Summary: If zooming beyond the local speed limit is punishable by law, then some scientists may have a gargantuan speeding ticket to pay. In a controversial experiment reported in this week’s journal Nature, scientists at the NEC Research Institute in Princeton, New Jersey claim to have broken the ultimate speed limit -- the speed of light. Though hotly contested, some say this achievement could dramatically increase the speeds at which we can send and receive information.
If zooming beyond the local speed limit is punishable by law, then some scientists may have a gargantuan speeding ticket to pay.
In a controversial experiment reported in this week’s journal Nature, scientists at the NEC Research Institute in Princeton, New Jersey claim to have broken the ultimate speed limit -- the speed of light. Though hotly contested, some say this achievement could dramatically increase the speeds at which we can send and receive information.
Taught in physics classes the world over, Albert Einstein’s theory of special relativity holds that no object or information can move faster than the speed of light in a vacuum, or 186,000 miles (300,000 kilometers) per second. But NEC’s Lijun Wang says he created an experiment in which a light beam raced through a gas-filled chamber so quickly, it exceeded the speed of light by a factor of 300. What’s more, the light pulse appears to have left the confines of the chamber before it even entered – a seemingly impossible occurrence according to theories of causality, which predict that causes must always precede their effects.
"It sounds crazy, but this can actually occur," said Raymond Chiao, a physicist at the University of California at Berkeley. Chiao, one of a group of researchers who have been working to break the speed-of-light limit, explained that although a common object such as a baseball could never be flung faster than the speed of light, pulses of energy with certain complex properties have been known to bend the rules.
In fact, several recent experiments, including one done by Chiao earlier this year, have pointed to energy pulses zooming faster than light speed. Yet each of these experiments has been encumbered by severe limitations on measurement or observation of the energy pulses. In contrast, this latest experiment is being touted by some as the most dramatic example yet of light breaking its own speed barrier.
"The effects are much larger and more spectacular" than previous observations, said Chiao.
In Wang’s experiment, a pulse of light passed through a small chamber filled with atoms of elemental cesium. A light beam traveling through such a medium has two different velocities – a velocity for the individual light waves in the beam and a group velocity for the entire beam. Oddly, some light waves in the beam can actually travel backward for miniscule amounts of time, creating a sort of "tail" behind forward-moving waves. As such, a light wave and its tail can leave the gas cavity at different times, creating the effect that the light beam has left the cavity before it’s even entered.
Confused? You’re not alone. In fact, even scientists who are familiar with this area of study are unsure about the details of Wang’s experiment. And many scientists said the experiment’s results are still open to interpretation.
William Happer, a physicist at Princeton University argued that several specific problems exist with the experiment, including the fact that pulses get distorted when passed through any media other than a vacuum, or empty space. In addition, he said Wang and his colleagues performed the experiment in a way that doesn’t tell the whole story, and that it can be interpreted incorrectly. "This is anything but dramatic," said Happer. "If you look at the data, there’s essentially no evidence that [the beam] is going faster than the speed of light."
What’s more, most scientists agree that even if such a beam can be proved speedier than light, it would probably not be able to carry any information. Such a feat could conceivably allow data to be sent back in time, thus violating laws of causality and sending quantum physics into disrepair.
Others are more optimistic as to the possible benefits of Wang’s experiment. "For some applications, for example, to computer circuits, this might be very important and useful," said Chiao.