Take one extremely powerful magnet, and one slightly surprised but compliant frog, put one on top of the other, and what do you get? A levitating frog, according to British and Dutch scientists who carried out the experiment.
It might sound like sleight of hand, but the team from the University of Nottingham and the University of Nijmegen have repeated it with grasshoppers, fish and plants - and they say it could work with humans, too. One scientist in the US is already looking at a millennium project to build a magnet strong enough to levitate a volunteer 100 metres.
"We tried it because we thought it would work," said Peter Main, of Nottingham's physics department. "It was actually the idea of Andre Geim, of the University of Nijmegen. We had seen superconductors with magnets levitating above them. This is the same effect."
The frog was lifted two metres up a cylinder by a magnetic field of 16 tesla, a million times more powerful than the Earth's natural magnetic field.
"The important issue is your density - the force you feel is related to your volume, so the less dense, the better," said Professor Main. "Frogs have a density about equal to water, as do people. It works because it actually distorts the electron orbits in the frog's atoms. That generates a tiny electric current, which generates a magnetic field in the opposite direction from the main magnet."
Like opposing magnets, the repulsive force pushes them apart.
Is the mechanism potentially harmful to humans or frogs? "It did try to escape by scrambling off towards the side. But it went back to its fellow frogs looking perfectly happy," said Professor Main. "It must be a very strange sensation, though, being weightless. It's not a surface effect, like floating in water, though you might feel internal tidal effects."
Lifting a human would require a magnet several metres across, though it would not have to produce a more intense magnetic field. "You would have to be lying down, rather than standing. It might cost about pounds 1m," the professor said.
The discovery has serious applications. It could form a low-cost test bed for chemicals and systems which will be used in space. "It's a lot less expensive than sending a rocket up," said Professor Main.
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