Einstein’s experiment that remained hidden in plain sight for 60 years

While Alfonso San Miguel and Bernard Pallandre took that metal bar out of the warehouse, they could not contain their enthusiasm. They finally had in their hands a unique piece that had been lost for years. Along with the object, old letters and photographs showed the historical importance of the discovery. Who was going to tell you that, kept in an uninventory box in the museum, it would be found the first and only scientific experiment that the well-known physicist Albert Einstein proposed, designed, built, and with which he published three articles.

Einstein-de Haas experiment
Society of Friends of Ampère / Alfonso San Miguel / Bernard Pallandre

Alfonso San Miguel (left) and Bernard Pallandre (right) with the device of the Einstein-de Haas experiment.

Almost 110 years after Einstein carried out those experiments, the device was in the hands of the director and volunteer of the Ampère museum. “It all started practically by chance,” Alfonso San Miguel, Professor of Physics at the University of Lyon, tells us in a telephone interview.

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Former high school physics teacher and museum volunteer Bernard Pallandre was inventorying material in the warehouse when he stumbled upon a box containing photos of Einstein, Wander Johannes de Haas, letters, and a device. At that time, he began an investigation that led them more than 4 years to ensure the veracity of the instrument and, above all, understand how he got there.

Why is this discovery important?

The instrument they had just found was designed to prove the existence of the Ampere molecular currents. This hypothesis posed by André-Marie Ampère at the beginning of the 19th century tried to answer the question of how two objects as different as permanent magnets and electric currents could create magnetic fields. According to his hypothesis, there were currents that traveled between molecules without resistance.

With the discovery of electron in 1897 by JJ Thomson, the understanding of what matter and electricity were changed radically. Advances led to the development of Bohr atomic modelin which electrons spin around the nucleus of the atom in stable orbits. In this time of such fundamental changes, Albert Einstein and Wander Johannes de Haas decided to assemble a device with which they could demonstrate the existence of Ampère currents.

Dazzled by experimental physics

Most of us know Albert Einstein for his genius in the field of theoretical physics. Thanks to his prodigious mind, he made important advances in the understanding of the universe, including the postulates of general and special relativity, Brownian motion and the photoelectric effect. The latter would cement him as one of the great scientists of all time, since thanks to him, he was awarded the Nobel Prize in Physics in 1921.


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However, in his long and fruitful career as a theoretical physicist, he also wanted to perform some experiments to test his theories. As he confessed in letters to Michele Besso, a close friend who worked with him in the patent office, when he turned 35 He was starting to get really interested in experimental physics.

Due to this unexpected change in his interests, Einstein began to propose experiments with the physicist Wander de Haas. With them, they intended to prove that the modification of the magnetic field applied to a ferromagnetic object could interact with the rotating movement of the electrons and, therefore, the object would rotate on itself. Now, to test it, they would have to design and create a device.

The Einstein-de Haas experiment

The experiment consists of a iron bar suspended in the air by a very fine wire. This bar is located in the center of a cable coil through which one passes electric current. According to what had been observed at the time, the current passing through the cable would generate a magnetic field that would interact with the electrons present in the iron rod, aligning their angular moments. That is, as electrons revolve around the nucleus, if they are placed in a magnetic field, all the orbits will align. However, If the current is reversed, the electrons will try to reverse their spinwhich will make the bar moves slightly due to the law of conservation of angular momentum.

Haas EinsteinHaas Einstein
Society of Friends of Ampère / Alfonso San Miguel / Bernard Pallandre

Explanation of the theory behind the alignment of the rotation of electrons in the ferromagnetic material

The result was reflected in three articles published in 1915 and 1916, two signed only by Einstein and the other by the two physicists. Due to his findings, this phenomenon would be called the “Einstein-Hass Effect”. However, in the early 1920s other physicists tried to repeat the experiments and found somewhat different results. After much experimentation, they concluded that Einstein and de Haas, although they had been extremely careful, they would have underestimated the effect of certain factors external to the experiment.

An unexpected donation

In 1959, Geertruida de Haas-Lorentz, the renowned doctor in physics, wife of Wander de Haas and daughter of Nobel Prize winner Hendrick Lorentz decided to make a series of donations to museums in her area. Among the different objects were photographs, letters and devices that both she and her husband had used in the experiments.

After Wander’s death in 1960, Geertruida proceeded to make donations, mostly to the Leiden museum, where they both lived. In fact, Other parts of a similar device can be found in the Leiden museum. According to Alfonso San Miguel, these could be spare parts for the experiment.

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However, as reflected in the 1962 bulletin of the society of friends of André Marie-Ampère, a complete device that was used by Wander and Einstein was donated in its entirety to the Ampère museum. The reasons are not 100% clear, but it is likely because Wander de Haas was a member of the patronage committee of this society from its beginnings..

Exposed and lost

As observed in the news bulletins of the time and in the letters of the museum director during the 50s and 60s, The experiment was displayed along with other physical devices that were changing the world. There, surrounded by objects such as the transistor, or articles on particle physics, it had a prominent place as an object related to physics.

However, the exhibitor did not emphasize that it was an original piece and, as San Miguel tells us, transcendental in the understanding of modern physics. The Einstein-de Haas experiments laid the foundation for the discovery of such important physical phenomena as the electron spin (in 1928) and the beginning of quantum mechanics.

Einstein-de Haas experimentEinstein-de Haas experiment
Society of Friends of Ampère / Alfonso San Miguel / Bernard Pallandre

New exhibitor with the Einstein-de Haas experiment

After several years (although it cannot be said with certainty how many or if they were continuous), More than a decade ago, the display where the device was located was dismantled. At that time there was no electronic inventory, so it was stored in the museum’s warehouses and there it remained, forgotten.

In this case, chance or luck placed Bernard in the right place at the right time. Thus, the only experiment proposed, designed and built by Einstein now occupies a privileged place in a new exhibition that tells both stories, that of the experiment and its rediscovery.

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