist in frozen form at the poles and in the permafrost (for details, see How Mars Works). Two recent films, "The Red Planet" and "Mission to Mars," have a more realistic depiction of Mars based on the information gathered from Mars missions since 1976. However, in "The Red Planet," the astronauts crash on Mars and must walk a great distance across the surface to a habitat module. In the process, their space suits run out of oxygen; one crewmember commits suicide by jumping off a cliff rather than suffocate. In a dramatic scene, the remaining astronauts are suffocating in their suits, when one desperate astronaut opens the visor of his helmet and breathes. He miraculously discovers that Mars has oxygen. He tells remaining crew to do the same and they all survive by breathing the Martian air. Couldn't they have known that Mars had oxygen even prior to the crash?
Mars has a thin atmosphere composed mainly of carbon dioxide. At present, there is no oxygen to support humans. In addition, when heated or illuminated with light, elements and compounds absorb and radiate energy in various forms of electromagnetic radiation such as infrared. (See How Light Works for more information). The infrared spectrum is frequently used to determine what molecules exist in the atmosphere of a planet and how abundant they are. Earth-based telescopes equipped with infrared spectrometers can detect elements in the atmospheres of other planets and even planets around other stars. With these techniques, surely the astronauts in "The Red Planet" would have known that oxygen was present on Mars long before they even traveled there.
There has been research and proposals that it might be possible to terraform Mars in the future to make it more Earth-like (see How Mars Works). This has been the basis of Kim Stanley Robinson's sci-fi novels ("Red Mars," "Green Mars," "Blue Mars," "The Martians").
In the movie "Armageddon," astronomers spot an asteroid that will hit the Earth in a matter of days. The asteroid is the size of Texas and the impact will cause total annihilation of life on Earth (or at least the people on it). A crew of astronauts and oil drillers must land on the asteroid, drill 800 feet into it, implant a nuclear bomb, liftoff from the asteroid and detonate the bomb. The explosion will fracture the asteroid and send the pieces on either side of the Earth in a near miss that will save humanity. This rousing action-adventure story has little scientific basis.
In the movie, when they land on the asteroid, the astronauts have special thrusters on their spacesuits to help them walk normally in the low gravity environment. Okay, fair enough. But inside the spacecraft that lands on the asteroid, the unsuited crewmembers walk around just as normally. Gravity works the same whether they are inside or outside of the spacecraft.
In Armageddon, the asteroid is the size of Texas; most asteroids are only several kilometers wide (astronomers would spot an asteroid the size of Texas well before it was a few days away from Earth). In the movie, the asteroid is a rough surface with razor-sharp crags and huge canyons. Actual photos of the asteroid Eros from the NEAR spacecraft show the surface to be relatively smooth, albeit cratered.
A similar movie, "Deep Impact," was released at the same time as "Armageddon." The story line was similar, but it involved a comet instead of an asteroid. "Deep Impact" was less of an action-adventure film and handled the human side of what would happen in the event of such an impact. We know that such impacts have happened over the history of Earth and the solar system and even witnessed the impact of comet Shoemaker-Levy 9 into Jupiter (see How Comets Work).
We'll look at how sci-fi has made mistakes with antimatter, gravity and black holes next.
Matter-antimatter reactors power the starships in "Star Trek." Just like it sounds, antimatter is the opposite of normal matter. For example, a hydrogen atom is composed of a proton (a positively charged particle) and a much less massive electron (a negatively charged particle). An anti-hydrogen atom consists of an anti-proton, which has the same mass as a proton, but is negatively charged, and a positron, which has the same mass as an electron, but is positively charged. When matter and antimatter come into contact, they annihilate each other and produce vast amounts of energy (see How Antimatter Spacecraft Will Work). This process is perhaps the most efficient means of providing energy for interstellar travel.
The problem is not that antimatter exists or that it can produce power. The problem is that, for reasons unknown to physicists, very little antimatter exists in our universe. Theoretically, when the universe was formed, there should have been equal amounts of matter and antimatter; however, our universe consists primarily of matter. So, what happened to all of the antimatter? This is a major area of research in theoretical physics (such as quantum physics and cosmology). Tiny amounts of antimatter can be produced in particle accelerators, but it is expensive to produce. In "The Physics of Star Trek," Lawrence Krauss points out that it takes far more energy to produce antimatter today than you get from the annihilation reactions of this antimatter. In the time of "Star Trek", antimatter is common or commonly produced; we assume that humans have found an inexpensive method of producing antimatter by that time. This is a case of willing suspension of disbelief.
