So that's my best guess for how to build a lightsaber, but even this design has problems. For instance, in "Star Wars: Episode IV – A New Hope," Obi-Wan Kenobi cuts off an alien's arm in the cantina in Mos Eisley with a single, effortless swipe, just as Darth Vader sliced through Obi-Wan. This sets some serious constraints on how hot the plasma would have to be. (Maybe the Darth Vader cut doesn't count, as Obi-Wan's body disappeared. Clearly something else is going on there.)
And in "Star Wars: Episode I – The Phantom Menace," Qui-Gon Jinn sticks his lightsaber in a heavy blast door, first making a long cut and then simply melting it. If you watch the sequence, assume the door is steel, and time how long it takes to heat up the door and melt the metal, you can calculate the energy the saber must have.
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It turns out to be about 20 megawatts (MW). Given an average household power consumption of about 1.4 kilowatts (kW) at all times, the power draw of a lightsaber could run 14,000 average American houses until the battery ran out.
A power source of that density is clearly beyond current technology, but perhaps we can grant that the Jedi have advanced technology. They do have faster-than-light travel, after all.
However, there is a physical problem. That kind of power means that the plasma would be incredibly hot, and at a distance of only a few inches from the hand of the sword wielder. And heat is irradiated in the form of infrared radiation. The Jedi's hands should be essentially instantly charred. So some sort of force field must keep in the heat. And yet, the blades appear to be using optical wavelengths, so the force field must contain infrared radiation, but let visible light through.
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Such technical investigations lead inevitably to invocations of unknown technologies. But once you've done that, it is easy to simply say that the lightsaber consists of some kind of concentrated energy stored in a force field.
In this way, it could easily resemble how Michael Okuda, technical consultant for the "Star Trek" franchise, explained new technology that could make transporters possible. These were "Heisenberg compensators," he said, supposedly used to correct problems of the Heisenberg uncertainty principle. This is the famous quantum mechanical principle that says that you can't simultaneously know with high precision the location of the position and motion of a particle.
Since a person is made of lots of particles (i.e. atoms and their constituents), if you ever tried to scan someone to figure out where all their atoms are, you couldn't accurately measure their location and motion. Thus, when you tried to reconstruct someone, you wouldn't know exactly where to put all the protons, neutrons and electrons.
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At a deep and fundamental physical level, the Heisenberg uncertainty principle says that transporters are impossible. Of course, this didn't stop the creators of Star Trek. When asked by Time magazine how such devices worked, he said, "Very well, thank you."
However, it is equally interesting to see how close current science can get to achieving iconic science-fiction technology. In the case of a lightsaber, the best today's technology could achieve would be a plasma weapon contained by magnetic fields. It would have a ceramic core that utilizes a very dense power source and that employs a force field that blocks infrared, but not visible light. Easy peasy.
So, now that I've done the hard part by spec'ing what would be needed, let me now turn to the world's engineers and tell them to get to work. I mean, how hard can it be?
Read more from Don Lincoln on his Space.com Expert Voices content page.
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