Illustration: Alan Stonebraker

Figure 1: Schematic plot of the typical momentum distribution $n(k)$ of a fermion gas with short-range interactions, showing the characteristic behavior of $n(k)$ approaching a constant value below unity at $k→0$ and exhibiting a rapid variation near the Fermi wave vector $kF$ (that would be a sharp discontinuity at $T→0$ for a Fermi liquid). At asymptotically large $k$, as shown theoretically by Tan and confirmed experimentally by Stewart et al., one has $n(k)∼C/k4$ (characterizing the fermions as they undergo collisions, seen in the inset), with the contact $C$ governing thermodynamic quantities like the total energy of the gas.