Physics trivia

Levitating Frogs

Levitating living beings is no longer in the realm of science fiction. In 1997, physicist Andre  Geim managed to accomplish this feat at the University of Nijmegen in the Netherlands. In his experiments, Geim managed to levitate plants , small fish , grasshoppers , pizza pieces and even a small frog through the phenomenon of magnetic levitation .

Magnetic levitation occurs when opposing poles of magnetic fields interact with each other, producing repulsive forces. This has been known to the scientific community for a long time. What actually proved to be something new is that the experiment proved that, under certain conditions, it is possible to obtain a stable equilibrium.

There is a theorem in physics, called Earnshaw’s theorem, which states that it is not possible to produce a stable equilibrium in an object endowed with mass and electric charges in a fixed configuration using only magnetic and gravitational forces . In other words, you may be able to attract or repel magnets, but you will never be able to make them float stably by balancing the magnetic forces with your weight .

So how was it possible for Geim to make a frog float ? The answer to this question is that all the materials he uses have one thing in common: they are diamagnetic .
Why was the frog able to float?

When a diamagnetic material is placed in a region of non-zero magnetic field, a magnetic field is induced inside it in the opposite direction to the external magnetic field. The magnetic repulsion arises from there. But what about stable equilibrium ? The latter is due to the very nature of diamagnetism: all matter is made up of atoms, which have electrons around their nuclei. When these diamagnetic atoms are placed in interaction with external magnetic fields of order greater than 10.0 T (Tesla), their electrons align to produce a opposite magnetic field . As the magnetic field induced in the small amphibian is generated by the movement of electrons around the nucleus, this field is not generated by a fixed configuration , as predicted by Earnshaw’s theorem.

With his calculations, Andre Geim was able to show that the strength of the magnetic field needed to stably float a diamagnetic body is proportional to its volume . Therefore, the task of levitating a human being is much more complex and involves magnetic fields much higher in intensity and volume than those currently produced in laboratories.

If you are wondering if the frog has suffered any damage to your health, don’t worry, because even the MRI machines used in hospitals can reach magnetic fields of similar intensities (on the order of 4.0 T) without any harm to health . .

Curiosities

Thanks to his discoveries, Andre Geim received the IgNobel prize , dedicated only to the strangest scientific discoveries of the year, but which follow a pattern: they should make you laugh , then they make you think .

Andre Geim is the only person to accumulate a Nobel Prize and an IgNobel , as the Dutch physicist was awarded the highest award in the scientific community for having discovered one of the most promising materials of the future: graphene .