Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

Stop, Light.

michael posted more than 13 years ago | from the let-there-be-darkness dept.

News 254

parvati writes: "The New York Times is reporting that two separate research teams, both from Cambridge, MA, have managed to slow, stop, and then reconstitute light. The ability to stop and then accurately restore a beam of light has implications for quantum computing and communication in that it may provide a mechanism to store the information coded by single photons."

Sorry! There are no comments related to the filter you selected.

Re:does this break the theory of relativity? (1)

Klaruz (734) | more than 13 years ago | (#499301)

I don't think they way they did it would apply to space travel, but what about time travel? I suppose you could encase something in this gas, and achive time travel. But then again, if space and time are relavent, I guess it would be possible to travel with it... I'm not up on this subject at all, but does anybody care to post a real educated view on this?


Omega (1602) | more than 13 years ago | (#499303)

When do we get the damned spaceships?!! :)

This just serves to reinforce the position that NASA is grossly underfunded. In its heyday NASA went from having NO launch capabilities to the Apollo moon missions in 15 years.

What have we spent the last 15 years doing? Servicing the same damned shuttles and only going into low orbit on each trip. There should be a Moore's law for space technology. I think we've progressed computers far enough to keep us happy for a few years, why not concentrate on the space program?

Re:Quantum Communications (1)

Crowbar (1635) | more than 13 years ago | (#499304)

This is where heisenbergs uncertainty principle comes in... you can't measure the transmission (read-out) without affecting the transmission. So when you have quantum communications which are eavesdropped on, _BOTH_ sides know it instantly because the quantumlink is disturbed so far for the eavesdropping where eavesdropping is defined as listening to two parties without the 2 parties _knowing_ it...

Hmm, I'm confused. (1)

Mawbid (3993) | more than 13 years ago | (#499307)

Reading the article, I alternate between thinking that the atoms of the gas is store just information and thinking they store energy as well (the actual light). Can anyone clarify?

Re:does this break the theory of relativity? (1)

Mawbid (3993) | more than 13 years ago | (#499309)

Well, I'm pretty sure space and time are relevant.

Quantum Communications (1)

Delphis (11548) | more than 13 years ago | (#499311)

From the article ...

Quantum computers could crank through certain operations vastly faster than existing machines; quantum commmunications could never be eavesdropped upon.

Could NEVER be eavesdropped on? .. I'm not sure I understand this .. if there's a way to transmit something, then there can always be someone/something in the middle that can intercept it. Anyone with any insight into this care to explain or was this a case of the reporter getting carried away?


Re:Don't Forget (1)

Migrant Programmer (19727) | more than 13 years ago | (#499317)

I just enter what I would if I had to register.. user aaaaa, pass aaaaa. Someone else back yonder had the courtesy to create that. =)

Walking FTL! Care to explain ? (1)

karot (26201) | more than 13 years ago | (#499319)

So for all of the Sci-Fi authors out there, we finally have FTL Travel - We don't need to bend space, create wormholes or anything requiring any massive energy... Just open the front door and walk !!! ;-)

So would some kind soul care to explain how 'c' is a constant that is used throughout physics, but we can still slow/stop light? My physics isn't what it should be these days :-(

Layman's terms appreciated, but not mandatory.

Re:does this break the theory of relativity? (1)

CharlieG (34950) | more than 13 years ago | (#499328)

That's what I was saying. The original poster said "I thought Light always moved at C" and I replied "No, light moves at a MAXIMUM of C, and can move slower" - Now, stopped IS slower, right?

light transistors (1)

macpeep (36699) | more than 13 years ago | (#499329)

As I understand it, this would make it possible to create light transistors that switch by shining light into the transistor. AFAIK, this isn't possible at the moment. Obviously, you could flip mirrors or something, but that means you have something mechanical, which defeats the purpose. Does anyone know enough about light driven transistors to verify this?

Re:Correct /etc/hosts configuration (1)

cyberdonny (46462) | more than 13 years ago | (#499332)

Sure. Could you just mail me your ISP's IP address and root password.

Re:Quantum Communications (1)

StrawberryFrog (67065) | more than 13 years ago | (#499338)

Could NEVER be eavesdropped on .. without detection.

In a quantum system, the observer affects the state.

stupid sun... (1)

BMonger (68213) | more than 13 years ago | (#499340)

Maybe in a few years they can stop me from getting a day star tan... stupid day star... always coming down on me...

Heisenberg (1)

frode (82655) | more than 13 years ago | (#499343)

Is that possible, according to the heisenberg uncertanty principle you can never know both the location _and_ direction of movement of a quantum particle. So how would you be able to reconstitute it without this info?

Could be a weapon? (1)

Yodalf (83088) | more than 13 years ago | (#499344)

Maybe this could be engineered into a defensive weapon? Just store a super-intense pulse of laser light (expensive to produce) into this container (cheap gas cell?), and let it out at the right moment.

