Every material behaves in a different state according to their temperature. To explain this, we need to know what exactly temperature is. Temperature is the amount of which the individual atoms move in a material. The more they move, the higher the temperature and the more they need space to move. When temperatures are low, the atoms don’t move around that much, so a stable structure can be created. But when the temperature rises, which means the atoms are moving quickly, the bonds that hold the atoms together can break. At which point this happens depends on the bonds of the molecule i.e., what atoms the material is made of.
Now that we understand what determines the different states, we can talk about them.
There are four fundamental states of matter. Solids, liquids, gasses, and plasma. They are fundamental and well known because we can see them in our everyday life. Adding, we will talk about a list of exotic states of matter which can only be observed under extreme conditions and are governed by complex quantum mechanics. More information on this later in the article. All these states are called low energy states, but during the creation of the universe there are 3 hypothesised very high energy states which we will also talk about.
Well start with the solid state. This is when the bonds between the atoms are intact. A solid is characterized by its sturdiness and strength because the molecules are arranged in an orderly pattern. A solid can be made when a liquid freezes to a solid state or when a gas depositions into a solid. The atom with the lowest melting point is helium with -272 degrees Celsius (1 K), and the atom with the highest melting point is Carbon with a melting point of 3500 degrees Celsius (3227 K).
Now when we want to make a liquid, we can melt a solid or condense a gas. In a liquid there are no intramolecular forces (covalent bonds, metallic and ionic) holding the atoms together like we see in a solid. Here the intermolecular forces (Hydrogen bonding, ionic bonding, ion dipole forces, ion dipole induced forces and Van Der Waals forces) hold the atoms close by, but lets them flow freely but not as much as in a gas. A gas and a liquid can be differentiated by knowing that a liquid is near incompressible, while a gas can be compressed to extremely small sizes. A liquid always takes the shape of the container it’s in and always keeps its volume. Helium has the lowest boiling point of -268.93 degrees Celsius (4,07 K) and Rhenium has the highest with a boiling point of 5596 degrees Celsius (5323 K).
A gas can be formed by sublimating a solid or evaporating a liquid. In a gas there is a vast separation between the individual particles and there is a weak intermolecular force between them. This makes that there is no definite size and shape of a gas. A gas can be easily pressurized and will always try to spread apart as far as they can in an open space, or completely fill any closed container.
Our final fundamental state is plasma., plasma consist of a gas of ionized particles (atoms whose electrons have been stripped away) and free electrons, making the cloud a mix of negatively and positively charged particles. This makes a plasma influenceable by magnetic and electrical fields. Plasmas can be created as you would expect, by knocking electrons of off atoms. This can be done with extreme high temperatures (usually at 1 eV, around 10000-11000 K), high-voltage electricity, or some types of radiation, this goes to show that it isn’t hard to form it. Plasma is next to the incomprehensible dark matter the most natural existing state of matter, almost everything in our universe is made of plasma. Seems reasonable when you consider that stars consist of it. All this makes plasma a useful and versatile substance that scientist often use to experiment and allow us to live by radiating sunlight to our planet.
Now that we have talked about the four fundamental states of matter. We now must talk about the experimental states of matter. These states are almost unobservable in our daily lives and are hard to grasp as an understanding of quantum mechanics is needed. We will now list the different kinds and try to explain them briefly.
-Supercritical fluids: This is the state where there can be no distinction made between a liquid and a gas. With small changes in pressure and temperature you can change the properties for the substance to be more gas like or liquid like.
Bose-Einstein condensate: Sometimes called the fifth state of matter, is formed when you cool an extremely low-density gas of bosonic particles to ultra-low temperatures, within a fraction of 0 K even. This makes it that the particles almost completely stop moving so that the atoms will clump together, the result is that these become identical and behave as the whole group of particles was a single atom, creating a superfluid (a fluid with 0 viscosity). All these atoms fall into the same quantum and energy states, at this point the clump start obeying something called Bose-Einstein statistics. This process is at the heart of superconductivity.
-Degenerate matter: Commonly found in smaller stellar objects, it describes matter where the gravitational pressure is so high that quantum mechanical effects are significant. This matter is a gas that behaves like a solid. An interesting thing about degenerate matter is that when we increase the mass of a degenerate object, the particles will be forced closer together making the object smaller. So, a larger stellar object will have a lower mass than a smaller object. Generally, neutron stars are made from this kind of matter.
