When physicists discover new properties of matter, it usually means better technologies for the rest of us. Superconductors, liquid crystal displays like the ones found in most TVs now, medical imaging technologies that allow doctors to peer inside the human body, and magnetic levitation — which was used to create the Shanghai Maglev train — are all examples of how discoveries of new properties of matter have resulted in revolutionary products.
Now, physicists have discovered another new property of matter that could lead to a new generation of innovation.
Physicists are always on the lookout for new ways electrons can push each other around
For the past 25 years, physicists observed a persistent glitch while conducting experiments that involved cooling a uranium compound to near absolute zero. When the compound, URu2Si2, was cooled to -428 degrees Fahrenheit, they would see a fall in the amount of chaos in the system. The molecules seemed to snap into an ordered state, letting out a burst of heat the scientists couldn't account for. Where did this extra heat come from?
The likely answer, which was detailed in a paper published January 30th in Nature by Rutgers physics professors Piers Coleman, Premala Chandra and MIT postdoc Rebecca Flint, comes from the observation that this material was undergoing a phase transition (similar to how water undergoes a phase transition when it becomes ice) but at the quantum level, reflecting a property of matter that was previously unknown.
In the quest to find new materials with exotic properties such as superconductivity, physicists are always on the lookout for new ways electrons can push each other around. For example, last week scientists announced they'd created a new kind of solar cell by discovering new electronic properties using a large-scale computer simulation. To discover properties that occur under more extreme conditions, theoretical physicists like Coleman write the equations that are sent over to experimental physicists who run tests using devices like the Large Hadron Collider to see if they hold up. "Along the way, we sometimes stumble across something amazing like high temperature superconductivity, which works well for levitating trains," Coleman said.
New physical properties are characterized by breaks in physical symmetries, which we can see in everyday things. If you rotate a sphere around its axis, it looks the same at every point in the rotation — but if you rotate a cube this way, it only looks the same every 90 degrees of rotation. Therefore, a cube breaks continuous rotational symmetry. Magnets exemplify a broken symmetry that is a bit more difficult to envision because it breaks what physicists call "time-reversal" symmetry. This is the idea that the motion of particles looks the same running back and forth in time, "like running a movie backwards and forward," Coleman offered as a comparison. With magnets, if you run the movie backwards, the magnetic field produced reverses direction. You have to reverse time twice to get it back to its original state.
Hopefully this will involve teleportation, time travel, and more lasers
What the scientists observed was happening with this extremely cold uranium compound was that the substance was breaking double time-reversal symmetry — twice as complex as our magnet example. The physicists have dubbed this new property "hastatic order" after the ancient Latin word for "spear," which is what the particles resemble in this ordered state. Obviously there's no time-reversal machine to test this in, but data from particle colliders in the US and Japan has backed this theory. It's kind of like finding the square root of -1: it technically doesn't exist, but mathematically it helps solve all kinds of problems.
"It turns out that particles in nature divide into two categories. One has a property that when you time-reverse it, it comes back to itself," Coleman explained, like a marble completing a lap around a circular track.
"Others, only when you time reverse it twice does it come back to itself." Electrons have this property, the physical analogy for which is rolling a marble along a Möbius strip. One revolution brings it to the same place, but in an upside down orientation. Ars Technica writes about another good example.
The new theory of order, which involves the spin of electrons, breaks double time reversal symmetry and exhibits quadruple time reversal symmetry. Coleman warned there are no good physical examples, but I'd imagine it's something like this:
So what are the implications of this new property? "This would be like asking Michael Faraday how his new work on electromagnetism would impact steam engines," Coleman said, though he believes we are in the middle of "the quantum revolution" and anticipates great things to come. Hopefully that will involve teleportation, time travel, and more lasers.
"It took 200 years to understand classical mechanics and what energy was. Quantum mechanics is 100 years old, but there are ideas that we are just beginning to touch upon."