Only one shot though...

Don't Forget (1)

brunes69 (86786) | more than 13 years ago | (#499349)

I have no idea who originally created this, but I always log into these NY Times articles with the username/password of slashdot2000/slasshdot200.

Just a reminder / heads-up.

A question... (1)

Blackjax (98754) | more than 13 years ago | (#499355)

If there is anyone out there who is familiar with this area of research, there is something I've been wondering. Could this be used to build up a store of light (like a battery) or is it more for storing a short burst. Could you, for example, keep pouring light into this medium for a long time, to stop large amounts of it, then release it all at once?

No undetected eavesdropping (1)

DaveMac (100045) | more than 13 years ago | (#499356)

It is possible to have quantum crypto systems where eavesdropping will always (i.e., at any desired level of security) be detected. Here's an intro article that explains this:

Stop! (1)

kars (100858) | more than 13 years ago | (#499357)

So how'd they do that, anyway? Change the colour from green to red? :)

Re:Quantum Communications (1)

Niles_Stonne (105949) | more than 13 years ago | (#499361)

I think that the theory was that two particles can be linked by some "invisible" quantum force, then they can be seperated(By HUGE distances), and then when one particle is affected, the other one responds in kind... I have NO idea if this is correct, but I think I remember reading about it once...

So, basically, you would link two particles, then seperate them, placing one at each end that wants to communicate with eachother, and then use them as a transmission system. I suppose once we figure out what is connecting them, then we MAY be able to eavesdrop on it, but right now I believe that scientists just know the effect, and have no idea about what goes on in between.

Re:light stopped? Or destroyed and re-emitted... (1)

resonance (106398) | more than 13 years ago | (#499362)

The process described in the article sounds a LOT like conventional hologram creation, with the two interfering beams. It makes me wonder if they aren't just making a holographic impression on the storage gas, perhaps on the quantum level or something... I don't know. But it doesn't sound like the original light/energy that was put in is actually coming out. I look forward to the full report when it is published. This is fascinating shit!

Light sabres (1)

Mr.roboto (112555) | more than 13 years ago | (#499363)

I know it's a crazy thought but could this be some tech useable to make so called "beam swords," or at least "beam clubs"? =o

Re:Just wondering... (1)

DarkState (116388) | more than 13 years ago | (#499368)

Ideally, the number of photons in the pulse, after it left the apparatus in which it was trapped would be the same as when it went in. However, while the pulse is stopped, the number of photons is zero. All of the information about the pulse is stored in the atoms and the energy has been carried away by a control light beam.

In the current experiment by Phillips and co-workers [] which is only a demonstration of the ideas and not a useful device, they can only stop about half the light pulse and it decays away inside the atomic cloud fairly quickly, so only a small fraction of the incident photons actually come out.

time dilation (1)

hitchhacker (122525) | more than 13 years ago | (#499370)

disclaimer: I'm no physicist

I came to the same conclusion for why
time dilation occurs.
I always get stuck at: "motion in the
direction of time".

How can you "move" in time?
moving involves time already.


I left my cool "penguin physics" sig at home. :(

Re:time dilation (1)

hitchhacker (122525) | more than 13 years ago | (#499371)


I see now. So any time frame is already
moving through the 4thD at constant speed.
maybe speed c?
Then because of conservation of momentum,
any movement in 3D causes a slow down of
movement in the 4thD.

Is this correct?
any physicists out there?


Re:light transistors (1)

dvorsd (122811) | more than 13 years ago | (#499373)

A transistor which you can turn on and off by shining light on it is called a phototransistor. They've been around for a while. IIRC it really has little to do with the stuff they were talking about in that article. Think about the solor cells on a small calculator. You shine light on a piece of silicon and produce enough current to power the device. Similarly shining light on a phototransistor will inject current into the base of a BJT transistor causing it to switch.

At least thats what I seem to remember about them. I'm not quite awake yet, so hopefully that made some sense.


Quantum Encryption... (1)

pallex (126468) | more than 13 years ago | (#499376) probably shagged then (if you can read the bits without damaging them)

Re:Walking FTL! Care to explain ? (1)

WhiskeyJack (126722) | more than 13 years ago | (#499377)

Simple: the constant "c" is the speed of light in a vacuum. Light slows down when it travels through anything else.


Re:Correct /etc/hosts configuration (1)

ectizen (128686) | more than 13 years ago | (#499379)

please, sir, could you add that line to my isp's proxy's /etc/hosts?

Re:Correct /etc/hosts configuration (1)

ectizen (128686) | more than 13 years ago | (#499380)


Re:does this break the theory of relativity? (1)

carlos_benj (140796) | more than 13 years ago | (#499384)

I suppose you could encase something in this gas, and achive time travel.

I remember one time when I was encased in gas, but everyone else in the room travelled... or maybe I travelled to a time when there was nobody in the room.

