If you are already a Star Wars fan, you know that the stories take place in a galaxy far, far away, so the laws of physics should still apply. On the other hand, these are obviously works of fiction; is there any point in applying those laws? Yes—it is both fun and worthwhile to do so. Sometimes the physics shown in the movies is spot on while on other occasions it would require advanced technology or new discoveries in the realm of physics to make sense. Either way, science is about the critical thinking process needed to tackle a problem rather than the specific situation in which the problem appears. There’s no reason we can’t consider Yoda force-lifting rocks instead of pulleys lifting blocks!
Still, the films don’t always provide all the answers needed to explain a physics topic. What exactly is a lightsaber? Is it a plasma or a beam of light? Depending on the source you consult outside of the movies, it could be either. Here, what is depicted in the movies is taken as definitely true, but other sources are considered when needed. For the sake of clarity, not all calculations are shown in full detail. If you want to reproduce them on your own, you can do that with the help of an introductory physics book. The beauty of science is that no matter who or where you are, you should be able to reproduce the results of another person’s work.
Lightsabers are what makes Star Wars, Star Wars. On the surface, they’re just fun to watch. They also help us feel the conflict and emotional upheaval the characters are experiencing. What would the iconic “I am your father” moment in The Empire Strikes Back be without the preceding lightsaber duel between Luke and Darth Vader? They are clearly a brilliant element of the films, but ... does the science hold up?
The extended universe of Star Wars establishes that lightsabers are powered (and colored) by kyber crystals found in locations around the galaxy (including Jedha from Rogue One). Do these crystals have any basis in reality? Putting that aside, are all the different colors and designs practical?
Lightsabers are usually around 3 feet long. How easy it is to create a 3-foot beam depends on whether it is a beam of light or a beam of plasma.
Beams of light are tricky to contain because photons are very difficult to turn around or stop midair. Perhaps the easiest way to create a 3-foot-long beam would be a mirror opposite the hilt of the sword to reflect the light. This is obviously not the design presented, since when they’re off, lightsabers are no larger than their hilts. The sound of a lightsaber turning on could be the sound of a mirror extending outward as if it were uncapping a container full of light, but there are still other issues.
For example, the fact that the beam is visible light (we can definitely see it!). If you’ve ever shone a laser pointer on your arm, you know that it won’t slice skin. The power of a visible light laser pointer would need to be upped by a factor of about a thousand before it could do any damage, and a laser of that power would require an extensive cooling system. Further, as far as we know a beam of light, no matter how powerful, is incapable of deflecting a bolt of plasma shot by a blaster. Similarly, a beam of light could not absorb plasma.
Holding a miniature stick-shaped sun in our hands would require at least SPF 10,000.
If we consider the beam to be plasma, there is a different set of concerns. A well-designed electromagnetic field could, in principle, contain a plasma to a size of about 3 feet (maybe by sending the plasma in a highly elliptical path to create roughly the shape of a cylinder). Plasmas are also hot enough to cauterize wounds and melt metal (both aspects of lightsabers seen in the movies). We’re off to a good start, but problems arise if we consider dueling plasmas. Expecting some free-floating plasma to clash with some other free-floating plasma is like ... expecting soup to clash with other soup. The two plasmas would actually be attracted to each other (as they are made up of charged particles) and become one. This would also make it difficult to deflect a blaster bolt, but it could explain how it is able to absorb force lightning.
The color of plasmas depends on the temperature. In that respect, a red lightsaber would be lower energy than a green one, assuming they are each made of the same materials. This would also be true if they were made out of light since green light has more energy than red light. To generate plasmas of red or green is quite challenging. Most plasmas, both in labs and in stars, are generated predominantly using hydrogen. This means we know the color of hydrogen-based plasmas quite well. If we made a cobalt plasma, though, would it appear to be a different color? We will just have to do that experiment to find out.
Plasmas are hot, and being close to a plasma would also be hot, as long as enough of it is present. Since plasmas are often at temperatures of millions of degrees, holding a plasma stick in your hand would lead to some severe burns. The sun is 93 million miles away, and we need to wear sunscreen to protect us from it—despite the fact that there is an atmosphere blocking most of its harmful radiation. Holding a miniature stick-shaped sun in our hands would require at least SPF 10,000.
There could certainly be some other explanation as to how lightsabers work, but it would either be not based in reality (e.g., using the magic of kyber crystals) or an incredible feat of engineering involving much more than just light or even plasma.
Blasters are ubiquitous in Star Wars. The Galactic Empire and the Rebel Alliance use them, droids use them, and smugglers and bounty hunters seem especially inclined to use them. To some (namely, Jedi) they are “clumsy or random,” but to most they are an asset. In one especially controversial case, someone dodges a blaster shot from only a few feet away while seated. This is the “Han shot first” scene from Episode IV; in the original release, there is no need for Han to dodge a shot because he shoots and kills Greedo the bounty hunter preemptively. In later releases, the scene is edited so that Greedo shoots, Han dodges, and then shoots back. Knowing that shots can be dodged at such close range may help to explain the clumsy or random nature of the weapon.
