More is Different

An article by Philip W. Anderson.


But this 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.


The essential idea is that in the so-called N>N -> \infty limit of large systems (on our own, macroscopic scale) it is not only convenient but essential to realize that matter will undergo mathematically sharp, singular “phase transitions” to states in which the microscopic symmetries, and even the microscopic symmetries of motion, are in a sense violated.


The arrogance of the particle physicist and his intensive research may be behind us (the discoverer of the positron said “the rest is chemistry”), but we have yet to recover from that of some molecular biologists, who seem determined to try to reduce everything about the human organism to “only” chemistry, from the common cold and all mental disease to the religious instinct. Surely there are more levels of organization between human ethology and DNA than there are between DNA and quantum electrodynamics, and each level can require a whole new conceptual structure.

In closing, I offer two examples from economics of what I hope to have said. Marx said that quantitative differences become qualitative ones, but a dialogue in Paris in the 1920’s sums it up even more clearly:

FITZGERALD: The rich are different from us. HEMINGWAY: Yes, they have more money.