We are used to thinking of matter as something understandable and obvious: stone is solid, water is liquid, air is gas. But in reality, the world is much more complex. Modern physics shows that matter can exist in a huge variety of states, each of which is determined by the behavior of particles and the forces that bind them together.
The Four Classic States
In everyday life, we most often encounter four fundamental states of matter: solid, liquid, gaseous, and plasma.
- Solid state. In a solid, atoms and molecules are arranged as densely as possible and held together by strong bonds. They can only vibrate but cannot move freely. This gives solids a fixed shape and volume. Crystals are of particular interest: here, the particles are arranged in a strict order. A substance can exist in different forms, or phases. For example, ice has more than a dozen crystal structures, each of which occurs at specific temperatures and pressures. Along with this, there are amorphous solids, such as glass, where the order is disrupted.
- Liquid state. Liquids retain their volume but not their shape. Their particles are close to each other but have enough energy to move. Therefore, a liquid takes the shape of the container in which it is located. A characteristic feature of liquids is their relative incompressibility. Exceptions are rare: water, for example, behaves uniquely, expanding when it freezes.
- Gaseous state. Gases are radically different from solids and liquids. Their particles are far apart and move almost freely. Because of this, gas does not have a fixed volume and is capable of uniformly filling any space. Supercritical fluids are particularly interesting. These are states in which a substance is no longer distinguishable as a liquid or gas. For example, supercritical carbon dioxide is used in the food industry to remove caffeine from coffee beans.
- Plasma. This is sometimes referred to as the “fourth state of matter.” Essentially, it is an ionized gas containing free electrons and ions. Unlike ordinary gas, plasma actively reacts to electric and magnetic fields. Plasma can be found on Earth in the form of lightning, neon lamps, or electrical discharges, it is the dominant state of matter in the universe. Stars, including our Sun, are composed almost entirely of plasma.
These four states of matter are the most common and familiar to us. However, physics studies many other unusual intermediate states that have surprising properties.
Unusual and Exotic States
Classic states are just the tip of the iceberg. Modern physics has discovered a whole spectrum of phases that arise under extreme conditions of
temperature, pressure, or density.
- Liquid crystals. This is an intermediate state between solid and liquid. It retains some order, but the particles can move. Thanks to this duality, liquid crystals have found wide application, from displays to sensor technologies.
- Magnetic states. Sometimes internal properties play a key role. For example, magnetic moments (spins) can align themselves into specific structures, creating phenomena such as ferromagnetism (magnets in their familiar form) or antiferromagnetism.
- Superfluidity and condensates. At temperatures close to absolute zero, amazing effects appear. Bose–Einstein condensate behaves like a single “superatom,” demonstrating the properties of quantum mechanics on a macroscopic scale. Superfluid liquids can flow without friction, never stopping.
- Extremely dense matter. In the depths of neutron stars, matter is compressed to a state where atoms cease to exist in their familiar form. The nuclei are so close together that so-called neutron-degenerate matter is formed. At even higher energies, quark-gluon plasma emerges, a state that probably existed immediately after the Big Bang.
Such states are practically impossible to encounter in everyday life, but they play a huge role in theoretical physics.
Matter as an Endless Discovery
Matter is a familiar substance that holds a ton of secrets. It can show up in dozens of different forms, from everyday stuff to exotic ones that we only see in labs or deep in space.
The physics of the states of matter teaches us to see the hidden dynamics of particles, their interactions, and transitions behind familiar objects. And perhaps it is precisely this understanding of these transitions that will be the key to new technologies that will change our future.