Some sources call the blaster a laser weapon and some refer to it as a plasma weapon; we will explore both options. If it’s a plasma weapon, a blaster would compress tibanna gas, a substance mined in places such as Cloud City. After being compressed, the tibanna gas is energized and launched out of the barrel of the blaster toward its target in the form of a bolt. In this scenario, the blaster bolt is a beam of expelled plasma confined to a finite shape, often a line. We can look at some real-world materials to understand this since tibanna is a fictional substance.
First, we need to know at what temperature tibanna gas becomes tibanna plasma. The temperature at which materials turn into a plasma is fairly consistent, so we could estimate that a reasonable temperature at which tibanna gas becomes a plasma is 360,000 degrees Fahrenheit. If such a gas came into contact with your body, it would transfer its heat to you. At very high temperatures, most materials have approximately the same specific heat (ability to store thermal energy). We can say that a plasma bolt at 360,000 degrees would most likely vaporize any part of your body that it hit, if enough plasma is present.
There is a problem with blasters shooting plasma, though. A plasma is made up of a soup of charge particles that will experience forces from electromagnetic fields. A plasma bolt shot at 73 miles per hour (a decent estimate for the speed of blaster bolts in Star Wars) would only require a field about a million times weaker than Earth’s magnetic field to cause the bolt to move one-and-a-half feet to the right or left (if the target is 33 feet away). This could explain why blasters are apparently random and stormtroopers appear to have terrible aim. The slightest bit of stray magnetic field could unexpectedly alter the path of the bolts. In fact, if a stormtrooper were firing a shot on Earth, the bolt would not only miss its target, but would travel in such a tight circle that it would hit the gun from which it was shot.
Perhaps the best argument against the idea that these are laser beams is that all light travels at the speed of light.
Given how much a stray magnetic field would affect the trajectory of a plasma bolt, maybe blasters are indeed laser guns as indicated in the original script. The accuracy of a laser gun is much higher, since light is more difficult to redirect. It also requires less energy to produce a bolt. When picturing a laser, you probably think of one that will not cause any harm or destroy instrument panels when you “shoot” them. This is because laser pointers are the most prevalent and are (mostly) class 1 lasers. A laser weapon would most likely be a class 4 laser, which can burn the skin, ignite combustibles, and definitely cause vision damage.
Typically, class 4 lasers are above 500 milliwatts1 of power, which would mean that if one was in contact with your skin for several seconds, it would cause severe burns. Higher-power lasers would obviously do more damage more quickly, but this seems consistent with the damage that Leia receives when she’s hit on Endor.
Perhaps the best argument against the idea that these are laser beams is that all light travels at the speed of light. These blaster bolts are traveling significantly slower than light; they travel closer to 100 feet per second rather than the 186,000 miles per second that light travels. In the movies it takes a second or two from when the blaster is red and the person is hit. If this were an actual laser traveling at the speed of light, that would be the time it would take to hit somebody on the moon while standing on Earth.
Neither of these explanations match what is seen in the movie. If we have to choose one explanation to be the most likely, it is the plasma explanation. It is more likely that there are no magnetic fields in scenes where blasters are red than engineers who designed the blasters found a way to slow down light.
Star Wars provides a weaponized staff known as the electrostaff. Predominantly used by General Grievous’s personal guards, the electrostaff consists of a 6-foot stick with sustained electricity surrounding the last foot or so of either end. We see them used with moderate effectiveness against Obi-Wan and Anakin as they rescue the chancellor from General Grievous in Episode III. How difficult would it be to have a staff with electrified ends? Would there be any issues with wielding a weapon such as this? Would it be able to stop the blade of a lightsaber? If thrown hard enough, would one of these be able to break the window of a spaceship?
A large electric potential is required to create sustained electrical discharges over a distance of about a foot. In order to generate just a spark across that distance, you need to create a potential difference large enough to ionize air. On Earth, that means about a million volts per foot. That sounds like a lot, but the design of such a weapon would be easy enough. If each end had a metal ring about a foot from the edge and a high-voltage electrode on each end of the staff, it would act like a capacitor continuously charged by an internal power source and then discharged via the electrical breakdown of the air.
The creation of this weapon is feasible, but that doesn’t mean it’d be practical to use.
So how does this all work? There are two metal rings, one at the end of the staff charged up to a very high voltage. The other ring, closer to the center of the staff, is grounded. This creates what is called a capacitor, a device designed to store electrical charge. As the charge on a capacitor increases, the electric field between the two rings increases proportionally. Eventually, the electric field between the rings reaches a point where it can separate the electrons from their atoms and briefly turn the air into a highly conductive plasma. Once charge is allowed to flow between the rings, they become fully discharged (because the negative charge on one moves to cancel out the positive charge on the other). It is then up to the power source to recharge these metal rings again.
