|Lene Hau and her colleagues created a new form of matter to bring a light beam to a complete stop, then restart it again. (Staff photo by Kris Snibbe)|
“Two years ago we slowed it down to 38 miles an hour; now we’ve been able to park it then bring it back up to full speed.” Lene Hau isn’t talking about a used motorbike, but about light – that ethereal, life-sustaining stuff that normally travels 93 million miles from the sun in about eight minutes.
Less than five years ago, the speed of light was considered one of the universe’s great constants. Albert Einstein theorized that light cannot travel faster than 186,282 miles per second. No one has proved him wrong, but he never said that it couldn’t go slower.
Hau, 41, a professor of physics at Harvard, admits that the famous genius would “probably be stunned” at the results of her experiments. Working at the Rowland Institute for Science, overlooking the Charles River and the gold dome of the state Capitol in Boston, she and her colleagues slowed light 20 million-fold in 1999, to an incredible 38 miles an hour. They did it by passing a beam of light through a small cloud of atoms cooled to temperatures a billion times colder than those in the spaces between stars. The atom cloud was suspended magnetically in a chamber pumped down to a vacuum 100 trillion times lower than the pressure of air in the room where you are reading this.