Their fields are pulsed so as to push on the Halbach fields of the train, carrying it forward.

ECONOMIST: Maglev trains

Inductrack, as Dr Post calls his invention, uses carriages built on top of bogies made of Halbach arrays.

ECONOMIST: Maglev trains

And by using the right arrangement of Halbach arrays, the train can be made self-stabilising so that, short of an earthquake, it will never fall off the track.

ECONOMIST: Maglev trains

This yields some of the strongest permanent magnets around, but they would still not be quite strong enough without another innovation made a few years ago by Klaus Halbach, one of Dr Post's colleagues at Livermore's sister laboratory, Lawrence Berkeley.

ECONOMIST: Maglev trains

Dr Halbach works on particle accelerators.

ECONOMIST: Maglev trains