The creation of this weapon is feasible, but that doesn’t mean it’d be practical to use. The problem with an electrostaff is that you are charging up the ends, and the most convenient place to discharge them is the metal rings (one foot away from the ends). If you put the end of the staff less than a foot from any metal surface, it would likely discharge there instead. Try watching any of the fights between Obi-Wan and one of the MagnaGuards and see how often the ends of the staff are within a foot of something metal. As much as it’s a generally good idea to keep the ends of your weapon away from your body, it is especially imperative when you are made out of metal and your weapon will fry your circuitry.
Would one of these staves be able to stop a lightsaber or crack through the window of a spaceship? The short answers are no and if thrown hard enough, respectively. One could potentially stop a lightsaber, but not in the way shown in the movies. In order to create the lightning at the ends of the staffs, there must be a large electric field. Since a plasma (see the Lightsabers section) is a soup of charged particles, the staff’s electric field would exert a strong force on all of the charged particles and could disperse the beam of a lightsaber (if it isn’t held in place by a containment shield). As for breaking a window, the strongest glass will break with around 1 gigapascal of pressure (around one tenth of what is needed to form diamonds). This means that a staff would need to exert a force of about 2 million pounds in order to crack the window on the Invisible Hand. The fact that the ends are charged does not increase the force, so we’re basically wondering if a generic staff can crack a window, and the answer is ... sure, if you throw it hard enough.
In the opening of The Empire Strikes Back, the secret Hoth base is discovered by the Empire. In the ensuing evacuation, the rebels use their ion cannons to cover evacuating transport ships. With a couple of shots, they are able to take down a Star Destroyer. Later, as the Millennium Falcon is being pursued by the Death Squadron, Han and company fly into the Hoth asteroid field. During the pursuit, a Star Destroyer uses its cannons to vaporize asteroids to try to minimize damage dealt to the ship. In a single blast the asteroid is blown into microscopic pieces.
The destructive power of ion cannons is only explicitly shown once. This is at the beginning of The Empire Strikes Back when a Star Destroyer is taken out by a few blasts from the ground-based ion cannons near the rebel base. The blasts do not seem to do much structural damage, but they appear to send a strong enough electrical current through the ship to fry all of its computers. This would be the same effect as a very strong electromagnetic pulse. A blast of this strength would probably require about the same energy that a United States household uses in one year.
A second example of a heavy weapon in use is when the Star Destroyer vaporizes an asteroid. Although this is not explicitly shown to be an ion cannon, it is as powerful as one. In order to vaporize something, it needs to be heated to the point where it melts and then evaporates. Estimating how much energy this would require requires knowing the precise size and makeup of the asteroids in the Hoth field. Typical asteroids in the solar system are predominantly iron or silicate rock, so we can use the properties of those materials in our estimate. To estimate the size, we can look at the size of the impact of an asteroid colliding with the underside of the Star Destroyer. Putting all of these pieces together, we can say that the blast from the heavy weapons on the Star Destroyer would be about 1014 joules, or about 10 times the amount of energy released in the detonation of the atomic bomb over Hiroshima.
It is clear that it would require large amounts of energy to power these weapons, but it is not impossible to accomplish this. There are other concerns, though, when it comes to firing high-powered weapons such as this. For instance, a beam of ions can undergo a process known as blooming. If all the ions in the beam have the same charge (say an electron beam), they will repel each other over time causing the beam to spread out and become ineffective when it reaches its target. Thermal blooming also occurs when ions run into particles in the air. The fact that it’s snowing on Hoth will only increase the amount of blooming that will occur.
There are other concerns for both the ground-based ion weapons and potentially those mounted on the Star Destroyer. When firing a beam of ions in a magnetic field (which admittedly Hoth does not need to have), the ions will experience a force perpendicular to the direction of motion. This will lead to the particles moving in a circular path (see the Blasters section for more).
Even if Hoth does not have a magnetic field, certainly Star Destroyers fly through regions close to planets or stars that do have magnetic fields.
If one was to design an ion weapon, a design that is either disk-shaped or spherical would make sense. In order to heat up the ions enough to be an effective weapon, it would be easiest to have the ions move in a circular path while being accelerated. Once you wanted to fire, the magnetic field holding them in this path could be turned off and the weapon would fire off a beam in a straight line. This could explain why it would take a while between shots as it takes time to accelerate the beam of ions to sufficient speeds as well as the spherical shape of the Hoth-based ion cannons.
Patrick Johnson is a member of the teaching faculty at Georgetown University, primarily teaching introductory physics.
From Physics of Star Wars by Patrick Johnson, Ph.D. Copyright © 2017 by Simon & Schuster, Inc. Used with permission of the publisher. All rights reserved.