Gravity in Sci-Fi
We see depictions of gravity in many sci-fi films from weightlessness to artificial gravity, and we also see gravitational black holes and asteroids with little gravity. Before we examine how gravitational issues are addressed in sci-fi films, let's look at what gravity is. According to Isaac Newton, gravity is an attractive force between any two masses. Newton's law of gravity says that the force of gravity is directly proportional to the sizes of masses (m1, m2) involved and inversely proportional to the square of the distance (r) between the two masses (Specifically, the centers of the masses. He derived this equation: F = Gm1m2/r2, where G is the universal gravitational constant, 6.67 x 10-11 N-m2/kg2.). The force of gravity increases when the masses involved increase and it decreases as the distances between them gets farther apart.
Weightlessness has been depicted in many sci-fi films. In George Pal's classic "Destination Moon," the crew experiences weightlessness and use magnetic boots to attach themselves to the spacecraft's floor and walls. One crewmember even remarks that he can't swallow well without gravity (This is not true because swallowing relies on muscle contractions of the esophagus rather than gravity. You can swallow quite well in weightlessness.). The absence of gravity does not cause weightlessness, as is often thought. Instead, the occupants of the spacecraft are in a state of freefall with the spacecraft itself. Most sci-fi films depict weightlessness by having the actors attached to wires and pulleys during filming. In Ron Howard's film "Apollo 13," the weightless scenes were shot on board NASA's KC-135 "Vomit Comet" aircraft. This plane flew parabolic arcs repeatedly where the occupants (actors, camera operators, director) experienced many brief, 30-second periods of free-fall. Weightlessness causes many adverse effects; short-term effects include nausea and vomiting, while long-term effects include bone loss, muscle atrophy, fluid loss,and anemia (see How Weightlessness Works).
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Shifts in your blood and bodily fluids upon exposure to micro-gravity.
On spaceships, such as "Star Trek"'s Enterprise or Star Wars' "Millennium Falcon," there is some type of artificial gravity field that allows the occupants to experience normal gravity in flight. This is important to counteract the adverse effects of prolonged weightlessness. It is also easier to film a movie without having to make the occupants appear weightless. How these artificial gravity fields are generated are unknown (remember, sci-fi writers are free to extrapolate). Currently, the only known means of producing artificial gravity is spinning the astronauts in a wheel-like environment. Centripetal acceleration towards the center of the wheel produces centripetal force. The reaction to this acceleration (often called centrifugal force) throws the occupants against the wall and feels like gravity (many amusement parks have rides like this). The films "2001: a Space Odyssey, " "2010: The Year We Make Contact," and "Mission to Mars" all depict this type of artificial gravity correctly.
When you apply a force to an object, it accelerates. Newton's Second Law describes this relationship as F = ma, where F is the force, m is the mass of the object and a is the acceleration. In Star Trek and Star Wars, spacecraft often accelerate from rest or sub-light speed to light speed or more in a matter of seconds. The crews of these spacecraft would experience huge forces of acceleration (G-forces), even more than the G-forces experienced by jet fighter pilots when they accelerate and maneuver their aircraft. To compensate for this, Star Trek writers came up with the idea of inertial dampers, which counteract the forces of acceleration. In "The Physics of Star Trek," Lawrence Krauss speculates how these devices might work, but to date no such device exists.
Black Holes in Sci-Fi
In contrast to weightlessness, some sci-fi films tackle an object where gravity is extremely high: a black hole. Near the end of "Galaxy Quest," helmsman Tommy Laredo tells Capt. Jason Nesmith that the NSEA Protector must go through a black hole to return to Earth. In Disney's "The Black Hole," a spaceship crew goes through a black hole and ends up in another place far away. The problem is that you cannot go through a black hole.
A black hole is caused by the collapse of a star at the end of its life (The star must be at least three times more massive than the Sun). The core of the collapsed star becomes so dense and the gravitational forces so great that nothing, not even light, can escape. A black hole is not a tunnel. Any object that enters the edge or event horizon of the black hole falls into it. The gravitational forces inside would rip any matter apart.
One misconception about black holes is that they suck everything nearby into them like a huge vacuum cleaner. This is not necessarily true; only objects that fall within the event horizon go into the black hole. They will attract objects by virtue of their mass and gravity just as the star that bore them did (remember that the black hole has the same mass as the star, just more compact, or dense). If the Sun were to instantly become a black hole, many people think that it would suck the Earth into it (Although the Sun does not have enough mass to become a black hole). But if you examine Newton's law of gravity above, neither the mass of the Sun nor the Earth changes, and neither does the distance between them. So, the Earth would experience the same gravitational attraction to the Sun if it became a black hole as it does now. The Earth would merely orbit the black hole, just as it orbits the Sun now (The loss of sunlight would cause severe problems for life on Earth, however).
