Philip Anderson received the Nobel Prize in Physics in 1977 for his study of the effects of perturbations in solids
EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / Science Source
By Adrian ChoMar. 30, 2020, 6:25 p.m.
Philip Anderson, the theoretical physicist whose ideas reshaped condensed matter physics and extended to other fields, died yesterday in Princeton, New Jersey. He was 96 years old. Anderson had spent the past 45 years at Princeton University, a statement confirmed his death in a statement.
Powerful and combative, Anderson made contributions that rival those of the famous American theorist Richard Feynman, who died in 1988, says Michael Norman, theoretician at Argonne National Laboratory: “Phil was a true giant in physics, one of the greatest of all time.”
Anderson established himself in the 1950s by showing how perturbations in the arrangement of atoms in a crystal can trap otherwise free-flowing electrons in a specific location, a quantum effect called Anderson localization, for which he won the 1977 Nobel Prize in Physics. The phenomenon is much deeper than it sounds because the electron’s quantum wave has to overlap and perturb itself in order for it not to propagate.
Around the same time, Anderson was deciphering materials known as antiferromagnets, which make a strange reef for more common magnetic materials known as ferromagnets. In a ferromagnet like iron, all of the atoms act like tiny magnets, all pointing in the same direction to magnetize all of the material. In an antiferromagnet like chromium, adjacent atoms point in opposite directions to form an up-down-up-down pattern.
At the time, this pattern annoyed physicists. This was because, according to very general quantum principles, they could not imagine any interaction between the magnetic atoms that would have the correct symmetry to create this pattern. However, Anderson used a concept called spontaneous symmetry breaking to argue that this point was irrelevant. He showed that a material could have a lowest energy ground state that exhibits the pattern, even if the interactions don’t explicitly encode it. Essentially, the symmetry of the interaction is broken by the ground state.
In the early 1960s, Anderson used the concept of spontaneous symmetry breaking to explain why a superconductor – a material that, when adequately cooled close to absolute zero – carries electricity without resistance – emits a magnetic field. He showed that a photon would become massive in a superconductor. Just a year later, the British theorist Peter Higgs concretized this idea in a theory that ultimately became the particle theorists’ explanation of how all fundamental particles get their mass from interactions with the vacuum. (Yes, the theory assumes that the vacuum is like the inside of the superconductor in a very abstract way.) So Anderson was only a few steps away from inventing the Higgs mechanism and its associated particle, the Higgs boson, says Piers Coleman, theorist at Rutgers University in New Brunswick.
Anderson later claimed to have solved another mystery: high temperature superconductors. In the late 1980s, experimenters discovered a class of complex materials, including copper and oxygen, that can superconduct at temperatures well above those predicted by conventional superconductivity theory. Anderson quickly proposed his own theory, called the resonance-valence bond theory (RVB), which explained the phenomenon. Others, however, found the idea unconvincing – a prominent theorist joked that RVB stands for “pretty vague bullshit” – and that the riddle of high-temperature superconductivity remains unsolved to this day. However, the RVB theory proved essential for studying exotic magnetic effects in solid materials known as spin fluids.
Although Anderson’s efforts spanned many areas, they shared a common conceptual foundation, says Coleman. In the mid-twentieth century, many physicists took an extremely reductionist approach, which assumed that a problem was solved after the most fundamental component of a system had been identified and their interactions had been characterized. This is an example of particle physics. In contrast, Anderson explained the concept of origination, which stated that as any system grew in size, new phenomena such as antiferromagnetism and superconductivity could arise that could not be predicted from the fundamental interactions. “You have to see that he made these enormous scientific contributions, but also this philosophical point of view that was enormously powerful,” says Coleman.
During his long career, Anderson gained a reputation for being combative and at times personalizing scientific disputes. “He wasn’t afraid of a fight even if he was wrong,” says Norman. This approach likely emerged from Anderson’s years at the famous Bell Labs, where Anderson worked from 1949 to 1984, and where a culture of brutal honesty and willingness to fight reigned. Norman recalls a particularly sharp barb that Anderson threw one night. “We went to dinner and someone made the mistake of asking Phil what he thought of his theory,” says Norman. “Phil just looked at him and said, ‘Not much.'”
But Anderson was also kind to his students and staff, says Coleman, who was Anderson’s graduate student from 1980 to 1984. “He was very nice to his students and was very committed to them.”
* Clarification, April 1st, 4:15 p.m .: This story has been updated to reflect that the RVB theory played a fundamental role in the study of exotic magnetic materials.