May the force be with you!
DOI: 10.1063/PT.5.010113
Happy Star Wars Day! Because “May the fourth” sounds like “may the force ,” fans of the movie series have picked the day to celebrate and talk about the exploits of Luke Skywalker, Princess Leia, and other characters—humanoid, droid, or neither—in the rich Star Wars universe.
The third Star Wars movie, Return of the Jedi, was released on 25 May 1983. Two months earlier, President Ronald Reagan announced to the world that the US would develop a system that, in his words, “could intercept and destroy strategic ballistic missiles before they reached our own soil or that of our allies.”
The Strategic Defense Initiative was the official name of Reagan’s program, but it soon became known as Star Wars. I’m not sure how SDI acquired its nickname, but it’s possible that the originator of the nickname saw a resemblance between one of the early SDI proposals—a screen of satellites armed with nuclear-powered x-ray lasers—and the movie’s Death Star, the moon-sized base that houses a planet-destroying laser weapon.
The feasibility of SDI’s space-based x-ray lasers was doubted from the get-go. In 1987 a panel of physicists convened by the American Physical Society published a study on the lasers and other so-called directed energy weapons. The panel wrote:
We estimate that all existing candidates for directed energy weapons (DEWs) require one or more orders of magnitude (powers of 10) improvements in power output and beam quality before they may be seriously considered for application in ballistic missile defense systems. In addition, many supporting technologies such as space power, beam control and delivery, sensing, tracking, and discrimination need similar improvements over current performance levels before DEWs could be considered for use against ballistic missiles.
In conceiving of the Death Star and other Star Wars weapons, George Lucas was not obliged to follow the laws of physics or even military priorities. Obi-Wan Kenobi’s lightsaber may be a better weapon than its metal-bladed namesake, but it seems less effective at killing people than James Bond’s Walther PPK. And the Galactic Empire’s four-legged AT-ATs (All Terrain Armored Transports) are of a needlessly vulnerable size and slowness.
When I wrote a news story for Physics Today‘s October 2009 issue about protoplanetary collisions, I learned that it takes 1021 joules to vaporize 1 kg of silicate rock. Earth weighs 6 × 1024 kg. To vaporize our planet or one like it, the Death Star’s laser would have to deliver as much energy as a supernova explosion.
