Melting an ice cube requires 3.34 x 105 Joules per kilogram. A single ice cube with a mass of 50 grams would therefore require 16,700 joules. You can see that melting things takes a lot of energy. If you want to melt a metal door, you have to do two things: increase the temperature to the melting point and then actually liquefy it. The total amount of energy depends on the mass and type of metal.
Estimating performance
Now we have to make some assumptions. The big question is what spaceship doors are made of. I mean, if I were building a giant spaceship to carry battle droids around, I think my metal of choice would be aluminum, which offers a good balance of 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 the latent heat of fusion is 3.96 x 105 Joules per kilogram. (I know that’s a lot of numbers, but don’t worry, we’ll just drop them into a computer.)
What is the mass of the molten metal? That is a difficult question. When Qui-Gon makes his first cut, it looks like he’s cutting a path about 2 meters long. I’m not sure about the width of this path, but I’m assuming 1 centimeter. After all, the door is maybe 5 centimeters thick and he cuts all the way through in one pass. With these estimates I get a total mass of 2.7 kilograms of molten metal.
Now I can calculate the energy required to melt this amount of aluminum. It is simply the energy needed 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 paste your numbers into my Python code.) Using my numbers, I get a required energy of 2.6 million joules. Melting metal is not trivial.
Now as far as performance goes, I just need to determine how long it takes to melt this metal. With the tracker video analysis I get an editing time of 11.5 seconds. This gives a performance of 2.28 x 105 Watt. Yes, that is the actual, physical power of the Force. This corresponds to an output of 305 hp and is like a powerful car right in your hand.
A lightsaber battery
Maybe lightsabers don’t have batteries. Maybe they’re just drawing 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 look like? What type of battery would work?
We have already estimated the performance of the lightsaber. This allows us to 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 to waste war of starsand I’ve never seen them plugged into the wall, so I’m assuming they’ll last a long time.