Q: How many science fiction writers does it take to change a lightbulb?
A: Two. One to screw in the light bulb, and one to say, "In 1876, Jules Verne had the first intimations that electrostatic power was a viable energy alternative. Hitherto, the only sources ..."
A: Two, but it's actually the same person doing it. He went back in time and met himself in the doorway and then the first one sat on the other one's shoulder so that they were able to reach it. Then a major time paradox occurred and the entire room, lightbulb, changer and all was blown out of existence. They co-existed in a parallel universe, though.