The lightsabers they are one of the most iconic elements of the narrative universe of Star Wars. The famous weapons used by knights Jedi and come on Sith in countless duels throughout the saga created by George Lucas They resemble traditional swords, but they have one bright and energetic blade which can take on different colors (blue and green for the Jedi, red for the Sith) and emits a characteristic hum. In the films of Star Wars we see lightsabers cut through metal and amputate forearms, immediately cauterizing them. Generations of enthusiasts have played with models that reproduce these weapons, but are they destined to remain a science fiction gimmick or are they possible in reality? Our technology currently does not allow us to build them, but if we want to do so we will have to be able to produce high temperature plasma for long periods of time, we would need them extremely heat-resistant materials and above all we will need incredibly miniaturized systems for the production of large quantities of energy.
As we know it from the films of Star Wars, a lightsaber must be able to emit colored light, cut even resistant objects, be retractable and be able to collide with another lightsaber without passing through it. As you can imagine, having each of these features individually is doable, but having them all together is very complex. Despite the name, for example, it is not clear how we might use gods laser to create them: two laser beams cannot “collide” against each other, furthermore it would be extremely difficult to confine the electromagnetic radiation of the lasers.
A workable idea in principle makes use of plasma, a state of matter that is obtained by completely ionizing a gas (i.e. stripping all the electrons from the atoms that compose it). To ionize the gas you just need to heat it until it reaches a temperature of a few thousand degrees. To generate the necessary heat, a reaction can be used combustion which releases a lot of energy. By shooting jets of plasma we can give our hypothetical lightsaber the gift of retractility. Of course, firing plasma jets requires a large amount of energy, but it's something we know how to do, for example in ion propulsion engines used in the aerospace field.
Plasma can also be confined by magnetic fields, because by definition it is composed of charged particles and electric charges respond to magnetic fields. We know how to do this too: the magnetic confinement of ions is used for example in some prototypes of nuclear fusion reactors.
To make two jets of plasma “collide” they can be contained within materials capable of withstanding very high temperatures. The maximum thermoresistance we have achieved is with special ceramics composed of tantalum or hafniumwhich merge at approximately 4000°Cenough to contain a nice “bad” plasma.
And the colors? This part is simple: we've been coloring fireworks with chemicals for centuries, so we could do the same for our lightsaber. Substances likeboric acid can give our plasma the green color, while for red we can use, for example, the strontium chloride.
There are essentially two problems. The first is to be able to obtain a quantity of gas to transform into plasma sufficient to make the lightsaber last for more than a few seconds. The second – more insurmountable – is to be able to produce all the energy necessary to generate the plasma, shoot it and power the magnetic fields that confine it with a system capable of fitting inside the handle of the sword, which is a few centimeters wide and long little more than a span. This, today, is science fiction.
At the moment the closest thing to a real lightsaber that we have managed to create is the work of Hacksmith Industrieswhich in 2020 produced a proto-lightsaber powered by combustion of the propane which generates a plasma at 2200°C, enough to cut metal. The blade is made of glass and the aforementioned boric acid and strontium chloride are used for the colors. The biggest difference with a “real” lightsaber is that the energy source is external, as well as the propane tank. Here you can see it in action:
