A classic theory in physics includes Maxwell's equations, linking electric and magnetic fields as 'electromagnetism'.

Now, physicists from Imperial and Lancaster University have suggested an upgrade to the 150-year-old theory, which would allow electromagnetic fields to interact with new materials and theoretical particles called axions.

Their research is published in Physical Review A

Axions are mysterious particles that were thought to only interact with the surfaces of materials. Under the new version of electromagnetism, axions would also be detectable within blocks of materials.

The team suggest metamaterials - materials engineered to have properties not found in nature - could be designed that would mimic axions, allowing the first measurements of their behaviour.

By distilling the three principal components of Maxwell's equations into just two, and allowing the description of a wider range of materials, Jonathan Gratus and Paul Kinsler of Lancaster University, along with Martin McCall of Imperial College London, have invented a way to model a novel `axion-like' behaviour.

Dr Paul Kinsler said: "We have even designed some axion-like metamaterial elements. Such tiny electro-mechanical machines could be arranged in an array, respond to applied fields, and so create the micro-currents needed for the axion-like response."

Dr Jonathan Gratus said: "We can combine the excitation fields with our understanding of how the electric and magnetic fields interact with matter - so we devised a way to transform Maxwell's equations into something more general".

Maxwell's equations for classical electromagnetism have stood unchanged and unchallenged for over 150 years.

Professor McCall said: “These latest results present opportunities for new - and unexpected - advances in our understanding of light, electromagnetism, and material properties.”