Eighty years after they were first theorized, scientists have just created an artificial magnetic monopole.
Monopoles were first conceived in their modern form more than 80 years ago by Paul Dirac, one of the founders of quantum mechanics.
This discovery has some powerful implications for physics.
Magnets — how do they work?
Every magnet that we have ever observed is a dipole — it has both a north and south pole. If we draw magnetic field lines around a magnet, we always see the lines curve around, joining the two poles.
A regular, two-poled magnet.
If you cut this magnet in half, you are not left with one north magnet and one south magnet, but instead two new double-poled magnets.
This goes on and on to the atomic level — you can keep cutting the magnet apart, but each part will still have two poles. Even a single spinning electron has both a north pole and a south pole.
That is how every magnet we have ever seen or experienced works.
Now, researchers at Amherst College in Massachusetts and Aalto University in Finland have created a mysterious Dirac monopole in the lab.
The monopole acts as a single-point source for a magnetic field. The magnetic field lines stretch out from the monopole in all directions, without the looping back seen in a normal dipole.
The mysterious magnetic monopole.
Before the latest finding, researchers searched high and low but never found a magnetic monopole in nature.
Monopoles for other physical forces are ubiquitous in nature — electric monopoles exist all over the place. The protons and electrons that are some of the basic building blocks of matter generate electric fields centered on themselves without a corresponding opposite pole.
Finding the elusive monopole
The researchers used some high-tech lab work to create their artificial magnetic monopole, which they published Jan. 30 in the journal Nature.
M.W. Ray et. al., Nature, 2014
The top row shows the scientists' experimental results. The bottom row shows their mathematical predictions. The close similarity between the two suggests that a monopole was formed. The vortex can be seen as the dark spot in the center of the condensate.
Their first step was making a Bose-Einstein Condensate — a small cloud of atoms cooled to a few billionths of a degree above absolute zero.
The cooling process involves shooting atoms in a cold gas with lasers, sapping the atoms of their momentum, and then carefully manipulating the atoms with magnetic fields to slow them down even further.
At this temperature, the atoms are almost stationary, and weird quantum effects start to happen. The atoms begin acting very strange and form a new kind of matter — different from the solids, liquids, and gasses we are used to.
The researchers then carefully applied finely tuned magnetic fields to the strange matter, forming tiny tornado-like vortexes in the fluid.
This animation, taken from a YouTube video posted by the researchers at Aalto University, shows how the monopole is made. By carefully balancing out external magnetic fields to move a point at the base of a vortex into the middle of the condensate, the condensate itself begins to emit an outward pointing monopole-style magnetic field.
The researchers call this the "hedgehog configuration."
The mathematics that describe the theoretical behavior of the Dirac magnetic monopole very nicely line up with what this matter looks like in the hedgehog condition, the researchers said.
What's it all mean?
Being able to generate a monopole like this in a lab has some serious implications for physics. When Dirac first hypothesized the monopole in 1931, he realized that the existence of such a thing in nature would confirm a fundamental idea in modern physics — the quantum nature of electricity. This means that electric charge can only exist as whole number multiples of some fundamental basic charge — you can't have something with one half the electric charge of an electron.
Various theories of the Big Bang suggest that in the unfathomably high temperatures of the very early universe, exotic magnetic monopole particles should have formed. Some of these particles should still exist today, although they would likely be extremely rare. Finding a natural monopole would help us better understand the conditions of the newborn universe.
Scientists have searched for evidence of these naturally occurring monopoles in places ranging from Antarctic ice to lunar rocks. To date, these hunts for naturally occurring monopoles have all failed.
Making a synthetic monopole indicates that these kinds of magnetic fields can exist without violating the laws of physics, leaving open the door for a natural monopole. Future research into the properties of synthetic monopoles could lead to new insights into how to find these strange particles in nature.
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