Science and the Original Star Wars Trilogy
Let me say right up front that I enjoy the Star Wars movies. I really do. They’re lots of fun to watch, even though they don’t make much sense when you stop to think about them. Certainly, I don’t see anything wrong with popcorn movies –I don’t feel there’s any contradiction between enjoying a movie and noticing it has flaws.
Fantasy and science-fiction movies typically take place in universes where the laws of physics clearly function differently than they do in our own universe. That’s fine with me, so long as they’re consistent about it.
What follows, then, is a light-hearted examination of the original Star Wars trilogy, how believable the Star Wars movies are: do they make sense? Of course, lots of articles and books have been written that “explain” seeming inconsistencies in the Star Wars movies; some of them are quite good. I’m not concerned with those here; what I’m interested in is whether or not the movies make sense on their own. If you must go to outside sources to resolve seeming inconsistencies, the film-makers haven’t done their jobs properly, in my opinion.
The Physics of Star Wars
Let’s just say that the physics of the Star Wars universe bears only a vague resemblance to that of ours. An in-depth analysis would easily fill a book. Still, before we get to the actual movies, I thought it might be interesting to discuss some of the more obvious ways that Star Wars physics differs from our own.
Spacecraft Performances and Related Phenomena
The first thing you notice about spacecraft in the Star Wars universe is that the small ones seem to behave just like terrestrial aircraft and the big ones move like terrestrial naval vessels. This is odd, since they’re usually moving in a near-vacuum instead of air or water.
At this point, a brief discussion of how fixed-wing aircraft (as opposed to helicopters) fly seems to be in order. To fly, aircraft use their engines to generate thrust, which pushes them forward. Friction with the air creates drag, which will slow the aircraft – constant engine thrust is therefore necessary to overcome this drag and keep the aircraft moving forward at a constant speed. As air flows over the craft’s wings, it generates lift, which pushes the aircraft upward and overcomes the craft’s weight, keeping it from falling to earth. If something happens so that the wings are no longer generating lift, the aircraft stalls. This has nothing to do with whether or not the engines are functioning properly; stalling occurs when the wings are no longer generating sufficient lift to keep the aircraft up.
You’ve probably noted that aircraft wings are convex on the top and either flat or concave on the bottom. In addition, they’re typically tilted so that the leading edge (the front of the wing, where moving air first hits) is slightly higher than the trailing edge. So, as the aircraft moves forward, air hitting the underside of the wing is deflected downward to a degree. Since for every action there’s a reaction, as air hitting the wing is deflected downward, the air pushes the wing upward, helping to generate lift. More importantly, oncoming air is split as it hits the leading edge of the wing. Air traveling over the convex top of the wing has a greater distance to travel than does air traveling under the wing. So, the air moving over the top of the wing speeds up. According to Bernoulli’s Principle, the pressure generated by a fluid decreases as its speed increases. So, the air moving over the top of the wing generates less downward pressure than the air moving across the bottom of the wing generates upward pressure. The net difference pushes the wing upward, and so generates lift. The faster the aircraft is moving, the greater is the difference in speeds between air on the tops and bottoms of the wings, and so the more lift is generated.
Aircraft typically turn by using ailerons and rudders to push against the air they’re flying through. When you want your plane to turn left, for instance, you can elevate the ailerons on the left wing; this creates extra drag on the left side of the plane and slows it somewhat, causing the plane to turn left. It also has the effect of pushing the left wing downward, so the plane banks as it turns. To turn more quickly, you can elevate the ailerons on one wing and depress them on the other – this makes the craft bank even more sharply, since one wing is pushed upward and the other is pushed downward.
On a related note, ships moving through water also have to overcome drag to keep moving forward, so an ocean-going vessel must have a constant source of “thrust” as well. Otherwise, friction between the water and the ship’s hull will soon slow the ship to a halt, relative to the water.
What does this have to do with Star Wars? Well, for one thing, there’s no particular reason that space-going craft should need wings, though most fighters and even larger craft in the Star Wars universe appear to be built with aerodynamics in mind. This is not necessarily a criticism, since the designers may have intended the craft to spend a fair amount of time operating in planetary atmospheres. It still seems odd, though.
Much less reasonable is the fact that Star Wars fighters bank just like terrestrial aircraft when they turn. There’s no reason why spacecraft should bank like that, because there’s no air to push against – ailerons and rudders wouldn’t work. Real spacecraft turn as the space shuttle does – by using rockets or other thrusters to push the craft in the desired direction. To be sure, if you put enough thrusters on your spacecraft, you could make it bank as it turns, but it would be a pointless waste of fuel.
