I wonder.., Full story at http://www.physorg.com/news66582110.html

http://www.physorg.com/news66582110.html

If that animation is accurate, what would happen if ("magically" - maybe using an LCD?) the light pulse was prevented from entering the wire as soon as it was detected leaving it?

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we think that our universe the connexion of space and time( space-time ) derived of possible violation of opperatorPT and does appear two distictis torsions asymmetry that generates the curvatures of space-time " forward in time" and "backward in time".then in these curvatures the past and future alredy exist.
the universe multi dimensional is generated by two torsion disticts,and these deformation generate infinities "two torsion disticts".
we thinh that time also is generated by groups of infinities subtimes connected the subspaces correspondent.
antonio pocobi

Turns out that any physical way of cutting off the pulse... like dropping a little gate, turning on a LCD, cutting the cable, etc. has to be so fast to cut off the first pulse that the act of stopping the pulse will make a new pulse of it's own... and that could be the one coming out of the other end of the cable.

What I don't get is: why can't we use this to send info faster than light?

What if I send 2 pulses? If I get 2 detectable, distinguishable pulses instantly out the other side I can send binary.
Yes, the bit rate won't be any faster than I sent them in, but I didn't have to wait for them to come out the other side. I could run a cable from here to Mars and not have to wait on the delay with those two robots...

Whenever you see the words "faster than light", you should ask two questions:

Q1: Are they talking about the speed of light in a VACUUM?

A1: No, they're usually talking about the speed of light in some sort of material like glass, which is typically a third slower than light in a vacuum. The speed of light in a vacuum is the real speed limit.

Q2: Are they talking about phase velocity or group velocity? If the article doesn't say, then either the reporter didn't ask the right questions, or the researcher is trying to mislead investors.

Group velocity (q.v.) is the speed of an actual information-pulse, when you factor out reflections and stray ripples.

Phase velocity (q.v.) is an illusory movement of wavelets which SEEM to move faster than light, but actually don't. You can see an example of this at the front of a moving row-boat traveling faster than its own wake. The wake falls behind the boat on either side -- that's the group velocity. If you 'send a signal' by throwing a pebble in the water, the ripples fall behind the boat -- again, group velocity -- the speed of an information-carrying wave in water.

But if you look at the bow wave, you see wavelets that SEEM to be traveling faster than the larger wave they're part of. They appear at the back of the bow wave, move quickly to the front, and disappear. These are phase-velocity waves, and their high velocity is illusory. They don't carry information, because they don't appear until an information-carrying wave has already moved past, and disappear when they reach the front of the msin wave.

Most materials have a constant index of refraction, which tells you how much light slows down in that medium ( Snell's Law of refraction ). In a 'tricky' medium, the index of refraction can be shifted up or down using laser pulses, or can even be made negative. The catch is that the laser pulse which performs the trick are themselves traveling slower than light in a vacuum, so none of the ripple effects behind them can carry information faster than the causative wave -- what you get is a 'bow wave' with some phase-velocity ripples running around inside it.

There's nothing mystical about light slowing down ( index of refraction suddenly made large or very large with respect to that particular frequency of laser light ).

There's nothing mystical about STOPPING laser light -- which is simply captured by the atoms in a laser rrystal. A laser crystal can emit laser light, and under some circumstances can re-absorb it, transferring the energy of the light to excited electrons in the laser crystal. 'Stopped' light can essentially be stored and re-released.

There's nothing mystical about light traveling backward. A laser device called a "phase conjugating mirror", is described in _Scientific American_, January 1986. The phase conjugating mirror ( PCM ) creates a backward-moving clone of any light passing through it, referred to as "time-reversed light", which retraces the original path of the light.

Such devices are all very useful for optical computers, and that's why they're being funded / researched. Almost none of the researchers are aiming for faster-than-light effects, because laser effects work on well-known ( slower-than-light ) equations.

However there are always a few reporters who like to play with people's heads, by not explaining group velocity vs. phase velocity, and by playing with words so it sounds like somebody is doing FTL research. Again, general relativity only prohibits transfer of information faster than light in a vacuum. Quantum mechanics has a similar principle called the No-Communication Theorem -- which merely says that although quantum-entangled particles can 'agree' at a distance, they can't carry usable information. If you send one entangled particle to Alpha Centauri and measure the other one, the two particles will will 'agree' ( e.g. if one is spin up, then the other is spin-down. But since the measurement at Centauri comes out completely random, you still have to wait 4.2 years to compare results by radio, in order to 'decode' the information.

