Physicists have now discovered two types of sensors in animals that can detect magnetic fields close to the quantum limit, information that could improve our own design of magnetometer devices.
In multiple ways, such as iron-rich cells responding to the field’s pull, or a bias in photoreceptor chemistry at the back of eyes, magnetoreception has emerged through evolutionary history as a means of directing life around the globe.
Curious to know how biological solutions compare with advances in magnetometer technology, University of Crete physicists Iannis Kominis and Efthimis Gkoudinakis evaluated the energy resolution limit of three adaptations, finding at least two of them come within a whisker of the quantum limits of magnetic field detection.
Armed with little more than a suitably magnetized slither of iron, humans have navigated the unknown under the direction of Earth’s compass points for thousands of years.
Today, our ability to put an exact number on the strength of a faint or highly confined magnetic field demands a detailed and thorough understanding of the quantum nature of electromagnetism, which not only improves sensitivity but allows us to predict the physical limits of any measurement.
Fundamental to calculating the push and pull of a magnetic field is the ability to gauge the energy contained within.
As our ability to measure magnetism becomes increasingly precise, quantum uncertainty increasingly takes over, as if the Universe isn’t quite sure of anything as we continue to focus on its details.
Adding to the challenge is the tendency for quantum-level systems to entangle with their environment, blurring the lines even further on the energy mitigated by a magnetic field.
The energy resolution limit (ERL) is a mix of parameters representing the economics of a quantum system within a sensor’s grasp, which includes an estimate of its uncertainty, the size of the sensed region, and the time or bandwidth over which a measure is made.
The end result is a unit of energy over time, equivalent to a quantum unit known as Planck’s constant, which both allows engineers to compare existing technologies for their level of precision while also evaluating the ability of any potential system to reach, or even exceed what is considered a limit.
To Kominis and Gkoudinakis, calculations of a sensor’s ERL provide the perfect opportunity to hold biological magnetoreception to the quantum standards and see how they fare against our best attempts.
Currently, there are several generalized means by which living things are thought to detect Earth’s magnetic field, referred to as induction, radical pair, and magnetite mechanisms.
A fourth, combining magnetite with radical-pair approaches, was also considered.
Induction mechanisms turn the energy within a magnetic field into electrical energy in a biological system, setting off a series of changes that ultimately affect behavior.
For example, in 2019 researchers proposed Earth’s magnetic field might create a subtle difference in voltage detectable by hair cells inside a pigeon’s ear canals, affecting its balance.
Pigeons could use induction as a mechanism for detecting Earth’s magnetic field.
The radical-pair mechanism involves correlations between unpaired electrons attached to different molecules.
Under a magnetic field, the balance in this pairing will vary enough to affect the nature of chemical reactions, triggering a cascade of biological effects determined by the magnetic field’s orientation.
A graphic explaining radical-pairing to detect Earth’s magnetic field
The radical-pair mechanism, proposed for quantum magnetoreception in birds, takes place in cryptochrome molecules in cells in their retinas.
(Chiswick Chap/CC BY-SA 4.0/Wikimedia Commons)
Magnetite-based magnetoreception is a far more straightforward approach.
Tiny crystals of iron-based compounds in an organism’s cells are thought to react to magnetic fields with a force large enough to be detectable, forcing microbial cells to orientate themselves or triggering animals into sensing their north and south from their east and west.
While research in the field is ongoing, and still largely speculative, each mechanism has the potential to be highly sensitive, potentially revealing novel ways we might detect faint or confined signs of magnetic fields.
Calculations made by Kominis and Gkoudinakis find that induction mechanisms don’t come close to a quantum level of sensitivity. y
Yet measures that employ radical pairing just might come as close to quantum limits as our own tech.
Not only might it point in new directions for innovation, but the findings could inform future experiments into the diverse ways life on Earth has evolved to be guided by the invisible cage of magnetism overhead.
For centuries, humans have relied on compasses to navigate the world, guided by Earth’s magnetic field.
