Particle physics is to physics what big game hunting is to field biology. While theoretical physicists pore over their mathematical models, particle physicists are out in the brush with their pith helmets and shotguns, speaking softly, carrying big accelerators and blowing stuff up real good.
Five challenges still facing physics:
1) Combine general relativity and quantum theory into a single complete theory
2) Resolve the problem of observer-dependence in quantum theory
3) Determine whether the particles and forces in quantum theory can be unified
4) Explain how the constants in the standard model of particle physics are chosen by nature
5) Explain dark matter and dark energy