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What are the six (or seven) states of matter?
- Starone (age 12)
New York, New York State, USA
There are literally hundreds of different states of matter, in the physicists' sense of the words. Here are some of them. You can easily search online for more details about them, once you have their names.
- Crystals (of which there are 230 distinct symmetry types)
(but note: liquids and gases are not entirely distinct, since one can be converted to the other without any abrupt change, by pressurizing above the critical point.)
- liquid crystals, including several distinct smectic and nematic types
- Bose-Einstein condensates
- fermionic condensates, including fermion superfluids and superconductors
(but note: superconductors are electronic phases in materials that are also, usually, crystals. So if we are really including them on the list we should also include ferromagnets, antiferromagnets, ...)
- crystals with incommensurate charge or spin density waves
and so forth.
The point is that the usual little lists do cover some familiar cases (at least if you're willing to lump all sorts of different crystals into the same category) but they don't cover lots of other cases. Liquid crystals, for example, are not all that obscure- I'm looking at a screen made of them right now.
(published on 05/07/11)
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