Douglas Natelson

Condensed matter physicist, not-so-occasional wiseass. Science blogging at https://nanoscale.blogspot.com . Using nanoscale tools to address open problems in condensed matter physics.

Last Notes

2025-03-08 17:00:56 GMT

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I don't think there is a lot to be gained by saying, rigidly, that there are only 3 or 4 or 7 states of matter - that the only states or phases that count are the ones where you can readily tell the difference between them with your eyes and your fingers.
There is a lot of wonder to instill here, if done correctly. How does matter pick what state to be in under given circumstances?
(I still don't see where 7 comes from either.)
(Also, how do I make long posts?)

2025-03-08 17:00:36 GMT

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We now have a much more sophisticated notion of a phase or state of matter. First, now that we can examine materials by more than just touching them, we realize that not all solids are the same and not all liquids are the same. Second, often it is possible to tune some parameter (T, P, B) and see that a system can change from one state/phase to another, sometimes with dramatic consequences.

2025-03-08 17:00:22 GMT

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Somehow, despite being made up of what we now know can be different building blocks (different kinds of atoms and molecules), those seem to be the three options in terms of (easy to detect with your basic human senses) mechanical properties.

2025-03-08 16:59:30 GMT

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I think there is certainly an interesting scicomm angle here that I've tried to touch on in my (not nearly as well read as Ethan's) writing.
Way back when people started pondering "matter" as something to study, it was easy to identify three broadly different types. Solids are dense and rigid. Liquids are dense, but they are not rigid. Gases are very dilute and are also not rigid.

2025-03-06 19:54:26 GMT

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I agree with Steve. Depending on your definition, there are a huge number of phases of matter, and I don't see anything special about seven. The usual delineation involves uniformity of properties, particular symmetries, and these days particular (electronic or other) topologies.