“A tour de force.”Under the MesoscopeConsider a gas whose particles are very spread out. Instead, you’ll model the gas using an equation that the physicists James Clerk Maxwell and Ludwig Boltzmann developed in the late 19th century. This model of the gas lets physicists study how air moves at small scales—for instance, how it might flow around a space shuttle. Physicists view these three different models of the gas’s behavior as compatible; they’re simply different lenses for understanding the same thing. But by applying his expertise to the realm of particles, he has now resolved a major open problem in mathematical physics.