Dutch-born Christiaan Huygens is perhaps one of the most influential but overlooked physicists in history. His groundbreaking work in the late 17th century encompassed both the ethereal nature of light and the mechanics of moving objects.
Among Huygens’ many accomplishments, he proposed a revolutionary wave theory of light that formed the foundation of physical optics, which delves into the intricacies of light interference, diffraction, and polarization. Additionally, he invented the world’s first pendulum clock, a marvel of precision that served as the most accurate timekeeping device for nearly 300 years, even during the Industrial Revolution.
Surprisingly, little attention has been paid to the connections between these seemingly disparate fields of optics and classical mechanics. However, two physicists at the Stevens Institute of Technology in New Jersey have recently revisited Huygens’ pioneering research on pendulums, published in 1673, and have used his centuries-old mechanical theorem to unveil new connections between the enigmatic properties of light.
“Through our initial study, we have demonstrated that by applying mechanical concepts, we can gain a fresh understanding of optical systems,” explains physicist Xiaofeng Qian.
Qian and his colleague, Misagh Izadi, focused on two vital properties of light in their calculations: polarization and classical entanglement—a correlation without invoking quantum mechanics.
These properties reflect the mysterious duality of light that permeates throughout our universe. Light can be described as both waves rippling through space, much like matter in the quantum realm, and as particles localized at specific points.
Not limited to quantum phenomena, this wave-particle duality also manifests in the classical realm of gears and springs, evident in light waves rising and falling like ethereal ripples on an intangible ocean.
Qian remarks, “For more than a century, we have grappled with the challenge of reconciling light’s dual nature. Our work doesn’t provide a definitive solution, but it does highlight profound connections between wave and particle concepts, not only at the quantum level but also within the domain of classical light-wave systems and point-mass systems.”
Entanglement, most commonly associated with the quantum realm, refers to the correlations between properties of objects. Magnets or pairs of photons’ spins are examples of this entanglement; knowing the state of one influences the state of the other.
Classical entanglement describes similar correlations without contemplating an object’s undetermined nature before measurement.
Polarization refers to the directional property of a light wave, oscillating vertically or horizontally. Even particles, such as photons, can have polarization.
Capitalizing on the similarities between oscillating light waves and pendulums, Qian and Izadi endeavored to describe light’s properties through the mechanics of the latter.
“Effectively, we established a method to map optical systems onto mechanical systems, allowing us to describe them using well-established physical equations,” explains Qian.
Classical mechanics typically describes the motion of large physical objects like pendulums and planets. Huygens’ parallel axis theorem, for instance, characterizes the relationship between masses and their rotational momentum.
Qian and Izadi conceptualized light as a mechanical system to which Huygens’ theorem could be applied. Astonishingly, they uncovered a profound connection: the degree of polarization in a light wave directly corresponded to the level of a recently recognized property known as vector-space entanglement.
Their calculations suggest an inverse relationship between polarization and entanglement levels, enabling one to infer the level of entanglement from the polarization and vice versa.
“Ultimately, our research simplifies our understanding of the world, as it reveals the intrinsic connections between seemingly unrelated physical laws,” states Qian.
The study has been published in Physical Review Research.
