There are three states of matter
The core idea stands, but key numbers or details have changed.
TaughtSolid, liquid, gas. Water is the example: ice, water, steam.
NowPlasma is the fourth and by far the most common state in the universe. Bose-Einstein condensate, predicted in 1924, was finally created in a laboratory in 1995, and other exotic states exist.
What actually happened
Plasma should have been in your textbook regardless of when you graduated, because it is what stars are made of, and stars are most of the visible matter in the universe. Ionized gas behaves differently enough from neutral gas, conducting electricity and responding to magnetic fields, to deserve its own category. It is also in every fluorescent tube and lightning bolt.
Bose-Einstein condensate is the genuinely new one. Satyendra Nath Bose and Einstein predicted in 1924 that if you cooled certain atoms close enough to absolute zero, they would collapse into a single quantum state and behave as one entity. Doing it required cooling rubidium to about 170 nanokelvin, colder than anywhere in nature. Eric Cornell, Carl Wieman, and Wolfgang Ketterle managed it in 1995 and shared the 2001 Nobel Prize. Depending on how strictly you count, physicists also work with degenerate matter, quark-gluon plasma, superfluids, and supersolids. Three is a starting point, not a list.
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Sources
- The Nobel Prize in Physics 2001nobelprize.org
- NIST: Bose-Einstein condensatenist.gov
Who was taught this
Still standard through 2005, so anyone who finished school between 1950 and 1995 learned the earlier version.