In 2014, five engineers at NASA's Jet Propulsion Laboratory tested independent inventor Guido Fetta's Cannae Drive, a prototype space engine that's basically a microwave emitter within a small metal cone. In July, they reported their incredible conclusion: The device moved, despite lacking propellant or producing exhaust of any kind. It was a doubly bold claim, one that seemed to contradict conservation of momentum (a foundational principle of physics) and to promise a new era of fast, cheap space travel. The Internet was abuzz with excitement.
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