"Now, what we need is clever people that are not afraid of thinking deep, of getting their hands dirty, and of tackling great problems. If you feel like giving it a try and you meet some headwind howling that "everything is understood", that "understanding is not our job", or that it is "impossible" or "too difficult", if some colleagues tell you that "physics does not deal with whys", that "understanding is just being Newtonian" or that "Thou shall not philosophize", if they throw invented norms to you, or if weaknesses and career prospects enter the discussion when the debate gets all heated up... you can always answer "Shut up and let me think!" —and get back to work."

"Quantum field theory is the basic tool to understand the physics of the elementary constituents of matter. … It is both a very powerful and a very precise framework: using it we can describe physical processes in a range of energies going from the few millions electrovolts typical of nuclear physics to the thousands of billions of the Large Hadron Collider (LHC). And all this with astonishing precision."

"In spite of the impressive success of quantum mechanics in describing atomic physics, it was immediately clear after its formulation that its relativistic extension was not free of difficulties."

"If Dirac’s idea restores the stability of the spectrum by introducing a stable vacuum where all negative energy states are occupied, the so-called Dirac sea, it also leads directly to the conclusion that a single-particle interpretation of the Dirac equation is not possible."

"In 1929 Oskar Klein stumbled into an apparent paradox when trying to describe the scattering of a relativistic electron by a square potential using Dirac’s wave equation. … In order to capture the essence of the problem without entering into unnecessary complication we will study Klein’s paradox in the context of the Klein– Gordon equation."

"If you made a short visit to CERN's Theory Division you might think that you are in a zoo. But that is not entirely right. True enough, you will find women and men of dozens of nationalities, cultures, languages and what not... some of them may even look like ET. But what these people are doing is what defines our species in its ensemble: asking, and sometimes answering, some of the deepest questions. Thus the zoo is more like a circus of magicians, in which the performers — uncharacteristically — would insist in showing you their cards... and the entrance is free!"

"Science is what we do when we don't know what we're doing."

"What is important is to invent something last, not first."

"The relation between experimentalists and theorists is often one of healthy competition for truth and less healthy competition for fame."