Light Go Bakwards Even faster

[Diamond Cross]

In the past few years, scientists have found ways to make light go both faster and slower than its usual speed limit, but now researchers at the University of Rochester have published a paper today in Science on how they've gone one step further: pushing light into reverse. As if to defy common sense, the backward-moving pulse of light travels faster than light. Confused? You're not alone.

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"I've had some of the world's experts scratching their heads over this one," says Robert Boyd, the M. Parker Givens Professor of Optics at 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. But he's now taken what was once just a mathematical oddity—negative speed—and shown it working in the real world.

"It's weird stuff," says Boyd. "We sent a pulse through an optical fiber, and before its peak even entered the fiber, it was exiting the other end. Through experiments we were able to see that the pulse inside the fiber was actually moving backward, linking the input and output pulses."

So, wouldn't Einstein shake a finger at all these strange goings-on? After all, this seems to violate Einstein's sacred tenet that nothing can travel faster than the speed of light.

"Einstein said information can't travel faster than light, and in this case, as with all fast-light experiments, no information is truly moving faster than light," says Boyd. "The pulse of light is shaped like a hump with a peak and long leading and trailing edges. The leading edge carries with it all the information about the pulse and enters the fiber first. By the time the peak enters the fiber, the leading edge is already well ahead, exiting. From the information in that leading edge, the fiber essentially 'reconstructs' the pulse at the far end, sending one version out the fiber, and another backward toward the beginning of the fiber."

Boyd is already working on ways to see what will happen if he can design a pulse without a leading edge. Einstein says the entire faster-than-light and reverse-light phenomena will disappear. Boyd is eager to put Einstein to the test.

So How Does Light Go Backwards?

Boyd, along with Rochester graduate students George M. Gehring and Aaron Schweinsberg, and undergraduates Christopher Barsi of Manhattan College and Natalie Kostinski of the University of Michigan, sent a burst of laser light through an optical fiber that had been laced with the element erbium. As the pulse exited the laser, it was split into two. One pulse went into the erbium fiber and the second traveled along undisturbed as a reference. 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.

But to find out if the pulse was truly traveling backward within the fiber, Boyd and his students had to cut back the fiber every few inches and re-measure the pulse peaks when they exited each pared-back section of the fiber. By arranging that data and playing it back in a time sequence, Boyd was able to depict, for the first time, that the pulse of light was moving backward within the fiber.

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To understand how light's speed can be manipulated, think of a funhouse mirror that makes you look fatter. As you first walk by the mirror, you look normal, but as you pass the curved portion in the center, your reflection stretches, with the far edge seeming to leap ahead of you (the reference walker) for a moment. In the same way, a pulse of light fired through special materials moves at normal speed until it hits the substance, where it is stretched out to reach and exit the material's other side [See "fast light" animation].

Conversely, if the funhouse mirror were the kind that made you look skinny, your reflection would appear to suddenly squish together, with the leading edge of your reflection slowing as you passed the curved section. Similarly, a light pulse can be made to contract and slow inside a material, exiting the other side much later than it naturally would [See "slow light" animation].

To visualize Boyd's reverse-traveling light pulse, replace the mirror with a big-screen TV and video camera. As you may have noticed when passing such a display in an electronics store window, as you walk past the camera, your on-screen image appears on the far side of the TV. It walks toward you, passes you 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 it 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. To use the TV analogy again—it's as if you walked by the shop window, saw your image stepping toward you from the opposite edge of the TV screen, and that TV image of you created a clone at that far edge, walking in the same direction as you, several paces ahead [See "backward light" animation].

"I know this all sounds weird, but this is the way the world works," says Boyd.

Source: University of Rochester, by Jonathan Sherwood

Light's Most Exotic Trick Yet So Fast it Goes Backwards



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[mididoctors]

phase

the "peaks" are not a group of waves traveling in space but the observations on a STATIC material (the fibre) being observed..

this is the same as the spinning beam arc phase stuff...

there is no faster than light motion.. the peak is a different observation from moment to moment

if i look at ship traveling across my field of view i can see parts of the ship facing me at the same time.. i do not conclude information travels instantaneously from one end of the ship to the other.

MISLEADING ARTICLE

Boris
London

[Diamond Cross]

Considering he observed the effects in a laboratory under controlled conditions, using exotic materials, sorry try again. You're the onbe being misleading.

[mididoctors]

Originally Posted by Diamond Cross

Considering he observed the effects in a laboratory under controlled conditions, using exotic materials, sorry try again. You're the onbe being misleading.

http://en.wikipedia.org/wiki/Group_velocity

group velocity is the sped of a thing or collection of things with a single frame of reference

http://en.wikipedia.org/wiki/Phase_velocity

Phase velocity of a "wave" is not a measure of the speed of a thing but the OBSERVATION of things on other things

There you go

his observations can be correct in one sense and not the other

Boris
London

[Diamond Cross]

None of that matters. It does not discount the laboratory results with the use of exotic materials that have been recorded. Stop beiong dogmatic and look at the laboratory results.

Here's the deal.

Do the exact same experiments and you'll be able to see for yourself. And keep an open mind.

[mididoctors]

Originally Posted by Diamond Cross

None of that matters. It does not discount the laboratory results with the use of exotic materials that have been recorded. Stop beiong dogmatic and look at the laboratory results.

Here's the deal.

Do the exact same experiments and you'll be able to see for yourself. And keep an open mind.

The observations are not only NOT incompatible with phase velocity observations but the EXPERIMENTER in your link agrees that they are.

"Einstein said information can't travel faster than light, and in this case, as with all fast-light experiments, no information is truly moving faster than light," says Boyd.

Boris
london

[Diamond Cross]

You're still being misleading. They were conducted under laboratory conditions and happened. Keep an open mind. Stop being dogmatic and move on.

You haven't debunked them at all.

"I know this all sounds weird, but this is the way the world works," says Boyd. In relation to the experiments he did and observed in the laboratory.

Something you obviously fail to understand.

In a lab he broke the speed of light by having it go backwards. In a lab he's been able to modify the speed of light using exotic materials.

While it's wise to be skeptical, there is a difference between being a skeptic and a debunker. A debunker refuses to believe the evidence at hand even if it bit him on the ass while a skeptic would admit to the conclusions the evidence supports.

And that ev idence supported measurable effects in a laboratory under observable considtions.

It's easy to dismiss something when one's not even there.

[AVengeance]

There is alot of bad wording in the article, and it is misleading.

Aside from that, if you mess with the "fact" that speed of light is a constant, there are a number of theories darkness gets cast on (pun intended), like the age of the Earth. Can't mess with evolution, or we'll be back in the Bible-thumpin' stone ages!

[Diamond Cross]

Except the speed of light is not a constant, it is affected by gravity, and is slowed down by gravity.

[WickedLou9]

Originally Posted by Diamond Cross

Except the speed of light is not a constant, it is affected by gravity, and is slowed down by gravity.

No it's not. Gravity is not fully understood however it is believed that gravity is a warping of spacetime itself, the light is merely following the curvature of space. The speed of light is constant for all observers. This is not hte first scientific exercise that purports to show some sort of faster than light phenomonon. It's an illusion. Nothing is actually being transmitted or moved faster than light.