Cool, but... (1)

evil_one (142582) | more than 13 years ago | (#499385)

From the article: "the beam then left the chamber carrying nearly the same shape, intensity and other properties it had when it entered."
Umm... NEARLY?
This is very very cool, but I don't want my computer to be displaying nearly what it should, or doing math that is nearly correct. Remember the original pentium?

how is this possible? (1)

SupahVee (146778) | more than 13 years ago | (#499387)

How can they measure the speed without affecting it? kinda like measuring something at absolute zero, as soon as you try to measure it, it absobs thats energy and heats up. Well, same thing, as soon as you measure the speed, you move it, and increase the speed.

Isn't this the Heisenberg Uncertainty Principle? However, I am not a world class physicist, so take what I say with a proton size grain of salt. :-)

Re:Faster, Light (1)

JCMay (158033) | more than 13 years ago | (#499395)

That's a joke I always bring up with PC board material vendors. As we use higher and higher frequency bands (we're about to start a 40 GHz comm system), circuit elements get unmanufacturably small. I often ask the less cluefull salespeople if they could provide us with board materials with relative dielectric constants less than one (speed of light in material == c/sqrt(Er) ). I usually get a chuckle or two.

Re:Heisenberg (1)

TeknoHog (164938) | more than 13 years ago | (#499397)

Disclaimer: I'm a third year undergraduate of physics. (We just started a course on quantum optics today, this discovery makes it even more interesting :-)

According to Heisenberg it's impossible to simultaneously measure the exact position and momentum of a quantum particle. However, it is possible to recreate a quantum particle exactly, without its properties being measured. Theoretically this enables quantum teleportation, 'beaming up' of even complex systems such as humans.


Re:Don't Forget (1)

fatphil (181876) | more than 13 years ago | (#499401)

But you're violating the terms and conditions by doing that.
I registered as 'idonotcomply', thus indicating to them that I do not comply with the terms and conditions, and generously they let me use the service even though I don't comply.

-- Real Men Don't Use Porn. -- Morality In Media Billboards

Sounds remarkably like a LASER (1)

fatphil (181876) | more than 13 years ago | (#499402)

Using a distantly related but much more powerful effect, the Walsworth-Lukin team first slowed and then stopped the light in a medium that consisted of specially prepared containers of gas. In this medium, the light became fainter and fainter as it slowed and then stopped. By flashing a second light through the gas, the team could essentially revive the original beam.

Send light into the lasable medium (ruby/gas/whatver), the quanta are absorbed. Then stimilate (the second flash) and the quanta are released again.

I can see a fair bit of similarity, no?

My physics may be a little rusty so please correct me.

-- Real Men Don't Use Porn. -- Morality In Media Billboards

Re:does this break the theory of relativity? (1)

tankefugl (193399) | more than 13 years ago | (#499405)

Actually, no. The speed of a photon is always c. However, when a photon is absorbed and reemitted (as happens a lot when you send light throug glass, gasses and any other medium), it will use more time to travel through the medium than vacum.

But the extra time used, it does not spend as a photon - it's spend as absorbed energy in the medium.

As the photon again reemerges, it's got the speed c.

- "mhrg-tap-tap-ping" - famous typewriter, 1846 AD
[ [] ]

Think its Danish (1)

kyrre (197103) | more than 13 years ago | (#499407)

On norwegian television this Danish female scientist was featured doing exacly over a year ago. Its nothing new.

Re:Faster, Light (1)

ar0n (197245) | more than 13 years ago | (#499408)

You can't. There can't be anything 'thinner' than vacuum, which by the way is a purely theoretical concept.

c, or 300,000 km/s is the maximum speed of light. Nothing can travel faster than it.

If you mean speeding it up after it's been stopped, I'd imagine you'd just release from the chamber of gas it's in.

Re:Artificial Black Holes (1)

Kite (200111) | more than 13 years ago | (#499411)

From what I gather from the article, the light wave is dimmed (effectively destryed) and its information is stored in the gas. When a second lightray is sent through the gas, it takes on the properties on the wave.

I don't know the article you are referring to, but normally to create a black hole you have to have some pretty extreme circumstances (like the mass of a small mountain (or its equivalent in energy) packed into the volume of a hydrogen atom), this is far beyond anything possible in modern laboratories.

super and supra luminal speed (1)

Deanasc (201050) | more than 13 years ago | (#499412)

Most all substances that can transmit light slows light down. This is commonly refered to as the index of refraction. What's really interesting are tachyons which are anti-particles which travel faster than light.

It is also possible to measure speeds of light >C in a substance with a frequency dependant index of refraction where some wavelengths of light travel faster than C.

