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Elon Musk, speaking at a 2011 event in Fremont, California. Stephen Lam / Reuters

Elon Musk, founder of the electric car company Tesla (among other things), has been dropping references to a new mode of rapid transit he calls the "Hyperloop" and described as "a cross between a Concorde, a railgun and an air hockey table." Supposedly, he'll share more this summer.

Musk said in an interview with CNBC Friday that California's massively expensive high-speed rail project got him thinking about it. He criticized its slowness, at least compared to similar systems in China and Europe, and its cost, which may be as high as $100 billion.

The Hyperloop, on the other hand, will be blazing fast, getting people from Los Angeles to San Francisco in under half an hour. And, he says, "it can be done for probably a tenth the cost per mile." But what is it?

No one knows, though many are speculating based on Musk's recent remarks. The Concorde was a famously fast (and famously expensive) supersonic passenger jet; a railgun propels a projectile using high-power magnetic forces; and air hockey tables hover the puck above the table with tiny jets of air.

The world already has magnetically levitated trains, of course, so it's not that. In fact, Musk has called it a "fifth mode of transportation," totally distinct from planes, trains, automobiles and boats.

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Beyond that (and a few other tidbits here and there over the last few years), Musk has declined to give any further details other than that he himself won't be focusing on the project, but promised that following a major Tesla announcement on June 20, he'll have time to elaborate.





































Devin Coldewey is a contributing writer for NBC News Digital. His personal website is coldewey.cc.