But what if nature had already perfected a way to sense magnetism long before we invented tools?
Animals, from birds to bacteria, possess an astonishing ability known as magnetoreception—an innate sense that allows them to detect magnetic fields and use them for navigation.
Now, physicists have taken a deep dive into the natural mechanisms behind this extraordinary ability.
A new study has revealed that two biological magnetoreception methods operate with a sensitivity close to the fundamental quantum limits of measurement—a level of precision comparable to the best human-made magnetometers.
This discovery could have profound implications, not only for understanding animal navigation but also for advancing human technology.
How Do Animals Sense Earth’s Magnetic Field?
Scientists have long known that many animals can detect magnetic fields, but the mechanisms behind this ability are still being uncovered.
Research has pointed to three primary biological systems that enable animals to sense magnetism:
- Magnetite-Based Magnetoreception: Some species, like certain bacteria and birds, contain microscopic iron-rich crystals called magnetite. These particles react to Earth’s magnetic field, allowing the organism to orient itself accordingly.
- Radical-Pair Mechanism: Found in the eyes of birds and some other animals, this system relies on the behavior of unpaired electrons in special proteins called cryptochromes. Changes in magnetic fields affect these electrons, influencing chemical reactions and sending navigational signals to the brain.
- Induction Mechanisms: Proposed as a mechanism in some animals, this method suggests that electromagnetic fields induce electrical changes in specific biological tissues, such as hair cells in the inner ear.
These three mechanisms have allowed species across the animal kingdom to navigate with incredible precision.
But just how sensitive are these natural systems compared to our most advanced technology?
How Close is Nature to Quantum Precision?
To measure just how precise these biological magnetoreception systems are, physicists Iannis Kominis and Efthimis Gkoudinakis from the University of Crete put them to the test.
They evaluated the energy resolution limit (ERL) of these adaptations—a fundamental measure of how accurately a system can detect magnetic energy while accounting for quantum uncertainty.
Their findings were remarkable: the radical-pair mechanism and magnetite-based detection appear to function at sensitivity levels approaching the quantum limits of measurement.
This means that, in some cases, nature has engineered biological magnetometers nearly as precise as the best human-made devices.
Breaking Assumptions:r years, many assumed that animals’ ability to sense magnetic fields was crude compared to human-engineered devices.
But this new research challenges that assumption, showing that in some cases, biological systems may be as sensitive as state-of-the-art quantum magnetometers.
The radical-pair mechanism, in particular, appears to operate at near-quantum precision.
This is surprising because it suggests that some animals—especially birds—may be engaging in a form of quantum biology, utilizing fundamental quantum effects to detect and respond to magnetic fields.
But there’s more: induction-based magnetoreception, once thought to be a strong candidate for how some animals sense magnetism, does not come close to quantum sensitivity.
This raises questions about whether induction is a viable explanation for magnetoreception in birds and other creatures.
What This Means for Future Technology
Understanding how animals sense magnetic fields at near-quantum limits could revolutionize human technology.
Could we one day develop quantum-inspired magnetoreception implants for human navigation? Could biomimicry lead to ultra-sensitive, nature-inspired magnetometers?
This research not only expands our knowledge of biology but also suggests new frontiers for technological innovation.
If evolution has already fine-tuned these sensory systems over millions of years, then scientists may be able to harness these mechanisms to develop next-generation magnetic field sensors.
The Future of Magnetoreception Research
As we continue to unravel the mysteries of biological magnetoreception, several questions remain:
- Are there undiscovered organisms with even more precise magnetoreception mechanisms?
- Can we replicate and enhance these biological processes in human-made devices?
- How does climate change and electromagnetic pollution impact animal magnetoreception?
One thing is certain: Nature has already designed extraordinary ways to sense and navigate the invisible forces around us.
As researchers continue to explore these mechanisms, we may find that the answers to some of our most pressing technological challenges have been hiding in the natural world all along.