Fermionic condensate: this state is closely related to the BEC, but instead of bosonic particles (gluons, Higgs bosons, photons…) the substance is made from fermionic particles (electrons…) and the temperatures are even lower, also creating a superfluid. While a BEC and a Fermionic condensate are closely related, it is more challenging creating a Fermionic one, because of the Pauli exclusion principle. As we stated the superfluid is formed when the particles take on the same quantum state. But the Pauli exclusion principle states that fermions are prohibited from taking on the same quantum state. Therefore, the temperatures must be lower than a BEC because when below a certain temperature a bond can be formed between the fermions, creating the superfluid, and making the condensate superconducting.
Quantum spin liquids: characterized by long-range quantum entanglement and fractionalization (a complex interaction between quasi-particles), is formed by an interaction of quantum spins in certain magnetized materials
Heavy fermion materials: containing intermetallic bonds between electrons with partially filled f-shells. Heavy fermions provide a varied class of unconventional superconductors.
String-net liquid: Is a quantum phase which is observed in a spin liquid and whose collective behavior has been proposed as a physical mechanism for topological order (order in the zero-temperature phase of matter)
Dropleton: in a quantum droplet quasiparticles (particles where complex interferences make it behave as it has a different mass) behave like a liquid. The dropleton is made from a collection of electrons and holes inside a semiconductor. Even though they have a lifespan of 25 picoseconds (1 picosecond is 1 trillionth of a second) they remain stable enough to be studied.
Time crystal: In this crystalline structure the particles are in the lowest energy state where the particles are in repetitive motion. The system can’t lose energy as the particles are already in the lowest state. So, the particles here are in a constant state of motion without losing energy, so movement without kinetic energy, which seems impossible but due to quantum mechanics this movement is possible. These crystals are being proposed to be used as qubits due to their stable state.
Rydberg polaron: created at low temperatures, this state exists out of a combination of a BEC and Rydberg atoms (atoms where the electrons are excited to the highest state). Because of the Rydberg atoms other atoms can be placed in between the free space between the nucleus and electrons. The bond between the Rydberg atom and the atoms inside it is called the Rydberg polaron. Like in a BEC, the polaron stops behaving like individual atoms but as one massive particle, with a larger mass than the atoms occupying it.
Now that we have talked about the low energy states, we have 3 very high energy states left to talk about, but only one state is known, and the other ones are just theories.
Quark-gluon plasma: to understand this experimental state of matter we first must know what a quark and a gluon are. A quark is an elementary particle that when combined with other quarks can create fundamental particles like neutrons and protons. Gluons act as an exchange particle between the strong force of the quarks, exchange particles tell other particles what forces work on them. Now we know what quarks and gluons we can now talk about the state. QGP was found in the entire universe before matter was created at extreme high temperatures and pressure and existed for the first 20 to 30 microseconds after the Big Bang.
Well now for the last 2, they are speculated to be found just after the Big Bang, when the four forces of nature, the weak, strong, gravitational, and electromagnetic forces, where combined into one super force. For the other state the gravitational force supposedly had branched off, leaving the other 3 forces combined. The state of matter during these 2 time periods is unknown.
Now that we have talked about all the different kinds of matter, I want to add one more segment to this article. While not a state of matter but more a consequence of a certain state of matter, superstates can be formed. We talked about certain states in this article like superfluid and superconductor, but I’ll explain more thorough. Let’s start with a term familiar to us, a superconductor. In a superconductor the electrical resistance and magnetic flux fields are expelled from the material. A superconductor has a critical temperature where the resistance of the material drops to 0, which lets the electrons in the material float freely. An electric current through a loop of a superconducting material can persist without a power source. Superconductors work by allowing atoms to overcome their usual repulsion to each other due to their negative charges. When they overcome this repulsion they can clump together into Cooper pairs, Cooper pairs are formed in extremely low temperatures and makes the electrons get close together and even attract one another. Because of these cooper pairs the identity of these electrons become less certain and allows them to slip through crowds of atoms.
Now that we talked about superconductors we can move on to superfluids. In a superfluid a fluid is formed with 0 viscosity (viscosity measures how easy a fluid flows over a surface, the closer to 0 the easier it flows). So, this liquids flow without resistance thus without losing kinetic energy. Superfluidity mostly occurs in the isotopes helium-3 and helium-4.
Finally, we have supersolids, it is hard to explain a supersolid because it contradicts everything we know about solids. A supersolid flows like a liquid but without any viscosity. So, it is a material whose atoms are arranged into a regular, repeating crystal structure and whose atoms can flow freely without losing kinetic energy. This state has only be made in a 2D structure and has been theorized for a long time.
Well, this was a long article, I hope that I helped you grasp the different kinds of matter and briefly summarized each one of them. If some subjects seem to abstract don’t worry, many of these require a firm understanding of quantum mechanics and can be quite challenging. But in time these concepts may seem clearer!