Other: Bose-Einstein condensate.
It is, now. Back when we were in school it was theoretical, but never attained. But in physics it's only a matter of time till technology catches up with theory.
Predicted in the 1920s, a Bose-Einstein Condensate was not actually created in a lab until June 5, 1995 when Eric Cornell, Wolfgang Ketterle, and Carl Wieman used a combination of laser cooling (a technique which won Steven Chu, Claude Cohen-Tannoudji, Wm Phillips the 97 prize for physics: for development of methods to cool & trap atoms with laser light, “optical molasses”) and magnetic evaporative cooling to compress the velocity distribution of a cloud of approximately 2000 Rb atoms to 20 nK, lowest temperature ever achieved at that time--cold enough to form a BEC & get nobel prize.
So nowadays we don't just have five theoretical but only four practical states of matter. We really have five states of matter. My favorite is also the gas, but I voted other (BEC) for moral support.
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