One irony of history is that while Thomas Edison invented the first practical and affordable light bulb, he didn’t invent a practical and affordable system for keeping those lights on nationwide. The distinction for developing the system for transporting electricity that way goes jointly to George Westinghouse, the inventor of the railroad air brake, and to Nikola Tesla, a visionary engineer from the Austrian empire.

In the 1880s, the three went to battle over who had the superior technology for electrical transmission. The three-way rivalry between the inventors is the premise of The Current War (a movie that has its own dramatic back story), starring Benedict Cumberbatch as Edison, Nicholas Hoult as Tesla and Michael Shannon as Westinghouse. Edison was promoting direct current (DC), while Westinghouse was promoting alternating current (AC). As the U.S. Department of Energy explains, direct current “runs continually in a single direction, like in a battery or a fuel cell,” while “alternating current reverses direction a certain number of times per second — 60 in the U.S. — and can be converted to different voltages relatively easily using a transformer.”

But the differences between the two went beyond their definitions.

“If we were living in Edison’s world, we’d have a large coal-operated generating plant every mile or two, because DC couldn’t travel any distance,” says Jill Jonnes, author of Empires of Light: Edison, Tesla, Westinghouse, and the Race to Electrify the World. (Jonnes was not involved in the film.) “The brilliance of AC was that you could send it long distances, bring the voltage down via another transformer station, and distribute it as needed out into the surroundings.”

On the other hand, DC systems were ahead of AC systems in terms of developing a motor. There was huge business potential for nailing the design of electric motors, in terms of the future of powering machines, factories and appliances. Tesla wanted to develop an AC-power motor, and had tried to get Edison on board when he worked for Edison in New York City in 1884; Tesla left after six months when it was clear that Edison wasn’t interested in that idea.