Wednesday, September 29, 2010
Reductionism, emergence, and Sean Carroll
In the last couple of weeks, Sean Carroll has made two separate posts (here and here) on his widely read Cosmic Variance blog at Discover magazine, in which he points out, in a celebratory tone, that we fully understand the laws of physics that govern the everyday world. In a reductionist sense, he's right, in that nonrelativistic quantum mechanics + electricity and magnetism (+ quantum electrodynamics and a little special relativity) are the basic rules underlying chemistry, biology, solid state physics, etc. This is not a particularly new observation. Fifteen years ago, when I was a grad student at Stanford, Bob Laughlin was making the same comments, but for a different reason: to point out that this reductionist picture is in many ways hollow. I think that Sean gets this, but the way he has addressed this topic, twice, really makes me wonder whether he believes it, since beneath all of the talk about how impressive it is that humanity has this much understanding, lurks the implication that all the rest of non-high energy physics (or non-cosmology) is somehow just detail work that isn't getting at profound, fundamental questions. The emergence of rich, complex, often genuinely "new" physics out of systems that obey comparatively simple underlying rules is the whole point of condensed matter these days. For example, the emergence, in 2d electronic systems in semiconductors, of low energy excitations that have fractional charge and obey non-Abelian statistics, is not just a detail - it's really wild stuff, and has profound connections to fundamental physics. So while Sean is right, and we should be proud as a species of how much we've learned, not everything deep comes out of reductionism, and some fraction of physicists need to stop acting like it does.
Posted by Douglas Natelson at 9:39 PM