Melting an ice cube requires 3.34 x 105 joules per kilogram. Thus, a single ice cube with a mass of 50 grams would require 16,700 joules. You can already see that melting things requires a lot of energy. If you want to melt a metal door, you need to do two things: raise the temperature to the melting point and then liquefy it. The total amount of energy depends on the mass and type of metal.
Estimating the power
Now we have to make some guesses. The big question is what spaceship doors are made of. I mean, if I were making a giant spaceship to carry battle droids, I think the metal I would choose would be aluminum, which has a good balance between weight and strength.
Luckily, we know everything about aluminum. It has a density of 2,700 kilograms per cubic meter and a melting temperature of 660 degrees Celsius. The specific heat capacity is 900 joules per kilogram per degree Celsius and it has a latent heat of fusion of 3.96 x 105 joules per kilogram. (I know that’s a lot of numbers, but don’t worry, we’ll just put them into a computer.)
What is the mass of the metal that is molten? That’s a tough one. In Qui-Gon’s first cut, he appears to be cutting a path about 2 meters long. I’m not sure how wide this path is, but I’ll choose 1 centimeter. Finally, the door is about 5 centimeters thick and cuts through it completely in one go. With those estimates, I get a total mass of 2.7 kilograms of molten metal.
Now I can calculate the energy needed to melt this amount of aluminum. It is simply the energy required to raise the temperature of the metal to the melting point and then melt it. (Want to try the calculation with a different metal? Just enter your numbers in my python code.) With my numbers I obtain a necessary energy of 2.6 million joules. Casting metal is not trivial.
Now for power, I just need to determine how long it takes to melt this metal. Wearing Tracker Video Analysis, I get a cutting time of 11.5 seconds. This gives a power output of 2.28 x 105 watts. Yes, that is the real physical power of the Force. It’s equivalent to 305 horsepower, so it’s like having a high-powered car in your hand.
A lightsaber battery
Maybe lightsabers don’t have batteries. Maybe they just draw energy from an extra dimension or something. No one knows because lightsabers aren’t real (and that’s okay). But if they had a battery, what would it be like? What type of battery would work?
We already estimated the power output of the lightsaber. With this we can calculate the total energy stored in the device. We just need to know how long it will run on a single charge. I’ve never seen a lightsaber go out Star Warsand I’ve never seen them plugged into the wall, so I’m guessing they’ll last a long time.