Slowing down and stopping light

[Jobe]

Switching light on and off

Seems they can slow light down and stop it using some sort of gas. I presume this is caused by interactions between matter and light, and that light still travels at c for all observers between these interactions?

[Swift]

No, I believe that light is really going slower. Remember, C is the speed of light in a vacuum, and is an upper limit; in different media it travels at slower speeds. The index of refraction of a material is actually a measure of how much light slows down in that media.

[AstroSmurf]

Jobe's got it right - the apparent slowdown of light in a material is the result of the light interacting with the atoms. What they're doing is apparently controlling this interaction, raising the refractive index to infinity (or close to it).

[sarongsong]

Not so fast... 8)
"...In a 2001 experiment, light pulses were briefly stored when particles of light were taken up by atoms in a gas.
The Harvard experiment tops that achievement by holding light and its energy at a standstill..."
http://news.bbc.co.uk/2/hi/science/nature/3308109.stm

[Jobe]

Not so fast... 8)
"...In a 2001 experiment, light pulses were briefly stored when particles of light were taken up by atoms in a gas.
The Harvard experiment tops that achievement by holding light and its energy at a standstill..."
http://news.bbc.co.uk/2/hi/science/nature/3308109.stm

Quoting that article;

As the regenerated signal pulse tries to continue on its way through the glass cylinder, the photons bounce back and forth, but the overall signal pulse remains stationary. The light beam was essentially frozen.

It seems that the "overall signal pulse" is the only thing that remains stationary- the photons keep bouncing back and forth at c.

[Sam5]

It seems that the "overall signal pulse" is the only thing that remains stationary- the photons keep bouncing back and forth at c.

I doubt if they are traveling at c if they are traveling through rubidium gas.

[Jobe]

It seems that the "overall signal pulse" is the only thing that remains stationary- the photons keep bouncing back and forth at c.

I doubt if they are traveling at c if they are traveling through rubidium gas.

My understanding, Sam is that they still travel at c, but because of refraction caused by atoms of the gas, they travel a longer path, and therefore the "overall signal pulse" seems to travel slower than c.

[Sam5]

My understanding, Sam is that they still travel at c, but because of refraction caused by atoms of the gas, they travel a longer path, and therefore the "overall signal pulse" seems to travel slower than c.

Ok, I see what you mean. I’ve heard about three different theories about this, and I don’t know which one is correct. I’ve heard one popular theory that the photons that go into things like glass are not the same ones that come out on the other side. Something about them hitting molecules of glass that absorb the original photons and reemit new photons. But I don’t know for sure.

[swansont]

I’ve heard about three different theories about this, and I don’t know which one is correct. I’ve heard one popular theory that the photons that go into things like glass are not the same ones that come out on the other side. Something about them hitting molecules of glass that absorb the original photons and reemit new photons. But I don’t know for sure.

That's the quantum interpretation - the photons travel at c, but are absorbed and re-emitted along the way, which increases the transit time. Since the photons are identical, there's no way of knowing of the photons coming out the other side is the same.

Clasiically, the increased permeability and permittivity of the medium slows the wave down.

[Eta C]

Although CNN, New Scientist, etc., tend to be the place where the general public first sees results like this, I prefer to go to the source. This is a link to the American Institute of Physics's summary of this result on their Physics News Update page. This is usually the place where the other news outlets first learn of significant results. It's better written and with more detail than the re-written blurbs, contains more details of the actual experiment, but is still understandable by a non-specialist.

The AIP release explains how in the 2001 result the photon beam's signal information was stored in the spin orientations of the vapor. Then a new beam was created that had the original information restored. The 03 results are different. Here the photons are trapped in a "Hall of Atomic Mirrors." Two "control laser beams" herd the atoms in the vapor into a structure that causes the signal beam to reflect around inside. Thus the original photons are trapped in a substance that effectively has an infinite index of refraction. When the control beams are turned off, the signal beam is released.

[Jobe]

Although CNN, New Scientist, etc., tend to be the place where the general public first sees results like this, I prefer to go to the source. This is a link to the American Institute of Physics's summary of this result on their Physics News Update page.

Thanks, handy.

[RBG]

This research is really quite interesting, as is its possible usefulness in a quantum computer.

Seems to me that when we are able to develop such a machine, our human race will have moved up the evolutionary scale a significant bit.

I know the most basic of quantum computers are being experimented with now, solving some obscure number problems, but are there any predictions out there as to when the "real deal" might be created?

RBG

[Wingnut Ninja]

Seems to me that when we are able to develop such a machine, our human race will have moved up the evolutionary scale a significant bit.

Or a byte, even.

I know the most basic of quantum computers are being experimented with now, solving some obscure number problems, but are there any predictions out there as to when the "real deal" might be created?

