"The behavior of large and complex aggregates of elementary particles, it turns out, is not to be understood in terms of a simple extrapolation of a few particles. Instead, at each level of complexity entirely new properties appear, and the understanding of the new behaviors requires research which I think is as fundamental in its nature as any other."

“My Harvard classmate, Thomas S. Kuhn wrote, some years ago, an influential book about scientific revolutions. Fortunately, many scientific revolutions do not follow his scenario, but the one he focused on, the discovery of quantum mechanics, is well described by his model, which is most valid for a revolution occurring in the central core of a mature science.”

“By symmetry we mean the existence of different viewpoints from which the system appears the same. It is only slightly overstating the case to say that physics is the study of symmetry. The first demonstration of the power of this idea may have been by Newton, who may have asked himself the question: What if the matter here in my hand obeys the same laws as that up in the sky—that is, what if space and matter are homogeneous and isotropic?”

“All I can say to the younger theorists is: don’t trust anyone over 45, except maybe me, and I’m not so sure about me.”

“... the state of a really big system does not at all have to have the symmetry of the laws which govern it; in fact, it usually has less symmetry.”

““We atheists can . . . argue that, with the modern revolution in attitudes toward homosexuals, we have become the only group that may not reveal itself in normal social discourse”.”

“I learned, practically in my cradle , that the ground state wave function of a system of bosons should necessarily be real and positive, a fact which made his early Monte Carlo simulations infinitely easier.”