"Quite Repellent"

We can all admit that superconductors are pretty nifty. They carry electrical currents with zero resistance (hence the "super" part of their name), so anytime you want to build The City Of The Future, you'll want to include superconductors to transmit electricity from your ecologically-friendly power station to your self-driving car without any losses.

Because of that lack of resistance, superconductors repel magnetic fields - in other words, they prevent any magnetic field lines from penetrating their surface. This feature makes superconductors double-nifty: if you place one on top of a magnet, the field lines envelope the superconductor like a net, overcoming gravity and making it levitate.

The downside is that we've only been able to make superconductors that do their thing at very cold temperatures, which is why The City Of The Future isn't The City Of Today. But the hunt is on for the right combination of materials that superconduct at everyday lukewarm temperatures, which will make free electrical transmission - and levitation - routine.