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.

Ok, lemme take a poke at what is might be

[realcoolguy425]

I've been hearing group velocity. I understand nothing, but I remember from a class, no idea which one now, that you can seem to exceed the speed of light, but you're not really doing it. For example take a tube of balls, packed end to end. There is no more room for any of the balls, so the moment you put one in on one end, the other one immediatly pops out. Now, if that tube of balls was empty, then it would take n amount of time for that ball to roll the length of the tube. Is this the same conceptionally or is it different?

Question

[Lord Aurora]

Ok, so all this nonsense about group velocity and whatnot tickles inside of me like so much uncooked rice, and I have a little question. Say you set up a couple million little blocks across the Atlantic Ocean. Block 1 is set to pop up at 12:00, Block 2 at a time just the tiniest bit afterwards, and so on, so eventually what you have is a wave of blocks popping up, and let's say this 'wave' 'moves' faster than the speed of light. Follow? Now, put the blocks inside a perfect vacuum, slope their tops toward the next block, and put a bouncy ball filled with old love letters on top of Block 1. Press Start. All things being equal, isn't the little bouncy ball gonna move faster than the speed of light? And since we get to read the old love letters at the end, we're transmitting information, right? Now, that obviously doesn't solve the problem of information moving faster than light (as I'm relatively (no pun intended) sure it has to move of its own recognizance), but it's kinda fun, and the bouncy ball IS moving faster than light. Someone clear me up here.

(Oh. No friction, by the way. Let's assume everything's soaked in WD40 or whatever.)

Not in Nature...

[tgv]

Well, it's from Nature 406 (6793): 277-279 Jul 20 2000. The article is cited 315 times and seems dispted. Here is the abstract for those poor souls without access to Nature, Web of Science, Scopus, etc.:

Einstein's theory of special relativity and the principle of causality(1-4) imply that the speed of any moving object cannot exceed that of light in a vacuum (c). Nevertheless, there exist various proposals(5-18) for observing faster-than-c propagation of light pulses, using anomalous dispersion near an absorption line(4,6-8), nonlinear(9) and linear gain lines(10-18), or tunnelling barriers(19). However, in all previous experimental demonstrations, the light pulses experienced either very large absorption(7) or severe reshaping(9,19), resulting in controversies over the interpretation. Here we use gain-assisted linear anomalous dispersion to demonstrate superluminal light propagation in atomic caesium gas. The group velocity of a laser pulse in this region exceeds c and can even become negative(16,17), while the shape of the pulse is preserved. We measure a group-velocity index of n(g) = -310(+/-5); in practice, this means that a light pulse propagating through the atomic vapour cell appears at the exit side so much earlier than if it had propagated the same distance in a vacuum that the peak of the pulse appears to leave the cell before entering it. The observed superluminal light pulse propagation is not at odds with causality, being a direct consequence of classical interference between its different frequency components in an anomalous dispersion region.

For another, more understandable report, here is a BBC website: http://www.whyevolution.com/einstein.html [whyevolution.com] (search for Wang).

here is my example

[deathcow]

You put a lightbulb inside a spinning coffee can with slits at 4 equally spaced spots around the circumference.
The photons are projecting out of the slits. As the can spins, the pattern of light and shadow turns and projects on the surroundings.

The outside surface of the can is moving at 1 full turn per second.

10 feet away from the can, the pattern of light and shadow is moving at 31.4 feet per second.

100 feet away from the can, the pattern of light and shadow is moving at 314 feet per second.

At just 2 miles from the can (we are using a BRIGHT bulb), the light and shadow is moving 22,619 miles per hour!

Re:It works...

[BigBuckHunter]

I was under the impression that they simply used waves within a medium already moving close to the speed of light to overcome the Fitzgerald contraction (avoid addition of velocities). In my mind, it would work like the following....

Drive a bus at .99C. Have the back row stand and sit. Then the next row stand and sit, then the next, so you get a wave going from the back of the bus. If you get people doing the wave fast enough, the wave may exceed the speed of light while the transport mechanism does not.

I can see how this would be useful for faster-than-light communication, but since nothing (well, no "matter")actually exceeds the speed of light, none of the fundamental laws are broken.

I could be totally and absolutely wrong about all of this.
BBH

thiotimoline

[bobv-pillars-net]

Was I the only one who skimmed the story header and thought of Thiotimoline? [wikipedia.org]

Re:It works...

[Fastolfe]

Time dilation would prevent us from agreeing on your speed or changes in your speed. Since you're traveling at c-1mph, time is passing MUCH more slowly for you than it is for me. When you add 5mph to your speed, since we disagree about what an "h" in that "mph" is, I see a far more modest increase in your speed. From my perspective, no matter how fast you try to go, you'll always be slightly slower than the speed of light.

From your perspective, however, this isn't true. With enough energy (a hopelessly implausible amount), you could accelerate way beyond the speed of light from your perspective, and travel from one end of the galaxy to the other in 12 years, but for those back home watching you in telescopes, it would take well over 100,000 years, because you've never actually gone faster than light.