When Light Was Slowed to a Bicycle’s Speed What happens when humans force light to crawl instead of race? In 1999, physicists achieved something that sounds impossible: they slowed a pulse of light to just 17 metres per second — about the speed of a bicycle. The breakthrough was led by Lene Hau and her team at Harvard University, using a Bose–Einstein condensate — an ultra-cold cloud of atoms chilled to a fraction of a degree above absolute zero. Inside this strange quantum state, atoms act as a

Absolute Convergence, Conditional Convergence, and Divergence