Also, you’ve probably noticed that Star Wars spacecraft seem to have their engines going constantly while in space, which makes no sense. When in normal space, Star Wars spaceships don’t seem to be moving any faster than modern aircraft do, so there would be essentially no drag. This means that a spacecraft moving at speed “X” will continue to move at speed “X” if it shuts off its engines, since there’s no drag to slow it. As long as its engines are on, a spacecraft should be accelerating. Oddly, though, in the Star Wars movies we frequently see ships moving through space with their engines glowing brightly and therefore presumably generating lots of thrust – yet the craft don’t appear to be accelerating. For instance, as the Rebel X-wings and Y-wings approached the Death Star in A New Hope, we could clearly see their engines glowing, but they didn’t seem to be accelerating. In fact, the attack leader told them sometime after this shot to accelerate to attack speed. Similarly, in The Empire Strikes Back, we saw an Imperial stardestroyer approaching the planet Hoth with its engines glowing brightly, yet it didn’t appear to be accelerating at all.
Isn’t it odd that spacecraft in the Star Wars universe always agree on which end is up? “Up” is a virtually meaningless term in space, so why do spacecraft always orient themselves in the same plane? To be fair, this is probably due to viewer expectations more than anything else – many viewers would doubtless think it disorienting to see two spacecraft approach each other with Spaceship A “on its side” or “upside down” compared to Spaceship B. Supposedly, Gene Roddenberry (the creator of Star Trek) claimed that test audiences complained when he showed them footage of spaceships approaching each other while oriented on different planes.
Personally, I think it’d be neat if movies more often dared to show us spaceships that actually moved like spaceships and that didn’t pay any particular attention to their orientation. The television series Babylon 5 showed us spaceships that generally moved realistically, but even the creators of B5 didn’t have the guts to show spaceships operating with different orientations.
What is galling about Star Wars spaceships is that they’re asymmetrical – that is, they have definite “top” and “bottom” halves which makes no sense at all for spacecraft, even if you accept Star Wars physics. In space, you have three complete degrees of freedom in your movements. This means you can approach ships from the front/back, from the sides, and from above/below! Despite this, you’ve no-doubt noticed that the fighters in the Star Wars movies virtually always attack capital ships from above, just as if they were terrestrial aircraft attacking naval vessels. Why not fly under the big ships to attack them, which they can certainly do? Why fighters don’t do this is even more inexplicable when you notice that the big ships appear to have few guns or none at all on their undersides. To say that this is a stupid design for a space-faring warship is quite the understatement!
Some of the spaceships in the Star Wars universe use ion propulsion, notably the TIE (Twin Ion Engine) Fighters. Ion engines could be used to boost spaceships to quite impressive speeds, it’s true; but they would have terrible acceleration. Somehow, I doubt the Empire would be building interceptors that take weeks to reach speeds chemical rockets could achieve in seconds!
Sounds in Space
Sound is a compression wave moving through a medium such as air. Space is a near-vacuum. No medium = no sound. So, we should not be hearing spaceships go “whoosh” as they fly past the camera, we should not be hearing laser guns go “zap” as they shoot at those spacecraft, and we should not hear the explosions go “boom” when the laser guns find their targets.
Some have suggested that spaceships’ computers in the Star Wars universe are programmed to create sounds so as to give pilots auditory clues as to what’s going on around them. This actually makes a lot of sense, but it doesn’t explain why we, the viewers, can hear these things.
Explosions in Space
It’s not entirely clear what the various spacecraft use for fuel in the Star Wars universe, but some of them presumably use chemical propellants, complete with oxidants. Since there’s no oxygen available in the vacuum of space, you need to supply your own. The ships must contain oxygen for their occupants to breathe. Also, fire requires oxygen to burn. Typically, when a Star Wars ship is hit, it explodes and burns brightly for several seconds. In reality, the available oxygen would be used up almost instantly, and the fireballs would be snuffed out almost immediately. Instead of a brightly-burning fireball, you’d probably see a brief flash followed by pieces of the ship flying off in all directions.
While we’re on the subject, why do the explosions typically come to a relative stop? If a spaceship has velocity “X” at the moment it’s hit by enemy fire, the explosion (which is simply the pieces of the spaceship) will have – as a whole – exactly the same velocity as the spaceship did at the moment of its destruction. In other words, the explosion will continue to move forward at the same speed the spaceship was traveling at the moment of its destruction.
Characters occasionally refer to both shipboard weapons and sidearms as “lasers” in the Star Wars movies. Whatever else they may be, they definitely are not lasers, though. A laser beam is a beam of coherent light. In a vacuum, a laser beam is invisible, since there are no particles to scatter the beam and make it visible. It’s typically invisible in air too, unless there is smoke, fog, or dust in the air to scatter the beam. The “laser” beams in Star Wars would not be visible if they were actually lasers. The only person who would be able to see a laser beam is the unfortunate sod at the receiving end – and he wouldn’t see it for very long.
Light moves at the goodly clip of 186,282 miles per second in a vacuum. Whatever those things are that are being fired from the “laser” guns in the Star Wars movies, they’re moving a lot slower than this!
