Electricity and magnetism are two aspects of the same unique electromagnetic force. This simple but powerful fact requires a symmetry between the two, the so-called electric-magnetic duality. The laws of electromagnetism appear symmetric, but a team of physicists argue that at the most fundamental level, they are not because they are disrupted by gravity.

The hypothesis, published in Physical Review Letters, was put forward by Professor Ivan Agullo from Louisiana State University and collaborators from the University of Valencia. They suggest that at the quantum level, the conservation of electromagnetic charges is broken.

This symmetry has an intriguing consequence. It requires the existence of magnetic charges that are known magnetic monopoles. Electric charges can be positive or negative (protons and electrons, for examples), but magnetized objects always have two poles. If you break a magnet, you end up with two magnets, not a north pole and a south pole.

The search for magnetic monopoles has been inconclusive and it had people working on alternative takes to save the symmetry. Agullo instead argues that the symmetry itself is not correct.

"Gravity spoils the symmetry regardless of whether magnetic monopoles exist or not. This is shocking," Agullo said in a statement. "The bottom line is that the symmetry cannot exist in our universe at the fundamental level because gravity is everywhere."

Their starting point for this work was looking at how the fermions – the family of particles that include quarks, electrons, and neutrinos – behave. They applied a classical gravitational field (we still don’t have a quantum theory of gravity) to photons and saw this lack of symmetry.

"We have been able to write the theory of the electromagnetic field in a way that very much resembles the theory of fermions, and prove this absence of symmetry by using powerful techniques that were developed for fermions," Agullo added.

Agullo is currently investigating a potential test for this idea. Photons are oscillations in the electromagnetic field and they can be emitted with oscillations in a particular direction. This effect, called polarization, has many applications (3D cinemas, for example) and might be found in several astronomical sources.

The polarization of photons emitted by the Big Bang, the cosmic microwave background, is believed to not be influenced by the gravity of the universe. But if the electric-magnetic duality is not valid, then this is no longer true. Agullo is currently trying to estimate how big the effect would be, so stay tuned: We might soon find out if gravity has killed the magnetic monopoles.