Gnomes

When I asked a friend to suggest topics for this blog, she replied by email, “Would love to see a blog about gnomes,” and appended a link to a web page entitled “Physics doesn’t exist, it’s all about Gnomes.” You might have encountered the heterodox gnome theory before. The section on electricity reads:

Of course, physics does exist and it isn’t all about gnomes, but the notion that some physical phenomena arise from the collective action of tiny particles lies at the heart of many branches of physics.

In 1662 Robert Boyle published his experimental discovery that the pressure and volume of a gas are inversely proportional to each other at a fixed temperature. Seventy-six years later, Daniel Bernoulli derived the same law by assuming that gases consist of molecules (but not gnomes) whizzing about in all directions and applying Newtonian mechanics to their motion.

As a physics student, I remember my first encounter with Ludwig Boltzmann’s derivation of the entropy of gas in terms of the statistics of its constituent molecules. It felt like an epiphany!

If I’d remained an astrophysicist, I don’t think I’d have encountered further and more recent attempts to relate thermodynamic laws to the behavior of molecules. But now that I’m a science writer I see quite a few of them, especially in biological physics.

For Physics Today‘s May 2003 issue I wrote a news story about a paper by Françoise Brochard-Wyart and her colleagues. The paper tackled the problem of how pores open and close in cell membranes—or, rather, in simple stand-ins for cells called artificial vesicles.

Poking a hole in the membrane of a living cell or artificial vesicle entails forcing apart the lipids and other molecules that constitute the membrane. Line tension—the one-dimensional analogue of surface tension—resists the formation of the hole and will reseal the membrane once the poker is withdrawn.

Through experiment and theory, Brochard-Wyart and her team found that they could control the rate at which pores reseal by adding certain molecules to the solution that surrounded their artificial vesicles. What’s more, the relation between the line tension and the molecules’ concentration followed a thermodynamic law that J. Willard Gibbs had derived a century earlier.

Much of modern biology is focused on identifying the molecular origin of biological processes. When I asked Brochard-Wyart about the philosophy behind her thermodynamic approach, she reminded me that thermodynamical laws are universal: “Even less general, microscopic models must obey thermodynamics—if they are right.”