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Comment by stephengillie | Hacker News Reader

So this color-glass condensate is a very-high-energy type of matter. It goes on the list with:

  Solid
  Liquid
  Gas
  Plasma
  Glass
  Crystal
  Superfluid
  Supersolid
  Superglass
  Dark

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At some point it becomes silly to keep adding 'phases of matter'. And if you want to be exhaustive, don't forget the other oddball types: the high-density states like neutronium, the high-energy states like quark-gluon plasma, etc.

You've got a good point, and there's lots of exotic types and in-betweens on Wikipedia which I didn't list. My list was to point out that we've named more than the 3 classical states of matter.

Dark matter doesn't belong on that list.

Why not? Because the energy of which it's composed doesn't interact with photons?

I was under the impression that the term "dark matter" was a stand-in term for something unknown that seems to contradict what we know about how gravity works at large distances.

Cosmologists will tell you more but it doesn't contradict how gravity works at large distances at all - we just see gravity working on something in a familiar way and don't know quite what it is.

Actually, I think, we take it as if it's the gravity we know at work. We deduce the distribution of dark matter using the premise that dark matter is governed by the same gravity law.

If the distribution is actually different or if there's something entirely different, but with the same observable effect, then...

No, because if nothing else we don't actually know what it's composed of. It's entirely possible that it will turn out to be a new family of particles, for example.

But more to the point, dark matter is certainly not made up of quarks and/or electrons (because it doesn't interact electromagnetically), so shoehorning it into a list of phases of "normal" matter is misleading at best, if not simply wrong.

A phase/state is usually tied to structure and/or energy of matter. Dark matter is the blanket term we give to particles that interact (observably) through gravitational forces.

In general, cosmology is concerned with the quantification and characteristics of dark matter through observation, so a cosmologist is likely to mean the congregation of dark matter in the universe. Particle physicists are generally concerned with direct observation and characteristics through experiment.

I don't know who messed with the wikipedia article on state of matter, but they're wrong.

Coincidentally that's also next year's Pokemon game title list

Since when is glass (I assume we mean soda-lime glass) a separate phase of matter?

My impression was that it was a solid, and that the myth that it's a highly viscous liquid was based off of incorrect analysis of stained glass windows, etc. that were more likely explained by imperfections in the production process.

"Phases" are poorly defined. They exist wherever there's a statistical mechanics reason to define them, and they make sense only within the limits of the approximations on which they are based. Glass is "solid" to a mechanical engineer (in most regimes), but it's not a crystal and doesn't behave like one to a solid state physicist. Likewise "plasma" is a great tool to describe a fluorescent light bulb or lightning bolt, but not so much a white dwarf. Even stuff you think you understand, like "liquid and gas are clearly different" turns out to be wrong (http://en.wikipedia.org/wiki/Supercritical_fluid).

My impression was also incorrect. Wiki says it's an "amorphous solid" aka one that doesn't form into crystals.

https://en.wikipedia.org/wiki/Glass

There's also Amorphous Ice, which is arranged in a "glass-like" form: https://en.wikipedia.org/wiki/Amorphous_ice

Dark matter is still a hypothesis.

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