Scientists like to think that true measures of our understanding are our ability to predict something, and, in experimental physics, control something. This year’s Nobel Prize in physics has been awarded to Serge Haroche and David Wineland for controlling the quantum world in ways that, not so long ago, were simply unthinkable. When I say “controlling the quantum world,” I mean controlling not just the physical motion of a single atom, but also the internal state of the atom. It is the difference between being able to set off an avalanche, and being able to control where every snowflake goes once the avalanche is in motion.