Saturday, August 21, 2010

A Different Universe: Robert B. Laughlin

Robert B. Laughlin's A Different Universe is full of interesting ideas without being a coherent narrative on a single theme. In the preface Laughlin explains that the book is an attempt to address the inherent tensions between reductionism and emergence. In particular, he (not very coherently) tries to argue that it's sometimes more useful to think of physical law as emerging from the interactions of particles rather than causing them. And he constantly interrupts his discussions of physics at various levels in order to tell anecdotes. Sometimes he seems to have chosen the topics in order to be able to either drop names (unusual for a Nobel laureate) or impugn the motives of people he's worked with.

Still, there are several fascinating examples of scientific phenomena that are well established, but for which there aren't good explanations that are integrated into the main texture of our understanding of physical law. I suspect that several good reputations could be made by physics grad students by latching onto one of Laughlin's stray thoughts and developing an explanation that fits the effect into the mainstream. One example is the phonon effect:

Suppose, for example, a sound transducer is attached to a solid and turned on, thus beaming sound into the solid, and then reduced in intensity to make the amount of sound small. A sound receiver on the other side of the solid detects not a faint tone but sharp pulses of energy arriving at random times. This quantized transmission of pulses evolves into the more familiar transmission of tone when the intensity is increased—an everyday example of the emergence of Newtonian reality out of quantum mechanics, But at low intensities this emergence does not occur, and the conclusion becomes inescapable that particles of sound exist, even though they do not exist when the solid is disassembled into atoms.

Laughlin calls this "The closest thing to real magic I know."

His discussion of symmetry (pp 124-5), and why it makes more sense to think of it as caused by the interactions between particles at various scales rather than as a set of rules that enforces their behavior is similarly tantalizing and brief.

He points out ways in which the physics mainstream is sweeping some problems under the rug, but doesn't truly resolve the issue. "If Einstein were alive today, he would be horrified at this state of affairs. He would upbraid the profession for allowing this mess to develop and fly into a blind rage over the transformation of his beautiful creations into ideologies and the resulting proliferation of logical inconsistencies. Einstein was an artist and a scholar but above all a revolutionary."

In chapter 13, "Principles of Life", near the end of the book, Laughlin spends several pages explaining that life is a mass phenomenon, and that collections of large numbers of parts act differently than you'd predict by analyzing the parts themselves. Rigidity, for example, is an important aspect of explaining how molecules get together to build living creatures, and it is only a coherent concept once you get into realms where the behavior of individual particles doesn't matter in detail. Similarly, proteins are enormous structures if you're trying to figure out how the behavior of atoms contribute to their effects, but if you deal with the atoms statistically, and as a mass, you can make more headway. Early in the book he had pointed out that "The only way one can start out from wrong principals and get the right answer is if the property one is calculating is robustly insensitive to details, i.e. is emergent. Thus the lesson from superconductivity is actually not that quantum field theory is a superior computational technology but that quantum fields can themselves emerge."

I'll end with Laughlin's summary of the (wine-fueled) conclusions of an interdisciplinary workshop on emergence:

Emergence means complex organizational structure growing out of simple rules. Emergence mans stable inevitability in the way certain things are. Emergence means unpredictability, in the sense of small events causing great and qualitative changes in larger ones. Emergence means the fundamental impossibility of control.

He manages to tie emergence in with some complex effects but leaves us with nothing more than a recognition that we don't understand what's going on yet.

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