0.01 0.1 0.1 1 10 . Dipole moment (Debye) T/(T $_{2}$n) ( 10 $_{-5}$cm $_{3}$s $_{-1}$K-1 ) FIG. 3: Normalized fractional heating rate ˙ T $_{T}$/ ( T n ) as a function of dipole moment. The heating rate is extracted using a linear fit to the initial temperature increase and is then normalized by the initial density and temperature of the ensemble. The line is the expected heating rate given by ˙ T / ( T $^{2}$n ) = ( β/T ) / 12 (see text). Typical initial conditions for these data are n = 0 . 3 · 10 $^{12}$/ cm 3 and T = 0 . 5 µ K, and the absolute heating rate ranges from 0 . 1 µ K / s at zero electric field to 2 µ K / s at our largest electric fields. the particles removed by inelastic collisions have, on average, lower energies than typical particles in the gas. One way to understand this heating mechanism is simply to note that inelastic collisions preferentially remove particles from the center of the trap where the number density is the highest, and where the particles have the lowest potential energy from the trap. We also include in our calculations a competing “cooling”effect that comes from the fact that the p -wave inelastic collision rate increases linearly with the collision energy. Including these two competing effects, we obtain ˙ T/ ( T $^{2}$n ) = ( β/T ) / 12 (see Supplementary Information). Remarkably, this simple prediction, Fig. 3 (solid line), using the β/T values from the fit to our loss rate data in Fig. 1 with no additional free parameter, agrees very well with the independently measured heating rates for the molecule gas. The anisotropy of the dipole-dipole interaction is directly revealed in an anisotropic dis- tribution of molecules in the trap. The average energy per particle, which we measure from the expansion of the gas following a sudden release from the trap, can be different in the 8