A real Lightsaber?

An elegant weapon... for a more civilized age. This is the how a lightsaber was introduced to viewers nearly 40 years ago. Trademark weapon of the semi-mystical Jedi, it is said that the glowing blade kept peace for millennia in the Galactic Republic. For those introduced to the weapon in 1977, when the first Star Wars movie came out, the characteristic hum of the lightsaber and the epic fight between Darth Vader and Obi-Wan Kenobi is etched in those viewers' minds.

Given the impact the Star Wars franchise has had on society, it’s inevitable that a segment of the public would love to make a lightsaber, and even train with it. But what technology could possibly yield the lightsaber? With that desire, came the first attempts to reverse-engineer the device. Reverse engineering, in this context, is thinking about how to do it… not actually building one. However, this research about clumping photons made the rounds a while ago.

If one could explore the device’s performance, perhaps a few engineers could turn the lightsaber into next Christmas’ hot, new “must-have” gift.

At the risk of crushing the dreams of some readers: Remember: Star Wars is science fiction. But what do scientists know that could, in theory, reveal how to build a lightsaber?

The movies show that lightsabers are glowing blades about four feet (1.2 meters) long. They clearly contain a tremendous amount of energy and can quickly melt large amounts of metal. This suggests that these weapons must contain a powerful and compact energy supply. They can cut through flesh without any difficulty, yet their hilts are not so hot as to burn the hand that holds them. Two light sabers will not pass through each other, and there are different colors of scintillating blades.

Given the name and appearances, the first obvious thought is that perhaps lightsabers consist of some kind of laser. However, this hypothesis is easy to rule out. Lasers don’t have a fixed length, as you can determine using a simple laser pointer. Further, unless the light is somehow scattered, a laser is essentially invisible as it passes through the air. Neither of these characteristics describes a lightsaber.

A more realistic technology is a plasma. Such a material is created by stripping a gas’s atoms of their electrons, a process called ionization. This stripping causes the material to glow. A plasma is a fourth state of matter, after the familiar three states of solid, liquid and gas. You have seen examples of plasmas all of your life. The glow of a fluorescent light is a plasma, as are neon lights.

Those plasmas seem pretty cool, as one can touch the tubes without singeing any fingers. However, plasmas are typically rather hot, on the order of several thousand degrees. But because the density of the gas in a fluorescent light tube is so low, even though the temperature is high, the total amount of heat energy is very low. An added complexity is that the electrons in the plasma have a much higher energy than the ionised atoms from which the electrons originated. For example, the heat energy in a cup of coffee (which has a much lower temperature) is much higher than the energy stored in a fluorescent light.

Some plasmas can actually generate considerable heat. These are called plasma torches. The principle is the same as a light bulb, but with more electrical current involved. There are many ways to make a plasma torch, but the simplest one employs two electrodes and a flowing material, usually a gas such as oxygen, nitrogen or something similar. A high voltage on the electrodes ionizes the gas, converting it into a plasma.

Because a plasma is electrically conductive, it can convey a large electrical current to the target material, heating it up and melting it. While such a device is called a plasma cutter, it is really an electrical arc cutter (or welder), as the plasma actually acts as a conductor to let an electrical current flow through it.