"All the World's a Stage We Pass Through" R. Ayana

Showing posts with label light speed changes. Show all posts
Showing posts with label light speed changes. Show all posts

Saturday, 18 December 2010

Speed of Light Exceeded in Labs

Speed of Light Exceeded in Labs

Gain Assisted Superluminal Light Propagation


by Dr. Lijun Wang
Gain Assisted Superluminal Light Propogation

Scientists have apparently broken the universe’s speed limit. For generations, physicists believed there is nothing faster than light moving through a vacuum - a speed of 186,000 miles per second. But in an experiment in Princeton, N.J., physicists sent a pulse of laser light through cesium vapor so quickly that it left the chamber before it had even finished entering. The pulse traveled 310 times the distance it would have covered if the chamber had contained a vacuum.

This seems to contradict not only common sense, but also a bedrock principle of Albert Einstein’s theory of relativity, which sets the speed of light in a vacuum, about 186,000 miles per second, as the fastest that anything can go.

But the findings--the long-awaited first clear evidence of faster-than-light motion--are "not at odds with Einstein," said Lijun Wang, who with colleagues at the NEC Research Institute in Princeton, N.J., report their results in today’s issue of the journal Nature.

"However," Wang said, "our experiment does show that the generally held misconception that ’nothing can move faster than the speed of light’ is wrong." Nothing with mass can exceed the light-speed limit. But physicists now believe that a pulse of light--which is a group of massless individual waves--can.

To demonstrate that, the researchers created a carefully doctored vapor of laser-irradiated atoms that twist, squeeze and ultimately boost the speed of light waves in such abnormal ways that a pulse shoots through the vapor in about 1/300th the time it would take the pulse to go the same distance in a vacuum.

As a general rule, light travels more slowly in any medium more dense than a vacuum (which, by definition, has no density at all). For example, in water, light travels at about three-fourths its vacuum speed; in glass, it’s around two-thirds.

The ratio between the speed of light in a vacuum and its speed in a material is called the refractive index. The index can be changed slightly by altering the chemical or physical structure of the medium. Ordinary glass has a refractive index around 1.5. But by adding a bit of lead, it rises to 1.6.

The slower speed, and greater bending, of light waves accounts for the more sprightly sparkle of lead crystal glass.

Gain Assisted Superluminal Light Propogation

The NEC researchers achieved the opposite effect, creating a gaseous medium that, when manipulated with lasers, exhibits a sudden and precipitous drop in refractive index, Wang said, speeding up the passage of a pulse of light.

The team used a 2.5-inch-long chamber filled with a vapor of cesium, a metallic element with a goldish color. They then trained several laser beams on the atoms, putting them in a stable but highly unnatural state.

In that condition, a pulse of light or "wave packet" (a cluster made up of many separate interconnected waves of different frequencies) is drastically reconfigured as it passes through the vapor. Some of the component waves are stretched out, others compressed. Yet at the end of the chamber, they recombine and reinforce one another to form exactly the same shape as the original pulse, Wang said. "It’s called re-phasing."

The key finding is that the reconstituted pulse re-forms before the original intact pulse could have gotten there by simply traveling though empty space. That is, the peak of the pulse is, in effect, extended forward in time. As a result, detectors attached to the beginning and end of the vapor chamber show that the peak of the exiting pulse leaves the chamber about 62 billionths of a second before the peak of the initial pulse finishes going in.

That is not the way things usually work. Ordinarily, when sunlight -- which, like the pulse in the experiment, is a combination of many different frequencies -- passes through a glass prism, the prism disperses the white light’s components.

This happens because each frequency moves at a different speed in glass, smearing out the original light beam. Blue is slowed the most, and thus deflected the farthest; red travels fastest and is bent the least. That phenomenon produces the familiar rainbow spectrum.

But the NEC team’s laser-zapped cesium vapor produces the opposite outcome. It bends red more than blue in a process called "anomalous dispersion," causing an unusual reshuffling of the relationships among the various component light waves. That’s what causes the accelerated re-formation of the pulse, and hence the speed-up

In theory, the work might eventually lead to dramatic improvements in optical transmission rates. "There’s a lot of excitement in the field now," said Steinberg. "People didn’t get into this area for the applications, but we all certainly hope that some applications can come out of it. It’s a gamble, and we just wait and see."


LANL scientist makes radio waves
travel faster than light
http://www.zamandayolculuk.com/cetinbal/AE/Arelativistic.jpg

Scientist John Singleton insists that Albert Einstein wouldn't be mad at him, even though at first blush Singleton appears to have twisted the famous physicist's theories about light into a pretzel.
by Sue Vorenberg

Most people think Einstein said that nothing can travel faster than the speed of light, but that's not really the case, Singleton said.

