Learning Science is Just Being Lied to a Little Less Each Time

            I’ve said it before, now let’s put it to practice. Don’t worry, I’ll pick an easy topic… well, easy to start with. You’ll see. Let’s learn about the states of matter. This is a topic that is typically introduced by first grade. Like I said, easy. So as we all know, there are three states of matter: solids, liquids, and gasses. These have unique defining properties. Solids hold a definite shape and size, whereas liquids take the shape of their container, but still have a definite size, and gasses take on both the shape and size of their container. Still with me? Don’t worry, it gets better.

            Matter transitions between these phases as temperatures increase. As solids get warmer, they eventually melt into liquids. As liquids get warmer, they eventually boil into gasses. Conversely, cooling gasses will condense into liquids, and cooling liquids will freeze into solids. But wait, there’s more. Pressure can also influence the state of matter in the inverse manner of temperature. As pressure increases matter shifts towards solids and as it decreases it shifts towards gasses. This means that matter can transition from one phase to another even at a constant temperature.

            Now phase changes between the states are not always a linear transition from solid to liquid to gas and back. Since they are affected by both temperature and pressure, we add a second dimension into the mix. At relatively low pressures, it is possible for solids to sublime directly to gasses, and conversely at higher pressures, gasses can deposit to solids. Again, I am talking relative pressures here, they very from substance to substance, and for some, ambient pressure may be sufficiently low for sublimation.

Now water is an exception to the typical phase relationships, so forget everything I just said. Water’s freezing temperature actually decreases with increasing pressure, meaning the more pressure the colder water has to be to freeze. This is due to hydrogen bond formation disrupting the expected interactions of molecules. In fact, variations in the formation of the solid phase brought on by differing rates and conditions under which the solid is formed can lead to numerous different solid forms of the same substance. There are several different kinds of ice, for example, all comprised of pure water. This can even be observed with pure elements; think diamonds and graphite. So to say something is solid is not necessarily as straightforward as you may think. Other interesting phenomena occur with mixtures, due to the interactions between the components, including changes in the transition point, separation of the components, and combinations of two different phases, but we’ll leave that be.

            Now, what happens at high temperatures and pressures? Everything falls apart and you get supercritical fluids, effectively both a liquid and a gas at the same time. This is considered a continuous transition, in contrast to the changes previously mentioned which all had a latent thermal period; that is, where matter is either absorbing or releasing energy during its transition, but the temperature remains constant. Continuous transitions also include things like transitions between magnetic states and transitions into superconducting states.

            So there are the three states of matter. Except that there are actually four states of matter. Let’s talk about plasma. This is a classically identified, distinct phase of matter. It is characterized by the coexistence of stripped electrons and ionized particles. The net charge is typically near neutral, as there are an equal number of electrons and ions coexisting. Often the process occurs through collisions displacing electrons, and displaced electrons begetting more collisions. Plasma is ionized gas and thus cannot transition between the other states of matter directly. The degree of ionization at which a gas becomes a plasma can be up to interpretation, but physical properties differ greatly between the two. One of the key differences is potential, as plasma has very high conductance, whereas gasses have very low conductance.

Similarly to the other phases, plasma can take unique forms when produced under atypical circumstances. For example, although plasma is typically very hot (we’re talking 17,000^oF), so called ‘cold plasma’ can form where the electrons take on their typical high energy, high temperature nature, but the ions in the mix exist at near ambient temperature.

So there are the four fundamental states of matter with some of their less conventional variants. Other variants on the traditional states include glass which is a non-amorphous solid, liquid crystals which act as both liquids and solids, superfluids which have no resistance and thereby perfect fluidity, supersolids which are superfluids that maintain their shape, and even superglasses, as well as others, some of which are likely still to be discovered.

What about the non-classical states of matter? You didn’t think it was just those four? No, depending on who you ask there are seven or more states of matter. Some of the more well-known include Bose-Einstein condensate (BEC), quark-gluon plasma, and degenerate matter. A BEC occurs when temperatures approach absolute zero and matter no longer behaves as independent particles, but rather a quantum singularity. Quarks are subatomic particles held together by the strong force mediated by gluons. At very high temperatures (now we’re talking about 7,000,000,000,000^oF), energy becomes sufficient such that quark can overcome the strong force and move freely amid gluons. Degenerate matter is what happens at pressure extremes, think the center of stars. At these high pressures, particles become so compressed that matter behaves quite differently than it would otherwise be expected to. There are many flavors of degenerate matter, but it’ll probably turn out that those are just oversimplified versions of the truth too.

-AMS