Physicists are using a 350-year-old theory to discover new properties of light waves
Since the 17th century, when Isaac Newton and Christian Huygens first discussed the nature of light, scientists have debated whether light is a wave or a particle – or perhaps both at the quantum level. Now, researchers at the Stevens Institute of Technology have demonstrated a new connection between the two views, using a 350-year-old mechanical theory — often used to describe the motion of large physical objects like pendulums and planets — to explain even the most complex elements. Behaviors of Light Waves – Stevens Institute of Technology reports at phys.org.
The work, which was led by Xiao Fengqian, a professor of physics at Stevens University, was published in the August 17 online issue of the journal Physical Review Research, and the work also shows for the first time that The degree of non-quantum entanglement of a light wave is direct and complementary to the degree of its polarization. As one rises, the other falls. Therefore, it is possible to infer directly on the level of entanglement on the level of polarization and vice versa on the level of entanglement. This means that hard-to-measure optical properties such as amplitudes, phases and correlations – and perhaps even those of quantum wave systems – can be extracted from light intensity, which is much easier to measure.
Qian said we’ve known for more than a century that light behaves sometimes as a wave and sometimes as a particle, but reconciling the two frameworks has proven extremely difficult. Their work does not solve the problem, he says, but shows that there is a deep connection between wave and particle concepts, not only at the quantum level, but also at the level of classical light-wave and point-mass systems.
The team used a mechanical theory originally developed by Huygens in 1673 in a book on the pendulum, which explains how the energy that causes an object to rotate varies depending on the object’s mass and the axis around which it rotates. The theory describes the relationship between mass and the momentum that spins it. But how does this apply to light where there is no mass?
The team interpreted the intensity of light as equivalent to the mass of a physical object, and then mapped these measurements into a coordinate system, which can be explained by applying Huygens’ mechanistic theory.
They found a way to implant an optical system, so they could visualize it as a mechanical system, and then describe it with physical equations. When the team visualized a light wave as part of a mechanical system, the relationship between wave properties became immediately apparent, among which entanglement and polarization are clearly linked. This wasn’t obvious before, but it becomes very clear once we plot the properties of light on a mechanical system. What was once abstract becomes tangible: using mechanical equations, we can literally measure the distance between the center of mass and other mechanical points to show how the different properties of light relate.