Laser guns would have no recoil, unlike the guns in the Star Wars movies. Long story short: the ship-mounted guns and the personal blasters we see in the Star Wars movies are most-definitely not laser guns. Or if they are, lasers don’t behave the same way in the Star Wars universe that they do in ours.
It’s unclear what a lightsaber is, exactly. If a lightsaber generates an intense laser beam, what makes the beam stop a meter or so out from the weapon’s emitter? The only thing that could make a beam of light turn back on itself would be a gravity field from an object so dense that it formed a black hole. Needless to say, there’s no way that each lightsaber has a black hole in its hilt! Light wouldn’t be able to escape in the first place to form the blade; no one could lift the thing, since it would weigh as much as a mountain; and it would have a disturbing tendency to absorb all matter in the vicinity while emitting lethal gamma radiation.
Maybe there’s a rigid rod that extends outward a meter or so from a lightsaber’s hilt when it’s activated and the saber’s “blade” consists of laser beams that are focused to converge on the tip of the rod where they’re absorbed. That’s my hypothetical explanation anyway. This would explain why lightsabers can interact with each other since if the “blades” were actually made of light, they’d pass right through each other.
Or maybe the “blades” are actually made of plasma. If so, there must be some mechanism to confine the plasma so as to form the blades. No such mechanism is evident though. There’s also the nagging problem that plasma blades sufficiently powerful to cut through metal would emit so much heat that they’d cook the user almost instantly. This would limit their effectiveness as weapons, I should think.
Incidentally, this is one more reason to believe that the “lasers” in the Star Wars universe aren’t actually lasers. A lightsaber (whether the blade was a laser or confined plasma) would not deflect a laser beam.
Some have suggested that the actual blade of the lightsaber is invisible and that the bright glow is from ionized air. If that were the case, the blade would be emitting so much heat that it’d quickly cook the user’s hands.
Does the blade of a lightsaber weigh anything? They’re not too consistent on this in the Star Wars universe. If the blade is (somehow) made of light or is a plasma, it should be essentially weightless. Whether or not the blade is weightless is an important consideration, though, because it influences the saber’s performance as a weapon.
In the real world, different swords are designed for different functions. Some swords are intended as chopping weapons. They typically have thick, heavy blades. Since heavier blades have more momentum, they’ll cut through resistant materials more easily than will lighter blades of the same sharpness. This shouldn’t be an issue with lightsabers though, since they’ll apparently cut through just about anything.
Every sword has a center of balance. This is the point where the sword is exactly balanced. The sword will tend to pivot around this point. For a chopping sword, you typically want the center of balance to be fairly close to the tip of the blade; the closer to the tip is the center of balance, the more momentum it can deliver to its target as it strikes. Such a sword is unwieldy, however. For a sword that is designed with dueling in mind (lightsabers clearly fall into this category), you want the center of balance to be as close to the hilt as possible. The ideal dueling sword has the center of balance in or very near the hilt. This means the user can pivot the sword much more quickly than if the center of balance is somewhere closer to the tip, and so the user has far more control over the blade and can move the blade much more quickly for attack and defense.
If you watch how the lightsabers move in the Star Wars movies, it’s clear that the center of balance is usually (but not always) some distance beyond the hilt. This means the blades must have some weight to them; if the blades were weightless, the centers of balance would be in the hilts. When Luke was playing with his father’s lightsaber right after Ben gave it to him, it was clear that the saber’s center of balance was in the hilt, because it was pivoting around the hilt, even though he was using only one hand. Using two hands, you can make a sword pivot around a point other than the center of balance; it's difficult with only one hand. Later in the same movie, when Luke was “fighting” with the remote, he was using two hands, and the lightsaber’s center of balance was clearly a few inches out from the hilt, meaning that the blade had some weight to it.
On a related note, the blades of lightsabers sometimes cast shadows which they wouldn’t if they were made of light, and at other times, they don’t. For example, in The Return of the Jedi, when Luke and Vader were fighting on the catwalk over the pit, both their sabers’ blades were casting clear shadows. At the end of the fight, when Luke was standing over the defeated and supine Vader, Luke’s blade cast no shadow.
Hyperspace and Hyperdrives
Space is big – really big! No, seriously. You can’t imagine how vast it is! The fastest rockets we have built would take thousands of years to make it to the next-nearest star. Even if you could somehow build a spaceship that travels at the speed of light (you couldn’t – according to Einstein, it would require literally an infinite amount of energy to accelerate any material object to lightspeed), it would still take more than 4 years (as measured from Earth) for it to reach the next-nearest star. Clearly, we need some way around this. Star Wars would be a lot less exciting if it took the Millennium Falcon 10,000 years to travel from Tatooine to Alderaan!
So, I have no problems with inventing “hyperspace” where the normal laws of physics that restrict ships’ speeds to less-than-lightspeed apparently don’t apply and “hyperdrives” that somehow allow ships to enter hyperspace. I have no idea what “point-5 beyond lightspeed” is supposed to mean, though!
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