Every physics student has thought "there's gotta be a way...", and has eventually realized [often by trying it] that the 'usual tricks' don't work.
For better news on slow light experiments, backward light etc. see weekly Physics News Update at Amer. Inst. of Physics http://www.aip.org/physnews/update

Another good source on FTL questions is the the sci.physics FAQ
http://math.ucr.edu/home/baez/physics/

NOTE: When choosing science resources for your child, you might want to steer clear of sites that claim to offer 'science' information but don't actually have experts screening it. Some 'science' sites rely on user ratings to select their material, the problem being that flakes like to read what they hope is true, and many reporters cultivate 'tabloid science' readers.

Chris N writes:

"What I don't get is: why can't we use this to send info faster than light?

"What if I send 2 pulses? If I get 2 detectable, distinguishable pulses instantly out the other side I can send binary."

The catch is that when you chop the wave, the PERTURBATION travels at the slower group velocity, not the faster phase velocity. In practice, you're probably going to chop the wave by using an ultrafast laser pulse to turn a square of material opaque. OK, you've just cut off the forward-moving electromagnetic field passing through that square. Now suppose you have two computer-simulations you can compare, one if you don't chop the wave and one if you do chop it. Compare the simulations in slow motion. The change you introduced ( called a "perturbation" ) propagates slowly forward. It doesb't immediately come out the other side.

Now zoom the simulation on what's going on. Just beyond the chopping point, un-chopped light is still moving forward, at the speed of light in that medium -- those waves don't know you chopped the waves behind them. Other waves are coming the other way, toward the chopping point. They haven't gotten the message either that anything has changed.

Now zoom in further, to the atomic scale. Again you see the light waves traveling at their normal speed in the medium ( slower than in a vacuum ). More specifically, the light waves are following Maxwell's equations and quantum electrodynamics -- both of which are causing the PERTURBATION to advance slower than light. You notice that different wavelengths are present, because the experimenter has been monkeying with the index of refraction and whatnot. The differing wavelengths move through each other causing a vernier effect, a rapid interference-ripple that seems to move quickly, but isn't carrying the perturbation forward. In fact as your perturbation wave advances slowly forward, you notice that your perturbation has its OWN phase-velocity waves trapped inside, like the bow wave of the boat. Uour perturbation wave is undulating slowly forward ( group velocity ), quivering like jell-o as it goes ( phase velocity ). Such simulations are valid because they track perfectly with the experimental data.

You're correct in a sense that chopping the wave introduces a new wave -- and can be modeled as adding a cancellation wave. The catch is that you're not only creating a different wave -- you're starting a new WAVE PACKET, separate from the old one.

The act of chopping also 'chops off the tail' of each individual photon wave packet that has just passed through the guillotine -- but that merely reshapes the back end of the quantum wave packet(s), not the front end, if you play with a Fourier applet. There was an excellent article in _Scientific American_ several years back, showing how the wave packets look for a tunneling electron, and why you can't just 'clip' the trailing edge of a quantum wave packet to make the average wave packet go faster. No matter how you trim the ttail end, the leading edge of the wavepacket still can't arrive at the destination any faster than light -- and each time you apply a trim, you create a new wavepacket for the portion you sculpted. Your sculpting tool can't catch up with the portion of the wave that's already gone on ahead, because your sculpting tool ( an ultrashort laser pulse ) can only travel at the speed of light in a vacuum.

Tricks with phase velocity are a little like the Cosmic Used Car Lot illusion. The cosmic car lot is square, one light-year across, with a strong of lights running around it. All the lights are wired to your desktop. You can program the lights so that the light seems to race around the big square once per second, far faster than light. The catch is that when you turn on the power, it takes several months for the electricity to travel ( at the speed of light ) to all the lights on the square. So what you see is a 'bow wave' of illumination moving out from your desktop. Within that bow wave are racing waves of light chasing each other, but they don't carry any information for you because they've already been sent and you can no longer recall or change them. That's exactly what happens in a slow light experiment, when the experimenter sends pre-programmed waves on ahead to 'set up' the experiment for the target pulse, to make the target pulse slow down, stop, run backward or whatever.

