Why can a superconductor hold a magnet in midair?

The full narration of the video.

Hold one magnet above another, like poles facing. It won't just float there. It tips, flips over, and snaps on. Swap in this little black disc, still steaming with cold. The magnet stops in midair, perfectly still.

Turn the whole thing upside down, and the magnet hangs underneath without falling. This little disc is a superconductor. So what is it actually doing? Most people assume it's just like poles pushing apart.

But pushing alone can't hold anything steady. Back in 1842, the English mathematician Samuel Earnshaw proved it: however you arrange ordinary magnets, they slip off to one side. So the superconductor does two more things.

First, what it is. Cool some materials enough, and current flows through them without losing anything at all. This disc has to soak in liquid nitrogen. That's minus 196 degrees Celsius. Around every magnet run invisible lines, looping from one end to the other. They're called field lines.

Thing one: the superconductor won't let field lines in. As the magnet comes close, a loop of current starts running on its surface. It's as if a flipped magnet appeared underneath, pushing the one above upward. The field lines get squeezed outside, pressed into a soft cushion.

But a cushion is slippery. With only this, the magnet would still slide away. Thing two is what makes it steady. This kind of superconductor isn't perfect. It's full of tiny flaws, like the holes a needle leaves in cloth.

A few field lines slip through those holes. Once through, they're stuck. It's like sewing on a button: thread goes through the holes, and the button is stitched in place. So the magnet is stitched into midair by invisible threads.

Lift it, and the lines pull it back. Press it down, and they push it back up. Nudge it sideways, and it springs right back. Upside down, same thing. The stitches hold, so it just hangs there. Wherever you hold the magnet as it cools, that's where the lines thread through. What it remembers is the height of that moment.

In 2000, Southwest Jiaotong University in China put this trick to work: the first passenger-carrying high-temperature superconducting maglev car. Under the car, discs like this soak in liquid nitrogen, floating over a track made of magnets. Its one weakness is heat. Once the nitrogen boils off, the disc warms, the stitches loosen, and the magnet drops.

That's why scientists keep hunting: for a material that superconducts without the cold. In 2023, someone claimed they'd found it. Within weeks, labs around the world had the answer: it wasn't. Something that floats like this at ordinary temperature and pressure still hasn't been found.

If one day it no longer needed the cold, what would you float first: your bed, or your bike?