Einstein predicted that particles and information can't travel faster than the speed of light — but phenomenon like radio waves? That's a different story, said Singleton, a Los Alamos National Laboratory Fellow.

Singleton has created a gadget that abuses radio waves so severely that they finally give in and travel faster than light.

The polarization synchrotron combines the waves with a rapidly spinning magnetic field, and the result could explain why pulsars — which are super-dense spinning stars that are a subclass of neutron stars — emit such powerful signals, a phenomenon that has baffled many scientists, Singleton said.

"Pulsars are rapidly rotating neutron stars that emit radio waves in pulses, but what we don't know is why these pulses are so bright or why they travel such long distances," Singleton said. "What we think is these are transmitting the same way our machine does."

And beyond explaining what has been a bit of a mystery to the astronomical community, Singleton's discovery could have wide-ranging technological impacts in areas such as medicine and communications, he said.

"Because nobody's really thought about things that travel faster than light before, this is a wide-open technological field," Singleton said.

One possible use for the resulting speedy radio waves — which are packed into a very powerful wave the size of a pencil point — could be the creation of a new generation of cell phones that communicate directly to satellites, rather than transmitting through relay towers as they now do.

Those phones would have more reliable service and would also be more difficult for hackers to intercept, Singleton said.

Another application could be in very targeted chemotherapy, where a patient takes the drugs, and the radio waves are used to activate them very specifically in the area around a tumor, he said.

The concept of phenomenon traveling faster than light has been discussed in the back alleys of the scientific community since the 1970s, but observations were based on strange aberrations, like the distorted images of stars as they traveled near the speed of light, said Mario Perez, a Los Alamos scientist who worked with Singleton on the project.

"Radio astronomers found sources that looked like things were traveling faster than light, but they were not truly superluminal, like this is," Perez said.

And other effects have also shown the possibility of phenomenon traveling faster than light, but Singleton's experiment has taken that to a new level, Singleton said.
http://www.navigadget.com/wp-content/postimages/2009/05/pulsar.jpg


"If you take a laser and shine it on the moon and swing it rather gently, for example, the spot on the moon travels faster than the speed of light," Singleton said. "If an effect can do that, it makes you wonder if you can do things with light to get the equivalent of a sonic boom."

That's what the faster-than-light radio waves — more scientifically known as superluminal transmissions — do. They're the light version of a sonic boom, he said.

"When something travels faster than its own wave speed you get a very large disturbance," Singleton said. "And these powerful signals that result, well, this would be how E.T., if he were out there, would likely try to communicate with us."

If Einstein were still alive, he probably wouldn't be all that surprised by the discovery, Perez said, even if it does seem on the surface to conflict with some of his theories.

"He might have thought, 'why did this take so long,' " Perez said.

Last week, the two scientists presented the work to the American Astronomical Society at its conference in Austin, Texas.

Singleton wasn't sure how it would be received by the astronomical community, but so far, other scientists seem very interested in his work, he said.

"I thought there would be more resistance to it, because traditional astronomers are very resistant to things traveling faster than the speed of light," Singleton said.

In the next few years, the scientists plan to build a series of newer, more powerful machines to further demonstrate the technology, Perez added.

The Department of Energy has given them a three-year,
$3 million grant to work on the project.

And Einstein — he wouldn't be mad about that at all, Singleton said.
Contact Sue Vorenberg
at 986-3072 or svorenberg@sfnewmexican.com


Xtra Images - http://www.zamandayolculuk.com/cetinbal/AE/Arelativistic.jpg
http://www.navigadget.com/wp-content/postimages/2009/05/pulsar.jpg

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Monday, 13 December 2010

Light and matter united: : Light slowed, stopped and restarted

Light and matter united
Opening the way to new computers and communication systems

 http://gopaultech.com/wp-content/uploads/2006/03/Lene%20Hau%20Slowing%20Light.jpg

Justin Ide/Harvard News Office
Lene Hau explains how she stops light in one place then retrieves and speeds it up in a completely separate place.


By William J. Cromie


Lene Hau has already shaken scientists’ beliefs about the nature of things. Albert Einstein and just about every other physicist insisted that light travels 186,000 miles a second in free space, and that it can’t be speeded-up or slowed down. But in 1998, Hau, for the first time in history, slowed light to 38 miles an hour, about the speed of rush-hour traffic.

