Elon Musk finally explains how he'd get from L.A. to S.F. in 30 minutes

It's called a "cross between a Concorde, a railgun and an air hockey table," though for any fuller description, you'll probably need a degree in physics. After putting in an all-nighter, the billionaire founder of Tesla and Space X has provided details of his magical mystery hyperloop system that's supposed to travel at more than 700 miles per hour and gets folks to the Bay Area in half an hour. Musk said he felt compelled to develop a high-speed alternative to the California bullet train, which he considers a boondoggle that won't even go all that fast (Musk isn't thrilled with the 405 construction project either). One key feature is that the system would be elevated on columns 50 to 100 yards apart. That eliminates potential land issues and keeps down construction costs. Musk says the hyperloop could be built for $6 billion ($10 billion if you include space for cars), while the bullet train's price tag, now estimated at $70 billion, could easily hit $100 billion. The tubes would leave L.A. and SF every 30 seconds and mostly follow I-5. As to how it would work - from Bloomberg:

Tell us about the basics of the design. You have pods, with skis on the bottom, zipping through tunnels put under low pressure. Why did you pick this design?

The pods will ride on air bearings. The pod produces air, and it's pumped out of little holes on these skis. This is something that is used quite a bit in industry. You can move huge, heavy objects with very low friction, using air bearings. In the consumer sense, people would be familiar with air hockey tables, except in this case the air bearings are being generated by the pod itself, as opposed to the tube. You don't want the tube to be expensive. Because the tube is so long, you want the expensive stuff to be in the pod.

Some people said what you were proposing sounded impossible because it would require too much energy to get something through a tube at such high speeds and long distances.

There were guys questioning the energy that would be required to move the air and the pod. They didn't quite appreciate that it's not the air that is moving the pod. The pod is accelerated to velocity by a linear accelerator, which is basically a rolled-out electric motor. The air in the pod is going maybe 200 to 300 miles an hour, and it is low-density. So some of these guys were thinking: 'Oh, the air is sea-level density, and the air itself will be the thing that pushes the pod.' But that is not the case. You do want to have a continuously circulating loop of air so that you are not losing energy by letting the air slow down. But it is more efficient to have the pod go faster than the air. If you just try to pump air--particularly at sea-level pressure--through what is effectively a 700 mile loop, the energy required would be extremely high if you wanted that air to go fast because of friction against the side walls of the tube.

How would the linear accelerator work that gets the pods going?

It's actually a linear electric motor. It's a very basic thing. They have been around for a very long time. The air skis in the pod would have a thin row of magnets--you don't need much. The linear motor would electromagnetically accelerate the pod. It would be just below where the skis are. It just creates an electromagnetic pulse that travels along the tube and pushes the pod to that initial velocity of 800 miles per hour.

See what I mean? Bloomberg contacted Martin Simon, a professor of physics at UCLA, who said that the plan appeared feasible from a technological standpoint. But it's bound to face all sorts of political and financial roadblocks, perhaps instigated by the folks who have lobbied hard for the bullet train.