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

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.

About the University of Rochester

The University of Rochester (www.rochester.edu) is one of the nation's leading private universities. Located in Rochester, N.Y., the University's environment gives students exceptional opportunities for interdisciplinary study and close collaboration with faculty. Its College of Arts, Sciences, and Engineering is complemented by the Eastman School of Music, Simon School of Business, Warner School of Education, Laboratory for Laser Energetics, and Schools of Medicine and Nursing.

From University of Rochester

May 11, 2006

Comments

what is this string theory

April 2, 2009 by Anonymous, 13 weeks 1 day ago
Comment id: 35786

I want to know about the string theory which is a part of quantum phisics

theory celestial influence by rodney collin

March 15, 2009 by Anonymous, 15 weeks 5 days ago
Comment id: 35346

my direct eye observation sun with my eyes. i postulated long ago 15 years that light traveled back to its source. If we take sun as most aware intelligent being like lots old mythologies assert like japanese sun goddess, egypts aton etc. then sun knows everything light inpinges on. is it possible light is on earth stuck here due to gravitational forces onb a micro or macro scale? with my eyes i can see passively, eyes light travels into optic nerve. try sending light as force going out the eyes! active seeing where you project light n form. read book by collins who in 1947 studied all current scientific theorys combined with gurdjieff's theorys

Light (5-D particles) propogate forwards and backwards in time

March 7, 2009 by Anonymous, 16 weeks 6 days ago
Comment id: 35179

First off, the basic "Directional Space" primer. Dimensions are FINITE length measurements of an infinite spatial directional plane. Displacement is movement of an object through space. The velocity at which things move as we hit higher directional measurements is not accurately measured against "time" when we exceed 4-Directional Space as "time" is only 1 angular direction plus spin of 5-D spacetime. "Length" + "Width" + "Depth" are merely 90 degree against 90 degree perpendicular divisions of any spherical centerpoint-to-outer-surface angle and not properly "directions", merely "angular divisions" of 3-directional space.

A circle is a 2-Directional object.
One direction is the "Spin direction". A circle can be spun in place to your left or towards your right (or not at all). The velocity of the spin (if any) is variable.
The other direction is from the centerpoint of the circle to any of the infinite points toward the outside (actually infinite rim) of the circle, the "Spatial Displacement Direction". The velocity of movement (or no movement) and angle are variable.
The reason that a circle is a TWO-DIRECTIONAL object is that it can move in 2 directions at (with a differing velocity for both the "Spin" and "Displacement" the same time.

A sphere is a 3-Directional object.
One direction is the "Spin Direction" on the primary axis. The angle of spin and velocity of spin are variable (if spinning at all).
The second direction is the "Tumble Direction" (think of a spinning model globe on a pivot -- the pivot is your "Spin Direction"). The "Tumble Direction" is the angle and velocity at which you can rotate the spinning (or stationary) globe on the "Spin Direction".
The third direction is the "Displacement Direction" which exists as the centerpoint of the sphere moving (or not moving) through space toward any infinite point on the exterior of the sphere at any angle in 3D space.
All 3 Directional forms of movement and angles are independent of the others and any can be moving in unrelated angles or velocities (if moving at all).

Since the pattern is now obvious, I will just skip to the summaries of 4-D and 5-D space.
4-D = Hyper-Sphere which has one more "Displacement Angle" and "Rotational Direction" that a 3-D sphere cannot be consciously moved in because it lacks access to the proper Displacement Energy.
5-D = Quantum-Sphere which has one more "Displacement Angle" and "Rotational Direction" that a 4-D Hyper-Sphere cannot be consciously moved in because it lacks access to the proper Displacement Energy. Higher up you go, the more you add in another "Displacement Angle" and "Rotational Direction" to the routine.

What are electromagnetic fields? The "pushing" (not puncturing) of a 4-D object into our 3-D spacetime. Note that the 4-D object can be rotating at a velocity in 4-D spacetime at any 4-D angle mix giving rise to all sorts of interesting 3-D results non-standard for the average electromagnetic field.
What are gravity fields? The weak "pushing" (not puncturing) of a 5-D object into our 3-D spacetime. These big 5-D objects affect "Potentiality".

5-D particles that puncture our spacetime (but do not actually rest within it) appear as photons. Using a totally over-simplified insufficient example... think of an inflated beachball sitting upon a still indoor pool. The surface of the pool is 4-D spacetime. The beachball is a "Hyper-Photon". The point that touches the 4-D spacetime surface of the pool appears to be a 3-D photon in our spacetime.

Now let's say the beach ball is rotating in place giving the appearance of a "vibrational frequency" moving back and forth in time (AKA the "Quantum Effect"). Also note that this "Hyper-Photon" ball can rotate in 4 independent angular directions at differing velocities without actually moving in a "Displacement Direction" or moving at a "Displacement Angle".