Next, we'll look at how science fiction has handled lasers, sound and aliens.
Lasers in Space
The various Star Wars fighters (e.g. X-wing, TIE, Death Star) fire laser or pulsed laser cannons. In "Star Trek," the Enterprise fires its phasers at enemy space ships. In both "Star Wars" and "Star Trek," people fire hand-held laser or phaser weapons. In all of these scenes, we see the laser beams travel and hit their targets. The problem with this is that you cannot normally see a laser beam.
A laser is a highly focused beam of light with the photons traveling in one direction. None escape to hit your eye and make the beam visible. In a vacuum, you would only see the beam light up where it hit the target (light is scattered by the matter in the target). There is nothing in the path to make the beam visible. You can demonstrate this with a laser pointer or flashlight in a clear room. Point the laser/flashlight at the wall and you will only see the spot on the wall. To make the beam visible, you must place fine particles in its path to scatter the light (such as chalk dust or baby powder).
I don't know of even one sci-fi film or TV series that demonstrates the proper functioning of the laser beam. Most make the beams visible through special effects because it would be unsatisfying for the viewer to see a character fire a laser and not see anything.
Sound in Space
When the rebel forces destroy the Death Star in "Star Wars Episodes IV" and "VI," each Death Star goes out with a loud explosion. Such explosions happen in many sci-fi movies and TV series, such as when "Star Trek"'s Enterprise destroys an enemy vessel, or when the Nostromo self-destructs in "Alien." The problem here is that sound does not carry in space.
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Sound is an example of a longitudinal wave. The sound energy moves along by vibrating molecules of gas, liquid or solid. When the bell in the above animation flexes away, it pulls in on the surrounding air particles. This creates a drop in pressure, which pulls in more surrounding air particles, creating another drop in pressure, which pulls in particles even farther out. Each vibrating air molecule passes its vibration on to the next air molecule between the bell and your ear to make the sound wave propagate. When the vibrating air in you ear canal hits your eardrum, it causes the eardrum to vibrate with the same frequency as the sound wave. The bones of the middle ear transmit this vibration to the inner ear, where the vibration sets up a standing wave in the fluid of the inner ear. The wave vibrates certain hair cells in the inner ear, which transmit nerve signals to the hearing center of your brain and you sense the sound. The important part of this process is that air molecules propagated the sound wave from its source to your ear. The same thing happens when you hear sounds underwater or through walls (liquids and solid propagate the sound waves as well). However, in the vacuum of space, there are no molecules to propagate sound waves and you don't hear anything. The movie poster of "Alien" was correct with its tagline, "In space, no one can hear you scream!"
One example of the correct depiction of the lack of sound in space is Stanley Kubrick's classic film, "2001: a Space Odyssey." We see shots of the inside of spacecraft (Discovery, pods, moon vehicles) with sounds of machinery and alarms. When the scenes cut to the outside of these spacecraft, there are no sounds at all. Most dramatically, there is a scene where astronaut David Bowman must get inside the spaceship Discovery from a space pod without his helmet. He decides to decompress his space pod exposively to propel himself into an open airlock aboard the space ship Discovery. The film shows the explosion and subsequent propulsion of Bowman from the airlock in total silence. Sound only resumes when Bowman manages to close the airlock and let it fill with air. The sci-fi Western "Firefly" and its subsequent film, "Serenity," depicted a lack of sound in space as well. As with the visible lasers, most sci-fi films and TV shows accompany explosions in space with sound because it would be unsatisfying for the viewer to see an explosion and not hear anything.
Aliens in Sci-Fi
In an episode of the original Star Trek series titled "The Immunity Syndrome," the Enterprise encounters a gigantic single-celled organism resembling an amoeba. The organism is perhaps thousands of kilometers across, much larger than the Enterprise. In fact, the Enterprise penetrates the organism's cell membrane and goes into its cytoplasm to destroy it. Could such an organism be possible?
A single cell depends upon the process of diffusion to get materials across its membrane and move materials within it. Diffusion is the movement of a substance from an area of high concentration to an area of low concentration. You can smell an onion cut in the kitchen in another room because odor molecules from the onion move from an area of high concentration (the onion) to an area of low concentration (the kitchen and other rooms). For cells, diffusion works most efficiently over short distances (1 to 100 microns, 1 micron is 1 millionth of a meter).
