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Author Topic: Speed of light and Slow light  (Read 5683 times)

Alan McDougall

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Speed of light and Slow light
« on: 13/11/2008 11:15:50 »
Greetings Forum,

Although it is impossible to exceed the speed of light in a vacuum, but light can definably go slower in a non vacuum!

If light moves through a medium that is not in a vacuum, light doesn't travel at c, it travels slower. (depending on the medium)

Present scientific experiments with light have engineered things so well that they have got light to slow down to 38 miles-per-hour.

What happens if I send something moving faster than 38 mi/hr through through this material where light only goes at 38 mi/hr?

Is the answer is it continues to move faster than 38 mi/hr or the speed of light in that medium.?

So one can break the speed of light as long as you're not in a vacuum. In fact, if you do, you'll start emitting light (i.e., Cherenkov radiation) until you slow down to below the speed of light in that medium.

This slowing down of light is very interesting. I read a sci-fi story long ago called slow light.

In the story one could buy a window that slowed light so much that it could contained centuries of history, and you could sit at this interesting window and observe history as it happened

This slow light could also be used to store up scenes of beauty just as realistic as reality. While the spectator sat in a burned out world

Of course this special hypothetical slow light window would have had to absorb all the light is real time and then slow is down enormously

Alan

lyner

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Speed of light and Slow light
« Reply #1 on: 13/11/2008 13:08:28 »
Presumably the window had been built and placed there a long time ago.

Alan McDougall

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« Reply #2 on: 13/11/2008 13:48:56 »
sophiecentaur

Quote
Presumably the window had been built and placed there a long time ago

Yes that is how the story went,of course the speed of light in the atmosphere
still holds good as the slow light window has to wait and absorb the events in real time and sort of compact them into the slow light window.

So light in the window medium might take a year to flow through the windows? Maybe these windows could be made to order, some with the light taking just a week to flow through the window and in other slow light windows a hundred or even a thoudsand years

This is not beyond the realms of possibility these sci fi authors have so often come up with real scientific possibilities.

I  will do a web search and see if I cant locate this story

Alan

Alan McDougall

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« Reply #3 on: 13/11/2008 13:57:52 »

I found it on the net, the Internet is just amazing, and I read this story as a young man over forty years ago and only yesterday thinking about light this long forgotten story came back to me

http://variety-sf.blogspot.com/2008/04/bob-shaw-light-of-other-days-aka-slow.html

Bob Shaw's "Light of Other Days" aka "Slow Glass" (short story, science fiction): Improving the view you see from your window!

I'd tucked away a short comment on this story in Hartwell's "Ascent of Wonder" post, but was struck again by similarity of its "slow glass" with the time travel gates in Chiang's "The Merchant & the Alchemist's Gate" when I saw this year's Nebula winners' list yesterday.

In both cases, you have a sort of thin sheet through which things pass & come out in a different time. "Slow glass" only passes radiation; Chiang's gate passes both matter & radiation.

Both permit transfer in either direction, but with differences. Each side of slow glass shows you past seen by other side - how far back depends on specifications of glass. Chiang's gate moves you forward in time in one direction, & back in the other.

The most interesting thing about this story is: "slow glass" is a realistic gadget, even if we don't have any idea of how to build one today. Plot itself is not bad, but not great either; this story gets listed among classics because of its description of the gadget, & its possible applications.

What is "slow glass"? It looks like ordinary glass sheets that go into your windows. But it drastically slows down the passage of light through it; light takes years to pass through the sheet of glass - depending on specs.

What does this mean? You take a newly made glass sheet, & place in near a lake or in a forest. Let it stay there for 2 years - assuming that is how long the light takes to pass through it. At the end of the time, the glass effectively has memory of the place - & in a far more realistic manner than any video shoot. A bird swooping down, some dears coming for a drink, ... whatever happens on the scene is recorded.

Now sell this glass to a city dweller with a window overlooking a neighbor's kitchen. What have you got? The lovely lake view in your window - for next 2 years. At the end of this time, 2 year old local light will begin penetrating so you will want to replace it again.

Alan

lyner

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Speed of light and Slow light
« Reply #4 on: 13/11/2008 14:32:40 »
We have DVD recorders which will do the same thing for us.

yor_on

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Speed of light and Slow light
« Reply #5 on: 13/11/2008 14:36:56 »
A fellow SF_fan:)
That's cool.

-----
And a very moving story too.
« Last Edit: 13/11/2008 14:39:46 by yor_on »

lightarrow

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« Reply #6 on: 13/11/2008 14:54:34 »
So light in the window medium might take a year to flow through the windows? Maybe these windows could be made to order, some with the light taking just a week to flow through the window and in other slow light windows a hundred or even a thoudsand years
This is not beyond the realms of possibility these sci fi authors have so often come up with real scientific possibilities.
In an article of Scientific American of some times ago, don't remember which one, it was described how to "store" entire wavepackets of light for a future use in computer's memories.

