7 Chapter 1: Introduction measurements of nonperturbative quantities computed on the lattice and finds agreement to data to within statistical and systematic errors of 3% or less. (a) (b) Figure 1.2: (a) Heavy quark potential at T = 0 from LQCD calculations in [61]. The lattice results are well approximated by the Cornell potential, V ( r ) = − α/r + r . Figure adapted from [62]. (b) Lattice QCD results divided by experimental data for a range of nonperturbative quantities; the values agree to within statistical and systematic errors of 3% or less. Figure adapted from [63]. To resolve the Pauli problem mentioned earlier one needs at least three colors; several measurements demonstrate that Nature in fact uses no more than three (for a review see [64] and [65]). The ratio of the cross sections, σ ( e $^{+}$e − → hadrons) /σ ( e $^{+}$e − → µ $^{+}$µ $^{−}$) = N$_{c}$ $^{∑}$Q 2 $_{f}$, tests both the number of colors ( N$_{c}$ ) and active flavors ( N$_{f}$ ) as a function of center of mass energy, shows that at energies above the bottom mass but below the top that N$_{c}$ = 3 and N$_{f}$ = 5; see Fig. 1.3. The decay rate of the Z 0 to hadrons compared to