The lightsabers from the Star Wars movie series are one of the most instantly-recognized icons of modern science fiction. Just about every kid growing up in the last thirty years has wished desperately to have one. They are the epitome of modern scifi-cool.
But even if they could be made to work in the real world, their actual value as a weapon in practical circumstances is somewhat questionable. There are very good reasons why modern soldiers no longer carry swords, and after all is said and done, a lightsaber is nothing more a superscience sword. Modern guns are simply too fast and overwhelming, and can strike from a far greater distance, than any sword can easily counter. Even fully-trained Jedi Knights in Revenge of the Sith could not survive concentrated autofire armed with only lightsabers.
However, there is one use for which lightsabers would excel under any circumstance: as a cutting tool. Even though the exact origin of lightsabers is left obscure in the source material, it seems logical that the technology behind them would first arise as the future-tech equivalent of a power saw or chainsaw, a cutting tool of extreme versatility that could be adopted to a large number of jobs. One can easily see the advantages of using lightsaber-like devices for felling trees, clearing vegetation, working metal, drilling concrete, and a hundred other practical tool uses. It was probably only after they became common in that role were they eventually adopted as a melee weapon.
The fact that they came to such prominence as weapons in the Star Wars galaxy probably has a lot more to do with cultural factors than with practical technological ones. One of the main considerations might be for fighting on board spaceships, which in the Star Wars universe are usually depicted having somewhat cramped interiors similar to modern sea-going warships. Long rifles of any sort would be at a disadvantage in such an environment, and a lightsaber would be a decent back-up to a pistol if the fighting became up-close and personal.
Another factor is the ranged weapons they are usually pitted against; apparently the low-powered plasma weapons with slow-moving bolts, aka "blasters," that permeate galactic society. A well-trained user equipped with a lightsaber actually has a decent chance of intercepting incoming blasts from these than they would most other modern or near-future weapons.
Again, this may be the result of having such a heavily spaceship-oriented culture. Using high-penetration weapons with fast-moving projectiles on a spaceship could prove disastrous for both defenders as well as attackers if the weapon destroys vital equipment, ricochets to hit fellow crew members, or worse yet, precipitates a hull breach. Over the many thousands of years that a starfaring culture has existed in the Star Wars universe, these weapons may have eventually worked their way into the mainstream of galactic culture, to the point where few people use any other kind of firearm, including various militaries.
Lastly, there is their symbolic role as the primary weapon of the two most feared and legendary groups in their culture, the Jedi and the Sith. By the time of the era depicted in the movies, just the sight of a Jedi with a lightsaber was enough to rattle most opponents, and allow the Force-user a great psychological advantage.
Trying to pin down the technological workings of lightsabers has proven problematic for a number of reasons. One, Star Wars is among the softest of soft science fiction franchises, even more so than the admittedly squishy Star Trek or Stargate. It is very obvious that the makers of the movies were much more concerned with making stuff look visually stunning than adhering to any kind of consistent technological framework. Which is of course the way most fans prefer it.
Second, as with many long-running franchises, contradictions have cropped up over the years as to the exact workings of a number of Star Wars tropes, lightsabers among them. "Official" explanations are usually left deliberately vague or filled with nonsensical tech babble. Fan speculations as to their workings are all over the place, some plausible and thoughtful, some truly absurd. (One explanation posed that lightsabers were rods of metal spinning at half-light speed or more--never mind it would take a Jedi from the planet Krypton just to handle the weapon's insane progressional instability.)
Third, the presence of the pure-fantasy Force among most users of lightsabers casts a great deal of uncertainty on just what the weapon's real capabilities are. Where exactly does the saber's effects end, and the user's Force-enhancement of the weapon begin? This can be difficult to tell, sometimes.
What follows should be considered a few best guesses by an independent observer only, and does not reflect official 'canon' explanations of the technology.
The 'easiest' way to make a lightsaber-like device would be to use a small, potent plasma jet, held in shape by powerful magnetic fields. The saber's handle would hold the fuel and power source, and would ignite the fuel into a plasma-like state. Magnetic fields projected forward would constrict this stream of plasma into a thin cylinder, and the intersection or overlap point of these fields would terminate the length of the 'blade.'
There are of course a number of major potential problems with this approach. The first is an appropriately potent but compact enough power source that could keep the saber active for more than a few minutes. By this Tech level, a number of power sources can produce high spikes or pulses of current, but generating the steady amount of power to such a high-energy plasma jet as well as the magnetic fields to hold it in place may be problematic. Early versions of this technology may need to hold the power source separately, in a backpack or beltpack, and attached to the saber handle by a superconducting cord.
An alternative would be that the users may be resigned to using the weapons only for minutes at a time. In fact, in the movies, lightsabers are rarely activated for more than a handful of minutes non-stop, and this may be the upper limit on the charge its capacitors (or their futuristic equivalents) can normally hold. The "holster" many Jedi are see wearing for their lightsabers may hold recharging ports for a power source contained either within the holster or its attached belt.
