Hoverboard? Not too far away

A lot of things can hover. There are helicopters. There are hovercraft. But for the last three decades, a generation of engineers and movie fans have been waiting for something else: a hovering skateboard like the one used by Michael J Fox in Back to the Future Part II.

For the last 25 years, garage tinkerers, physics professors and top engineers at Google have been trying to make one. Inside a drab office park here in Northern California, Greg and Jill Henderson are working on the latest effort. On a recent visit the couple allowed a reporter to stand atop a noisy magnetic skateboard that can float above a copper surface.

It hovers about an inch above the ground. But when the 190-pound visitor stood atop the 100-pound board, one gentle push was enough to send him spinning across the room over a cushion of air. The Hendo Hoverboard is not yet for sale.

Dustin Rubio, 39, an electrician who grew up skateboarding and saw Back to the Future Part II when he was a teenager, is not thinking quite that big. This year, Rubio turned - a leaf blower, some plywood, some plastic and duct tape - into a small hovercraft that his daughters used to glide down the driveway at his home in Napa, California. "I was like I'm just gonna make something funny and see if it works," he said.

Unfortunately, his invention is not really a hoverboard. Bob Gale, who wrote the Back to the Future trilogy, said that, in his imagination anyway, the hoverboard floats on a magnetic field similar to magnetic levitation trains. This has been extremely difficult, mostly because of something called Earnshaw's theorem, which states, more or less, that repelling magnets are tough to balance. One way is to use a track that would hold the magnetic skateboard in place, but what self-respecting skateboarder wants to be constrained to a track?

Superconductors can also levitate things. In 2011, a research group directed by Alain Sacuto, a physics professor at the University Paris Diderot, used smoking-cold superconductors to levitate a liquid-nitrogen-filled skateboard that he and others rode across a five-meter magnetic rail. Rich DeVaul, a senior engineer at Google X, the company's research division, is also a longboard skater and a snowboarder. Last year, DeVaul and a Google mathematician, Dan Piponi, tried to crack the hoverboard. They got as far as a fingernail-size piece of carbon that could hover above a lattice of small magnets.

They remain confident they could have built a board, but are less confident they could have found a use for it. DeVaul imagined several applications, like a futuristic assembly line where robotic machine tools could levitate from job to job.

Henderson became enamoured of hover technology in 1989. His inspiration was not Back to the Future, but the Loma Prieta earthquake. His idea was that if you could make buildings float, you could build cities to better withstand earthquakes. Two years ago, he started his company, Arx Pax. The business plan is to develop magnetic technologies and license patents to builders, engineering firms, the Green Goblin and anyone else who might need to hover something.

Henderson may be a dreamer, but he is enough of a realist to understand that people are likely to be more interested in hovering skateboards than they are in his ideas for new kinds of building foundations. "That's why we picked the hoverboard: to capture that attention," he said. Crowd funding site Kickstarter already lists several campaigns for hovering contraptions, including HoverSkater, a hovercraft-like board, and the NeoLev, a miniature hoverboard.

© 2015 The New York Times