Alan McDougall

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« Reply #7 on: 13/11/2008 17:58:04 »
Hi, Guys when I started this thread I was not aware that the slowing down of light was already a fact and seemly vital for future computer processing

Alan

Everyone knows of the speed of light as one of the unshakable properties of the universe. It's not surprising, then, that experiments to radically alter light's speed require some serious equipment and hard work. Running such an experiment requires first a careful tune-up and optimization of the setup and then a long period of painstaking data gathering to get a consistent set of measurements.

At the Rowland Institute for Science in Cambridge, Mass., our original slow-light experiments typically took place in stints lasting 27 hours nonstop. Instead of breaking for meals, we learned to balance a slice of pizza in one hand, leaving the other clean to flip mirrors in and out on the optics table during 38 seconds of total darkness at a crucial stage of each run.

Our goal was to drastically slow down light, which travels through empty space at the universe's ultimate speed limit of nearly 300,000 kilometers a second. We saw the first sign of light pulses slowing down in March 1998. As happens so often in experimental physics--because it can take so many hours to get all the components working together for the first time--this occurred in the wee hours of the morning, at 4 A.M. By July we were down to airplane speed.

At that time I had to go to the Niels Bohr Institute in Copenhagen to teach a class. I remember sitting in the plane marveling that I was traveling "faster than light";--that I could beat one of our slow pulses to Denmark by a full hour.

News - December 20, 2007

A New Way to Help Networks Handle Ever-Heavier Data Loads
R
esearchers discover a way to briefly store data acoustically to alleviate traffic bottlenecks

By Larry Greenemeier

As demand for streaming video over the Web, voice over
Internet protocol (VoIP) calling services and other forms of
Internet-based multimedia communication skyrockets,
content creators and consumers are counting on fiber-optic
networks to handle these increasing loads quickly and
efficiently.

One way to ensure this happens is to enhance
the ability of such networks, which transmit data over glass
or plastic threads, to capture and retain data even for very
brief intervals.

Toward that end, a team of researchers from Duke
University and University of Rochester's Institute of Optics
recently reported in Science that it successfully transferred
encoded information from a laser beam to sound waves and
back to light waves, a breakthrough that could speed
development of faster optical communication networks.

Swapping data between optics and acoustics allows it to be
"stored in pockets of acoustic vibration" created when laser beams interact along a short strand of optical fiber.

The research is significant, because it addresses how memory can be created for optical pulses. "The primary
thrust is investigating slow light via stimulated Brillouin scattering, where we slow down a pulse as it propagates
through an optical fiber," says study co-author Daniel Gauthier, chairman of Duke's department of physics.

Brillouin scattering occurs when light traveling through a medium, such as glass, changes its path as it
encounters varying densities.

The main goal of the research is to pave the way for better fiber-optic communication systems, which today
consist of fiber placed underground and linked by routers. The typical way to send data over an optical network
is to break it up "into chunks called packets". When a packet comes into a router, its address information is read.

The problem with routers is that they each contain a single switch that can only process one packet at a time. As
a result, some packets are dropped unless others coming in are buffered (saved) or can wait until it is their turn
to be routed. "If you drop the packet, you reduce the throughput of the entire network," Gauthier says. "If you
buffer, then the packets are processed one after the other."

As greater demands are placed on telecommunication infrastructures, "it's important to start to investigate

Gauthier and his colleagues discovered that when two laser beams of slightly different frequencies are pointed
at one another along a piece of glass fiber, they create acoustic vibrations called phonons. When co-author

Zhaoming Zhu, Gauthier's postdoctoral research associate, encoded information onto one of these beams, the
data could be imprinted on these newly created phonons and retained for 12 billionths of a second, long enough
to be transferred back to light again by shining a third laser through the fiber.

"When thinking about how to store light in optical fibers," Zhu says, "we realized that we can convert optical
information to acoustic vibration, something that hasn't been done before."

Scientific American: A New Way to Help Networks Handle Ever-Heavier Data Loads Page 1 of 2
http://www.sciam.com/article.cfm?id=network-fiber-optic-laser-acoustic&print=true 12/20/2007

The researchers are seeking ways to create longer storage times and reduce the peak power of the laser beam
needed for retaining and reading out the information, a process that will take years before a commercial version
of the technology is available.

"There is still a great need for developing new strategies for optimizing the flow of information over the Internet,"
says Robert Boyd, a professor of optics and physics at the Institute of Optics and a research co-author. "If two
data packets arrive at a switch at the same time, you need to store one until the other packet clears the switch,
maybe 100 nanoseconds later. Our technique is aimed at … building buffers for high-speed
telecommunications."

During the first phase of the project—which is part of the Defense Advanced Research Projects Agency's
(DARPA) Defense Sciences Office slow-light program—Zhu says he learned that pulses could be stored and
read out at a later time. The second phase was the actual experiment in which data pulses were stored (as
acoustic waves in an optical fiber) and retrieved after a certain period of time.

