Ever since I learned how inaccurate Star Wars battles really were, I've been thinking about how off the entire Star Wars universe is. I get it, in a place where people have telekinetic powers and can shoot lightning from their fingers; you can't exactly expect things to line up with… well, physics. When I started digging into the Death Star in particular, though, I learned that it doesn't even make sense under its own rules.
The destruction of Alderaan is one of the most famous scenes in movie history, and for good reason. I can't think of any other time where I've seen a planet just… explode. Unfortunately, the Death Star wouldn't be able to do that. Not even a fleet of them could pull it off.
According to the Death Star Technical Manual, the main reactor uses a substance called hypermatter. The reactor can kick out the power of several main sequence stars. These are stars that are close-ish to the size and energy output of the Sun. That's a HUGE amount of power, but it turns out that planets are REALLY tough to destroy.
Gravity is the main force holding planets, stars, and the like together. To break something completely apart such that it's no longer bound by that gravity requires that you exceed its gravitational binding energy. For reference, Earth's GBE is 24 million trillion trillion joules and that's… a lot.
Alderaan, according to Wookieepedia, is just a tiny bit smaller than Earth. Given that humans can live on the planet, we can assume it's pretty close in other respects as well – breathable atmosphere, reasonable gravity, etc. Alderaan's gravitational binding energy would be pretty damned close to our own home planet's. Therefore, we'll be using the figure from earlier.
Now… given that our Sun is an average main sequence star, we know it's power output to be 400 trillion trillion watts. One watt is the same as one joule every second. In the Star Wars film, we can see it takes 12 seconds for the superlaser to charge up and fire. I'll pretty forgiving and say that "several" main sequence stars means ten, and the reactor has 12 seconds to build up the power for the shot. That gives us 480 thousand trillion trillion. That's a big number, but it's quite a bit less than we need to make a planet explode. Just under 417 times less, actually.
There are some resources for Star Wars that suggest that it takes 24 hours for the laser to "recharge", but that also doesn't quite fit. It's more likely that the time is needed for dissipating the heat from the shot, which would be absolutely staggering.
So in addition to having some silly ideas of how space combat would potentially work, Star Wars can't even follow its own rules. Even if we pretend that hypermatter did exist, it still wouldn't be enough. I guess the rebels wouldn't have had much to worry about after all.
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