People in this discussion keep on referring to the levitation as "maglev." It is a form of magnetic levitation, but it's significant that they're planning to use Halbach arrays. Musk's original idea was to basically "fly" the pod inside a low-vacuum tube using air bearings on the bottom of the pod. Halbach arrays basically fly above a series of passive metal coils. The faster the Halbach arrays are traveling, the stronger the field, which lifts the pod, which decreases the field, lowering it again. The system experiences negative feedback. It's self regulating. This makes it much cheaper than other forms of Maglev.<p>The advantage over Musk's original idea, is that Halbach array levitation doesn't require the tight clearances that air bearing levitation would require. Apparently, the cost of manufacturing linear arrays of aluminum coils is cheaper than ensuring tight tolerances.