Re:More on the subject (1)

bowb (209411) | more than 13 years ago | (#499415)

No, not a gaping asshole in sight; in fact it is a more technical article than that NYT fluff. Bose-Einstein condensates are interesting beasts (from the article):
In the case of a Bose-Einstein condensate, atoms chilled nearly to absolute zero can barely move at all, and their momentum therefore approaches zero. But because zero is a very precise measure of momentum, the uncertainty principle makes the positions of these atoms very uncertain. In a condensate, as a result, such atoms are forced to overlap each other and merge into superatoms sharing the same quantum mechanical "wave function," or collection of properties.


nostradorkmus (209852) | more than 13 years ago | (#499417)

1st, special relativity (which is what really pertains here) isn't really in dispute. There are very few, very radical researchers who seem to think that its false and their ideas mostly hinge on things of which there is no physical evidece, like gravity waves or such.
2nd, relativity only describes what happens, not why it happens and it accurately describes it. The GPS system had to be corrected for special relativity, particles from space can reach the surface of the earth even though their halflives would seem to forbid it. Special relativity is accurate to any percision we can measure.
When people refer to extra dimensions it is typically with reguard to string theory (a branch of particle physics), not in reguard to the tranimission of light (usually optics).

Distributed Quantum Computing (1)

RedLaggedTeut (216304) | more than 13 years ago | (#499418)

How many spins do you need to store one beam ?

And if you take just one cooled atom, can you take apart the beam to several places ? And more importantly, does the freezing operation preserve the quantumness of the light in the spins of the atoms ?

Now this surely must be a way to realize super-lightspeed-communications .. and distributed quantum computing .. imagine receiving your SETI parcel in a fridge brought to you by FedEx.

And remember, you read it on slashdot first :-)

Re:I tried to stop myself (1)

RedLaggedTeut (216304) | more than 13 years ago | (#499419)

You are welcome.. . That reply was fully expected :-)

Re:time as a fourth dimension (1)

madro (221107) | more than 13 years ago | (#499422)

If speed is a change in distance per unit time, you'll need a different unit of measurement if you're trying to describe a change in distance *and* time per unit ... what? "ether"?

I predicted this... (1)

James Foster (226728) | more than 13 years ago | (#499423)

I mean... who wouldn't?? How can anyone expect to go that fast and not get pulled over?

Re:does this break the theory of relativity? (1)

ChrisPaget (229422) | more than 13 years ago | (#499424)

c is the speed of light in a vacuum. The actual speed of light is entirely dependant on the material in which it is travelling.

Re:does this break the theory of relativity? (1)

mmol_6453 (231450) | more than 13 years ago | (#499425)

But that doesn't necessarily mean it can't be stopped...

Re:Just wondering... (1)

mmol_6453 (231450) | more than 13 years ago | (#499426)

You mean, 'does it lose energy'?

I'm not sure, but I doubt it. It would have to radiate other quanta...

Re:Faster, Light (1)

mmol_6453 (231450) | more than 13 years ago | (#499427)

As I understand it, 'space' is a region where there is a net energy level of zero...Perhaps they were able to give it a negativie net energy level?

Re:keeping light still (1)

mmol_6453 (231450) | more than 13 years ago | (#499428)

A 'beam' of light was the path that a photon took...It doesn't have any energy or substance of its own...

Think of it like a trail in an ion-cloud chamber.

Re:Holography? (1)

mmol_6453 (231450) | more than 13 years ago | (#499430)

That's how holographs already work...

Re:Just wondering... (1)

billybob2001 (234675) | more than 13 years ago | (#499432)

When you stop light, you have to rename it heavy.

Something to do with rest mass...

Re:does this break the theory of relativity? (1)

billybob2001 (234675) | more than 13 years ago | (#499433)

Also, when you want to stop light, you have to make c static

Re:Faster, Light (1)

nefertari (240766) | more than 13 years ago | (#499439)

As i understand, they slow it by putting it in a denser medium. So to speed it up, they would need something wich is thinner than vacuum. How would you do this?

I tried to stop myself... (1)

RareHeintz (244414) | more than 13 years ago | (#499442)

...but I can't!

Imagine a Beowulf cluster of those!

There! I said it! Ha!

- B

keeping light still (1)

kipple (244681) | more than 13 years ago | (#499444)

will they be able to 'store' a beam of light and keep it? how much storage space will they got? :)

Re:does this break the theory of relativity? (1)

the real jeezus (246969) | more than 13 years ago | (#499445)

Boy, is Einstein gonna be pissed!!!

I'd rather be a unix freak than a freaky eunuch

More on the subject (1)

oerf (247572) | more than 13 years ago | (#499446)

There is more about Dr. Hau's methods in an older article [] . A bit of the method as well, they are using Bose-Einstein condensate as the medium.

Re:Think its Danish (1)

oerf (247572) | more than 13 years ago | (#499447)

...and curiously the Danish female physiscist happens to be exactly the same person (Dr. Hau) who is featured in the article.