Two years later, she brought light to a complete halt in a cloud of ultracold atoms. Next, she restarted the stalled light without changing any of its characteristics, and sent it on its way. These highly successful experiments brought her a tenured professorship at Harvard University and a $500,000 MacArthur Foundation award to spend as she pleased.
Now Mallinckrodt Professor of Physics and of Applied Physics, Hau has done it again.

She and her team made a light pulse disappear from one cold cloud then retrieved it from another cloud nearby. In the process, light was converted into matter then back into light. For the first time in history, this gives science a way to control light with matter and vice versa.

It’s a thing that most scientists never thought was possible. Some colleagues had asked Hau, “Why try that experiment? It can’t be done.”
 
In the experiment, a light pulse was slowed to bicycle speed by beaming it into a cold cloud of atoms. The light made a “fingerprint” of itself in the atoms before the experimenters turned it off. Then Hau and her assistants guided that fingerprint into a second clump of cold atoms. And get this – the clumps were not touching and no light passed between them.
“The two atom clouds were separated and had never seen each other before,” Hau notes. They were eight-thousandths of an inch apart, a relatively huge distance on the scale of atoms.

The experimenters then nudged the second cloud of atoms with a laser beam, and the atomic imprint was revived as a light pulse. The revived light had all the characteristics present when it entered the first cloud of atomic matter, the same shape and wavelength. The restored light exited the cloud slowly then quickly sped up to its normal 186,000 miles a second.

 Communicating by light

 

Light carries information, so think of information being manipulated in ways that have never before been possible. That information can be stored – put on a shelf, so to speak – retrieved at will, and converted back to light. The retrieved light would contain the same information as the original light, without so much as a period being lost.

Or the information could be changed. “The light waves can be sculpted,” is the way Hau puts it. “Then it can be passed on. We have already observed such re-sculpted light in our lab.”

A weird thing happens to the light as it enters the cold atomic cloud, called a Bose-Einstein condensate. It becomes squeezed into a space 50 million times smaller. Imagine a light beam 3,200 feet (one kilometer) long, loaded with information, that now is only a hair width in length but still encodes as much information.

From there it becomes easier to imagine new types of computers and communications systems – smaller, faster, more reliable, and tamper-proof.
Atoms at room temperature move in a random, chaotic way. But when chilled in a vacuum to about 460 degrees below zero Fahrenheit, under certain conditions millions of atoms lock together and behave as a single mass. When a laser beam enters such a condensate, the light leaves an imprint on a portion of the atoms. That imprint moves like a wave through the cloud and exits at a speed of about 700 feet per hour. This wave of matter will keep going and enter another nearby ultracold condensate. That’s how light moves darkly from one cloud to another in Hau’s laboratory.
This invisible wave of matter keeps going unless it’s stopped in the second cloud with another laser beam, after which it can be revived as light again.

Atoms in matter waves exist in slightly different energy levels and states than atoms in the clouds they move through. These energy states match the shape and phase of the original light pulse. To make a long story short, information in this form can be made absolutely tamper proof. Personal information would be perfectly safe.

Such a light-to-matter, matter-to-light system “is a wonderful thing to wrap your brain around,” Hau muses.

In a practical manner

 

You won’t see a light-matter converter flashing away in a factory, business, or mall anytime soon. Despite all the intriguing possibilities, “there are no immediate practical uses,” Hau admits.

However, she has no doubt that practical systems will come. And when they do, they will look completely different from anything we are familiar with today. They won’t need a lot of wires and electronics. “Instead of light shining through optical fibers into boxes full of wires and semiconductor chips, intact data, messages, and images will be read directly from the light,” Hau imagines.

Creating those ultracold atomic clouds in a factory, office, or recreation room will be a problem, but one she believes can be solved. “The atomic clouds we use in our lab are only a tenth of a millimeter (0.004 inch) long,” she points out. “Such atom clouds can be kept in small containers, not all of the equipment has to be so cold. Most likely, a practical system designed by engineers will look totally unlike the setup we have in our lab today.”
There are no “maybes” in Hau’s voice. She is coolly confident that light-to-matter communication networks, codes, clocks, and guidance systems can be made part of daily life. If you doubt her, remember she is the person who stopped light, converted it to matter, carried it around, and transformed it back to light.

Details of the experiments appear as the cover story of the Feb. 8 2007 issue of Nature. Authors of the report include graduate student Naomi Ginsberg, postdoctoral fellow Sean Garner, and Hau.


Xtra Images - http://gopaultech.com/wp-content/uploads/2006/03/Lene%20Hau%20Slowing%20Light.jpg
http://img117.imageshack.us/i/cosmicindian2et5.jpg/sr=1




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