Ah, yes, the three states of matter: Solids, liquids, and gases. What a simple way to understand our physical world.
Of course, if you remember a bit of high school science, you probably recall a fourth state of matter, plasma. And if you pay attention to science news, you’ve probably heard of another, Bose-Einstein condensates. So, five states of matter.
But what about degenerate matter? Topological superconductors? Time crystals? Yes, these are legitimate states (or phases; the terms are interchangeable) of matter, albeit ones that we wouldn’t encounter in our everyday lives.
In reality, physicists know about many states of matter—the number is likely in the thousands. And they keep finding new ones. There are probably millions of potential states to find.
The basic three, of course, have long been obvious. But the idea that there might be more was vindicated in the second half of the 19th century, when experiments with electricity first began to yield plasmas. Bose-Einstein condensates, first proposed theoretically in 1924, followed, and our expanding understanding of physics soon made clear that even everyday life is full of more states of matter than we might realise.
To a physicist, the magnets on our fridge are a different form of matter than the fridge itself. A wineglass and the wooden shelf it sits on likewise represent two different states of matter.
A state of matter simply refers to the way that the atoms or constituent particles are ordered. And that order gives rise to different properties. In a solid, for example, the molecules are arranged in a lattice structure that lends the material rigidity. In a liquid, the molecules flow around each other, but they can’t easily move toward or away from each other like they could in a gas. And in a plasma, the molecules flow like in a gas, but their electrons are moving freely, allowing it to easily conduct electricity.
There are countless ways that matter can be arranged. For example, there are 230 “space groups,” or ways that molecules can be arranged to form three-dimensional crystal structures in a solid. Each of these is its own form of matter. And depending on how their electrons are arranged, each of those 230 can be a conductor or an insulator, which would also make it a different form of matter.
And when temperatures get very hot or very cold and pressures are extreme, normal matter can deform into exotic states with wild properties. Inside neutron stars, for example, nuclei might be condensed into a type of what’s known as degenerate matter, where electrons and protons are forced together to form neutrons, or even further into a quark-gluon plasma made just of fundamental particles. On the other side of the spectrum, when molecules are at temperatures near absolute zero, quantum mechanics begins to become visible on the macroscopic scale. Bose-Einstein condensates form when collections of atoms are cooled near to absolute zero and begin to act as though they’re a single atom. This gives them unique properties, like a complete lack of viscosity, meaning you can make tiny whirlpools in them that will swirl forever.
Part of the reason we keep finding new states of matter, said Jasper van Wezel, an associate professor in condensed matter theory at the University of Amsterdam, is simply that there are so many to find.
“There are all of these properties of atoms or molecules or whatever that you can use to order them,” he told Gizmodo. “It just takes time to go through all the possibilities.”
As technology has improved, we’ve also been able to perform experiments in more extreme conditions and with greater precision.
We can now see, for example, that the particles in various materials have different spins. Spin is a property intrinsic to particles, and it’s what creates magnetism.
“In the 1950s, you would just measure magnetization and say, ‘Look, these are both magnetic—I can stick both of them on the fridge,’ and that’s it,” van Wezel said. “But now we have tools to go into the material and look at every individual spin, and we can say, ‘Look, they are both magnetic, but in this one every third spin is turned, and in this one it’s not, so they’re different.’”
With that newfound knowledge, physicists might be able to manipulate those spins to create materials with entirely new properties.
The possibility of finding different ways to use matter is also one reason that physicists are so obsessed with finding new phases and why new ones can be so exciting.
“Each time we discover a new phase of matter, it gives us a set of properties that would have been inconceivable with any prior phase of matter,” said Kaden Hazzard, an assistant professor in Rice University’s physics department. “If all you have are liquids, and someone hands you a brick, all of a sudden you have the ability to resist things you couldn’t resist before.”
When some materials are cooled to very low temperatures, for example, they can become superconductors, meaning they transmit electrical currents with zero resistance. Applying that on a commercial scale could mean power lines that carry electricity to your house with little loss or computers that are far more efficient.
A recently discovered state of matter known as a topological superconductor acts as an electrical insulator inside but is conductive around its edges. These unique abilities could be put to use in quantum computers to protect the fragile qubits that store information.
There are also some exciting properties of matter we haven’t found yet, but which physicists believe should exist. Room-temperature superconductors, for example, have long been considered the Holy Grail of condensed matter physics. Such a material would revolutionise how we use electricity (so, pretty much everything).
Another type of matter physicists are in hot pursuit of is something called a quantum spin liquid. In a quantum spin liquid, the spins of its particles begin to affect each other, in a way that results in unexpected magnetic properties. This type of matter could lead to better quantum computers and even help create room-temperature superconductors.
Instead of searching for materials that should exist based on theory, physicists must also sometimes do the reverse: try to explain why something they’ve created is acting in a way they never thought possible.
Perhaps the best example of this is something called the fractional quantum Hall effect. Imagine a bunch of electrons moving in a magnetic field on a 2D material. The charge associated with the system should simply be e, the charge carried by electrons. But when scientists measured it, they found the charge was exactly e divided by three.
“This flabbergasted the experimental [community], because there’s nothing in there with a charge less than e,” Hazzard told Gizmodo. He compared it to throwing a bunch of billiard balls on a pool table and watching them fall through the pockets, and, somehow, the moving balls weigh just a third of what a billiard ball normally weighs.
It sounds preposterous when put in terms of billiard balls, but things are different on the quantum level. It turns out, when the electrons are moving together, their motion causes them to act as though they carry a third of the charge they actually do. It also means the electrons have become a totally new state of matter.
Finds like this make searching for forms of matter a kind of treasure hunt for physicists. More unexpected properties surely exist buried in the laws of physics. They await only the right arrangement of particles and confluence of physical states to leap into being, once again granting us abilities we had never dreamed of before.