Transitions occurring in nanoscale systems, such as a chemical reaction or the folding of a protein, are strongly affected by friction and thermal noise. Almost 80 years ago, the Dutch physicist Hendrik Kramers predicted that such transitions occur most frequently at intermediate friction, an effect known as Kramers turnover. Now, reporting in Nature Nanotechnology, a team of scientists from the ETH Zurich, ICFO in Barcelona and the University of Vienna have measured this effect for a laser-trapped particle, directly confirming Kramers’ prediction in an experiment for the first time.