A HA !! (1)

lesnessman (247904) | more than 13 years ago | (#499448)

So that's how you make a light saber!!!

Re:Holography? (1)

Arkleseizure (251525) | more than 13 years ago | (#499452)

For a hologram, you really want to reconstruct the original light (with same phase and amplitude). If you stored the light itself and released it later, you would have a read-once hologram, of dubious usefulness.

Bomb? (1)

ThisIsSuchACoolNick (257705) | more than 13 years ago | (#499458)

When light is 'stopped' where does the energy of the light go?

Is this a generation of new bombs? I.e. what happens if I fill the medium with an enormous amount of `light' and release it?

Excuse my ignorance.

Just wondering... (1)

moz25 (262020) | more than 13 years ago | (#499463)

When light is 'stopped', does it decrease in intensity after a while or can it just be stored indefinitely?


Storing Information (1)

picoears (302223) | more than 13 years ago | (#499469)

They said they needed another light beam to release the stored one, but can they store more than one beam of light in the stored chamber? Or would putting a second beam through always restore the first? And if it is possible to store more than one, the amount of information that could be stored would be amazing. - picoears

Re:does this break the theory of relativity? (1)

Captain Daveman (305684) | more than 13 years ago | (#499472)

It does, but no-one remembered to make c final so it's a variable.

Right. What we know as the supposed physical constant of C is actually the mean (?) value of a series of observations. I believe the "true cosmic" maximum speed of light is somewhat (fractionally, I'm sure) higher.


Aryos (306513) | more than 13 years ago | (#499473)

The speed of light (c) is considered to be a barrier. This means that nothing below c can reach the speed of light and nothing moving with a speed more than c can go down to c. I was just informed about these two experiments and I must admit I wasn't surprised. I've also heard about another experiment at the MIT, in which a beam of light was speeded up to 2c and rumours about it being pattented after 5 years or so (unless someone buys or kills the researchers who dit it, of course!). Furthermore, there have been very serious indications (if not proof) that the light in space doesn't travel with the same speed in all directions, but seems to travel at a higher speed in a specific one. ...which enhances my theory...anyway...I believe that speed is only a relevant means of understanding (up to a point) the relationship beween space and what we call "time". Neverthless, there have to b inserted many mor dimensions into the game, to get things a little more clear and the bad thing is that they can only be approaches with higher mathematics an not by observation/comprehension, cause we're only 3-4-dimensional beings. Well, I only hope these experiments will not be burried and become the begginning of at least reconsidering some things about relativity. .-

Re:A HA !! (1)

Aryos (306513) | more than 13 years ago | (#499475)

Nearly. Hehehehe! To make a lightsaber you can use a normal laser beam (of high frequency, thus energy and temperature, so it can burn), a well-cut rubby (to pass the beam through) and exclude finally the beams tha go to a direction >=90 degrees when leaving the sword. An exclusion of >=60 degrees will give you some mters of burning laser. Just don't do it at home. No to mention I neglected to give you 3 more basic things you 'll need to reflect the beem and feed the sword with energy. Find it yourselves. Just don't do it at home! .- Questions: Does anyone know what happns when two photos, with the same frequency, the same fase (and generally the same energy) and different directions hit one another?

Oooops! (1)

Aryos (306513) | more than 13 years ago | (#499476)

Sorry about the mess with my copy & paste!

Re:light stopped? Or destroyed and re-emitted... (2)

Anonymous Coward | more than 13 years ago | (#499481)

I would look for the body.

But you are right, for interference phenomenae to work the way they do, you need to have identical particles.

But this is important only if you want to understand how their clever trick works. (And you need to know more -- you mostly need to know electronic energy levels, what transitions are allowed, and how waves can interfere.) Understanding the importance of the result is simpler. Light has two properties: polarization and momentum. For a particular band of momentum (corresponding to the Rubidium line they are using) the polarization state is effectively recorded into the atoms of the vapor. And this is what is used in quantum encryption, "teleportation", and other newfangled ideas.

Of course, the atoms will lose this information as they collide with each other and the vessel walls, but for a thin vapor the time scale for this is over a microsecond which these days seems like an eternity.

Recording polarization may sound simple, but it's not. And this is an indirect recording... you can't look at it to tell what the state is, but the state is preserved. I do have a clumsy explanation which hopefully some readers may be able to decipher:

You know light can be linearly polarized.. horizontal is x, vertical is y, diagonals go like (x + y) and (x - y), etc. Well, if someone hands you a beam of light, you can measure the polarization of it with a sheet of polaroid. Perpendicular to the plane of polarization no light is transmitted, parallel almost all gets throught, at 45 degrees the intensity is half. So, this seems easy.

