A 180-Year Assumption About Light Was Just Proven Wrong

By The Hebrew U. of Jerusalem, Nov. 19, 2025
https://scitechdaily.com/a-180-year-assumption-about-light-was-just-proven-wrong/

Scientists have discovered that the magnetic field of light plays a surprisingly strong role in twisting light as it passes through materials. This insight reshapes fundamental physics and could spark new breakthroughs in spin-based and optical technologies. 

Credit: Enrique Sahagún

New research shows that the magnetic part of light actively shapes how light interacts with matter, challenging a 180-year-old belief.

The team demonstrated that this magnetic component significantly contributes to the Faraday Effect, even accounting for up to 70% of the rotation in the infrared range. By proving that light can magnetically torque materials, the findings open unexpected pathways for advanced optical and magnetic technologies.

Revealing Light’s Hidden Magnetic Power

Researchers at the Hebrew University of Jerusalem have uncovered new evidence that the magnetic portion of light, not only its electric component, plays a meaningful and direct part in the way light interacts with materials. Their results, published today (November 19) in Scientific Reports, call into question a long-held explanation of the Faraday Effect, a key physics phenomenon first described nearly two centuries ago.

The work, led by Dr. Amir Capua and Benjamin Assouline of the university’s Institute of Electrical Engineering and Applied Physics, provides the first theoretical demonstration that the oscillating magnetic field within light actively shapes the Faraday Effect. This effect occurs when the polarization of light rotates as it moves through a substance placed in a steady magnetic field. 

Challenging 180 Years of Faraday Effect Assumptions

“In simple terms, it’s an interaction between light and magnetism,” explains Dr. Capua. “The static magnetic field ‘twists’ the light, and the light, in turn, reveals the magnetic properties of the material. What we’ve found is that the magnetic part of light has a first-order effect, it’s surprisingly active in this process.”

Since Michael Faraday first identified the effect in 1845, scientists have largely attributed it to the electric field of light interacting with electric charges inside matter. The new findings show that the magnetic field of light also plays a direct and measurable part in the process through its influence on spins, a contribution that had long been considered negligible.

 
Magnetic Field of Light Takes Center Stage

Through advanced calculations using the Landau–Lifshitz–Gilbert (LLG) equation, which models how spins behave in magnetic materials, the researchers demonstrated that light’s magnetic field can create magnetic torque within a material in the same way a static magnetic field can. “In other words,” Capua explains, “light doesn’t just illuminate matter, it magnetically influences it.”

To measure the strength of this influence, the team applied their theory to Terbium Gallium Garnet (TGG), a crystal commonly used to study the Faraday Effect. Their results indicate that the magnetic field of light contributes roughly 17% of the rotation seen in the visible spectrum and as much as 70% in the infrared.

“Our results show that light ‘talks’ to matter not only through its electric field, but also through its magnetic field, a component that has been largely overlooked until now,” says Benjamin Assouline.
 

Light–Matter “Conversation” Redefined

 
This discovery points to new opportunities in areas such as optics and magnetism, with potential applications in spintronics, optical data storage, and magnetic control using light. It may also play a role in the development of future spin-based quantum computing technologies.

 

 

 

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