End of an era

One of the giants of twentieth century physics, Philip Anderson, died at the weekend, aged 96. He retired from Bell labs in the 1980s and from Princeton University maybe 20 years later, but a couple of years ago we were briefly at the same workshop at Princeton. Bell labs was where the solid state transistor — at the heart of all modern computers — was invented.

The Physics World news article is very good, it ranges from his providing inspiration to Higgs, to his somewhat curmudgeonly nature. Perhaps his best known article is very readable, it is a non-technical manifesto for the importance of emergent behaviour in science, published in 1972. It is well worth reading.

Simply speaking, his point is that laws of physics like those of Newton, are not enough to understand a lot of the phenomena we are interested in. Examples are how transistors work, how living organisms work, why water boils, why traffic jams form, …. These phenomena are all in some sense the result of the laws of physics, but that statement is just not useful. In a modern computer, it is not difficult to put some model molecules in a computer simulation, apply Newton’s Laws and see boiling. But it is also true that you could put a different set of Laws in, and still see boiling.

Boiling is just one example of what are called collective or emergent phenomena, which are phenomena that emerge when many molecules (or cars, or proteins, …) act collectively. One water molecule can never boil, a thousand or a million, or a trillion, can and does. The title of Anderson’s article is More is Different, which is just a statement of fact. Applying it to understand the world around us, was one of the most productive areas of physics, in the second half of the last century. An area that Anderson contributed as much as as anybody.

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