There are obvious problems with building a Death Star like construction costs and personnel. Then there are less obvious problems like the trillion kilograms of antimatter you’d need to power the main gun.
If you can come up with the $850,000,000,000,000,000 it would cost to construct Star Wars‘ infamous Death Star, the next step is making it a fully operational battle station. That means powering the Alderaan-blasting plasma/laser/pew pew weapon of the films. Clearly, it would take a lot of energy to destroy a planet. How does the Death Star do it?
First you have to get around a few problems. As physicist Ethan Siegel notes at Starts With A Bang, the very minimum amount of energy that is needed to blow apart a planet is called the gravitational binding energy. That’s the amount of work you’d have to put in a celestial body to overcome the gravity holding all its molecules together. Understandably, that’s an enormous amount of energy. If Alderaan was an earth-sized planet, the energy is 224,000,000,000,000,000,000,000,000,000,000 Joules enormous. Our Sun puts out less total energy than that per week, Siegel explains.
Delivering that amount of death beam that quickly is the next problem. The heat transfer alone from firepower of that magnitude would melt pretty much anything the Death Star was made of. And thanks to Newton’s laws, we know that rapidly throwing that energy at a planet would rocket the Death Star backwards in response, killing everyone on board, Jedi or not.
Antimatter is the answer. As Siegel explains in his blog post, we could in theory manipulate an asteroid’s worth of antimatter and throw it at Alderaan. When it collided, it would annihilate the regular matter — creating a nova of pure heat and light — and overcome Aldreraan’s gravitational binding energy:
All it would take, if you want to destroy an (Earth-like) planet like Alderaan, is a little over a billion tonnes of metallic antihydrogen, and to transport it down to the planet’s surface. Once it hits the planet’s surface, it should have no trouble clearing a path down near the core, where the densities are highest.
So if you can get your hands on a billion tonnes of stable antimatter– it costs 62.5 trillion dollars per gram, mind you– using that to destroy a planet gets around the heat and equal/opposite reaction problems of the laser/plasma weapon we see in the Star Wars films. Then it’s time for an effective demonstration, and you can deal with your rebel friends soon enough.
Head over to Starts With A Bang for a more in-depth discussion of the film’s physics.