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Light's Most Exotic Trick Yet: So Fast it Goes ... Backwards?
University of Rochester Press Release ^ | 5.11.06 | Jonathan Sherwood

Posted on 05/12/2006 9:27:34 AM PDT by el_chupacabra

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.

"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.

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.


TOPICS: Miscellaneous
KEYWORDS: light
I have no idea what anything in this article really means, but I thought that by posting it people might think I was smart. Have at it.
1 posted on 05/12/2006 9:27:36 AM PDT by el_chupacabra
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To: el_chupacabra

Try searching next time


2 posted on 05/12/2006 9:28:14 AM PDT by Izzy Dunne (Hello, I'm a TAGLINE virus. Please help me spread by copying me into YOUR tag line.)
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To: el_chupacabra

It means that you forgot to search before posting.


3 posted on 05/12/2006 9:28:57 AM PDT by Thrusher ("...there is no peace without victory.")
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To: el_chupacabra

Somebodys been smoking too much dope. The concept of light moving backwards is meaningless.


4 posted on 05/12/2006 9:31:14 AM PDT by tomzz
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To: el_chupacabra

my head hurts


5 posted on 05/12/2006 9:33:45 AM PDT by 4more4Bush
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To: el_chupacabra; Izzy Dunne; Thrusher
Don't let them bother you.

They are faster than light, while you and I are in reverse. ;)




6 posted on 05/12/2006 9:35:29 AM PDT by G.Mason (And what is intelligence if not the craft of outthinking our adversaries?)
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To: Izzy Dunne

Don't blame el chup. He did do a search. The other posting was later but its information was typed so fast it went backwards in time.


7 posted on 05/12/2006 9:35:43 AM PDT by far sider
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To: el_chupacabra
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.


If there is a true faster-than-light phenomenon and that phenomenon can be manipulated in a non-ambiguous fashion, then that phenomenon can be used for faster-than-light communication. Although it may be true that no "thing" can travel faster than light, it doesn't follow that there can be no faster-than-light communication because communication doesn't ultimately depend on the sending of a "thing," like a piece of mail, faster than light. It depends upon a shared symbology. So if someone can use a faster-than-light signal to send a short-short-long burst and has assigned a meaning to that phenomenon that is shared between the sender and the recipient so that when the recipient sees short-short-long he knows what the sender is trying to say, faster-than-light communication has been achieved.
8 posted on 05/12/2006 9:37:26 AM PDT by aruanan
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To: Thrusher; el_chupacabra
It means that you forgot to search before posting.

No. It means he posted before he forgot about searching.

;^)

9 posted on 05/12/2006 9:38:58 AM PDT by brityank (The more I learn about the Constitution, the more I realise this Government is UNconstitutional.)
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To: 4more4Bush

If I'm driving my truck at the speed of light, and I suddenly turn my headlights on and I throw it into reverse... Ah to hell with it.


10 posted on 05/12/2006 9:39:14 AM PDT by Shaun_MD (In God We Trust. In might we remain free.)
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Comment #11 Removed by Moderator

To: far sider

This can be proved very easily.
Put an instant breakfast in a microwave oven
and you will go back in time. LOL


12 posted on 05/12/2006 9:42:52 AM PDT by batmast
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To: far sider
"I once put instant coffee in a microwave oven and almost went back in time."
-- Steven Wright
13 posted on 05/12/2006 9:48:42 AM PDT by robertpaulsen
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To: far sider
let's use this analogy. We pay taxes and before we send in the money it's spent. It's what I would like to call reverse economics.
14 posted on 05/12/2006 9:51:51 AM PDT by street_lawyer (Conservative Defender of the Faith)
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To: Baynative

And he met Chuck Norris doing just the opposite thing.
History remained unchanged.


15 posted on 05/12/2006 9:56:15 AM PDT by Waverunner
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To: el_chupacabra

If we can calculate the speed of light, your post begs the question, "what's the speed of dark?"


16 posted on 05/12/2006 10:33:47 AM PDT by FDNYRHEROES (Always bring a liberal to a gunfight)
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To: el_chupacabra
Yeah, sorry mate, PatrickHenry already posted this one here.
17 posted on 05/12/2006 11:08:23 AM PDT by DaveLoneRanger ("You're not going crazy! You're going sane in a crazy world!" - The Tick)
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To: el_chupacabra

somebody has too much time on their hands.


18 posted on 05/12/2006 11:14:07 AM PDT by prjohnsonjr
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To: el_chupacabra

This seems very similar to a pipe that is already full of some uncompressable liquid?

Or am I nuts?


19 posted on 05/12/2006 11:16:56 AM PDT by Widdy
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To: el_chupacabra

So, if your mom hit you hard enough, she really could knock you into tomorrow.


20 posted on 05/12/2006 1:17:27 PM PDT by Defiant (I love Mexico....exactly where it is.)
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