An anonymous reader writes "Google has a huge research budget and an apparent willingness to take on huge projects. They've gotten themselves into autonomous cars, fiber optic internet, robotics, and Wi-Fi balloons. But that raises a question: if they're willing to commit to projects as difficult and risk as those, what projects have they explored but rejected? Several of the scientists working at Google's 'innovation lab' have spilled the beans: '[Mag-lev] systems have a stabilizing structure that keeps trains in place as they hover and move forward in only one direction. That couldn't quite translate into an open floor plan of magnets that keep a hoverboard steadily aloft and free to move in any direction. One problem, as Piponi explains, is that magnets tend to keep shifting polarities, so your hoverboard would constantly flip over as you floated around moving from a state of repulsion to attraction with the magnets. Any skateboarder could tell you what that means: Your hoverboard would suck. ... If scaling problems are what brought hoverboards down to earth, material-science issues crashed the space elevator. The team knew the cable would have to be exceptionally strong-- "at least a hundred times stronger than the strongest steel that we have," by Piponi's calculations. He found one material that could do this: carbon nanotubes. But no one has manufactured a perfectly formed carbon nanotube strand longer than a meter. And so elevators "were put in a deep freeze," as Heinrich says, and the team decided to keep tabs on any advances in the carbon nanotube field.'"