George Whitesides

Harvard University

Department of Chemistry and Chemical Biology

Simplicity of Condensed Matter

Condensed matter physics has an unequalled ability to uncover the underlying simplicities in systems, and to represent this simplicity mathematically. It has successfully examined many such systems, and it does not presently find itself faced with as many new, important, unexplored systems that require its attentions as might be ideal. While physics has a wonderful capacity to analyze established systems, it does not have an equal ability to invent (or synthesize, or discover) new systems, or to deal with systems in which the interest lies in their intrinsic complexity. Some of the new problems that most deserve attention are those that require a new style.

Complexity.

Many of the most interesting problems in science and engineering involve complex systems. These problems come in every discipline: from simple problems in condensed matter—the behavior of collections of bubbles (an interest of ours)—through biology, to economics and the social sciences. Whether there is a common set of problems and techniques in complexity, and whether the key discipline in their examination is physics (or applied mathematics, or some other area(s)) remains to be established. Some problems in complexity—especially in biology and biochemistry—seem to come entangled in detail. Others—especially in the social sciences—have sparse and noisy data. Learning how to work with detail with these new classes of problems will either require new styles for physics, and/or greater skill in collaboration with those who know the detail.

Biology.

Biology is, in some sense, an entire field consisting of problems begging for solutions: biology has developed (and remains) a largely observational field and the opportunities to bring improved analytical methods to important problems are limitless. The problems are, however, usually ill-defined from the vantage of physics. “What is life?” and “What is intelligence?” are big problems, with many moving parts. Rethinking how to approach these sorts of problems, in a way that leaves open a broad range of possible and acceptable solutions, requires knowing the detail of the surrounding science qualitatively, or working collaboratively with someone who does. The “smaller” pieces of the problem—“How do signaling pathways work?” “What is the nature of biological information, and how does it flow in the cell?” “How do proteins recognize ligands, and how do proteins fold?” “How is metabolism controlled?” “What is the basis for the cell cycle?”—are all major problems in their own right.

Included in these problems is a need for new, physical tools for exploring the cell, tissues, and organisms at all levels of resolution, from nanoscale (functional molecular aggregates such as the ribosome and the flagellar motor) to macroscopic (metabolic change in animals). The border between the physical and the biological sciences and biomedicine is especially rich in new opportunities for measurement.

Soft Condensed Matter. We still understand very little of the properties of condensed matter. The nature of water (especially near interfaces); the basis for adhesion, friction, fracture, and wear; the basis for tribocharging; crystallization and growth of crystals—in fact, almost any of the characteristics of complex soft matter—all present interesting, unsolved problem.

Invention. Physics does not embrace invention. Most interesting, difficult new problems go through a phase in which they can be explored only qualitatively or semi-quantitatively, and the normal rigor of physics is not (yet) applicable. More enthusiasm for this type of research might generate more interesting problems for physics to work on.