This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Tiny atoms and molecules are constantly bombarding each other all around us. While we regularly measure the large-scale effects of these interactions, measuring the effect of each individual collision is far more difficult.
But now, researchers have managed to measure how tiny gas particles affect a single silica particle in the lab. In their new study, published in Physical Review Letters, the team describes how they detected the momentum transfers of individual collisions of gas particles with a nanoparticle levitated in laser light. On a large scale, the billions of constant collisions in the air create what we experience as pressure.
At higher altitudes, the particles are more spread out and the pressure is weaker than at sea level. The same thing happens in liquids, resulting in increasing pressures at increasing depths. Researchers have all kinds of tools (and multiple units) for measuring pressure.
In 1827, Robert Brown noticed that grains of pollen jiggled in water under a microscope. Later work by Einstein showed that this random movement of particles suspended in a fluid was caused by constant collisions with fast-moving atoms or molecules in the surrounding medium, now referred to as "Brownian motion." Usually, the individual impacts are too small and frequent to distinguish without getting lost in background noise. The authors of the new study write, "Detection of individual gas collisions with a macroscopic mechanical system is directly relevant to ongoing experimental programs studying such systems in the quantum regime.
While many sources of decoherence can be mitigated by levitation, uncontrolled information loss due to scattering from background gas molecules remains a fundamental challenge." Much later, researchers realized that laser-trapped nanoparticles offered a way to measure these tiny collisions without interference from a supporting surface. The ability to measure the effects of these individual collisions would be useful for multiple types of research. For example, theoretical studies proposed using individual gas collisions to measure extremely low pressures.
Better detection of this motion could even help researchers measure the mass of a neutrino. In their experiment, the researchers isolated a silica sphere about 100 nanometers in diameter in a laser trap inside an ultrahigh-vacuum chamber. Then, they separately introduced three different heavy gases (krypton, xenon and sulfur hexafluoride) at controlled pressures and tracked the sphere's motion through scattered laser light.
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