http://www.newscientist.com/news/news.jsp?id=ns99992796

Sounds very unbelieveable to me.

Here's what I presume is happening: the only thing going faster than light is an abstract mathematical quantity.

This was brought up on another BB I read and basically as long as no information can actually be transmitted it's OK.

See these links:
http://www.aip.org/physnews/update/536-2.html
http://scienceworld.wolfram.com/phys...erluminal.html

Also quantum entanglement works the same way. If you seperate two entangled photons by a significant distance, a change to one will very nearly instantly change the other. However, you can't use this to send information, being that you can't observe one without changing it.

Kudos to MrBrak from TrekBBS: Trek Tech!

My research is actually related to this subject. What they have appeared to do is managed to get group velocities greater than c. The phase velocity is still about 2/3 c. The group velocity of an electromagnetic pulse will vary from c in any material where there is dispersion. The group index that a pulse sees is: n_g = n_0 + omega*dn/d{omega} where n_0 is the phase index and omega is the frequency of the light. What these researchers have done with their cables is to tailor the dispersion so that there is a very rapid change in the phase index as a function of frequency (dn/d{omega} << 0). Thus they get a negative group index and "fast" light.

Since they only have two frequencies, it is only the interference pattern that appears to be superluminal. However, this doesn't violate causality. If you were to quickly "cut-off" the two waves, the "cut-off" will appear L/(2*c/3) later (where L is the length of the cable). It seems to me that if creating "fast" light was so easy, they should be able to create "slow" light (dn/d{omega} >> 0) as well.

__________________
Old laser physicists never die, they just become incoherent.
These days, every Tom, Dick, and Harry thinks he knows what a photon is, but he is wrong. - Albert Einstein

From the article:

"Signals also get weaker and more distorted the faster they go, so in theory no useful information can get transmitted at faster-than-light speeds, though Robertson hopes his students and others can now rigorously and cheaply test those ideas."

Most of the technicalities here are over my head but I have been very intrigued by this research since seeing it on a NOVA program on 'Time'. In that program, the researchers sent a signal through a solid barrier faster than light that was not impeded. Quantum tunneling was occurring in some way.

The researchers who were German said that other scientists had claimed no useful information could be sent this way. The German's played back a tape of Mozart that had been sent faster than light by their experiments to show information could be sent.

It sure seems like we may be about to make some kind of breakthrough. Maybe there are circumstances where the speed of light is not the limit in the quantum part of our world.

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Democracy Now! - The lost art of investigative news reporting.

From the http://www.aip.org/physnews/update/536-2.html
article -

"Sent into a chamber of specially prepared cesium atoms, the light pulse exited the chamber before the peak of the input pulse entered it."

For a moment there I figured they could set up a device to cut the power to the cable on receipt of the "light pulse" before the input pulse could be sent, which would be kind of fun to watch, but it certainly looks like "information" is being transmitted ftl, whichever way you look at it. Mozart huh? Was that the "A Little Light Music" CD perhaps...?

(okay, I'll get the bucket...)

I'm still very confused by the claims of this article. Every resource I find simply says, "there is nothing preventing apparent motion faster than c...", but "no energy or information actually travels faster than c."

This article says,
"Once inside the chamber, the pulse is rearranged such that the peak reappears at a position a little farther ahead in the chamber. This causes the composite pulse to emerge from the chamber earlier than if it had been traveling through the chamber at the speed of c."

Maybe it's just blind faith in Albert E., but it seems like causality is violated if real information exceeds c and that just doesn't make sense. Is the composite pulse or peak different than the original signal?

There is no violation of causality if the signal does not travel backwards in time. In the cited experiment, the peak reaches its destination faster than it should at light speed, but still in a measurably positive amount of time.

__________________
Does earth plug a hole in Heaven or Heaven plug a hole in Earth? -Peter Gabriel

Atko,
Just in case you didn't know, it's all here.

I'm familiar with this work. What happens is that the very leading edge of the input pulse is transmitted forming the output pulse and the rest of the pulse (including the peak) becomes absorbed. This gives the impression that the peak of the pulse has moved through the cesium atoms at a velocity greater than c. In actuality, the peak of the input pulse becomes the far tail of the output pulse. Also note that the output pulse is very weak since most of the energy has been absorbed.

Superluminal propagation using evanescent fields may have a similar intuitive explanation. I'm not as familiar with this research, but it is interesting. Nevertheless, I think I can confidently say that it doesn't violate causality.

__________________
Old laser physicists never die, they just become incoherent.
These days, every Tom, Dick, and Harry thinks he knows what a photon is, but he is wrong. - Albert Einstein

By demonstrating that the wave can propogate faster than c, does this provide hypothetical grounds for a disproof of causiality as a function of c?

I don't think so. Lots of things can go faster than light, without violating special relativity at all.

I'm gonna have to wait for the user friendly version to come out on a NOVA program or some equivilent. In the mean time I'll just add this little discovery to my contemplating the Universe file. [img]/phpBB/images/smiles/icon_smile.gif[/img]

__________________
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Democracy Now! - The lost art of investigative news reporting.

Nice example, though it is not an example of FTL speed though. The point, as it was indicted, is merely a reflection, that by your example did not violate SR because the photons reflected from the moon arrived in the appropriate time frame of 2.6 seconds later, causing the illusion. The point did not move, as it were, it was impeded by a closer object, causing reflections from each point down the line of the paper as you turned. You would have gotten, in effect, a nice streak down the page as the light reflected from each relatively closer point in proportionately less time. That is actually as nicely packaged PROOF of GR.

That was the point.
I'm flattered, but I have no idea what you mean by a proof. Of general relativity?

GrapesOfWrath

Presumably too, as you swung the beam away from the moon you would have created a nice arc of light across space. Since light only bends around gravity sources you would have created a strong gravity well between the Earth and the Moon (just for starters). This could well have had catastrophic effects. Be more careful with that light beam in future!

(kids - don't try this at home)
[img]/phpBB/images/smiles/icon_biggrin.gif[/img]

I wish you had warned me sooner. I just shown a laser in the mirror, not realiziig how mcuh grivaty a mrrior had, and nwo I cant' see.