A tiny glass bead hangs in a laser beam like a speck of dust in sunlight. Around it is a rarefied gas: atoms of krypton, xenon, and heavy molecules of sulfur hexafluoride. They collide with the bead, and each hit transfers a tiny impulse, like a pea thrown at a taut sheet makes it tremble.
The authors of the study recorded these shifts and reconstructed the force of each individual hit. It turned out that the frequency of hits precisely indicates how much gas is around: count the hits — know the pressure. Also, from the nature of the trembling, the temperature of the bead's surface can be determined. The faintest nudges they could detect carry an impulse of just 200 kiloelectronvolts divided by the speed of light — trillions of times less than the impulse of a flying mosquito.
Such a sensitive "nanobarometer" could become a new standard for measuring pressure in vacuum — without mercury columns or membranes, simply by counting molecular hits. And in the future, such levitating sensors could help study how particles interact with each other at the smallest distances.
If the bead were a soccer ball and the gas molecules were the size of tennis balls, then to accurately measure pressure, you'd have to count about a billion hits per second.