But how do you measure the direction of polarization of a single photon? The answer is: you can't. The beam of light is an ensemble of photons that are (by assumption) in the same polarization state. When we hold it diagonally, we see 50% intensity because each photon individually has a 50% chance of making it through or being blocked. When we have say 1e6 photons, we can see that 5e5 made it through and say, ah yes, we are diagonal. But if we have only one photon to go on, it either makes it through, or it doesn't. So if it makes it through, the polaroid may be aligned to the polarization, or it may be any amount off. All that we do know for sure is that it is not perpendicular.

Also, add to this an additional subtlety that coefficients describing polarization are actually complex. e.g., you can have have a polarization in the direction (x + iy) which may be circularly polarized clockwise. (x - iy) would be counterclockwise. For this light the probability of being transmitted is 50% no matter how you orient the polaroid. But I digress... The point is, quantum mechanics is a wonderful description of the world, and this new trick will be very helpful in taking advantage of quantum mechanics in engineering applications.

Re:does this break the theory of relativity? (2)

Dr. Evil (3501) | more than 13 years ago | (#499485)

That makes no sense...

It was either Faraday or Maxwell... or somebody else around there which did some work which strongly indicated that c was a constant. Looking into that is on my list of things to do... this work prompted Michaelson and Morley to perform their experiments showing light moved at a constant speed in all directions.

And if you're interested in the "cosmic" speed, there were those pesky calculations involving the speed of light based on the orbits of the moons of Jupiter. This leveraged the width of the earth's orbit against Newtonian physics and the observed position of Jupiter's moons. Not horribly precise, but nothing is known to an infinate number of significant digits.

The constant 'C' is defined as the speed of light in a vacuum, as one poster here worded it so eloquently, the speed of light in different medium is due to absorption and retransmission.

But I'm only saying that 'C' is constant. I'm not saying what 'C' is. Just like PI is a constant, only known to a million or so significant digits (in an unaccelerated reference frame).

Stopping a photon is probably just some media spin.

No, it's true. (2)

mindstrm (20013) | more than 13 years ago | (#499498)

Eavesdropping by definition means a third party listening in on a conversation between two other parties.

With quantum communications, any intermediate listener would cause the signal to be modfied (or garbled) and one party would know the conversation was tapped, hence, they are no longer eavesdropping...

Re:does this break the theory of relativity? (2)

CharlieG (34950) | more than 13 years ago | (#499502)

Light IN a vacuum moves at a MAXIMUM of C - It CAN and does move slower, especally in other mediums.

Re:time as a fourth dimension (2)

macpeep (36699) | more than 13 years ago | (#499503)

I forgot to mention one thing.. If photons move in both the direction of time AND in some 3D spatial direction (with the speed C), then their total speed is HIGHER than C, isn't it?

Bah! (2)

MrP- (45616) | more than 13 years ago | (#499504)

I can stop light too!

::gets out flash light::

See? Now give me a Nobel prize or something, I'm a freaking genius!

Correct /etc/hosts configuration (2)

cyberdonny (46462) | more than 13 years ago | (#499505)

Many people still surf with misconfigured /etc/hosts files. In order to browse NY Times, you need to add an entry for it to this file.

Re:Just wondering... (2)

maraist (68387) | more than 13 years ago | (#499510)

When you stop light, you have to rename it heavy.

It seems to me that the photons are not physically stopped.. In fact there is little physical difference between this and regular obsorbtion of light by matter.

The main difference seems to be that instead of giving wrought energy to the electrons / nucleus, they're exclusively affecting the spin (???). Supposedly this means that the wave-front is captured instead of just a raw packet of energy. Normally an atom obsorbs a photon, then at a later time ejects either it, or some combination of photonic energy in random directions (kind of like scattering). But what I believe is happening here is that the wave-front is reconstituted by possibily analogously gyroscopic-inertial forces (I know it's not really spin, but never truely understood it) in the exact same direction.

So basically it's no different than your common everyday sun-light off a white tee-shirt sort of event except that there's no scattering, and you can use a trigger instead of random quantum fluxuations for the retransmittion.

As a final response to your statement, since the light isn't actually stopped, it isn't "heavier", much like the undetectible additional mass of an atom when it obsorbs photons. Beyond that, the slowing of matter makes it lighter, rather than heavier (according to the theory of relativity and the lorenz factor).


NYTimes exaggerates again (2)

MobyDisk (75490) | more than 13 years ago | (#499513)

This is another case of the NYTimes screwing up the technical details and making something have totally different implications than one it sounds like. They are NOT stopping light AT ALL IN ANY WAY. I like the NYTimes, but the BBC reports this tech stuff better. They are not stopping light, just copying it's parameters into the gas, then recalling them.

Read the posts by zCyl and Ferzerp to see why.

Re:light stopped? Or destroyed and re-emitted... (2)

Ferzerp (83619) | more than 13 years ago | (#499514)

in saying it's a snapshot, i mean, information of the light is stored and new light is emitted from that information. The article states that the light exitting the device does not have the exact same characteristics of the light entering. So, it is changed.