In addition to short distances, cells need a large surface area for diffusion to be efficient. Most cells are spherical or cuboidal. Let's look at an example of a spherical cell with a radius (r). The volume of a sphere is given by the formula V = 4/3 r3, while the surface area is given by the formula A = 4 r2. As the cell grows and r increases, the volume gets much larger than the surface area (volume is a cubic function of r, while, surface area is a square function of r). As the cell grows, diffusion can no longer bring materials into the center of the cell because the distance becomes too great. So, a practical limit on the size of a single cell is about 100 microns in diameter or less. Gigantic single cells like that depicted in the Star Trek's "The Immunity Syndrome" could not survive. Large organisms, including humans, are made of many small cells and use circulatory systems to deliver oxygen and nutrients to cells and to remove carbon dioxide and wastes from them.
On a related note, several 1950s films such as "Them" depict large insects like ants and spiders that are as large or larger than a man. Even "Harry Potter and the Chamber of Secrets" has a huge spider and many spiders the size of dogs. Insects have no active ventilation system (such as lungs) to bring in air. Instead, they rely on a system of branching tubes called trachioles to bring air close enough to each cell in their body and rely on diffusion of air through these tubes. The larger the insect, the greater the distance the air must travel and the less efficient diffusion becomes. So, this is why you do not see gigantic spiders and ants roaming the planet.
Another reason for not seeing large insects is that their long thin legs would not support large bodies in normal Earth gravity. So, the alien from the "Alien" movie series would probably not be able to walk around in normal gravity. The largest land animal is the African elephant and it has four large, broad legs to support its body weight. The appearance of large aliens is still a popular attraction in many sci-fi films, but you do not see large single-celled aliens much anymore.
Science continues to evolve and new discoveries are made all of the time, so someday we may look back on some of these mistakes with the amused nostalgia that viewers of films like "Robinson Crusoe on Mars" feel today. But as long as the science is plausible, the film doesn't push our willingness to suspend disbelief and (some would say, most importantly) the story is engaging, we can always enjoy science fiction.
For lots more information about science fiction and related topics, check out the links on the next page.
- Star Wars Quiz
- How Airplanes Work
- How Space Shuttles Work
- How Lasers Work
- How Light Works
- How the Sun Works
- How Special Relativity Works
- How Mars Works
- How Black Holes Work
- How Asteroids Work
- How Weightlessness Works
- How Atoms Work
- How Atom Smashers Work
- How Antimatter Spacecraft Will Work
- How SETI Works
- How Planet Hunting Works
- How Aliens Work
- How Rockets Work
- How Time Travel Will Work
More Great Links
- Andreadis, A. "To Seek Out New Life: The Biology of Star Trek." Crown Publishers, Inc., New York, 1998.
- Bormanis, A., "Star Trek Science Logs." Pocket Books, New York, 1998.
- Bova, B. and A. R. Lewis. "Space Travel." Writer's Digest Books, Cincinnati, 1997.
- Card, O. S. "How to Write Science Fiction and Fantasy." Writer's Digest Books, Cincinnati,1990.
- Cavelos, J. "The Science of Star Wars." St. Martin's Press, New York, 1999.
- Dubeck, L. W., S. E. Moshier, and J. E. Boss. "Fantastic Voyages: Learning Science Through Science Fiction Films." (2nd Edition), Springer-Verlag, New York, 2004.
- Gillett, S. L., "World-Building." Writer's Digest Books, Cincinnati, 1996.
- Henderson, D. J. "The Encyclopedia of Science Fiction Movies." Checkmark Books, New York, 2001.
- Jenkins, R. and S. Jenkins. "Life Signs: The Biology of Star Trek." HarperCollins, New York., 1998
- Krauss, L. M. "The Physics of Star Trek." BasicBooks, New York, 1995.
- Nahin, P. J. "Time Travel." Writer's Digest Books, Cincinnati, 1997.
- Plait, Phil. "Bad Astronomy Movies." http://www.badastronomy.com/bad/movies/index.html
- Rogers, Tom. "Intuitor, Insultingly Stupid Movie Physics." http://www.intuitor.com/moviephysics/
- Schmidt, S. "Aliens and Alien Societies." Writer's Digest Books, Cincinnati, 1997.
- Sheffield, C. "Borderlands of Science." Baen Books, Riverdale, New York, 1999.