A fully degenerate, adiabatic gas with this property is modeled by the polytrope n equals three. The energy density of a universe of particles with this property scales with scale factor to the negative fourth. Degenerate electrons with this property have pressure proportional to density to the four-thirds, which occurs (10[1])near the Chandrasekhar limit. (10[1])For the first 50,000 (10[1])years after the Big Bang, the universe was dominated by particles with this property. (-5[3])Hot (-5[1])dark matter consists of particles that (10[1])had (10[1])this property in the early universe, (10[2]-5[1])like neutrinos. (10[1]-5[5])An (-5[1])alternate (10[1]-5[3])name (-5[1])for astrophysical (-5[1])jets (-5[1])indicates that they have this (10[1]-5[1])property, (10[1]-5[3])corresponding (-5[1])to a Lorentz (10[1])factor larger than (10[1]-5[1])one. (10[2]-5[8])For (10[2])10 points, (10[3]-5[1])name this property (10[1])of (-5[1])particles (10[1]-5[1])that cannot (10[1]-5[1])be described with classical (-5[1])mechanics, (10[4]-5[1])since their velocity (10[1]-5[4])is near the (10[1])speed (-5[1])of light. (10[3]0[1])■END■ (10[23]0[30])