Tweezing apart optical tweezers using Brownian motion

Science is a bit weird sometimes. I spend a lot of time writing about quantum mechanics, where, no matter how squirrelly your mind is, the results and explanations are never obvious. So, it comes as something of a relief to read a paper for which my response to the paper was “well, duh.” But this is a cool technique, and leaves me imagining what might be coming down the pipeline.

The experience was triggered by a recent Physical Review Letters paper, which reported on the direct measurement of the exact force-field experienced by particles in an optical trap. The focus on the paper is the discovery that optical traps are not exactly conservative—something explained below—if a lack of surprise were fatal, this paper would be deadly. But the findings, even if expected, came to light through a rather interesting technique.