# Why is plasma the highest “state” of matter?

As far as solid, liquid, gas, plasma go, why is plasma the highest state?

Are there any other states of matter?

• notice here I use the word "state" and not "phase" – Argus Jun 22 '12 at 1:36
• What makes you think there is a hierarchy at work here? – dmckee Jun 22 '12 at 2:00
• It seems to me there must be a stepping up in heat that causes the phase change between relative states – Argus Jun 22 '12 at 2:21
• If the question is why does plasma occur at the highest temperature then you should write that---and people will want to discuss the complexities that can arise in phase diagrams. As it stands it sounds like you've assigned some kind of worth to the states. – dmckee Jun 22 '12 at 2:42

If by highest, you mean temperature (proportional to mean kinetic energy of the particles), then the plasma state is "higher" than the other states you list.

I think that there are other "higher" states of matter. For example, when it becomes energetically favorable for protons and electrons to combine into neutrons, you get a state called "neutron degenerate matter". (By the way, have you ever read "Dragon's Egg"?)

An even "higher" state would be QCD matter, e.g., quark-gluon plasma.

• Neutron stars don't have to be particularly hot. The linear order breaks down at strong pressure--- it's a two dimensional space really. Above quark gluon plasma is baryon-number-violating higgs neutral plasma, where weak instantons are no longer suppressed by Higgs mechanism and cause lepton to quark conversion (and vice-versa). – Ron Maimon Jun 22 '12 at 0:49
• No I have not read that. Yes relative kinetics. – Argus Jun 22 '12 at 1:30

Why is plasma the highest state.

The highest state in terms of what?

There are lots and lots of states of matter. Personally, I like Bose-Einstein Condensates, but just because it's so fun to say.

Not all materials fit into the 3 classic states. Plasma is only one of many. Glass, for example, isn't really a solid, but it's not a liquid either.

Wikipedia has a nice description of the states of matter

• Glass is technically in the classical definition a liquid as if you put a cube of glass in a bowl and wait a few thousand years(depending on size of course" the glass will take the shape of its container. – Argus Jun 22 '12 at 1:44
• @Argus: That gets said a lot, but it appears to be untrue. The simplest counter example are prehistoric obsidian (i.e. naturally occurring glass) projectile points, many of which have retained their cutting edges for thousands of years. – dmckee Jun 22 '12 at 2:03
• Without being too argumentative glass can be considered a "phase" not a state in the classical sense because adding heat to sand makes glass then removing that heat does not give you sand again. – Argus Jun 22 '12 at 2:12
• That's not even wrong. – Colin K Jun 22 '12 at 2:13
• I learned that about glass in school too, but I'm pretty sure it's a myth...Wikipedia agrees ^.^ en.wikipedia.org/wiki/Glass#Glass_versus_supercooled_liquid – silvermaple Jun 22 '12 at 2:50

Well...Critical phases are characterized by the temperature where more fundamental degrees of freedom do appear. If you heat a solid, you can "melt" it to reveal its molecules, revealing firstly "liquid" and later gases...Where molecules (or atoms!) move freely. Plasmas as merely a phase where matter is so hot that electrons go free like a vegetables inside a soup, so they reveal the electrons in the atoms (fundamental or elementary so far). What is next? The next higher TEMPERATURE state is not the melting of electrons (we do know if electrons are elementary or not), but protons or more generally hadrons. Hadrons deconfine at higher temperature than atoms, indeed you will need about 10¹²K degrees to make quark-gluon plasma an reveal (melting hadrons) the inner substructure of hadrons. Well, ... The next issue would be...Something else? Yes. At least from theoretical reasons we do know additionally 2 temperatures where something "higher" happen at very very high temperature...What is it? They are two temperatures where a phase transition of higher type, as you called it, will happen:

1. The Hagedorn transition in string theory. String theory has a mysterious temperature, at which string theory is completely meaningless (at least from perturbative expansions). It is called the Hagedorn temperature and it is related to Gran Unified Theories. Around 10³⁰ K, long strings are copiously perturbatively produced, in such a way, the theory can not handle it. I would like to highlight the word PERTURBATIVELY. Anyway, even when non-perturbatively you could build up a theory, the issue relative to the Hagedorn transitions in string theory is unsolved to my current knowledge. I suppose there are experts here who could add some words about this topic.
2. The Planck transition. The Planck temperature, $10^{32}K$, is the limit of the spacetime continuum approximation (at least, again, from a naive extrapolation of known physics and coupling constants). Above the Planck temperature, a new phase should emerge, revealing the inner substructure of spacetime itself, so the spacetime quanta would be revealead just as atoms or molecules were revealed from heating solids, spacetime will reveal its quantum nature, naively, close to Planck temperature... In summary, you have at least, above quark-gluon plasma, the Hagedorn plasma (GUT) and the Planckian plasma (spacetime atoms). I am much more concerned about the Hagedorn transition because its relation to GUT, so I don't like to think about it like the planckian transition, despite the fact they could be related, I don't know what are the degrees of freedom that Hagedorn transition could reveal...I have the confidence Planckian temperature is related to a higher phase transition where atomic spacetime degrees of freedome are revealed, but I have always find myself hard to imagine to what picture (neglecting the string picture) of what Hagedorn transition is or could reveal (even if I think in elementary particles as non-fundamental as far as we do know them all at present time). Hagedorn or planckian "plasmas" (dubbed space-time foam by physicists clever than me), are only hypothetical, normal plasmas and quark-gluon plasmas have been showed to exist. But if you allow theoretical plasmas, you will have (or your descendants!) Hagedorn plasmas and/or planckian plasmas (space-time foam, though, I have never heard about the name planckian plasma in all my life but I think it would be a plasma like thing...If someday we produce them!).

Final note: if electrons or quarks were indeed bound states by some hyperforce, of preonic particles, well, they should have also a higher transition temperature.