Speed of Light Exceeded?

PreacherTom writes "Scientists at the NEC Research Institute in Princeton, NJ are reporting that they have broken the speed of light. For the experiment, the researchers manipulated a vapor of laser-irradiated atoms, causing a pulse that propagates about 300 times faster than light would travel in a vacuum. The pulse seemed to exit the chamber even before entering it." This research was published in Nature, so presumably it was peer-reviewed. It's impossible from the CBC story to determine what is being claimed. First of all they get the physics wrong by asserting that Einstein's special relativity only decrees that matter cannot exceed the speed of light. Wrong. Matter cannot touch the speed of light in vacuum; energy (e.g. light) cannot exceed it; and information cannot be transferred faster than this limit. What exactly the researchers achieved, and what they claim, can only be determined at this point by subscribers to Nature.

Comments

It works...

[fortunato]

I wrote this yesterday.

Re:It works...

[Anonymous Coward]

expect a dupe tomorrow

Re:It works...

[AchiIIe]

It must be true, I read this article months ago....

http://science.slashdot.org/article.pl?sid=05/08/2 0/1440228 ..

Now pardon me as I karma whore:

By Trip11

Everyone say it together with me: "Phase velocity vs Group velocity" There are no photons in this experiment that are traveling faster than the speed of light. Only collections of them that 'appear' to be doing so. Think of this as an example: I space people out in a line, each of them two light minutes apart from the people next in line (all at rest with respect to each other). Now I go about talking to them and informing them of my plan. At 12:00 the first person waves, at 12:01 the second person waves, at 12:02 the third person waves, and so forth. My "wave" is propogating, therefore, at twice the speed of light. This is the same thing that this experiment is doing more or less. By spending extra time setting up the experiment, you can make it appear that a light pulse travels faster than c, but like my "wave" it is only an appearance.

By: Justanyone

Information flow (see: Steven Hawking's theories) cannot propogate at faster than the speed of light, or causality is violated and we have (dead virgins/future grandfathers) all over the place.

All 4 basic forces: electromagnatism, gravity, strong nuclear, and weak nuclear (not Nukular; bite me, George) forces propogate at the speed of light in their reference frame. If we switch frames we're not fooling anyone; if we preposition information we're not watching causality violations.

This kind of story is quite irritating, not due to the actual achievement involved (playing with light propogation is actually very cool geek-cred stuff), but the overhype and miscommunication to all the laypersons out there who just go, "Yup, that's an 'oops', they said it was a law and now it ain't. I guess evolution might not really be true, dad-gummit, I don't trust me none o' dem smarty pants anyway."

By: Alwin

Set up say, 1000 domino blocks in a row. Then tip the first one over. Given constant size, weight, spacing of individual blocks, and a horizontal surface, you will observe blocks falling down at a constant rate/speed ('c'). Given that constant rate/speed, tipping over the first block will cause all blocks to fall down, tipping over the last block some time later. Time delay calculates as distance divided by 'c'.

Now, create 'extreme conditions', where the first domino block is down, the last one is still standing, and halfway down the row, blocks are falling, but not quite down on the floor. Then, observe the 'wave front' of falling domino blocks. It will appear to move faster than the previously determined 'c'. How come?

Look more closely: as each block falls down, there's a fixed delay before it hits the next block. But what happens under our 'extreme conditions'? At the exact time a previous block would have hit the next one (under normal circumstances), that next block is already falling down! The time it takes for the 1000 blocks to fall down, is less than what normally would be expected.

Did this 'c' constant get violated? Nope, it still took the same amount of time for each block to fall down. Was the maximum 'c' speed exceeded? Nope. After tipping the first block, it still took the same amount of time before this 'information' was passed on to the next block. With a set of 1000 blocks all standing, the time needed for an initial 'disturbance' to be passed on to the last block, is still limited by 'c'.

So these 'extreme conditions' are like pre-tipping each block, and let you observe something that appeared to move faster than 'c'.
Nice for the lab folks, but other than that, sensationalist journalism. Wake me up when trans-atlantic ping times (sending actual packets with random data) dive below the time dictated by the speed of light.

Re:It works...

[EinZweiDrei]

'Nothing travels faster than the speed of light with the possible exception of bad news, which obeys its own special laws. The Hingefreel people of Arkintoofle Minor did try to build spaceships that were powered by bad news but they didn't work particularly well and were so extremely unwelcome whenever they arrived anywhere that there wasn't really any point in being there.'

Results of experiment published in the past

[Epsas]

This story is from November 2000. If Princeton scientists *did* exceed the light-speed barrier, then it the evidence would only naturally show up in the past. Interesting!

Re:Results of experiment published in the past

[darkitecture]

This story is from November 2000.

So the dupe will be posted 6 years ago? Awesome! I'm looking forward to it.

Re:Results of experiment published in the past

[unitron]

So the dupe will be posted 6 years ago? Awesome! I'm looking forward to it.

Shouldn't you be looking backward to it?

Group Velocity Again

[Effugas]

99% chance it's this again:

You're stuck in traffic, behind an accident. They clear the accident. Slowly, every car speeds up now that the blockage is gone. If you're looking from above, you'll see a "wave" move through the line of cars, as each takes a few seconds to realize he can accelerate.

