The lightsaber. For fans of Star Wars, samurai movies and accidentally cutting your own arm off, it has long been “an elegant weapon, for a more civilised age” (your childhood). And with the premiere of Disney+’s Obi-Wan Kenobi this May, it seems safe to assume that we’re about to see a lot more of them.

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But while every big kid has at one point or another swung a big broom around the house while going ‘vwommm’, is there any way lightsabers could ever become a reality? Well, to answer that, we need to first figure out what a lightsaber is.

Physicist Patrick Johnson, an associate teaching professor at Georgetown University and author of The Physics Of Star Wars, suggests two options.

“The first is that it is exactly what it is described as, a sabre made of light, a laser sword,” he says. “The problem with it being a laser, though, is that because photons move at the speed of light, the laser will just keep going until it runs into something. Lasers don’t stay in a self-contained beam.”

The more plausible option, says Johnson, is that lightsabers are made of plasma, the electrically charged gas that makes up lightning and the Sun. Plasma cutting machines are often used in manufacturing to slice through materials such as steel.

“Plasma is hot enough to melt metal, it can change colour depending on the material you’re using and is able to cauterise wounds, just like in the movies,” explains Johnson. “But the problem is that it’s really, really hot. We’re talking about holding something that is the temperature of the Sun in your hand, which is not going to be pleasant for you without special equipment.”

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There is also the matter of size. Portable plasma cutters are bulky because they need to be attached to a container filled with fuel and a cooling mechanism. And even then, the beams that they produce are typically only a few millimetres long.

The reason for this is perhaps the biggest obstacle standing between you and a fully operational movie-style lightsaber. Because plasma is essentially a soup of ions and electrons, creating a self-contained beam is a big challenge.

Illustration of Star Wars characters using light sabers
© Joe Waldron

“You can have a jet that’s shooting out really hot plasma in front of you,” says Johnson, “but you’re going to almost certainly run out of fuel pretty quickly, because all the stuff you shoot out has to come from somewhere.

"What you need is plasma that is self-contained and typically the way we would do that is with a magnetic field, but magnetic fields make things go in circles rather than in beams. You might be able to create a very thin elliptical shape that could approximate a beam, but you would have to really work to distort the magnetic field.”

Some people have come close to replicating the look of a lightsaber. In 2021, Canadian engineer and YouTuber James Hobson used tanks of liquid propane gas and oxygen to create an impressive beam of lightsaber-esque plasma. But as Johnson says, replications like these are “essentially nothing but a fancy crème brûlée torch.”

For example, such plasma lightsabers would be incapable of having a duel with another lightsaber. “Because they are made up of charged particles, the two plasmas would just end up being attracted to each other and become one,” he says. “It would be like expecting soup to clash with other soup.”

So alas, it seems as though our dreams of becoming a lightsaber-wielding Jedi knight like Obi-Wan Kenobi are as dead as he is. But Johnson has hope. “The computers of the 1950s took up entire rooms,” he says. “I would never say never.”

Verdict: For now, we’ll have to make do with swinging a broom around our heads and making our own lightsaber sound effects.

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About our expert, Patrick Johnson

Patrick Johnson is an assistant teaching professor at Georgetown University. He previously taught at Marquette University and William Jewell College after receiving his PhD in physics from Washington University in St Louis.

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Authors

Stephen Kelly is a freelance culture and science journalist. He oversees BBC Science Focus's Popcorn Science feature, where every month we get an expert to weigh in on the plausibility of a newly released TV show or film. Beyond BBC Science Focus, he has written for such publications as The Guardian, The Telegraph, The I, BBC Culture, Wired, Total Film, Radio Times and Entertainment Weekly. He is a big fan of Studio Ghibli movies, the apparent football team Tottenham Hotspur and writing short biographies in the third person.

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