Tetris: Played in real time with microscopic optical tweezers! The video shows 42 glass microspheres (1 μm diameter) trapped by laser beams and steered by a computer.
What is an optical tweezer? Invented by Arthur Ashkin of Bell Labs in the 80’s, this is the closest we have to a tractor beam. US Secretary of Energy Steven Chu won the 1997 Nobel for its use in trapping neutral atoms. Small dielectric objects, from beads to bacteria, can be trapped by a highly focused laser beam. The force of radiation pressure is exploited to manipulate these objects. The method is sensitive enough to measure displacements of 1 angstrom: the diameter of a H atom!
Biophysicists use optical tweezers to measure movement and force generated by single molecules such as an enzyme walking along a DNA ladder or a motor like kinesin, dragging the bead along the tracks of a microtubule. (More on single molecule biophysics in subsequent posts).