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Researchers at Princeton University have succeeded in generating an electric current, albeit a tiny one, by exploiting our planet’s rotation and magnetic field. This experimental feat validates a controversial idea that is almost 200 years old, opening up fascinating theoretical perspectives despite colossal practical challenges.
A 200-year challenge!
Humanity has long dreamed of clean, inexhaustible sources of energy. But what if one of them was literally under our feet, or more precisely, in the very movement of our planet? A team of American scientists, led by Christopher Chyba of Princeton University, has just published results in the prestigious journal Physical Review Research that spectacularly revive this idea. They have succeeded in demonstrating experimentally that it is possible to generate a DC electrical voltage using the Earth’s rotation through its own magnetic field. A concept theorised as far back as the 19th century, but until then considered by many to be a physical dead end.
The story goes back to Michael Faraday, one of the fathers of electromagnetism. As early as 1832, this pioneer was investigating the possibility of inducing an electric current by using the movement of a conductor in the Earth’s magnetic field. The basic principle is that of electromagnetic induction, the same principle that governs the operation of our dynamos and alternators: a conductor moving in a magnetic field is subjected to a force (the Lorentz force) that sets its electrons in motion, creating a current.
However, the attempts of Faraday and his successors came up against a major difficulty. The so-called axisymmetric part of the Earth’s magnetic field (the main component, roughly aligned with the axis of rotation) is relatively uniform on a local scale. When an ordinary conductor rotates with the Earth in this field, Lorentz forces tend to accumulate charges, creating an internal electric field. This electrostatic field then very quickly opposes the Lorentz force (E = -v x B), cancelling out the driving effect on the electrons and preventing the generation of a measurable direct current. This conclusion seemed to seal the fate of the idea, so much so that Christopher Chyba’s team itself published a mathematical demonstration in 2016 that seemed to confirm this impossibility under standard conditions.
Getting round classical physics
Yet the researchers’ perseverance paid off. By re-examining the fundamental assumptions underlying the impossibility demonstration, Chyba and his colleague Kevin P. Hand identified a crucial subtlety in 2016. The perfect cancellation of forces only occurs if the magnetic field inside the conductor remains unchanged or follows a simple law. They theorised that by using a magnetically permeable material (capable of channelling magnetic field lines) and shaped according to a specific topology – in this case, a hollow cylindrical shell – it would be possible to locally perturb the magnetic field pattern in such a way that force cancellation is no longer perfect (mathematically, ∇ × (v × B) ≠ 0 inside the material).
Another essential condition identified related to the properties of the material itself. It had to be a magnetically ‘soft’ material, with electrical conductivity and magnetic permeability such that its magnetic Reynolds number (Rm) was low (Rm << 1). This dimensionless number characterises the ratio between the advection of the magnetic field by the movement of the conductor and its diffusion through the conductor. A low Rm means that the magnetic field diffuses faster than it is ‘driven’ by the rotation, a necessary condition for the predicted effect to manifest itself.
Armed with this new theoretical basis, the researchers designed a meticulous experiment to test their hypothesis. Their main device consisted of a hollow cylinder 29.9 cm long and 2 cm in external diameter, made of M100 manganese-zinc (MnZn) ferrite. This material was chosen specifically for its high magnetic permeability and relatively modest electrical conductivity, ensuring a low magnetic Reynolds number (estimated at around 0.088 under their conditions).
This cylinder was placed on a non-conducting platform and oriented with extreme precision: its long axis had to be perpendicular to both the Earth’s rotation speed vector (approximately 354 m/s at Princeton latitude) and the local component of the Earth’s magnetic field (approximately 45 microteslas, inclined downwards). Electrodes were connected to the ends of the cylinder to measure the voltage or current generated using a high-precision multimeter.
The main experimental difficulty lay in measuring an extremely low predicted voltage, of the order of a few microvolts, and distinguishing it from any artefacts or background noise. The researchers therefore took drastic precautions:
- Controlling the thermoelectric effect (Seebeck): MnZn ferrites have a high Seebeck coefficient, meaning that a tiny difference in temperature (ΔT) between the ends of the cylinder can generate a parasitic voltage far greater than the desired effect. To counter this, the researchers continuously measured the temperature at both ends and analysed their voltage data as a function of this ΔT. In this way, they were able to isolate the temperature-independent voltage component attributable to the rotation effect.
- Orientation tests: As predicted by theory, the maximum voltage (around 17 microvolts on average) was measured when the cylinder axis was oriented South-North (0°). By rotating the device through 180°, the voltage was reversed, becoming positive with the same magnitude. Crucially, when the cylinder was oriented East-West (90°) or West-East (270°), the measured voltage (excluding the Seebeck effect) fell to zero, as predicted.
