Hokey religions and ancient weapons are no match for a good blaster at your side,” Han Solo told Luke Skywalker in the 1977 Star Wars. He was right–not least because light sabers, like the famous laser sword Skywalker wielded, would never work.

Laser beams are made of light, and they continue until they hit something. They cannot be fashioned into sword blades a mere 2 feet long. A bigger problem: Swords made of light would pass right through one another. Instead of having a swordfight, they would slice each other immediately in half.

In fact, the photon, or light particle, is renowned in quantum physics for its standoffish refusal to interact with anything. MIT’s Frank Wilczek, a 2004 Nobel Laureate in Physics, has joked that instead of photons, perhaps lightsabers are made of gluons–quantum particles that stick together with ease. These would not pass through one another, although they might explode.

“The combination of medieval chivalry and modern lethal technology is pretty ridiculous,” says Wilczek. “In real history, gunpowder–or even good crossbows–pretty much put knights out of business.”

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