Light travels faster than the speed of light?
In the past few years, scientists have found ways to make light go both faster and slower than its usual speed, but now researchers have gone one step further: pushing light into reverse. As if to defy common sense, the backward-moving pulse of light travels faster than light.
"I've had some of the world's experts scratching their heads over this one," said lead author Robert Boyd of the University of Rochester. "Theory predicted that we could send light backwards, but nobody knew if the theory would hold up or even if it could be observed in laboratory conditions."
Boyd recently showed how he can slow down a pulse of light to slower than an airplane, or speed it up faster than its breakneck pace, using exotic techniques and materials. Now, his team has taken what was once just a mathematical oddity - negative speed - and shown it working in the real world.
"It's weird stuff," Boyd said.
Reporting in the May 12 issue of Science, the researchers said they sent a burst of laser light through an optical fiber that had been laced with the element erbium. As the pulse exited the laser, they split it in two. One pulse went into the erbium fiber and the second traveled along undisturbed as a reference.
They found the peak of the pulse emerged from the other end of the fiber before the peak entered the front of the fiber, and well ahead of the peak of the reference pulse.
To find out if the pulse was truly traveling backward within the fiber, the team cut back the fiber every few inches and re-measured the pulse peaks when they exited each pared-back section. By arranging that data and playing it back in a time sequence, they were able to depict, for the first time, the pulse of light was moving backward within the fiber.
Boyd describes the reverse-traveling light pulse as the equivalent to a person's image captured by a video camera and played on a big-screen TV. When a person passes such a display in a store window, as he or she walks past the camera, the on-screen image appears on the far side of the TV. It walks toward the subject, passes in the middle, and continues moving in the opposite direction until it exits the other side of the screen.
A negative-speed pulse of light acts much the same way: As the pulse enters the material, a second pulse appears on the far end of the fiber and flows backward. The reversed pulse not only propagates backward, but also releases a forward pulse out the far end of the fiber.
In this way, the pulse that enters the front of the fiber appears out the end almost instantly, apparently traveling faster than the regular speed of light.
"I've had some of the world's experts scratching their heads over this one," said lead author Robert Boyd of the University of Rochester. "Theory predicted that we could send light backwards, but nobody knew if the theory would hold up or even if it could be observed in laboratory conditions."
Boyd recently showed how he can slow down a pulse of light to slower than an airplane, or speed it up faster than its breakneck pace, using exotic techniques and materials. Now, his team has taken what was once just a mathematical oddity - negative speed - and shown it working in the real world.
"It's weird stuff," Boyd said.
Reporting in the May 12 issue of Science, the researchers said they sent a burst of laser light through an optical fiber that had been laced with the element erbium. As the pulse exited the laser, they split it in two. One pulse went into the erbium fiber and the second traveled along undisturbed as a reference.
They found the peak of the pulse emerged from the other end of the fiber before the peak entered the front of the fiber, and well ahead of the peak of the reference pulse.
To find out if the pulse was truly traveling backward within the fiber, the team cut back the fiber every few inches and re-measured the pulse peaks when they exited each pared-back section. By arranging that data and playing it back in a time sequence, they were able to depict, for the first time, the pulse of light was moving backward within the fiber.
Boyd describes the reverse-traveling light pulse as the equivalent to a person's image captured by a video camera and played on a big-screen TV. When a person passes such a display in a store window, as he or she walks past the camera, the on-screen image appears on the far side of the TV. It walks toward the subject, passes in the middle, and continues moving in the opposite direction until it exits the other side of the screen.
A negative-speed pulse of light acts much the same way: As the pulse enters the material, a second pulse appears on the far end of the fiber and flows backward. The reversed pulse not only propagates backward, but also releases a forward pulse out the far end of the fiber.
In this way, the pulse that enters the front of the fiber appears out the end almost instantly, apparently traveling faster than the regular speed of light.
posted by The Constant Skeptic at 7:17 AM
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