While at first glance the crackle of electricity and invisible tug of magnetism seem to be fairly different things, for about 150 years scientists have accepted that they're both fundamentally aspects of the same phenomenon.
But there has been a mystery attached to this electromagnetic duality – if electric fields have electric charges, why don't magnetic fields have something similar like a magnetic charge? Scientists now think they might have an answer.
New research led by scientists from Louisiana State University suggests that gravity mucks up the symmetry that would otherwise require magnetic charges – or magnetic monopoles – to exist.
"Gravity spoils the symmetry regardless of whether magnetic monopoles exist or not," said team leader Ivan Agullo. "This is shocking."
"The bottom line is that the symmetry cannot exist in our Universe at the fundamental level because gravity is everywhere."
All this talk of magnetic monopoles and symmetry can get a little confusing, so let's take a step back for a second and revisit the basics.
Back in the mid-19th century, an awkward but brilliant Scottish scientist by the name of James Clerk Maxwell applied a bunch of existing mathematics to the experimental work of another great mind, Michael Faraday.
While Faraday was making magnets spin with electrical currents, and creating electrical currents by making magnets spin, Maxwell was crunching the numbers to show that magnetic and electric fields – the lines of arrows your high school physics teacher made you draw around bar magnets – could be swapped, and nobody would be any the wiser.
This describes a feature of the Universe called symmetry – some things look the same no matter how you rotate them, when you observe them, or where you stand.
The thing is, this electromagnetic symmetry only works if you ignore currents and charges; electrical fields are made up of points of force called electric charges that exist along a vector (in other words, the charge has a flow), but in spite of having a similar 'north-south/positive-negative' type flow, magnetic fields don't have magnetic charges, ruining the symmetry.
And if there's one thing theoretical physicists and mathematicians hate, it's the ugliness of ruined symmetry!
None of this is for want of looking, either; theoretical physicist Paul Dirac believed if a magnetic monopole could be found it would help explain why the electric charge existed as a point like it did.
Things that look like monopoles have been created under certain laboratory conditions, using super-chilled atoms, but something that behaves in the manner of a magnetic monopole isn't necessarily the same thing, meaning we still don't have empirical evidence that they exist.
And now the latest study suggests their existence is impossible. To better understand how the researchers came to the conclusion that gravity was responsible for the break in the electromagnetic duality, it helps to throw another phenomenon into the mix – light.
Light is made up of tiny particles called photons, which is more or less a unit of information in the electromagnetic field carrying the electromagnetic force.
Different frequencies of this quantum of electromagnetism are responsible for different colours, not to mention microwaves, radio waves, and X-rays.
Photons are a type of particle called a boson, which are defined by the fact two or more identical particles can occupy the same quantum state.
There are other particles called fermions, which include electrons and the quarks that make up protons and neutrons, that can't do this, which also helps explain why they can't overlap one another in physical space.
So the researchers looked at how gravity interrupts other symmetries, including those involving fermions, and found a way to rework the fundamental theory explaining the electromagnetic field so they applied to photons instead.
The result exposed evidence that magnetic monopoles might not be hiding - since gravity permeates the entire Universe, the broken symmetry between electric charges and magnetic monopoles exists on a fundamental level.
"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," said Agullo.
Now that doesn't rule out magnetic monopoles as such, but it does remove symmetry as a reason for looking.
If the new study supported, this is pretty big news not just for magnetic monopole hunters; astrophysicists will need to take it into account when studying the echoes of light from the early Universe.
So far, astrophysicists haven't worried about the effects of gravity on the polarisation of photons as they whiz through space, but that's purely on the assumption that there is such a thing as electromagnetic symmetry.
The next step is for researchers to see if the broken symmetry means the polarisation of light has changed as the Universe aged, and if it tells us anything new about our cosmic history.
This research was published in Physical Review Letters.