Particle physics: A personal view

The reader surely knows what particle physics is about: finding building blocks of nature that appear elementary at a given time and studying their interactions - so why in the world this essay? The problem is how to arrive at a fundamental theory, and maybe even more important, what is the theory supposed to do? I follow here a simple but profound prescription of Feynman for a true, self-contained theory, and then show how the Standard Model beautifully illustrates this prescription. That the issue is not trivial is clear from the fact that we had theories dominate our field for decades, in spite of completely failing Feynman's requirements and offering no clear predictions whatsoever. I next critically review two unique candidates for a Beyond Standard Model theory: the Left-Right Symmetric theory of electro-weak interactions and the minimal grand unified theory based on SU(5) gauge symmetry. I also comment on some generic aspects of grand unification, and what hope we may have in testing it.