- Material controls: They repeated the experiment with a full cylinder of the same M100 material. As the theory predicts (the hollow topology being essential), no significant voltage was generated, whatever the orientation. Another test was carried out with a cylindrical shell made of MuMetal, a material with very high permeability but a high magnetic Reynolds number (Rm >> 1). Here again, no voltage was detected, confirming the importance of the Rm < 1 condition.
- Environmental isolation: The experiment was conducted in an underground, dark laboratory to eliminate any photovoltaic influence. Stray electromagnetic fields (60 Hz from the mains, radio frequencies) were measured and found to be too weak to explain the results. The absence of a signal in a Faraday cage also confirmed that the effect did indeed depend on the external field.
- Replication: To rule out any unknown local influence specific to their main laboratory, the researchers replicated the experiment in a different residential building, 5.5 km away. Despite a noisier environment, the results confirmed the behaviour and the order of magnitude of the voltage initially observed.
All these measurements and rigorous controls enabled the researchers to conclude with a high degree of confidence that the DC voltage of 17.3 ± 1.5 microvolts and the DC current of 25.4 ± 1.5 nanoamperes measured were indeed due to the interaction between the Earth’s rotation, the magnetic field and the specific properties of their ferrite cylinder.
Colossal challenges
While this experimental confirmation represents an undeniable fundamental scientific advance, any enthusiasm about its short- or medium-term practical applications should be tempered immediately. The voltage generated is infinitesimal: 17 microvolts, less than one thousandth of the voltage of a simple button cell battery. To produce useful energy, this voltage would have to be multiplied by millions or even billions.
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The first essential step will be for these results to be reproduced independently by other research teams around the world. The scientific community remains cautious, especially as an earlier attempt in 2018 by Veltkamp and Wijngaarden in Amsterdam failed to detect a convincing signal. However, Chyba’s team suggests that the experimental conditions of this attempt (in particular the length/radius ratio of the cylinder used) may not have complied with all the theoretical constraints, in particular with regard to edge effects.
Even if the phenomenon is confirmed, the challenge of scaling up is immense. The current equations show *how* the effect occurs, but do not guarantee that it will be possible to drastically increase the voltage with existing or even conceivable materials. A number of avenues are being explored: miniaturisation and series production of numerous devices, use of materials with even more optimised magnetic and electrical properties, or operation in environments where the speed (v) or magnetic field (B) would be higher (such as in orbit). But for the time being, all this remains in the realm of speculation.
Tapping into the Earth’s rotation to generate electricity
A fundamental question arises: where does this electrical energy come from? The answer lies in the conservation of energy. The electricity generated comes directly from the kinetic energy of the Earth’s rotation. The device acts like a tiny magnetic brake. Theoretical analysis (using the Poynting vector) confirms that the electrical power generated corresponds to the power “lost” by the Earth’s rotation.
This corollary raises a fascinating, even worrying question: would massive exploitation of this energy source slow down our planet? The calculations by Chyba’s team are enlightening: if all the world’s current electricity consumption were supplied by this method, it would slow down the Earth’s rotation by around 7 milliseconds per century. A figure to be put into perspective: the length of daylight naturally fluctuates by several milliseconds per decade (due to the planet’s internal movements), and the slowdown due to the lunar tides is currently of the order of 2.5 milliseconds per century. The impact, while real, would therefore be very gradual and potentially negligible compared with other natural phenomena. The conservation of angular momentum is also respected, implying a transfer between the Earth’s mechanical angular momentum and that contained in the electromagnetic field.
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Experimental confirmation of the possibility of generating electricity from the Earth’s rotation is a major victory for fundamental physics. Nearly two centuries later, it validates Faraday’s intuition and demonstrates the theoretical and experimental ingenuity of modern researchers, who are capable of detecting and exploiting subtleties in well-established physical laws.
However, it is crucial to keep our feet on the ground. We are a long way from a new energy revolution. For the time being, this discovery remains a “laboratory curiosity” with uncertain practical implications. The next few years will show whether this avenue can be explored further, in particular through research into new materials or configurations, or whether it will join the pantheon of ideas that are physically sound but technologically inexploitable on a large scale. In any case, it reminds us that even the most familiar phenomena, such as the rotation of our planet, still harbour unsuspected secrets and potential. Perhaps niche applications, such as eternal low-power ‘batteries’ for isolated sensors, could one day emerge from this fundamental research. Only time, and the hard work of scientists, will tell.