Back to the 5-D "Beachball" example.
Now let us say in the example that the 5-D "Beachball" gets a tap from directly on top causing it to bob in place also causing the 4-D pool surface of spacetime to ripple out little fading waves of time-fluctuation. Within those ripples, time may move "sideways" or vary its rate of passing (moving faster than "1 second per second" and then slower than "1 second per second" until the 4-D displacement energy is used up and time reverts to the standard "1 second per second measurement again"). However, to our 3-D spacetime viewpoint, the 3-D photon has now become a cloud of virtual "quantum observation" photons which then move in a wavefront of "potentiality" patterns and then collapse into a single photon after observation. Interesting and weird, right?

Now here is the kicker, remember that the photon is a 3-D expression of a 5-D hyper-photon. Well, those 4-D temporal surface ripples ALSO move (4-D Displacement Energy) backwards in time and sideways in a hyper-circle (as well as weakly altering the local zone to no longer operate at standard "1 second per second" rates). That means the 3-D expression of the photon's probability location is moving weakly backwards (and sideways) in time. Oh, there's plenty more that will boggle your brains if you expand upon the "Kindergarten Friendly" DIRECTIONAL SPACETIME explanation I have listed above.

For example, matter that is too dense in our 3-D spacetime is basically piling up and pushing itself into 4-D spacetime. A black hole is not so much a 5-D pushpin, but more a 4-D lump of 3-D matter and spacetime crunched so heavy that it pushed itself into 5-D space and appears to be a "crunch-zone" for our 3-D space. Since that is "Hyper Dense" material, spreading it out over 3-D spacetime would release a huge amount of "Displacement Energy" and basic 3-D matter. Since us 3-D creatures have no intentional control over our 4-D "Displacement Angle" or 4-D "Displacement Spin" or control over any of the velocities therein, it is very difficult to do much of anything unless we think rationally in "Directional Space" terms. Oh, and some very unpleasant things are possible if moves are made thoughtlessly without accurate predictions of the outcome of those actions (AKA Hyper-Bombs blowing backwards, sideways, and in all the directions of 4-D spacetime = very human-extincting results).

All of this is pretty painfully obvious if you think about it a tad.
Note that not all elementary particle objects your are familiar with move at the rate of "1 second per second" and any given random "two atoms of Gold" are not guaranteed to be exactly identical when you view them in 4-D spacetime or 5-D spacetime. It might also amuse you to know that there are 3 "spin angle" different versions of the particle we improperly call the "Neutrino" (for reasons that should be pretty frickken' obvious if you read anything I wrote above here about "Higher up you go, the more you add in another Displacement Angle and Rotational Direction to the routine" in THREE DIRECTIONAL spacetime. Now apply that thought to the other THREE DIRECTIONAL particles (micro-toroid wormholes) the Electron, the Positron, the Neutron, and the Proton. See, a whole bunch of interesting thoughts are buzzing in your skulls now. Enjoy.

time travel

March 5, 2009 by Anonymous, 17 weeks 1 day ago
Comment id: 35118

if you were to just take light and send it through bigger things backwards in some sort of little container with a mini black hole residing in it wouldn't that prove to make time travel possible in to the future? If you were to just be able to divert the energy into a container big enough to fit a person in there wouldn't they be able to travel into time? From Robert Sribner, 14, robertscribner@rocketmail.com

I hope you use this information

Light going back in time?

April 23, 2008 by Anonymous, 1 year 10 weeks ago
Comment id: 29222

I doubt that is what is happening.. I think a better way of saying it is that some things can transcend their flat rate speed at certain points of acceleration.. However, I bet that even with acceleration building up, the speed of light is so fast, that by the time you can see it hit a certain point, the flat speed of light has already passed that spot. However, the light created at the point of acceleration still takes time to fade away and still emits in pretty much every direction. As such starts to happen, even more light is going to pass that point of reference and even more light is going to intersect, refresh and pass back to the point of origin. Therefore, that light starts to appear to be moving backwards, and it will seem faster because it was already going the speed of light, and then it hit more light that emits in all directions at the same time, which will lengthen the light backward, and make it seem to hit the point of origin faster than the original light could hit the same distance going forward. My bet is that if they measured that pulse of light, its not just faster, but a little longer. Anyway, thats my laymens take on it.

MainFragger

Not sure this relates...

April 23, 2008 by Anonymous, 1 year 10 weeks ago
Comment id: 29211

But I've noticed in Photography, if you use slow exposures for cars you get light trails. Now I'm not gonna get into numbers, but what I have noticed is that you can set your flash at first or second curtain (beginning or end of the exposure). If you set it first curtain, the light trail extends in front of the car, if you set it second curtain, it extends in back of the car.

Now, from what I have noticed, if you use the same exposure speed and take two different shots like that, it seems like the light trail behind the car is always longer than the light trail from the front of the car.

