“Two of the major questions left unanswered by the Standard Model of particle physics have to do with hierarchies of mass scales. The first is the {{w|Flavour (particle physics)|flavor}} problem: what determines the masses of the {{w|quark}}s and {{w|lepton}}s, and why do they span such a large range, e.g. why is the top quark 3 × 105 times heavier than the electron? The second is the gauge hierarchy problem: why is the weak scale seventeen orders of magnitude smaller than the {{w|Planck units|Planck scale}}?”