Another potential problem somewhat related would be the saber's fuel capacity. Even though the plasma is trapped in the weapon's magnetic bottle, every time a lightsaber stuck or cut through something, plasma would escape. Plus, entropy alone would ensure plasma would be constantly leaking past the fields as long as the weapon was activated. This means that the weapon would have to be refueled at regular intervals.
But the biggest obstacle in using a plasma torch lightsaber would be the heat. In order to easily cut through most material objects as seen in the movies, the plasma in the blade would have to be extremely hot, burning at thousands of degrees Celsius. The constriction of the jet into a small cylinder would only increase its temperature. This in turn would super-heat its generator, which would already be handling a large thermal load just generating the powerful magnetic fields needed to keep the blade coherent. Even if an active cooling apparatus could keep the systems in the handle operating, one has to wonder how a Jedi could stand handling the lightsaber when its blade is burning hotter than a blast furnace.
The like-charged magnetic fields would repel each other, and given their assumed strength, could not easily merge or penetrate each other. Thus lightsaber blades would act as physical barriers to each other, allowing for the thrilling sword-like duels we see on screen.
Even though this type of lightsaber seems impractical for the typically unshielded Jedis in the Star Wars movies, they could be just what the mechanic ordered for augmented, armored, or robotic combatants, which can carry around the heavy power sources and fuel tanks needed, and whose operators would be shielded from the worst of the heat and magnetic field effects. Such may be the case with the various mecha in the Gundam animated series which were seen wielding lightsaber-like energy blades in close combat.
A potential outgrowth of particle beam technology may be the tightly-constricted particle beam "fountain" or loop, that could have many of the characteristics seen in lightsabers in the movies.
Like a normal particle beam weapon, the lightsaber handle is a miniature electromagnetic accelerator that whizzes charged particles (typically electron, protons, positrons, or ionized atoms) to tremendous velocities. However, unlike conventional versions of such weapons, the electromagnetic fields extend a meter or more beyond the "barrel", shaping the beam to loop back on barrel even after it leaves the gun. The particle stream forms a tight ‘loop’, constantly feeding back onto itself, and only appears to an outside observer to be a static glowing blade.
Like with conventional particle beams, it would deliver most of its damage in the form of catastrophic superheating, able to "melt" through most physical objects almost instantly. Its glow would come from the ionization effect that most charged particle beams form in an atmosphere. In a vacuum, however, this may mean the blade of a particle fountain lightsaber would be invisible.
The true engineering challenge here would be to bend the beam back to the handle to form a complete loop, and to do so outside of the weapon "barrel" with no visible machinery. It could be that inside the blade would be one or more rigid extendable superconducting wires that help to guide the particle stream through the 180-degree turn, as well keeping the stream tight and focused along the blade’s length. In fact, this could be why some lightsaber blades need a second or so to project out of the handle instead of just flicking on and off fully formed; the superconducting guide wires at the center of the blade may need that time to physically telescope out.
This type of lightsaber wouldn’t have the blast furnace-hot blade of a plasma torch saber, though there might be a brief flash of intense heat when the blade hits a target. Like-charged magnetic fields would also repel each other here, allowing the blades to act as physical barriers to each other. However, generating the intense fields needed to keep the very energetic particle stream confined could still generate a lot of potential waste heat in the handle which may have to be dealt with in some way. And like the plasma-torch version, it would still need an insanely potent but compact energy source to keep the blade on for more than a few minutes.
A third possibility is that the lightsaber blade is a type of force field. But instead of a deflective barrier of energy, the blade contains particles that causes matter to disintegrate on contact.
Force fields are badly named, a misconception by many early sci-fi writers on how fields of force work in real life physics. But the term has become so commonly used now that we’re kind of stuck with it. A more accurate description for the concept might be "suspended particle barrier," basically a dense volume of one type of particle held rigidly in place by some unknown quantum effect.
A lightsaber using this technology would basically be a small but powerful force field projector. The particles making up the blade’s field would have to be a type that would either incinerate or disintegrate most types of matter on contact. Unlike particle fountain lightsabers, the particles in a force field saber won’t be travelling at high velocity, so they have to be of a type that can do their damage without being imparted tremendous kinetic energy.
Antimatter particles may work, but they would be accompanied by an intense flash of radiation every time they hit a significant mass. Even with the nigh-miraculous medical tech available at this Level, this is probably not something most wielders would want to deal with often.
Truly exotic particles may be needed in order to have a lightsaber work as they’re usually depicted on-screen. Anti-gluons, the antimatter version of the theoretical particles that hold atomic nuclei together, may work, but even these would be accompanied by a brief flash of neutronic radiation as the atomic nuclei in the targets they cut fly apart.
On Particle Beams:
On Plasma Science:
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