Light Gets Heavy in the Physics Lab

Once upon a time, nothing traveled faster than the speed of light. These days, all you need is a briskly moving car -- a Danish physicist and her team have found a way to slow light down from speed of 186,171 miles a second to 38 miles an hour. In an experiment published in Thursday's issue of Nature, Dr. Lene Vestergaard Hau has created the atomic equivalent of molasses in January by cooling a gas to just 50 billionths of a degree above absolute zero (a theoretical temperature, minus 273.15 degrees Celsius, which can never actually be reached). With the help of some quantum mechanical theory, the atoms, nearly immobile at such cold temperatures, become "sticky" and cluster together -- making it impossible for the light beam to get through with its usual Einsteinian haste.

Next question: Why? Dr. Hau's new power over light could be applied to optical computers, which would use friction-free photons instead of the electrons and silicon in use today. Then there's ultra-sensitive night vision glasses, ultra-bright laser projectors, or just about anything where light needs to be harnessed. Those applications for the breakthrough methodology are at least a decade away -- but until then, consider the theoretical niftiness. If you could peer through Dr. Hau's device and point it at a clock, you'd be looking back in time. And Dr. Hau is just getting warmed up: The team has plans to slow things down even further, to just 120 feet per hour. At that rate, you could get the milk out of the fridge before you saw the light come on.