October 18, 2021

I, Science

The science magazine of Imperial College

The physics behind hoverboards and levitating trains...


Want a hoverboard like Marty in Back To The Future? Well soon you might be able to. Recently a group of physicists at Université Paris Diderot showed off the “Mag Surf” – their experimental demonstration of superconductor magnetic levitation.

Supercold liquid nitrogen enables a superconductor on the bottom of the board to repel the magnetic field of a metal rail underneath it, fixing the board at a small distance above and creating an invisible guide for it to move along.

Pretty cool physics… but what’s going on?

Electricity is defined as the flow of electrons. As these electrons move through a material, they encounter resistance due to collisions with the atoms in the material. At higher temperatures these atoms have more energy so vibrate around more, causing a greater resistance due to an increased amount of electron-atom interactions. In a cooler material, the atoms vibrate around much less, so the electrons can travel through more freely.

This electrical resistance is the reason we can’t achieve perpetual motion; why the energy that comes out of a system is always less than the energy put in. The energy lost by electrons due to their impeded travel causes electrical devices to heat up, reducing their efficiency.

So what happens  to a material at absolute zero, that is, at -273°C. Here, the atoms in the material are stationary, so the electrical resistance is zero. This is known as superconductivity.

Superconductivity is the quantum-mechanical phenomenon of zero electrical resistance.  As materials are cooled down and become superconducting they emit a magnetic field, a process called the Meissner effect.

Superconducting wires transmit electrical current without interference and can hold electrical current indefinitely. There’s just one catch – they only work at very low temperatures. Research work is ongoing and has increased their working temperature, but we’re still a long way off being able to use them easily in everyday life.

If we can develop room-temperature superconductors, they’ll revolutionise our world. Using superconductors in power cables and electrical devices would mean the energy in would equal energy out, giving near-perfect efficiency.

The Meissner effect exhibited by superconductors gives rise to Quantum Locking – a phenomenon where a superconducting material is ‘locked’ in 3D space above a magnet. This levitation effect results from the magnetic field lines of the magnet penetrating the superconductor. The levitating material has the ability to support a substantially heavier objects, keeping it at a fixed distance above the magnet.

It is this concept that was demonstrated by the French physicists, and could have many future implementations, mainly through incorporation in mechanical devices to get frictionless moving parts.

That’s the sensible stuff… now here’s literally the coolest toy train set in the world:


 IMAGE: stephendepolo, flickr.