Re:Artificial Black Holes (2)

notenoughnamespace (136052) | more than 13 years ago | (#499520)

From my understanding of that work it was not intended to actually create black holes, but by slowing light down enough you could create a vortex in the material that would suck the slow moving light in, in the same way as a black hole.

This would allow lots of interesting studies of the effects, and would be a lot safer (read: less terminal) than actually creating a black hole.

This was from a New Scientist article relating to the same research.

Lots Of Love


Re:light stopped? Or destroyed and re-emitted... (2)

ar0n (197245) | more than 13 years ago | (#499526)

Correct me if I am wrong, but are they not, in essense, just taking a snapshot of a photon and then recreating it?

According to the Heisenberg Principle, that's not possible. If they had 'taken a snapshot' that would have serious ramifications for the way we perceive the world... (insert beethoven's 5th)

Re:Artificial Black Holes (2)

veranikon (202025) | more than 13 years ago | (#499527)

Hmmm. Artificial black holes, eh? Would make nice portable garbage disposals, wouldn't they? So, assuming black holes exist in all sizes, you just create a "quantum" black hole, then put it in a mason jar large enough to be just beyond the hole's event horizon. And with the intense radiation from the hole's perimeter, you could also attach a steam turbine and power your car or PC off it.

I smell a new startup. Venture capital! I need venture capital!

Re:does this break the theory of relativity? (2)

billybob2001 (234675) | more than 13 years ago | (#499529)

i thought that light always moved at c

It does, but no-one remembered to make c final so it's a variable.

Nothing is immutable - except flux.

Slow glass (2)

OlympicSponsor (236309) | more than 13 years ago | (#499530)

This reminds me of the "slow glass" stories. For the uninitiated: Slow glass is just like regular glass but the thicker it is, the longer it takes for light to pass through. So for a 1 inch thick piece it may take, say, 20 years. They put the glass out in the forest for 20 years, then install it in a house. Now the inhabitants have a 20 year forest scene streaming in the window. Other stories put the glass to other uses.

Anyway, my REAL point: what about heisenberg's uncertainty principle? As the photon slows shouldn't it's position become more and more indeterminable? And when it stops, how do they know where it is?
MailOne []

Re:Walking FTL! Care to explain ? (2)

OlympicSponsor (236309) | more than 13 years ago | (#499531)

C is a constant defined as "the speed of light in a vacuum". You can't just take any light you happen to have lying around (in gas chambers or underwater or wherever). Light slows down going through ANY substance.
MailOne []

Re:A HA !! (2)

lesnessman (247904) | more than 13 years ago | (#499532)

-snip- .- Questions: Does anyone know what happns when two photos, with the same frequency, the same fase (and generally the same energy) and different directions hit one another?

Not exactly sure, but I know that it's a good way to get rid of Stay Puff Marshmelow Man.

Re:does this break the theory of relativity? (2)

Arkleseizure (251525) | more than 13 years ago | (#499533)

Cerenkov radiation, I think

Re:Cool, but... (2)

eXtro (258933) | more than 13 years ago | (#499534)

The transistors in the memory of your computer store a value which is nearly identical to the "1" or "0" which was written to it. If a high voltage is written it is drained over time through parasitic capacitances. Periodically the value is refreshed (brought back up to the correct level) through refresh.

When you read from memory you're essentially reading through a high gain buffer which restores any signals which are almost high to a high signal or which are almost low to a low signal.

As long as there is some means to detect the appropriate value of a signal with a high enough probability of success nearly is good enough.

Re:does this break ....PROBABLY REDUNDANT BY NOW! (2)

Ashleigh (260287) | more than 13 years ago | (#499535)

First off, c is the speed of light in a vacuum, and light travels at differents speeds in different media. This means that when moving from a medium into one in which the speed of light is slower than the first, the lightwaves/photons (whatever) need to release some energy, (As energy=hf, and f=speed of light/wavelength [sorry, couldn't find lambda sign]so there would be a difference in energy after going into a "slower" medium) which is given off as, I believe, flashes of visible light (yes?, no? maybe? I'm unsure)[Also, then how does light speed up going into faster media? Does it? What accelerates it if it does? Anyone?)
(mmmm, a bit offtopic, aren't i?)

Relativity (or some part of it anyway) means, at least for this case, that nothing can travel faster than the speed of light in that medium. And most massive objects (like ships) cant come anywhere near close. Please, correct me if i am wrong, but as an object (not light) accelerates toward fairly fast speeds (or velocities, if you prefer, but I just want the scalar) it gets more and more massive, and hence acceleration gets harder and harder (a=F/m)
Very much out of my depth here, considering only formal education in physics so far is high school level, but does the above have anything at all to do with the wave behaviour of non-light particles? I mean, how can an object gain mass due to acceleration, unless looking at kinetic mass (?) being calculated by energy and velocity, energy being calculated by that formula given above.