"We really want to demonstrate that methods for storing optical information are much broader than people
thought," Gauthier says. "In the current telecommunication systems, you turn the optical signal into an electronic
signal and store it in RAM. The optical data pulses are then regenerated by using the electrical signals to turn on
and off an auxiliary laser source. But this process generates heat. The faster this is done, the more heat is
generated."

For this to work in the real world, the scientists say the communication fibers must be made of a material that
provides an acoustic time frame long enough to allow the information to move from optical to sound, then return
to optical. One option, Gauthier says, is to work with a new type of glass made from a chalcogenide, which has
good semiconductor properties and contains one or more elements from the periodic table's chalcogenide
group, also known as the "oxygen family," which includes oxygen, sulfur, selenium and tellurium.

Another option that researchers are exploring is to run the laser beams through a hollow optical fiber filled with
gas (such as xenon), which would allow them to use a less powerful laser to induce longer lasting sound waves
in the gas. This could potentially create a sound wave 50 times longer and allow the lasers used to be 100 times
less powerful—and less energy intensive—thereby delivering more data more quickly at a lower cost.
Scientific American: A New Way to Help Networks Handle Ever-Heavier Data Loads Page 2 of 2
http://www.sciam.com/article.cfm?id=network-fiber-optic-laser-acoustic&print=true 12/20/2007

lightarrow

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« Reply #8 on: 13/11/2008 18:24:01 »
Here there is an interview to Lene Hau, talking about stored light:
http://www.npr.org/templates/story/story.php?storyId=7314502

Bored chemist

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Speed of light and Slow light
« Reply #9 on: 13/11/2008 19:56:13 »
I don't know a lot about stored light but I do know that it's possible to have something travel faster than light (by, as you suggest, slowing the light down).
Electrons released by nuclear reactions (genarally called beta particles in this case)are very energetic and can have velocities near that of light. If these travel through water or glass they are moving faster than light would, for example in glass, light only travels about 2/3 of it's usual speed.
What hapens is that the electrons slow down rather quickly and their energy is released as cerencov radiation.

What I would like to know is what happens if a neutron traveling near c passed through water or glass?
It hasn't got a charge so it's hard to see how it can generate em radiation.

lightarrow

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« Reply #10 on: 13/11/2008 20:20:04 »
I don't know a lot about stored light but I do know that it's possible to have something travel faster than light (by, as you suggest, slowing the light down).
Electrons released by nuclear reactions (genarally called beta particles in this case)are very energetic and can have velocities near that of light. If these travel through water or glass they are moving faster than light would, for example in glass, light only travels about 2/3 of it's usual speed.
What hapens is that the electrons slow down rather quickly and their energy is released as cerencov radiation.

What I would like to know is what happens if a neutron traveling near c passed through water or glass?
It hasn't got a charge so it's hard to see how it can generate em radiation.
Essentially neutrons slow down through collisions with nuclei, so the material heats up.

lyner

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Speed of light and Slow light
« Reply #11 on: 13/11/2008 23:08:22 »
It also can cause ionisation as a result of nuclei rebounding so fast.

yor_on

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« Reply #12 on: 13/11/2008 23:25:49 »
This might be of interest?

"Although it is true that the neutron has zero net charge, it is nonetheless composed of electrically charged quarks, in the same way that a neutral atom is nonetheless composed of protons and electrons. As such, the neutron experiences the electromagnetic interaction.

The net charge is zero, so if you are far enough away from the neutron that it appears to occupy no volume, then the total effect of the electric force will add up to zero. The movement of the charges inside the neutrons do not cancel however, and this is what gives the neutron its nonzero magnetic moment."
http://www.newworldencyclopedia.org/entry/Neutron

lightarrow

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« Reply #13 on: 14/11/2008 20:35:12 »
It also can cause ionisation as a result of nuclei rebounding so fast.
Yes, very important note.

lightarrow

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« Reply #14 on: 14/11/2008 20:38:24 »
This might be of interest?

"Although it is true that the neutron has zero net charge, it is nonetheless composed of electrically charged quarks, in the same way that a neutral atom is nonetheless composed of protons and electrons. As such, the neutron experiences the electromagnetic interaction.

The net charge is zero, so if you are far enough away from the neutron that it appears to occupy no volume, then the total effect of the electric force will add up to zero. The movement of the charges inside the neutrons do not cancel however, and this is what gives the neutron its nonzero magnetic moment."
http://www.newworldencyclopedia.org/entry/Neutron
Yes. Think that even the neutrino, which is thought of as an elementary particle (not composed of other particles), nontheless experience (very weakly) electromagnetic interaction, because of the fact it has a spin.

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Speed of light and Slow light
« Reply #14 on: 14/11/2008 20:38:24 »