On Sunday March 29, Philip W. Anderson passed away. Anderson is doubtlessly one of the greatest condensed matter physicists who ever lived.
Anderson made foundational discoveries in localization, high-temperature superconductivity and antiferromagnetism. Indeed, his achievements stretch beyond condensed matter; his work on spontaneous symmetry breaking contributed to development of the Standard Model of particle physics. I’m sure many more competent people will eulogize him (update 2020-05-04 they have), but I wanted share one specific personal connection I have to his work.
One of my favorite scientific papers is Anderson’s “More is Different” [Science, 177 393 (1972)]. It shares a rare distinction among scientific papers of being both profound, and of broad interest, even to the general public.
It also contains an important lesson in humility for physicists. We are an arrogant bunch. We tend to think of physics as the most fundamental (and therefore most important) science because we study the smallest parts of the universe. Thus, the never-ending jokes that “chemistry is just physics done in water.”
In “More is Different” Anderson articulates an excellent refutation of this reductionist approach. I quoted this article in my dissertation in arguing that condensed matter physics is no less fundamental than particle physics.
The ability to reduce everything to simple fundamental laws does not imply the ability to start from those laws and reconstruct the universe…. hierarchy does not imply that science X is “just applied Y.” At each stage entirely new laws, concepts, and generalizations are necessary, requiring inspiration and creativity to just as great a degree as in the previous one. Psychology is not applied biology, nor is biology applied chemistry. [Anderson, Science 1972]
Emergent phenomena are not merely difficult to predict from the underlying microscopic laws, but they are effectively unrelated. At the most extreme scale, no one would argue that consciousness is somehow a property of standard model particles, or that democracy is a state that could ever be described in terms of quantum field theory.
As an aside, a little fun fact about Anderson: in graduate school his labmate in van Vleck’s group was Arianna Wright (later: Rosenbluth), who would go on to Los Alamos to work on hydrogen bomb calculations and develop the Metropolis algorithm.
Rest in peace Phil! You won’t be forgotten.