--
A computer does what you tell it, not what you want.
Quantum mechanics does what it wants, not what you tell it.
Quantum computers will all have labels "Schrodinger's cat inside."

we think that the continuum space-time is generated by two torsion distict that do generate particles and particles and both lorentz's transformations.it is the connexion of space-time is given by the connexion space and time through of strong violation of opperator PT=CPT and defined by non linear fields in space-time,generated by 2 -rotation systems in subspace-time of 8-dimension(octonions)complex and 16 dimension real that are projective for minkowkan imaginary in 4-dim. that violate causality due beakdown of pt,and therefore the existence superluminal signals.in that universe go forward in time and backward in time is not concrete,because "past" and "future" already there are into of continuities of space-time.
Antonio carlos motta
mott.phys@bol.com.br

we think that the continuum space-time is generated by two torsion distict that do generate particles and particles and both lorentz's transformations.it is the connexion of space-time is given by the connexion space and time through of strong violation of opperator PT=CPT and defined by non linear fields in space-time,generated by 2 -rotation systems in subspace-time of 8-dimension(octonions)complex and 16 dimension real that are projective for minkowkan imaginary in 4-dim. that violate causality due beakdown of pt,and therefore the existence superluminal signals.in that universe go forward in time and backward in time is not concrete,because "past" and "future" already there are into of continuities of space-time.
Antonio carlos motta
mott.phys@bol.com.br

Really? You never know what Divine Albert has discovered. Relativity hypnotists know no limits.

Pentcho Valev

There are things that do in fact travel faster than light. Thr Russian Scientist, Kozyrev, did experimentation with torsion fields that determined their propagation speed to be about a billion times the speetd of light. Also, Tesla was the first American scientist to experiment with Longtidudinal electromagnetic waves that traveled faster than light speed.

Regarding the strange behavior of light within the fiber optics,IE As an old sailor man I recognize wave form and action, in an ocean wave form there always is a
faster back moving wave under the central wave bulge. due to down pressure since light passes from
particle(photon) to wave and it can at the quanta level communicate at distances and speeds exceeding light this might explain this anti Einstein development.

Trying to take into consideration everything said in the column and in the posts, particularly Carbon_life's info, although I question his name (silcon based lifeform he may be). Could something like this technology be used to amplify LASER emissions. Lets say I've got a 5 kilo watt LASER (traveling north at 50 miles per hour, no no) and I bounce these waves (cause I like waves, I realize we are talking about more than just waves of light) back and forth in this or some similar type of recycling system. Could we hypothetically get amplification through wave harmonics?
One of the largest draw backs to LASER systems right now is power, for example it takes about the same volume as a bus or two worth of chemical energy to power a weapons grade zapper for missle defense. Could this tech be a first step towards finding a means to buff this technology without necessarily creating a new portable power system?

This all sounds suspiciously like Isaac Asimov's Thiotimoline. (look it up)

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we think that our universe the connexion of space and time( space-time ) derived of possible violation of opperatorPT and does appear two distictis torsions asymmetry that generates the curvatures of space-time " forward in time" and "backward in time".then in these curvatures the past and future alredy exist.
the universe multi dimensional is generated by two torsion disticts,and these deformation generate infinities "two torsion disticts".
we thinh that time also is generated by groups of infinities subtimes connected the subspaces correspondent.
antonio pocobi

Hey guest carbonlife, I'd like to talk about one particular ftl result of normal light phase conjugation. Reach me at ozmanusa@netscape.net

for every action there is an equal and oposite reaction. of course light goes backward, to enable pushing it forward. this paper just dramatizes basic knowledge. when you turn a light on in a room, it doesn't burn a whole in the floor, it pushes off it self, in many directions. when its' source is removed,it stops existing. when a star dies, its' light doesn't get sucked back in. it just stops moving forward.no opposite reaction, no more light. the idea that the light of a star takes a long time to travel space is lodgical, the concept that it travels backward as well is neccessary. the idea that if a star dies a million years ago and its' light is just getting here is without merit. light is energy, it needs to go backward to enable it to go forward. light is just energy, it has no life, it can't choose its' direction. it doesn't get a start, and then continue on its' own discretion.

an explosion of energy, looking for a receptor