The world’s smallest steam engine

At about 200 years from the invention of the steam engine researchers at the University of Stuttgart and Max Planck Institute for Intelligent Systems developed the world's smallest one, as they say in a news release.  

Experiment shows that an engine does work, even if it is on the microscale. It would mean that developing highly efficient small heat engines is possible.

In the heat engine invented almost 200 years ago by the Scottish Reverend Dr Robert Stirling (1790-1876), a gas-filled cylinder is periodically heated and cooled so that the gas expands and contracts. This makes a piston execute a motion with which it can drive a wheel, for example. Now, the physicists replaced the piston, which moves periodically up and down in a cylinder, by a focused laser beam whose intensity is periodically varied.

More info here.