Nobody really knows right now. There are estimates ranging from "10 years" to "100 years" to "never". Barring the possibility that there's a full-blown version ticking away in an NSA lab somewhere, there are a lot of tricky engineering problems to work out.

Curiously enough, that hasn't kept people from writing algorithms to run on a quantum computer.

[TempleoftheDog]

I had an idea just today about the possibilities of the stopping of light, and thought I'd share. I am hardly one able to do anything concerning this idea, maybe some of you are...

Stopping light would be great for these quantum computers, but, what about Invisibility. I would think, invisibility would only be a couple more steps from the point they have reached.

I picture it as, an invisibility suit, where once light enters, it is stopped, redirected, and sent on its way in some way, around the suit. Since the light never reflects to the viewer of the suit, the suit wearer is essentially invisible. (this is of course just the rough idea, and needs adjusted)

I'd like to hear your thoughts on this, is it concievable?

[Laser Jock]

First, welcome to the BABB!

I had an idea just today about the possibilities of the stopping of light, and thought I'd share. I am hardly one able to do anything concerning this idea, maybe some of you are...

Stopping light would be great for these quantum computers, but, what about Invisibility. I would think, invisibility would only be a couple more steps from the point they have reached.

I picture it as, an invisibility suit, where once light enters, it is stopped, redirected, and sent on its way in some way, around the suit. Since the light never reflects to the viewer of the suit, the suit wearer is essentially invisible. (this is of course just the rough idea, and needs adjusted)

I'd like to hear your thoughts on this, is it concievable?

You mean something like this? What is in that link would be a lot easier than stopping or slowing the light.

[Swift]

I picture it as, an invisibility suit, where once light enters, it is stopped, redirected, and sent on its way in some way, around the suit. Since the light never reflects to the viewer of the suit, the suit wearer is essentially invisible. (this is of course just the rough idea, and needs adjusted)

First, welcome on board.

There was a Japanese invention within the last year along those lines, though it didn't use quantum mechanical effects of stopping light. A link to one article below:
http://news.bbc.co.uk/1/hi/world/asi...ic/2777111.stm

[TempleoftheDog]

You mean something like this? What is in that link would be a lot easier than stopping or slowing the light.

Thank you for the welcome Laser Jock, and yes that is definately a start in the right direction to what I invisioned, I'm going to have to look into that further.

Seems that would be easier, but, I guess it depends on its overall functionality.

[SeanF]

Laser Jock and Swift think alike, eh?

That's not really an invisibility suit, though . . . it requires a camera behind the person wearing it, and the person looking at them has to look through a special viewfinder that combines the view from the camera behind the person with the regular view of the person.

What TempleoftheDog (welcome to the BABB, by the way!) suggested, though, would need to be a little bit more complicated. It's not enough to just redirect the light, it actually needs to be bent 180º around the person so that it continues on in its original direction. If you just keep it from being reflected back to the observer, they'd see a black shape instead of what's behind the "invisible" person.

[Laser Jock]

I picture it as, an invisibility suit, where once light enters, it is stopped, redirected, and sent on its way in some way, around the suit. Since the light never reflects to the viewer of the suit, the suit wearer is essentially invisible. (this is of course just the rough idea, and needs adjusted)

First, welcome on board.

There was a Japanese invention within the last year along those lines, though it didn't use quantum mechanical effects of stopping light. A link to one article below:
http://news.bbc.co.uk/1/hi/world/asi...ic/2777111.stm

Ha Ha, beat ya! :wink:

[Laser Jock]

Laser Jock and Swift think alike, eh?

I've been accused of worse things, but Swift might be offended. :wink:

[TempleoftheDog]

Laser Jock and Swift think alike, eh?

That's not really an invisibility suit, though . . . it requires a camera behind the person wearing it, and the person looking at them has to look through a special viewfinder that combines the view from the camera behind the person with the regular view of the person.

What TempleoftheDog (welcome to the BABB, by the way!) suggested, though, would need to be a little bit more complicated. It's not enough to just redirect the light, it actually needs to be bent 180º around the person so that it continues on in its original direction. If you just keep it from being reflected back to the observer, they'd see a black shape instead of what's behind the "invisible" person.

Yes, this would be more like what I was suggesting, stopping, and bending the light around the person. After reading both the above links, the Japan system seems that is more of a projector system.

All good info though, guess invisibility is just a matter of time before we figure it out in one form or another. I have an Idea, that stopping light will lead to all kinds of breakthroughs.

[Swift]

Ha Ha, beat ya! :wink:

"The race is not always won by the swift (no pun intended) nor the fight by the strong"



But that's the way to bet.