San Francisco to Los Angeles in half an hour. Do the math and you're zooming along at a speed of more than 600 miles per hour. That expedient California commute is what Tesla Motors and SpaceX chief Elon Musk is promising with his new project Hyperloop. At the moment, Musk is keeping mum on just about everything but the name and the boast, promising the big reveal of what he calls a "cross between a Concorde and a railgun and an air hockey table" on August 12.

But there are few options out there that can meet Hyperloop's promised velocity. Ordinary magnetic levitation (maglev) trains like Japan's speed demons can't do much better than 300 to 350 mph—above that speed the air resistance is simply too great.