Please correct me, i am rambling. May as well mod me down now.

Re:Just wondering... (3)

coreman (8656) | more than 13 years ago | (#499537)

Intensity is just the number of photons as percieved by your eyes. More intensity means more photos hitting your receptors. So, if the photons are conserved, just stopped and then restarted and redirected in the same direction, it would be percieved as the same intensity. You do have to ask if the number of photons is modified and/or increased by the slow down/stop/speed up process.

time as a fourth dimension (3)

macpeep (36699) | more than 13 years ago | (#499540)

Think about a football field that is 100 meters from end to end. Now think of a guy that runs in a straight line from one end to the other, along the sidelines. If he runs 10 meters per second, it takes him 10 seconds to run the entire length of the field. Now make the guy run from one corner to the other. He still runs at 10 meters per second, but it will take him more than 10 seconds to reach the other end. By spending some of his motion in the width-direction of the field, his motion in the direction of the length of the field becomes slower.

Think for a moment that time works just like a spatial dimension. You have a specific absolute speed in a specific direction.. time. When you start moving to some spatial dimension (one of the three traditional ones), your motion in the direction of time becomes slower because you are no longer fully "commited" in that direction.

Now think about photons. They move with ALL of their speed in some spatial dimension. Does this mean that photons stand still in time? If you slow down light, does this mean that time actually starts ticking for them? Could it be that the fading of the light has something to do with the fact that time runs for them? If they are in an absolute vacuum, light doesn't fade because time stands still, no matter how far you shine the light. Introduce "dust" and it slows down and fades.

I'm sure my theory is very flawed but I'm not exactly sure at what point. I mean time DOES slow down when you move, but am I looking at this the wrong way?

Holography? (3)

wowbagger (69688) | more than 13 years ago | (#499544)

Obligatory no log in link []

However, I wonder if this could also be used for holography: freeze the interference pattern into the material, and read it out later, reconstructing the image. In theory, since the material could record the interference pattern in three dimensions rather than two (like a photographic plate), this might allow for more detailed holograms.

Re:light stopped? Or destroyed and re-emitted... (3)

mmaddox (155681) | more than 13 years ago | (#499545)

...we sacrifice the idea that a particle has an individual identity...

That is the key concept that is poorly conveyed within the Times article. It's obvious that even good science reporting is not necessarily understandable by the masses without the teaching genius of a Sagan or the like.

This brings up an interesting topic, the subject of many late-night, coffee-fueled debates around here: If you could teleport a human through some means, would this property of "no-unique-identity" actually allow you to create an EXACT COPY of the teleported human (who is unaware that he/she/it is even a copy), while, in fact, you KILLED the original? How would you detect this?

Re:Don't Forget (3)

pseen (219746) | more than 13 years ago | (#499546)

I believe you forgot an 0 there! Login : slashdot2000 pass : slashdot2000 Worked for me!

Artificial Black Holes (3)

dachshund (300733) | more than 13 years ago | (#499548)

I've heard that this capability might allow scientists to create artificial black holes. Apparently if you can slow light down enough, you might be able to create a situation in which a singularity comes into existence. I wish I had more information on this-- I think I read it in Discover a few months back. I have no idea if this discovery would make such a thing possible. Anyone with more information? I'm obviously fairly ignorant in this area, but the article I read seemed to take the possibility seriously enough.

light stopped? Or destroyed and re-emitted... (4)

Ferzerp (83619) | more than 13 years ago | (#499550)

From reading the article, it sounds to me like the light is being destroyed and then new *nearly* (from the article it says it's not the same) identical light is emitted. While interesting, this phenomena is no where near as much of a breakthrough as if they had actually stopped light.

Correct me if I am wrong, but are they not, in essense, just taking a snapshot of a photon and then recreating it?

I would go in to some of the implications of actually stopping light (instantaneous communications, etc), but it is too early in the morning for my mind to work that deeply :)

Re:light stopped? Or destroyed and re-emitted... (5)

zCyl (14362) | more than 13 years ago | (#499551)

Technically, taking a quantum snapshot of a photon and then recreating it is the same thing as stopping it and restarting it. When we get down to such a level, we sacrifice the idea that a particle has an individual identity, and instead only acknowledge the existence of a set of properties for the particle. If the experiment simply resulted in light of the same frequency being emitted, then this would still be interesting as a means of optical storage, but by no means would it be as interesting from a theoretical perspective. What makes it interesting is that the imprint of the light is stored in the quantum spin states of the gas atoms, which means there is a theoretical possibility (which can't be determined too well from a nytimes article) that all the "uncertainty information" inherent in the photon is preserved across the restart. That would make this a true stopping and restarting of a photon.
Load More Comments
Slashdot Login

Need an Account?

Forgot your password?