This wave is the group velocity, and very much has nothing to do with the speed of each individual car.

Suppose all the cars were wired electronically to know that they could all accelerate at once. That knowledge would move at nearly the speed of light.

No car would be moving at the speed of light. Everyone would just hit their gas pedal at almost the same time.

Almost every time we see these stories, this is the type of speed they're talking about.

Re:Group Velocity Again

[jez9999]

So YOU were the one causing that damn red blob when I was trying to watch the eclipse? Go test out your new laser toy elsewhere!

Information?

[Jugalator]

So, was any information transmitted? Then it's big news I suppose, otherwise not? From the sound of it, a "pulse" make me suspicious, but I lack the full physics geekdom to completely dismiss the story. Anyway, speed of light only applies to transmission of information, not group velocity.

Re:Information?

[ZeroExistenZ]

Nothing can ever exceed speed of light, not even information,as proved by Hawking.

That, and earth is a sphere in the center of the universe, as Plato proved.

Time . . .

[OverlordQ]

"Good. No, the answer is an orange and two lemons."

"Lemons?"

"If I have three lemons and three oranges and I lose two oranges and a lemon, what do I have left?"

"Huh?"

"Okay, so you think that time flows that way, do you?"

-Mostly Harmless

Obligitory Futurama

[Rik Sweeney]

Farnsworth: These are the dark matter engines I invented. They allow my starship to travel between galaxies in mere hours.
Cubert: That's impossible. You can't go faster than the speed of light.
Farnsworth: Of course not. That's why scientists increased the speed of light in 2208.

How do I mod down kdawson and the /. editors?

[osu-neko]

I have mod points, but I can't figure out how to dole out some negative karma to either the person sending in a link for an over six year old story, or the editor who approved it. >:(

This research was done in 2000

[Anonymous Coward]

In fact, this research is so old that Dr. Lijun Wang's FAQ page describing the experiment is no longer on the Internet. It has to be located through the Internet Archive: http://web.archive.org/web/20041012175312/www.neci .nj.nec.com/homepages/lwan/faq.htm

Here's what he said:

Q. How to interpret those earlier press coverage?

A. It has been mistakenly reported that we have observed a light pulse's group velocity exceeding c by a factor of 300. This is erroneous. In the experiment, the light pulse emerges on the far side of the atomic cell sooner than if it had traveled through the same thickness in vacuum by a time difference that is 310 folds of the vacuum transit time.

In our experiment, a smooth light pulse of about 3-microsecond duration propagates through a specially prepared cesium atomic chamber of 6-cm length. It takes 0.2 nanosecond for a light pulse to traverse a 6-cm length in vacuum. In our experiment, we measured that the light pulse traversing through the specially-prepared atomic cell emerges 62 nanosecond sooner than if it propagate through the same thickness in vacuum. In other words, the net effect can be viewed as that the time it takes a light pulse to traverse through the specially prepared atomic medium is a negative one. This negative delay, or a pulse advance, is 310 times the "vacuum transit time" (time it takes light to traverse the 6-cm length in vacuum).

Q. Is Einstein's Relativity violated?

A. Our experiment is not at odds with Einstein's special relativity. The experiment can be well explained using existing physics theories that are consistent with Relativity. In fact, the experiment was designed based on calculations using existing physics theories.

However, our experiment does show that the generally held misconception "nothing can move faster than the speed of light" is wrong. The statement only applies to objects with a rest mass. Light can be viewed as waves and has no mass. Therefore, it is not limited by its speed inside a vacuum.

Information coded using a light pulse cannot be transmitted faster than c using this effect. Hence, it is still true to say that "Information carried by a light pulse cannot be transmitted faster than c." The detailed reasons are very complex and are still under debate. However, using this effect, one might be able to increase information transfer speed up to c. In present day technology, information is transmitted at speed far slower than c in most cases such as through the Internet and inside a computer.

The page also contains an "intuitive" explanation of the phenonmenon. A careful reading and some high school level physics make it simple to understand in a logical sense, but it remains completely incomprehensible intuitively (at least to me).

Not all forces travel at 'c'...

[Roger W Moore]

All 4 basic forces: electromagnatism, gravity, strong nuclear, and weak nuclear (not Nukular; bite me, George) forces propogate at the speed of light in their reference frame.

Not at all correct. First the weak force is transmitted by W and Z bosons which have mass and therefore CANNOT propagate at the speed of light. Secondly in their own reference frame, by definition the weak force bosons will not propagate at all since your own reference frame is defined as the frame you are at rest in. Thirdly massless particles have no reference frame of their own.

I know you were quoting someone else but please pick someone who at least has a clue what they are talking about!

Re:here is my example

[FractalZone]

A nice example, but what is it supposed to show?

Sufficient amounts of ingested caffeine can make everything seem faster! I like experiements which require one to consume an entire can of coffee in order to cut slots it in to do psudo-physics research. :-)

Re:here is my example

[kickedfortrolling]

you're just lucky you're not in soviet russia- where i understand the subject and objects of a statement are reversed for the sake of comedy

Re:here is my example

[ComaVN]

Actually, it shows that some things we, humans, perceive as an entity (the pattern of light and shadow), are not actually physical objects, and thus are not governed by the same laws as physical objects (such as v
The same goes for group velocity.