Eli5: What are the other states of matter aside from solid, liquid and gas and why are they not being taught in schools?
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There isn’t really universal agreement on what counts as a state of matter, but most people would agree that there are quite a lot of them, some of which are fairly obscure and difficult to understand. Kids really don’t need to know about neutron degenerate matter, for example.
The thing that is usually used to define states of matter is a phase transition. If you gradudally change one property of a substance (e.g. its temperature) and there is a certain point at which another property undergoes a sharp change (e.g. water at -0.1°C is much more rigid than water at 0.1°C), that’s called a phase transition. This definition works pretty well for most states of matter, but it leads you to some weird conclusions. For example, when molten glass cools, there doesn’t appear to be a phase transition, but surely molten glass and solid glass are two different states of matter. Similarly, at really high pressures the phase transition between liquid and gaseous water disappears. So a “state of matter” is ultimately one of those “I know it when I see it” things.
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