So you might be wondering how Stephen Hawking can communicate given that he can't, you know, move. Well you're wrong about that! He can move … his cheek muscle. That's right, he communicates by using his cheek muscle, to type and … okay, honestly, we have no idea how this actually works, so we're going with science being magic. Basically, there's a laser on his glasses scanning an alphabet of letters. When it gets to the one he wants, he twitches his cheek muscle and it recognizes that letter, then begins again. It's kinda like how the kid on Speechless talks, except more sci-fi. So yes, magic.
To make Hawking talk takes a lot of different machines, which he talked about a ton in a long blog entry called The Computer which, to be honest, is about as dense as his books. Oh, and you know how he has a voice synthesizer? Well, the person who first invented that was Hawking's second wife's first husband. Yeah, the man invented what he uses to talk, and Hawking said thanks by stealing his wife! Stephen Hawking: genius, visionary, world-changer, cad.