I've thought about this for some time, and I can only think of one reason for this to be the case. The path of least resistance. Wherever light hasn't been yet, the light has to fight to "enlighten", but anywhere that light has already been is already primed to accept more light. Another analogy might be its kind of the difference between restarting a car in summer vs. restarting a car in winter. The engine doesn't have to heat up as much in summer as it does in winter, so most engines start up faster in the summer.

I bet the same applies to electricity in a wire. If a completely uncharged wire is used it takes a certain amount of time for the electricity to fill and travel through the whole wire. But I bet if you start a circuit up, turn it off, and immeadiately turn it back on, the time for the electricity to reach the other side is ever so slightly shorter.

MainFragger

time travel

April 22, 2008 by Anonymous, 1 year 10 weeks ago
Comment id: 29193

what if the light is going back in time

Light moving backwards

July 7, 2007 by Frank Schiralli, Jr. (not verified), 1 year 51 weeks ago
Comment id: 24153

Sorry...the explanation is MUCH more simple. Once you exceed the speed of light (if you indeed could, which you can't) what you are REALLY observing is time moving backwards, hence the light's arrival BEFORE it left.

Any theorioes involving infinities are non-renormalizable, and mathematically useless to make predictions or in the assessment of "observations." Negative time IS CERTAINLY permitted and is an integral part of both newtonian and relativistic explanations of forces and fields.

Ha! I told my math teacher off...

February 22, 2007 by Anonymous, 2 years 18 weeks ago
Comment id: 17451

This is awsome... My teacher was on one of his rants about you can't have a negative speed. So I raised my hand and simply told him that you can. I gave him a simple description and he didn't want to belive it. So looks like somebody will have to make a major math edit...

My Idea

September 12, 2006 by Anonymous, 2 years 42 weeks ago
Comment id: 2836

There are some effects which are first very unbelievable, but you have to look at the circumstances. The preception that somethink can be faster than the speed of light, is nothing new. But this cause in tunnelng and just for a short time. In case of that, light can not travel for a long time with a speed higher than the speed of light.

So Einstein just make a statement with the theory of relativity about light in the big (long time, long distance)

Einstein is still right I think...

May 12, 2006 by shagghie, 3 years 7 weeks ago
Comment id: 1574

The light in the fiber is only traveling *relatively* faster than the reference pulse.
The relevance is a factor of the medium itself, as well as the spacial reference of the observers. Observers is a casual way to describe the measuring technique used to 'replay' the *relative* speeds of both light pulses.

One cannot determine that light is 'traveling faster than normal light' unless one actually IS a pulse of light. Let alone, the fact that the reference light pulse would have to exist in the SAME spacial coordinates as well (not parallel on the same plane, and not fired back to back alone the same plane/path, either!).

Of course, that is where the funky bit gets funkier... if you are trying to measure a DIFFERENCE in speed of two light pulses that are occupying the same space, well, it's impossible to do if the pulses actually ARE travelling at different speeds...b/c they cannot then occupy the same physical space except for the insant of conception.

Never mind the 'informational' side of light in the above example...because you would just have a double-amplitude single pulse at that point, and unless the waveform itself gets distorted, you'll never be able to have to pulses of light, occupying the same space, and travelling at different speeds.

So, Einstein is not yet proven 'wrong'; any more than a circus mirror would prove him wrong. 'sall relative, remember?

This is old stuff

May 12, 2006 by rperez33, 3 years 7 weeks ago
Comment id: 1573

A very interesting experiment and explanation about the same topic can be found at the following URL: http://physicsweb.org/articles/world/13/9/3/1

I knew it!

May 11, 2006 by alwbsok, 3 years 7 weeks ago
Comment id: 1572

One of my personal theories is the theory of infinity and how it applies to light. (This gets a bit thick)

Firstly, I thought of the hyperbola, with the graph extending to the two infinities along each of the two asymptotes. Now if you take a rotated rectangular hyperbola so that the asymptotes lie on the X and Y axes, you get an equation along the lines of Y = K / X, where K is a constant.

This equation should be smooth and continuous based purely on the observation that y = f(x), where f(x) is the sum of terms that consist of k1 * x^k2, where k1 and k2 represent a range of different constants. This is not the case though, since X cannot equal 0. What I proposed was that the graph joins up at positive and negative infinity, and that therefore positive and negative infinity are the same. Since infinity is the reciprocal of 0, which has no sign, it stands to reason that infinity also has no sign.

With this in mind, the speed of light has always been unobtainable, due to the increasing force required to increase the speed of the object. When extrapolated, it has been theorised that an infinite force is required to push an object to the speed of light. I would then hazard a guess (with my little knowledge) that the speed of light is the definition of infinity in our universe in terms of velocity. While speeds greater than the speed of light are possible to put down on paper, infinity is, in reality, much closer.

Enter my theory. If you manage to push past the speed of light (infinity), then it will be travelling backwards at the same speed (negative infinity). If you travel close the speed of light, you may find there is a component of your motion (I'm really just guessing) going backwards faster than the speed of light which is inversely proportional to the forward velocity.

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